Cytokine regulation of T-cell function: potential for therapeutic intervention

TiPS - May 1993 [Vol. 14)

16‘t 29 Koiitz. [, E, and Mertelsmann. R. (1991) Cirwcr Irtws!. 9. 529-542 30 kxenberg, S. A. et al. (1958) New Efipl. 1. .\lcri. 319, 1676-1680 31 Rosenberg, S. A. et al. (1989) Aw. SW$.

210,474-4s5

32 Thatcher, N. (1991) Clrrr. Opirz. O~WJ/. 3, 344-376 33 West, W. H. et af. (1987) Nem Exgl. 1. Med. 316,898-905 34 Kahan. 6. D. (1989) Nezu E& J. Med. 321,1725-1738 35 Sigal, N. H. and Dumont, F. J. (299.2) &ZllII. REV. ~~~~~i~~0~. 10. 5’19-560 36 Schreiber, S. L. (1991) Science 251, X%3-2%? 37 Schreiber, S. L. and Crabtree. G. R. (1992) rwm~otfof. Toduy 13, 136-142 38 SchRiber, S. L. (1992) Cell 70,365-36s 39 Price, D. J., Grove, J. R., Calvo, V., Avruch. 1. and Bierer. B. E. (1992) Science ij7, 973-977 40 Kao, C. J, et al. (1992) Nature 358,7C-73

41 Thomson, A. W. (1990) ff?tt~~t~t~~~. Today 11. 35-36 42 Morris, R. E. (1991) I~ntm~rrol. Today 12, 137-140 43 Kirkman, R. L., Barrett, L. V. and Gaulton, G. N. (1985) /. Exp. Med. 162, 358-362 4.4 Kirkman. R. L. et al. (1991) Trafrsplnrlfnfimr 51; 107-113 45 Uchiyama, J. et al. (1977) Blood 50, 481-492 46 Poiesz, B. J. ef al. (1980) Proc. Nat1Acad. Sci. USA77.7415-7419 47 Waldmann. T. A. et nI. (1984) 1. Clin. itruest. 73,1711-1718 4% Uchivama, T. et nf. (1985) J. C&n. invest. 76,4&53 49 Seiki, M. ef af. (1983) Proc. Nut! Acad. Sri. USA 80.3618-3622 50 Sodroski, J. G Rosen, C. A. and Haseltine, W. A. (1984) Science 225, 381-385 51 Jones, P. T., Dear, P. H., Foote, J.,

52 53 54 55 56 57 58

Newbereer. M. S. and Winter, G. 11986) Nntzrre 3?1,‘522-525 Queen, C. ef al. (1989) Pruc. Not1Acad. gi. USA 86.10029-10033 Junghans, R. I’. et al. (1990) Cancer Res. 50,1495-1502 Brown. P. S.. Ir ef al. 09911 Proc. Nat1 Acad. &i. UsA 88, 266$266j Hwang, J. et al. (1988) I. Biol. Chem. 263, 18650-18656 Lorberboum-Galski, H. et al. (1989) Proc. Nufi Acad. Sci. USA86, lOO%-1012 Kozak, R. W. et al. (1990) J, bnmllnot. 145,276&277l Bacha, P. ef af. (1988) 1. Exp. Med. 147,

612-622 59 Chaudhary, V. K. ef af. (1989) Nafure 339,396397 60 Kozak, R. W. ef al. (1989) Cancer Res. 49, 2639-2644 61 Kozak, R. W., Atcher, R. W., Gansow, 0. A. and Friedman, A. M. (1986) Proc. Nat1 Acad. Sci. USA 83,47&47%

lates on the possible therapeutic applicaticns of cytokine agcmists and antagonists to pert& the cytokine network as a means of generating, or controlling, T,land T-Z-type immune responses.

Fiona Powrie and Robert L. Coffman CD4+ T cells, via the cytokines that they produce, play a pivotal role in the induction and regulation of cell-mediated and humoral immunity. Recently it has become clear that the CD4+ T-ceil population is heterogeneous and that distinct CD4’ T-cell subsets, defