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Immunological aspects of controlled antigen delivery
Advanced Drug Delivery Reviews 54 (2002) 863–870 www.elsevier.com / locate / drugdeliv
Immunological aspects of controlled antigen delivery Shari Lofthouse* Centre for Animal Biotechnology, School of Veterinary Science, The University of Melbourne, Victoria 3010, Australia Received 14 January 2002; accepted 4 March 2002
Abstract Recent advances in controlled delivery systems for protein pharmaceuticals such as microspheres, liposomes, pumps and implants, have provided a new avenue for delivery of vaccine antigens. There has, however, been considerable confusion over the way in which continuous antigen delivery affects the outcome of an immune response. To date, there has been little systematic study of the influence of varying antigen exposure times and release profiles on the phenotype of the immune response, or indeed the balance between immunity and tolerance as most studies have concentrated on optimising responses to a particular antigen of interest in a single model system. As these delivery systems would find particular advantages in management of livestock species, where the use of a single administration vaccine would significantly enhance management practices, it is important to understand the relationship between controlled antigen delivery and immunity. This paper describes how existing controlled antigen delivery studies have contributed to our understanding of the development of the immune response and demonstrates how continuous antigen delivery is useful, and possibly advantageous in the generation of immunity, the maturation of the immune response and the extension of the effector response. 2002 Elsevier Science B.V. All rights reserved. Keywords: Vaccine delivery; Antigen delivery; Single shot; Vaccination; Immune response
Contents 1. Introduction ............................................................................................................................................................................ 2. Concepts in vaccine delivery .................................................................................................................................................... 2.1. The effect of controlled antigen delivery on generation, maturation and persistence of the immune response .......................... 2.1.1. Controlled antigen delivery and the balance between immunity versus tolerance ......................................................... 2.1.2. Induction of mature immune responses: affinity maturation and isotype switching ...................................................... 2.1.3. Induction of immune memory ................................................................................................................................. 2.1.4. Manipulation of Th1 / Th2 profile............................................................................................................................. 2.1.5. Mucosal versus systemic immunity.......................................................................................................................... 2.2. The use of controlled release antigen delivery for maintenance of effector response .............................................................. 2.3. Continuous delivery versus pulsatile delivery ..................................................................................................................... 3. Conclusion.............................................................................................................................................................................. References ..................................................................................................................................................................................
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1. Introduction *Tel.: 1 61-3-8344-7892; fax: 1 61-3-9347-4083. E-mail address: [email protected] (S. Lofthouse).
Vaccine research is often focussed on the identifi-
0169-409X / 02 / $ – see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S0169-409X( 02 )00073-X
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cation and application of novel antigens. The response to these antigens is routinely optimised by assessing a variety of delivery methods, including variation of the adjuvant used, the dose and number of injections, and the route of delivery. Advances in pharmaceutical delivery have resulted in the development of controlled delivery systems that can offer a further parameter for vaccine assessment and may provide a significant means of enhancing and manipulating the immune response. The application of new delivery systems to vaccination may allow effective utilisation of vaccine antigens that have previously not been able to induce adequate or appropriate responses as well as improving the responses to existing vaccines. To date, there has been little analysis of controlled delivery systems in livestock, with the majority of initial studies being performed in small laboratory animals. These experiments, however, offer important insights into how the immune response may be modified or manipulated and may later find application as practical and effective new generation vaccines. In developing these methods for use in livestock, there are important practical considerations. The implementation of vaccination programs in food animals is restricted by management practices as well as regulatory and consumer considerations for animal products destined for human consumption. Vaccination does, however, remain one of the most cost-effective forms of disease control. Recent progress in vaccination has resulted in the potential for wider usage of vaccines to control not only disease, but fertility, carcass quality and behaviour. As the variety of different delivery systems available for use in animals has been reviewed elsewhere [1,2], this paper will focus on how changing the mode of antigen delivery using slow release devices is able to influence various aspects of the immune response. 2. Concepts in vaccine delivery
2.1. The effect of controlled antigen delivery on generation, maturation and persistence of the immune response 2.1.1. Controlled antigen delivery and the balance between immunity versus tolerance Early studies in fundamental immunology suggested that continuous delivery of antigen induces
immune tolerance [3–5]. These studies, however, often used extreme high or low doses of antigen, poor antigenic molecules and no adjuvant and were not aimed at determining methods of effective vaccination. Further, as these studies were conducted in the 1950s and 60s, when effective controlled delivery methods that maintained the immunogenic state of the protein antigens for sufficient periods of time were not available, frequent injected doses of antigen were applied. It is only in recent years, following development of delivery methods for protein pharmaceuticals, that the responses to controlled antigen delivery can be effectively assessed. The ability of a vaccine to induce protection after one immunisation instead of the usual two to three administrations is a primary aim of vaccine studies. On the basis of early studies of immunological tolerance, the field of single dose vaccine development initially concentrated on the development of devices that mimicked the normal vaccination strategies of delivering antigen in discrete pulses. While pulsatile delivery methods may have particular advantages for certain vaccines (discussed below), assessment of the literature shows that it is indeed possible to induce strong immune responses using continuous delivery of antigen. This was demonstrated as early as 1979 when Preis and Langer first used polymer implants for delivery of antigen to mice [6]. Continuous delivery in fact offers a rational way to induce immunity. Moreover, it is completely consistent with immunological dogma as will be discussed below. One of the proposed mechanisms of vaccine adjuvant action is the ‘depot’ effect that retains the antigen for an extended period, allowing longer interaction of the antigen with the immune system prior to clearance. Zinkernagel [7,8] has proposed that this interaction time between antigen and the cells of the draining lymph node is one of the fundamental parameters that determine the outcome of any immune response. The duration of the antigenic stimulation has been demonstrated to be the ¨ and major factor determining the fate of both naıve ¨ effector T cells. Naıve T cells require prolonged signalling for at least 20 h [9] and up to 2–3 days [7] to become committed to proliferation, while effector T cells require only 1 h of antigen stimulation [9]. Prolonged stimulation, however, induces death of effector cells.
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Continuous release of soluble antigens has been able to induce adequate immune responses where the injection of the soluble antigens has not. Collagen minipellets, a form of injectable and biodegradable implant, induced higher antibody responses to tetanus and diphtheria toxoid than antigen injected in alum adjuvant [10]. Similarly, delivery of cattle tick antigens from Alzet姠 pumps induced superior responses to soluble antigen delivery in mice [11]. In other circumstances however, the continuous release of antigen alone was not sufficient to induce a response and adjuvant was still required. Release of avidin from collagen minipellets or silicone implants was shown to induce strong immune responses when rovIL-1b, a soluble adjuvant, was included [12,13]. Use of these implants with antigen alone induced low level responses that were equal to those induced by injection of soluble antigen without adjuvant. These studies suggest that extended stimulation with antigen is an essential component of induction of an immune response, but other factors are also required, such as the attraction of appropriate antigen presenting cells to the site of antigen release. In addition, the activation status of antigen presenting cells has been shown to be an important control in the balance between immunity and tolerance [14]. Some delivery systems, such as liposomes or microspheres may also have inherent adjuvant activity and do not require the addition of other adjuvants. It is important to note the circumstances under which continuous antigen delivery may induce tolerance. Low dose iv injection or localised peripheral infection has been shown to induce immunity while high dose iv injection results in immune tolerance [7]. Persistent and systemic expression of antigen also results in immune tolerance as demonstrated by the studies of Th. Den Boer et al. [14], using human adenovirus peptide antigens and in studies of LCMV in mice. Strains of this virus that cause rapid and overwhelming infection exhaust the antiviral CTL response, while those that replicate slowly induce a long lasting immunity [15]. Bolus induction of soluble antigen is likely to result in overwhelming stimulation of the lymph node, resulting initially in high level T cell activation and a high frequency of expression of MHC-peptide complexes, but followed by T cell anergy [16]. Further, the maintenance of tolerance is dependent on the persistence of antigen in vivo, and is reversible if the antigen source is removed [17].
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While it is possible, and may be preferable to use controlled antigen delivery for induction of vaccine responses, failures to induce immunity by controlled delivery have frequently occurred as a result of the inability of the delivery mechanism to maintain the antigen in an immunogenic form in vivo. Antigens are primarily protein based. Protective antigens frequently rely on the maintenance of three-dimensional conformation that mimic protective epitopes in their native form. Many protein antigens are highly labile. Conditions to which they are exposed during manufacture, following in vivo delivery and during in vivo degradation of the delivery device, may have adverse effects on the success of the controlled release vaccination. Recent efforts have, therefore, focussed on developing delivery systems that do not use organic solvents, high temperatures, or pH extremes during production, that retain the antigen in a dry state while in vivo, and that do not degrade into acidic by-products [18,19]. In addition there has been considerable efforts to enhance protein stability either by the addition of protective additives or by modification of the protein antigen itself [20,21].
2.1.2. Induction of mature immune responses: affinity maturation and isotype switching Maturation of the immune response is characterised by the change in antibody expression from IgM to a predominant IgG isotype, the development of a high affinity antibody response, and the presence of memory lymphocytes that will mount a rapid response following further antigenic challenge. This process is generally described as occurring after at least two doses of antigen administration. However, prolonged antigen exposure induced by controlled delivery systems will also allow immune maturation to occur and may enhance the process. Prolonged availability of antigen has been shown to be essential for somatic mutation and affinity maturation to occur [22]. While the action of follicular dendritic cells and adjuvants in facilitating this process has been proven, the role of controlled antigen delivery in the process is yet to be evaluated. In addition, as most controlled release mechanisms result in delivery of low levels of antigen over time, the limited antigen supply will first stimulate high affinity clones to proliferate. The induction of higher affinity antibody responses by low doses of antigen has been previously demonstrated [23–25].
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2.1.3. Induction of immune memory The aim of most vaccines is the induction of immune memory. However, vaccine studies frequently focus on the persistence of the effector response rather than true memory induction, i.e., the ability to restimulate resting cells on re-exposure to antigen. Data describing the memory responses induced by controlled delivery systems following natural decay of the initial effector response are, therefore, limited. Significant memory responses were demonstrated in mice following delivery of Y. pestis V antigen-releasing PLA microspheres [26] and BSA-releasing archaeosomes (glycolipids extracted from archaeobacteria and formulated into liposomes). Using injectable silicone implants that delivered avidin and IL-1b as adjuvant, Kemp et al. [12] showed that strong memory antibody responses were induced in sheep following antigenic stimulation 100 days after the initial one-shot vaccination regime. Surprisingly, while the effector response demonstrated a mixed antibody response of IgG1 and IgG2 isotypes, the memory response induced by soluble antigen alone, showed a predominance of IgG1. In the same experiment, release of antigen from Alzet姠 pumps was examined. Memory responses were induced after antigenic challenge in sheep vaccinated with a pump that released antigen over a 7 day period. However, there were minimal memory responses in sheep implanted with pumps that released antigen over 28 days. The role of persistence of antigen in the maintenance of immune memory has been shown to be of importance, although its exact role is yet to be resolved. The study of the role of persistence in memory has been complicated by differing antigen needs for different cell types. While it appears to be essential for certain CD4 1 T cells, CD8 1 memory T cells [27,28] and memory B cells [29] for example, can persist in the absence of antigen. While this persisting antigen is believed to occur on follicular dendritic cells in the draining lymph nodes or in response to persistent low level infection, controlled release devices that secrete antigen for long periods of time and result in low level and continuous drainage to the node may have a similar effect. 2.1.4. Manipulation of Th1 /Th2 profile Foucras et al. [30,31] have shown that IL-4
producing CD4 1 T cells arise from different precursors depending on the conditions of antigen exposure in vivo. Following continuous sensitization with soluble antigen, a Th2 response is induced. In these studies, low dose soluble antigen delivered over 10 days from a subcutaneously implanted Alzet姠 pump resulted in decreased T cell proliferation, decreased expression of Th1 cytokines IL-2 and IFNg, and increased expression of IL-4 and IL-5. This was suggested to be a result of the lower dose delivered to the lymph node at one time by the pump, in comparison to bolus delivery of the same soluble antigen. Experimental studies using a range of different delivery mechanisms have shown, however, that both Th1 and Th2 responses may be induced, depending on the type of antigen used and other parameters of delivery. For example, Moore et al. [32] induced strong CTL responses following vaccination of mice with a soluble recombinant HIV protein by encapsulating the antigen in polymer microspheres. Similar responses were induced by delivery of ovalbumin microspheres [33]. Delivery of antigens in liposomes has induced a variety of responses. These include a Th1 dominant response following liposome encapsulation of various allergens [34], and a Th2 dominant response using Leishmania antigens, characterised by poor DTH responses and predominant IgG1 antibody responses and resulting in limited protection [35]. An absence of polarisation and induction of both Th1 and Th2 responses has also resulted from liposome-entrapped antigen delivery [36,37]. The use of controlled antigen delivery cannot, therefore, be used to rationally manipulate the type of immune response alone. Instead it must be trialled on a case-by-case basis in combination with variations of dose, route and schedule of delivery.
2.1.5. Mucosal versus systemic immunity The induction of adequate immune responses at mucosal sites has been a long-standing quest in vaccine research owing to the importance of preventing the establishment of pathogenic infection at the portal of entry. To date however, the majority of vaccines induce systemic immunity characterised by serum IgG responses, rather than induction of secretory IgA at mucosal surfaces. A major area of recent research in controlled release methods has been the
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use of microspheres to induce a mucosal response. This is a result of the ability of these particles to be preferentially retained in various compartments of the body depending on their size (reviewed in [38– 40]). In addition, the use of delivery vehicles may protect the labile antigens against degradation in the extreme conditions of the alimentary canal following oral antigen delivery. Increased protection against Pasteurella haemolytica challenge of mice was demonstrated by encapsulating antigens in alginate microspheres and delivering them both orally and subcutaneously [41]. Alginate microspheres have also been used orally and intranasally to induce protection against lethal Streptococcus pneumoniae challenge of mice [42], and to induce pulmonary immunity in cattle against a model antigen [43]. Mucosal responses induced by use of microspheres has been shown to be improved by the addition of mucoadhesive polymers that retain the microparticulate antigen at the gut wall for a longer period and allow increased uptake [44,45]. Microspheres delivered via the mucosal route have also been shown to translocate to other compartments and induce a systemic response [26]. Due to differences in body size and anatomy, there have been few successful transfers of results in mice to target livestock species. This highlights the need to study target species early in development of such new vaccines so that particular characteristics of the species may be accounted for.
2.2. The use of controlled release antigen delivery for maintenance of effector response Duration of immunity is a primary factor affecting the success of a vaccine in the market, particularly for livestock products. The majority of vaccines are aimed at disease protection and can rely on induction of immune memory in the face of infectious challenge. In addition, low level environmental stimulation, such as by Clostridium tetanus occurring naturally in soil, may serve to stimulate immunity and maintain memory. The duration of effector responses, however, aids in rapid protection prior to establishment of infection. In addition, the recent developments in immunocontraceptive vaccines for livestock depend on long duration of an effector response. Natural memory (re-secretion of reproduc-
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tive hormones) does not stimulate a memory response following induction of immunity by peptidecarrier vaccines [46]. These factors, combined with livestock management practices that limit handling of stock, make controlled delivery systems prime candidates for use in vaccination programs for sheep, cattle, poultry, fish and pigs. Immunocastration with the LHRH superagonist Leuprolide was effective for 100 [47] to 120 [48] days following encapsulation in PLGA microspheres. Using the model antigen BSA, use of a cholesterol– lecithin implant induced antibody responses that persisted for up to 10 months following a single administration to mice [49]. The same implant when delivered to sheep however, did not induce an extended duration of response [50]. This is a typical problem encountered in the shift from small animal models to target livestock species and may be a result of dose variation, delivery route, or other parameters of delivery. In general, any delivery system able to prolong the effector response by over 6 months would be considerably advantageous over existing vaccines, particularly in the field of immunocastration.
2.3. Continuous delivery versus pulsatile delivery While there is sufficient evidence to show that a mature immune response can be induced by continuous antigen delivery, the maintenance of extended effector responses and the activation of immune memory is likely to require a further stimulation with antigen. Therefore, while livestock with short life spans, or seasonal problems such as parasitic infection may benefit from the use of one-shot systems, there is also considerable potential for the development of single-administration vaccines that deliver more than one distinct pulse of antigen. Provided these can be made cost-effective, they would greatly benefit livestock management by reducing the need for multiple handling of stock. This would reduce excessive labour costs, and eliminate exposing livestock to further conditions of stress that has a negative impact on growth and reproductive performance. Pulsatile delivery has been induced through the use of mixed microsphere populations that vary in density or size [51,52] and by implant systems that
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actively or passively release different pulses of antigens at set time points [53,54]. In general these systems provide a two-phase peak of antigen release rather than distinct pulses. Given that considerable extension of effector response may be achieved by continuous antigen delivery, the most useful pulsatile systems would release antigen in a second peak at times greater than 6 months. This could re-stimulate the memory response, resulting in extension of the effector response for up to one year. Immunocastration vaccines are again a prime candidate for this type of delivery system. An effective means of delivering antigen in this way is yet to be developed for use in large animals.
3. Conclusion Evidence is gradually arising that contrary to conventional thinking in immunology, continuous antigen delivery is able to induce immunity, and result in affinity maturation, isotype switching, and immune memory. The rational manipulation of delivery methods, in combination with variation of other parameters of delivery such as dose, route and use of adjuvants, is likely to result in significant improvement in the effectiveness of many existing vaccines. The development of these systems for use in livestock is dependent on testing of the products in target species as responses may differ substantially from those encountered in small animal models. Provided that these systems are able to preserve the integrity of the immunising protein, receive consumer acceptability and can be made cost-effectively, they will find considerable application in livestock management. Given the short life span of many food animal species, particularly poultry, fish and pigs, it is highly likely that single dose delivery will become a reality for selected veterinary vaccines.
References [1] T.L. Bowersock, S. Martin, Vaccine delivery to animals, Adv. Drug Delivery Rev. 38 (1999) 167–194. [2] Z. Zhao, K.W. Leong, Controlled delivery of antigens and adjuvants in vaccine development, J. Pharm. Sci. 85 (1996) 1261–1270.
[3] D.W. Dresser, G. Gowland, Immunological paralysis induced in adult rabbits by small amounts of protein antigen, Nature 203 (1964) 275–292. [4] F.J. Dixon, P.H. Maurer, Immunologic unresponsiveness induced by protein antigens, J. Exp. Med. 101 (1955) 237– 245. [5] N.A. Mitchison, Induction of immunological paralysis in two zones of dosage, Proc. R. Soc. London-B 161 (1965) 275– 292. [6] I. Preis, R. Langer, A single-step immunization by sustained antigen release, J. Imm. Meth. 28 (1979) 193–197. [7] R.M. Zinkernagel, S. Ehl, P. Aichele, S. Oehen, T. Kundig, H. Hengartner, Antigen localization regulates immune responses in a dose and time dependent fashion: a geographical view of early immunity, Immunol. Rev. 156 (1997) 199– 209. [8] R.M. Zinkernagel, Localization dose and time of antigens determine immune reactivity, Sem. Immunol. 12 (2000) 163–171. [9] G. Iezzi, K. Karjalainen, A. Lanzacecchia, The duration of antigenic stimulation determines the fate of naive and effector T cells, Immunity 8 (1998) 89–95. [10] M. Higaki, Y. Azechi, T. Takase et al., Collagen minipellet as controlled release delivery system for tetanus and diphtheria toxoid, Vaccine 19 (2001) 3091–3096. [11] C. Ehrenhofer, J.P. Opdebeeck, The effects of continuous and intermittent delivery of antigens of Boophilus microplus on the development of murine antibodies, Vet. Parasitol. 59 (1995) 263–273. [12] J. Kemp, M. Kajihara, S. Nagahara, A. Sano, M. Brandon, S. Lofthouse, Continuous antigen delivery from controlled release implants induces significant and anamnestic immune responses, Vaccine 20 (2002) 1089–1098. [13] S. Lofthouse, S. Nagahara, B. Sedgmen, G. Barcham, M. Brandon, A. Sano, The application of biodegradable collagen minipellets as vaccine delivery vehicles in mice and sheep, Vaccine 19 (2001) 4318–4327. [14] A.Th. den Boer, L. Diehl, G.J.D. van Mierlo et al., Longevity of antigen presentation and activation status of APC are decisive factors in the balance between CTL immunity and tolerance, J. Immunol. 167 (2001) 2522–2528. [15] D. Moskophidis, S. Lechner, H. Pircher, R.M. Zinkernagel, Virus persistence in acutely infected immunocompetent mice by exhaustion of antiviral cytotoxic effector T cells, Nature 362 (1993) 758. [16] S.K. Switzer, B.P. Wallner, T.J. Briner, G.H. Sunshine, C.R. Bourque, M. Luqman, Bolus injection of aqueous antigen leads to a high density of T-cell-receptor ligand in the spleen, transient T cell activation and anergy induction, Immunology 94 (1998) 513–522. [17] F. Ramsdell, B.J. Fowlkes, Maintenance of in vivo tolerance by persistence of antigen, Science 257 (1992) 1130–1133. [18] X.H. Li, Y.H. Zhang, R.H. Yan et al., Influence of process parameters on the protein stability encapsulated in pol-DLlactide-poly(ethylene glycol) microspheres, J. Cont. Rel. 68 (2000) 41–52. [19] S.D. Putney, P.A. Burke, Improving protein therapeutics with
S. Lofthouse / Advanced Drug Delivery Reviews 54 (2002) 863–870
[20]
[21]
[22]
[23]
[24]
[25] [26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
sustained release formulations, Nat. Biotechnol. 16 (1998) 153–157. M. Diwan, T.G. Park, Pegylation enhances protein stability during encapsulation in PLGA microspheres, J. Cont. Rel. 73 (2001) 233–244. S.P. Schwendeman, H.R. Costantino, R.K. Gupta, G.R. Siber, A.M. Klibanov, R. Langer, Stabilization of tetanus and diphtheria toxoid against moisture-induced aggregation, Proc. Natl. Acad. Sci. USA 92 (1995) 11234–11238. Y. Wang, G. Huang, J. Wang, H. Molina, D. Chaplin, Y.-X. Fu, Antigen persistence is required for somatic mutation and affinity maturation of immunoglobulin, Eur. J. Immunol. 30 (2000) 2226–2234. E.A. Goidl, W.E. Paul, G.W. Siskind, B. Benacerraf, The effect of antigen dose and time after immunisation on the amount and affinity of anti-hapten antibody, J. Immunol. 100 (1968) 371–375. A. Gonzalez-Fernandez, C. Milstein, Low antigen dose favours selection of somatic mutants with hallmarks of antibody affinity maturation, Immunology 93 (1998) 149– 153. G.W. Siskind, B. Benacerraf, Cell selection by antigen in the immune response, Adv. Immunol. 10 (1969) 1–50. J.E. Eyles, V.W. Bramwell, E.D. Williamson, H.O. Alpar, Microsphere translocation and immunopotentiation in systemic tissues following intranasal administration, Vaccine 19 (2001) 4732–4742. T. Kundig, M.F. Bachmann, S. Oehen et al., On the role of antigen in maintaining cytotoxic T cell memory, Proc. Natl. Acad. Sci. USA 93 (1996) 9716–9723. T. Kundig, M.F. Bachmann, P.S. Ohashi, H. Pircher, H. Hengartner, R.M. Zinkernagel, On T cell memory-arguments for antigen dependence, Immunol. Rev. 150 (1996) 63–90. M. Marumaya, K.-P. Lam, K. Rajewsky, Memory B-cell persistence is independent of persisting immunizing antigen, Nature 407 (2000) 636–642. G. Foucras, L. Gapin, C. Coureau, J.M. Kanellopoulos, J.-C. Guery, Interleukin-4-producing CD4 T cells arise froom different precursors depending on the conditions of antigen exposure in vivo, J. Exp. Med. 191 (2000) 683–693. G. Foucras, A. Gallard, C. Coureau, J.M. Kanellopoulos, J.-C. Guery, Chronic soluble antigen sensitization primes a unique memory / effector T cell repertoire associated with Th2 phenotype acquisition in vivo, J. Immunol. 168 (2002) 179–187. A. Moore, P. McGuirk, S. Adams et al., Immunization with a soluble recombinant HIV protein entrapped in biodegradable microparticles induces HIV-specific CD8( 1 ) cytotoxic lymphocytes and CD4( 1 ) Th1 cells, Vaccine 13 (1995) 1741– 1749. K.D. Newman, J. Samuel, G. Kwon, Ovalbumin peptide encapsulated in pol( D,L lactic-co-glycolic acid) microspheres is capable of inducing a T helper type 1 response, J. Cont. Rel. 54 (1998) 49–59. S. Sehra, L. Chugh, S.V. Gangal, Polarized Th1 responses by liposome-entrapped allergen and its potential in immunotherapy of allergic disorders, Clin. Ep. Allergy 28 (1998) 1530–1537.
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[35] F. Afrin, K. Anam, N. Ali, Induction of partial protection against Leishmania donovani by promastigote antigens in negatively charged liposomes, J. Parasitol. 86 (2000) 730– 735. [36] I. Babai, S. Samira, Y. Barenholz, Z. Zakay-Rones, E. Kedar, A novel influenza subunit vaccine composed of liposomeencapsulated haemagglutinin / neuraminidase and IL-2 or GM-CSF. II. Induction of Th1 and Th2 responses in mice, Vaccine 17 (1999) 1239–1250. [37] L. Krishnan, C.J. Dicaire, G.B. Patel, G.D. Sprott, Archaeosome vaccine adjuvants induce strong humoral, cell mediated and memory responses: comparison to conventional liposomes and alum, Infect. Immun. 68 (2000) 54–63. [38] J. Mestecky, Z. Moldoveanu, M. Novak et al., Biodegradable microspheres for the delivery of oral vaccines, J. Cont. Rel. 28 (1994) 131–141. [39] T.L. Bowersock, H. Hogenesch, M. Suckow et al., Oral vaccination with alginate microsphere systems, J. Cont. Rel. 39 (1996) 209–220. [40] A.M. Hillery, Microparticulate delivery systems—potential drug / vaccine carriers via mucosal routes, Pharm. Sci. Tech. Today 1 (1998) 69–75. [41] A. Kidane, P. Guimond, T.C.R. Ju, M. Sanchez, J. Gibson, T.L. Bowersock, The efficacy of oral vaccination of mice with alginate encapsulated outer membrane proteins of Pasteurella haemolytica and One-Shot (R), Vaccine 19 (2001) 2637–2646. [42] S.Y. Seong, N.H. Cho, I.C. Kwon, S.Y. Jeong, Protective immunity of microsphere-based mucosal vaccines against lethal intranasal challenge with Streptococcus pneumoniae, Infect. Immun. 67 (1999) 3587–3592. [43] T.L. Bowersock, H. Hogenesch, S. Torregrosa et al., Induction of pulmonary immunity in cattle by oral administration of ovalbumin in alginate microspheres, Immunol. Lett. 60 (1998) 37–43. [44] J. Kunisawa, A. Okudaira, Y. Tsutusmi et al., Characterization of mucoadhesive microspheres for the induction of mucosal and systemic immune responses, Vaccine 19 (2000) 589–594. [45] M. Abd El-Shafy, I.W. Kellaway, G. Taylor, P.A. Dickinson, Improved nasal bioavailability of FITC-dextran (MW 4300) from mucoadhesive microspheres in rabbits, J. Drug Target. 7 (2000) 355–361. [46] M. Bradley, J. Eade, J. Penhale, P. Bird, Vaccines for fertility regulation in wild and domestic species, J. Biotech. 73 (1999) 91–101. [47] K.W. Burton, M. Shameem, B.C. Thanoo, P.P. DeLuca, Extended release peptide delivery systems through the use of PLGA microsphere combinations, J. Biomater. Sci. 11 (2000) 715–729. [48] B.H. Woo, J.W. Kostanski, S. Gebrekidan, B.A. Dani, B.C. Thanoo, P.P. DeLuca, Preparation, characterization and in vivo evaluation of 120-day poly( DL-lactide) leuprolide microspheres, J. Cont. Rel. 75 (2001) 307–315. [49] M.Z.I. Khan, I.G. Tucker, J.P. Opdebeeck, Cholesterol and lecithin implants for sustained release of antigen: release and erosion in vitro, and antibody response in mice, Int. J. Pharm. 76 (1991) 161–170.
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[50] A.K. Walduck, J.P. Opdebeeck, H.E. Benson, R. Prankerd, Biodegradable implants for the delivery of veterinary vaccines; manufacture and antibody responses in mice, J. Cont. Rel. 51 (1998) 269–280. [51] A. Sanchez, R.K. Gupta, M.J. Alonso, G.R. Siber, R. Langer, Pulsed controlled-release system for potential use in vaccine delivery, J. Pharm. Sci. 85 (1996) 547–552. [52] J.L. Cleland, Single-administration vaccines: controlled-re-
lease technology to mimic repeated immunizations, Trends Biotech. 17 (1999) 25–29. [53] M. Cardamone, S. Lofthouse, J.C. Lucas, R.P. Lee, M. O’Donoghue, M. Brandon, In vitro testing of a pulsatile delivery system and its in vivo application for immunisation against tetanus toxoid, J. Cont. Rel. 47 (1997) 205–219. [54] W. Vogelhuber, P. Rotunno, E. Magni et al., Programmable biodegradable implants, J. Control. Rel. 73 (2001) 75–88.
Immunological aspects of controlled antigen delivery Shari Lofthouse* Centre for Animal Biotechnology, School of Veterinary Science, The University of Melbourne, Victoria 3010, Australia Received 14 January 2002; accepted 4 March 2002
Abstract Recent advances in controlled delivery systems for protein pharmaceuticals such as microspheres, liposomes, pumps and implants, have provided a new avenue for delivery of vaccine antigens. There has, however, been considerable confusion over the way in which continuous antigen delivery affects the outcome of an immune response. To date, there has been little systematic study of the influence of varying antigen exposure times and release profiles on the phenotype of the immune response, or indeed the balance between immunity and tolerance as most studies have concentrated on optimising responses to a particular antigen of interest in a single model system. As these delivery systems would find particular advantages in management of livestock species, where the use of a single administration vaccine would significantly enhance management practices, it is important to understand the relationship between controlled antigen delivery and immunity. This paper describes how existing controlled antigen delivery studies have contributed to our understanding of the development of the immune response and demonstrates how continuous antigen delivery is useful, and possibly advantageous in the generation of immunity, the maturation of the immune response and the extension of the effector response. 2002 Elsevier Science B.V. All rights reserved. Keywords: Vaccine delivery; Antigen delivery; Single shot; Vaccination; Immune response
Contents 1. Introduction ............................................................................................................................................................................ 2. Concepts in vaccine delivery .................................................................................................................................................... 2.1. The effect of controlled antigen delivery on generation, maturation and persistence of the immune response .......................... 2.1.1. Controlled antigen delivery and the balance between immunity versus tolerance ......................................................... 2.1.2. Induction of mature immune responses: affinity maturation and isotype switching ...................................................... 2.1.3. Induction of immune memory ................................................................................................................................. 2.1.4. Manipulation of Th1 / Th2 profile............................................................................................................................. 2.1.5. Mucosal versus systemic immunity.......................................................................................................................... 2.2. The use of controlled release antigen delivery for maintenance of effector response .............................................................. 2.3. Continuous delivery versus pulsatile delivery ..................................................................................................................... 3. Conclusion.............................................................................................................................................................................. References ..................................................................................................................................................................................
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1. Introduction *Tel.: 1 61-3-8344-7892; fax: 1 61-3-9347-4083. E-mail address: [email protected] (S. Lofthouse).
Vaccine research is often focussed on the identifi-
0169-409X / 02 / $ – see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S0169-409X( 02 )00073-X
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cation and application of novel antigens. The response to these antigens is routinely optimised by assessing a variety of delivery methods, including variation of the adjuvant used, the dose and number of injections, and the route of delivery. Advances in pharmaceutical delivery have resulted in the development of controlled delivery systems that can offer a further parameter for vaccine assessment and may provide a significant means of enhancing and manipulating the immune response. The application of new delivery systems to vaccination may allow effective utilisation of vaccine antigens that have previously not been able to induce adequate or appropriate responses as well as improving the responses to existing vaccines. To date, there has been little analysis of controlled delivery systems in livestock, with the majority of initial studies being performed in small laboratory animals. These experiments, however, offer important insights into how the immune response may be modified or manipulated and may later find application as practical and effective new generation vaccines. In developing these methods for use in livestock, there are important practical considerations. The implementation of vaccination programs in food animals is restricted by management practices as well as regulatory and consumer considerations for animal products destined for human consumption. Vaccination does, however, remain one of the most cost-effective forms of disease control. Recent progress in vaccination has resulted in the potential for wider usage of vaccines to control not only disease, but fertility, carcass quality and behaviour. As the variety of different delivery systems available for use in animals has been reviewed elsewhere [1,2], this paper will focus on how changing the mode of antigen delivery using slow release devices is able to influence various aspects of the immune response. 2. Concepts in vaccine delivery
2.1. The effect of controlled antigen delivery on generation, maturation and persistence of the immune response 2.1.1. Controlled antigen delivery and the balance between immunity versus tolerance Early studies in fundamental immunology suggested that continuous delivery of antigen induces
immune tolerance [3–5]. These studies, however, often used extreme high or low doses of antigen, poor antigenic molecules and no adjuvant and were not aimed at determining methods of effective vaccination. Further, as these studies were conducted in the 1950s and 60s, when effective controlled delivery methods that maintained the immunogenic state of the protein antigens for sufficient periods of time were not available, frequent injected doses of antigen were applied. It is only in recent years, following development of delivery methods for protein pharmaceuticals, that the responses to controlled antigen delivery can be effectively assessed. The ability of a vaccine to induce protection after one immunisation instead of the usual two to three administrations is a primary aim of vaccine studies. On the basis of early studies of immunological tolerance, the field of single dose vaccine development initially concentrated on the development of devices that mimicked the normal vaccination strategies of delivering antigen in discrete pulses. While pulsatile delivery methods may have particular advantages for certain vaccines (discussed below), assessment of the literature shows that it is indeed possible to induce strong immune responses using continuous delivery of antigen. This was demonstrated as early as 1979 when Preis and Langer first used polymer implants for delivery of antigen to mice [6]. Continuous delivery in fact offers a rational way to induce immunity. Moreover, it is completely consistent with immunological dogma as will be discussed below. One of the proposed mechanisms of vaccine adjuvant action is the ‘depot’ effect that retains the antigen for an extended period, allowing longer interaction of the antigen with the immune system prior to clearance. Zinkernagel [7,8] has proposed that this interaction time between antigen and the cells of the draining lymph node is one of the fundamental parameters that determine the outcome of any immune response. The duration of the antigenic stimulation has been demonstrated to be the ¨ and major factor determining the fate of both naıve ¨ effector T cells. Naıve T cells require prolonged signalling for at least 20 h [9] and up to 2–3 days [7] to become committed to proliferation, while effector T cells require only 1 h of antigen stimulation [9]. Prolonged stimulation, however, induces death of effector cells.
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Continuous release of soluble antigens has been able to induce adequate immune responses where the injection of the soluble antigens has not. Collagen minipellets, a form of injectable and biodegradable implant, induced higher antibody responses to tetanus and diphtheria toxoid than antigen injected in alum adjuvant [10]. Similarly, delivery of cattle tick antigens from Alzet姠 pumps induced superior responses to soluble antigen delivery in mice [11]. In other circumstances however, the continuous release of antigen alone was not sufficient to induce a response and adjuvant was still required. Release of avidin from collagen minipellets or silicone implants was shown to induce strong immune responses when rovIL-1b, a soluble adjuvant, was included [12,13]. Use of these implants with antigen alone induced low level responses that were equal to those induced by injection of soluble antigen without adjuvant. These studies suggest that extended stimulation with antigen is an essential component of induction of an immune response, but other factors are also required, such as the attraction of appropriate antigen presenting cells to the site of antigen release. In addition, the activation status of antigen presenting cells has been shown to be an important control in the balance between immunity and tolerance [14]. Some delivery systems, such as liposomes or microspheres may also have inherent adjuvant activity and do not require the addition of other adjuvants. It is important to note the circumstances under which continuous antigen delivery may induce tolerance. Low dose iv injection or localised peripheral infection has been shown to induce immunity while high dose iv injection results in immune tolerance [7]. Persistent and systemic expression of antigen also results in immune tolerance as demonstrated by the studies of Th. Den Boer et al. [14], using human adenovirus peptide antigens and in studies of LCMV in mice. Strains of this virus that cause rapid and overwhelming infection exhaust the antiviral CTL response, while those that replicate slowly induce a long lasting immunity [15]. Bolus induction of soluble antigen is likely to result in overwhelming stimulation of the lymph node, resulting initially in high level T cell activation and a high frequency of expression of MHC-peptide complexes, but followed by T cell anergy [16]. Further, the maintenance of tolerance is dependent on the persistence of antigen in vivo, and is reversible if the antigen source is removed [17].
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While it is possible, and may be preferable to use controlled antigen delivery for induction of vaccine responses, failures to induce immunity by controlled delivery have frequently occurred as a result of the inability of the delivery mechanism to maintain the antigen in an immunogenic form in vivo. Antigens are primarily protein based. Protective antigens frequently rely on the maintenance of three-dimensional conformation that mimic protective epitopes in their native form. Many protein antigens are highly labile. Conditions to which they are exposed during manufacture, following in vivo delivery and during in vivo degradation of the delivery device, may have adverse effects on the success of the controlled release vaccination. Recent efforts have, therefore, focussed on developing delivery systems that do not use organic solvents, high temperatures, or pH extremes during production, that retain the antigen in a dry state while in vivo, and that do not degrade into acidic by-products [18,19]. In addition there has been considerable efforts to enhance protein stability either by the addition of protective additives or by modification of the protein antigen itself [20,21].
2.1.2. Induction of mature immune responses: affinity maturation and isotype switching Maturation of the immune response is characterised by the change in antibody expression from IgM to a predominant IgG isotype, the development of a high affinity antibody response, and the presence of memory lymphocytes that will mount a rapid response following further antigenic challenge. This process is generally described as occurring after at least two doses of antigen administration. However, prolonged antigen exposure induced by controlled delivery systems will also allow immune maturation to occur and may enhance the process. Prolonged availability of antigen has been shown to be essential for somatic mutation and affinity maturation to occur [22]. While the action of follicular dendritic cells and adjuvants in facilitating this process has been proven, the role of controlled antigen delivery in the process is yet to be evaluated. In addition, as most controlled release mechanisms result in delivery of low levels of antigen over time, the limited antigen supply will first stimulate high affinity clones to proliferate. The induction of higher affinity antibody responses by low doses of antigen has been previously demonstrated [23–25].
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2.1.3. Induction of immune memory The aim of most vaccines is the induction of immune memory. However, vaccine studies frequently focus on the persistence of the effector response rather than true memory induction, i.e., the ability to restimulate resting cells on re-exposure to antigen. Data describing the memory responses induced by controlled delivery systems following natural decay of the initial effector response are, therefore, limited. Significant memory responses were demonstrated in mice following delivery of Y. pestis V antigen-releasing PLA microspheres [26] and BSA-releasing archaeosomes (glycolipids extracted from archaeobacteria and formulated into liposomes). Using injectable silicone implants that delivered avidin and IL-1b as adjuvant, Kemp et al. [12] showed that strong memory antibody responses were induced in sheep following antigenic stimulation 100 days after the initial one-shot vaccination regime. Surprisingly, while the effector response demonstrated a mixed antibody response of IgG1 and IgG2 isotypes, the memory response induced by soluble antigen alone, showed a predominance of IgG1. In the same experiment, release of antigen from Alzet姠 pumps was examined. Memory responses were induced after antigenic challenge in sheep vaccinated with a pump that released antigen over a 7 day period. However, there were minimal memory responses in sheep implanted with pumps that released antigen over 28 days. The role of persistence of antigen in the maintenance of immune memory has been shown to be of importance, although its exact role is yet to be resolved. The study of the role of persistence in memory has been complicated by differing antigen needs for different cell types. While it appears to be essential for certain CD4 1 T cells, CD8 1 memory T cells [27,28] and memory B cells [29] for example, can persist in the absence of antigen. While this persisting antigen is believed to occur on follicular dendritic cells in the draining lymph nodes or in response to persistent low level infection, controlled release devices that secrete antigen for long periods of time and result in low level and continuous drainage to the node may have a similar effect. 2.1.4. Manipulation of Th1 /Th2 profile Foucras et al. [30,31] have shown that IL-4
producing CD4 1 T cells arise from different precursors depending on the conditions of antigen exposure in vivo. Following continuous sensitization with soluble antigen, a Th2 response is induced. In these studies, low dose soluble antigen delivered over 10 days from a subcutaneously implanted Alzet姠 pump resulted in decreased T cell proliferation, decreased expression of Th1 cytokines IL-2 and IFNg, and increased expression of IL-4 and IL-5. This was suggested to be a result of the lower dose delivered to the lymph node at one time by the pump, in comparison to bolus delivery of the same soluble antigen. Experimental studies using a range of different delivery mechanisms have shown, however, that both Th1 and Th2 responses may be induced, depending on the type of antigen used and other parameters of delivery. For example, Moore et al. [32] induced strong CTL responses following vaccination of mice with a soluble recombinant HIV protein by encapsulating the antigen in polymer microspheres. Similar responses were induced by delivery of ovalbumin microspheres [33]. Delivery of antigens in liposomes has induced a variety of responses. These include a Th1 dominant response following liposome encapsulation of various allergens [34], and a Th2 dominant response using Leishmania antigens, characterised by poor DTH responses and predominant IgG1 antibody responses and resulting in limited protection [35]. An absence of polarisation and induction of both Th1 and Th2 responses has also resulted from liposome-entrapped antigen delivery [36,37]. The use of controlled antigen delivery cannot, therefore, be used to rationally manipulate the type of immune response alone. Instead it must be trialled on a case-by-case basis in combination with variations of dose, route and schedule of delivery.
2.1.5. Mucosal versus systemic immunity The induction of adequate immune responses at mucosal sites has been a long-standing quest in vaccine research owing to the importance of preventing the establishment of pathogenic infection at the portal of entry. To date however, the majority of vaccines induce systemic immunity characterised by serum IgG responses, rather than induction of secretory IgA at mucosal surfaces. A major area of recent research in controlled release methods has been the
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use of microspheres to induce a mucosal response. This is a result of the ability of these particles to be preferentially retained in various compartments of the body depending on their size (reviewed in [38– 40]). In addition, the use of delivery vehicles may protect the labile antigens against degradation in the extreme conditions of the alimentary canal following oral antigen delivery. Increased protection against Pasteurella haemolytica challenge of mice was demonstrated by encapsulating antigens in alginate microspheres and delivering them both orally and subcutaneously [41]. Alginate microspheres have also been used orally and intranasally to induce protection against lethal Streptococcus pneumoniae challenge of mice [42], and to induce pulmonary immunity in cattle against a model antigen [43]. Mucosal responses induced by use of microspheres has been shown to be improved by the addition of mucoadhesive polymers that retain the microparticulate antigen at the gut wall for a longer period and allow increased uptake [44,45]. Microspheres delivered via the mucosal route have also been shown to translocate to other compartments and induce a systemic response [26]. Due to differences in body size and anatomy, there have been few successful transfers of results in mice to target livestock species. This highlights the need to study target species early in development of such new vaccines so that particular characteristics of the species may be accounted for.
2.2. The use of controlled release antigen delivery for maintenance of effector response Duration of immunity is a primary factor affecting the success of a vaccine in the market, particularly for livestock products. The majority of vaccines are aimed at disease protection and can rely on induction of immune memory in the face of infectious challenge. In addition, low level environmental stimulation, such as by Clostridium tetanus occurring naturally in soil, may serve to stimulate immunity and maintain memory. The duration of effector responses, however, aids in rapid protection prior to establishment of infection. In addition, the recent developments in immunocontraceptive vaccines for livestock depend on long duration of an effector response. Natural memory (re-secretion of reproduc-
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tive hormones) does not stimulate a memory response following induction of immunity by peptidecarrier vaccines [46]. These factors, combined with livestock management practices that limit handling of stock, make controlled delivery systems prime candidates for use in vaccination programs for sheep, cattle, poultry, fish and pigs. Immunocastration with the LHRH superagonist Leuprolide was effective for 100 [47] to 120 [48] days following encapsulation in PLGA microspheres. Using the model antigen BSA, use of a cholesterol– lecithin implant induced antibody responses that persisted for up to 10 months following a single administration to mice [49]. The same implant when delivered to sheep however, did not induce an extended duration of response [50]. This is a typical problem encountered in the shift from small animal models to target livestock species and may be a result of dose variation, delivery route, or other parameters of delivery. In general, any delivery system able to prolong the effector response by over 6 months would be considerably advantageous over existing vaccines, particularly in the field of immunocastration.
2.3. Continuous delivery versus pulsatile delivery While there is sufficient evidence to show that a mature immune response can be induced by continuous antigen delivery, the maintenance of extended effector responses and the activation of immune memory is likely to require a further stimulation with antigen. Therefore, while livestock with short life spans, or seasonal problems such as parasitic infection may benefit from the use of one-shot systems, there is also considerable potential for the development of single-administration vaccines that deliver more than one distinct pulse of antigen. Provided these can be made cost-effective, they would greatly benefit livestock management by reducing the need for multiple handling of stock. This would reduce excessive labour costs, and eliminate exposing livestock to further conditions of stress that has a negative impact on growth and reproductive performance. Pulsatile delivery has been induced through the use of mixed microsphere populations that vary in density or size [51,52] and by implant systems that
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actively or passively release different pulses of antigens at set time points [53,54]. In general these systems provide a two-phase peak of antigen release rather than distinct pulses. Given that considerable extension of effector response may be achieved by continuous antigen delivery, the most useful pulsatile systems would release antigen in a second peak at times greater than 6 months. This could re-stimulate the memory response, resulting in extension of the effector response for up to one year. Immunocastration vaccines are again a prime candidate for this type of delivery system. An effective means of delivering antigen in this way is yet to be developed for use in large animals.
3. Conclusion Evidence is gradually arising that contrary to conventional thinking in immunology, continuous antigen delivery is able to induce immunity, and result in affinity maturation, isotype switching, and immune memory. The rational manipulation of delivery methods, in combination with variation of other parameters of delivery such as dose, route and use of adjuvants, is likely to result in significant improvement in the effectiveness of many existing vaccines. The development of these systems for use in livestock is dependent on testing of the products in target species as responses may differ substantially from those encountered in small animal models. Provided that these systems are able to preserve the integrity of the immunising protein, receive consumer acceptability and can be made cost-effectively, they will find considerable application in livestock management. Given the short life span of many food animal species, particularly poultry, fish and pigs, it is highly likely that single dose delivery will become a reality for selected veterinary vaccines.
References [1] T.L. Bowersock, S. Martin, Vaccine delivery to animals, Adv. Drug Delivery Rev. 38 (1999) 167–194. [2] Z. Zhao, K.W. Leong, Controlled delivery of antigens and adjuvants in vaccine development, J. Pharm. Sci. 85 (1996) 1261–1270.
[3] D.W. Dresser, G. Gowland, Immunological paralysis induced in adult rabbits by small amounts of protein antigen, Nature 203 (1964) 275–292. [4] F.J. Dixon, P.H. Maurer, Immunologic unresponsiveness induced by protein antigens, J. Exp. Med. 101 (1955) 237– 245. [5] N.A. Mitchison, Induction of immunological paralysis in two zones of dosage, Proc. R. Soc. London-B 161 (1965) 275– 292. [6] I. Preis, R. Langer, A single-step immunization by sustained antigen release, J. Imm. Meth. 28 (1979) 193–197. [7] R.M. Zinkernagel, S. Ehl, P. Aichele, S. Oehen, T. Kundig, H. Hengartner, Antigen localization regulates immune responses in a dose and time dependent fashion: a geographical view of early immunity, Immunol. Rev. 156 (1997) 199– 209. [8] R.M. Zinkernagel, Localization dose and time of antigens determine immune reactivity, Sem. Immunol. 12 (2000) 163–171. [9] G. Iezzi, K. Karjalainen, A. Lanzacecchia, The duration of antigenic stimulation determines the fate of naive and effector T cells, Immunity 8 (1998) 89–95. [10] M. Higaki, Y. Azechi, T. Takase et al., Collagen minipellet as controlled release delivery system for tetanus and diphtheria toxoid, Vaccine 19 (2001) 3091–3096. [11] C. Ehrenhofer, J.P. Opdebeeck, The effects of continuous and intermittent delivery of antigens of Boophilus microplus on the development of murine antibodies, Vet. Parasitol. 59 (1995) 263–273. [12] J. Kemp, M. Kajihara, S. Nagahara, A. Sano, M. Brandon, S. Lofthouse, Continuous antigen delivery from controlled release implants induces significant and anamnestic immune responses, Vaccine 20 (2002) 1089–1098. [13] S. Lofthouse, S. Nagahara, B. Sedgmen, G. Barcham, M. Brandon, A. Sano, The application of biodegradable collagen minipellets as vaccine delivery vehicles in mice and sheep, Vaccine 19 (2001) 4318–4327. [14] A.Th. den Boer, L. Diehl, G.J.D. van Mierlo et al., Longevity of antigen presentation and activation status of APC are decisive factors in the balance between CTL immunity and tolerance, J. Immunol. 167 (2001) 2522–2528. [15] D. Moskophidis, S. Lechner, H. Pircher, R.M. Zinkernagel, Virus persistence in acutely infected immunocompetent mice by exhaustion of antiviral cytotoxic effector T cells, Nature 362 (1993) 758. [16] S.K. Switzer, B.P. Wallner, T.J. Briner, G.H. Sunshine, C.R. Bourque, M. Luqman, Bolus injection of aqueous antigen leads to a high density of T-cell-receptor ligand in the spleen, transient T cell activation and anergy induction, Immunology 94 (1998) 513–522. [17] F. Ramsdell, B.J. Fowlkes, Maintenance of in vivo tolerance by persistence of antigen, Science 257 (1992) 1130–1133. [18] X.H. Li, Y.H. Zhang, R.H. Yan et al., Influence of process parameters on the protein stability encapsulated in pol-DLlactide-poly(ethylene glycol) microspheres, J. Cont. Rel. 68 (2000) 41–52. [19] S.D. Putney, P.A. Burke, Improving protein therapeutics with
S. Lofthouse / Advanced Drug Delivery Reviews 54 (2002) 863–870
[20]
[21]
[22]
[23]
[24]
[25] [26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
sustained release formulations, Nat. Biotechnol. 16 (1998) 153–157. M. Diwan, T.G. Park, Pegylation enhances protein stability during encapsulation in PLGA microspheres, J. Cont. Rel. 73 (2001) 233–244. S.P. Schwendeman, H.R. Costantino, R.K. Gupta, G.R. Siber, A.M. Klibanov, R. Langer, Stabilization of tetanus and diphtheria toxoid against moisture-induced aggregation, Proc. Natl. Acad. Sci. USA 92 (1995) 11234–11238. Y. Wang, G. Huang, J. Wang, H. Molina, D. Chaplin, Y.-X. Fu, Antigen persistence is required for somatic mutation and affinity maturation of immunoglobulin, Eur. J. Immunol. 30 (2000) 2226–2234. E.A. Goidl, W.E. Paul, G.W. Siskind, B. Benacerraf, The effect of antigen dose and time after immunisation on the amount and affinity of anti-hapten antibody, J. Immunol. 100 (1968) 371–375. A. Gonzalez-Fernandez, C. Milstein, Low antigen dose favours selection of somatic mutants with hallmarks of antibody affinity maturation, Immunology 93 (1998) 149– 153. G.W. Siskind, B. Benacerraf, Cell selection by antigen in the immune response, Adv. Immunol. 10 (1969) 1–50. J.E. Eyles, V.W. Bramwell, E.D. Williamson, H.O. Alpar, Microsphere translocation and immunopotentiation in systemic tissues following intranasal administration, Vaccine 19 (2001) 4732–4742. T. Kundig, M.F. Bachmann, S. Oehen et al., On the role of antigen in maintaining cytotoxic T cell memory, Proc. Natl. Acad. Sci. USA 93 (1996) 9716–9723. T. Kundig, M.F. Bachmann, P.S. Ohashi, H. Pircher, H. Hengartner, R.M. Zinkernagel, On T cell memory-arguments for antigen dependence, Immunol. Rev. 150 (1996) 63–90. M. Marumaya, K.-P. Lam, K. Rajewsky, Memory B-cell persistence is independent of persisting immunizing antigen, Nature 407 (2000) 636–642. G. Foucras, L. Gapin, C. Coureau, J.M. Kanellopoulos, J.-C. Guery, Interleukin-4-producing CD4 T cells arise froom different precursors depending on the conditions of antigen exposure in vivo, J. Exp. Med. 191 (2000) 683–693. G. Foucras, A. Gallard, C. Coureau, J.M. Kanellopoulos, J.-C. Guery, Chronic soluble antigen sensitization primes a unique memory / effector T cell repertoire associated with Th2 phenotype acquisition in vivo, J. Immunol. 168 (2002) 179–187. A. Moore, P. McGuirk, S. Adams et al., Immunization with a soluble recombinant HIV protein entrapped in biodegradable microparticles induces HIV-specific CD8( 1 ) cytotoxic lymphocytes and CD4( 1 ) Th1 cells, Vaccine 13 (1995) 1741– 1749. K.D. Newman, J. Samuel, G. Kwon, Ovalbumin peptide encapsulated in pol( D,L lactic-co-glycolic acid) microspheres is capable of inducing a T helper type 1 response, J. Cont. Rel. 54 (1998) 49–59. S. Sehra, L. Chugh, S.V. Gangal, Polarized Th1 responses by liposome-entrapped allergen and its potential in immunotherapy of allergic disorders, Clin. Ep. Allergy 28 (1998) 1530–1537.
869
[35] F. Afrin, K. Anam, N. Ali, Induction of partial protection against Leishmania donovani by promastigote antigens in negatively charged liposomes, J. Parasitol. 86 (2000) 730– 735. [36] I. Babai, S. Samira, Y. Barenholz, Z. Zakay-Rones, E. Kedar, A novel influenza subunit vaccine composed of liposomeencapsulated haemagglutinin / neuraminidase and IL-2 or GM-CSF. II. Induction of Th1 and Th2 responses in mice, Vaccine 17 (1999) 1239–1250. [37] L. Krishnan, C.J. Dicaire, G.B. Patel, G.D. Sprott, Archaeosome vaccine adjuvants induce strong humoral, cell mediated and memory responses: comparison to conventional liposomes and alum, Infect. Immun. 68 (2000) 54–63. [38] J. Mestecky, Z. Moldoveanu, M. Novak et al., Biodegradable microspheres for the delivery of oral vaccines, J. Cont. Rel. 28 (1994) 131–141. [39] T.L. Bowersock, H. Hogenesch, M. Suckow et al., Oral vaccination with alginate microsphere systems, J. Cont. Rel. 39 (1996) 209–220. [40] A.M. Hillery, Microparticulate delivery systems—potential drug / vaccine carriers via mucosal routes, Pharm. Sci. Tech. Today 1 (1998) 69–75. [41] A. Kidane, P. Guimond, T.C.R. Ju, M. Sanchez, J. Gibson, T.L. Bowersock, The efficacy of oral vaccination of mice with alginate encapsulated outer membrane proteins of Pasteurella haemolytica and One-Shot (R), Vaccine 19 (2001) 2637–2646. [42] S.Y. Seong, N.H. Cho, I.C. Kwon, S.Y. Jeong, Protective immunity of microsphere-based mucosal vaccines against lethal intranasal challenge with Streptococcus pneumoniae, Infect. Immun. 67 (1999) 3587–3592. [43] T.L. Bowersock, H. Hogenesch, S. Torregrosa et al., Induction of pulmonary immunity in cattle by oral administration of ovalbumin in alginate microspheres, Immunol. Lett. 60 (1998) 37–43. [44] J. Kunisawa, A. Okudaira, Y. Tsutusmi et al., Characterization of mucoadhesive microspheres for the induction of mucosal and systemic immune responses, Vaccine 19 (2000) 589–594. [45] M. Abd El-Shafy, I.W. Kellaway, G. Taylor, P.A. Dickinson, Improved nasal bioavailability of FITC-dextran (MW 4300) from mucoadhesive microspheres in rabbits, J. Drug Target. 7 (2000) 355–361. [46] M. Bradley, J. Eade, J. Penhale, P. Bird, Vaccines for fertility regulation in wild and domestic species, J. Biotech. 73 (1999) 91–101. [47] K.W. Burton, M. Shameem, B.C. Thanoo, P.P. DeLuca, Extended release peptide delivery systems through the use of PLGA microsphere combinations, J. Biomater. Sci. 11 (2000) 715–729. [48] B.H. Woo, J.W. Kostanski, S. Gebrekidan, B.A. Dani, B.C. Thanoo, P.P. DeLuca, Preparation, characterization and in vivo evaluation of 120-day poly( DL-lactide) leuprolide microspheres, J. Cont. Rel. 75 (2001) 307–315. [49] M.Z.I. Khan, I.G. Tucker, J.P. Opdebeeck, Cholesterol and lecithin implants for sustained release of antigen: release and erosion in vitro, and antibody response in mice, Int. J. Pharm. 76 (1991) 161–170.
870
S. Lofthouse / Advanced Drug Delivery Reviews 54 (2002) 863–870
[50] A.K. Walduck, J.P. Opdebeeck, H.E. Benson, R. Prankerd, Biodegradable implants for the delivery of veterinary vaccines; manufacture and antibody responses in mice, J. Cont. Rel. 51 (1998) 269–280. [51] A. Sanchez, R.K. Gupta, M.J. Alonso, G.R. Siber, R. Langer, Pulsed controlled-release system for potential use in vaccine delivery, J. Pharm. Sci. 85 (1996) 547–552. [52] J.L. Cleland, Single-administration vaccines: controlled-re-
lease technology to mimic repeated immunizations, Trends Biotech. 17 (1999) 25–29. [53] M. Cardamone, S. Lofthouse, J.C. Lucas, R.P. Lee, M. O’Donoghue, M. Brandon, In vitro testing of a pulsatile delivery system and its in vivo application for immunisation against tetanus toxoid, J. Cont. Rel. 47 (1997) 205–219. [54] W. Vogelhuber, P. Rotunno, E. Magni et al., Programmable biodegradable implants, J. Control. Rel. 73 (2001) 75–88.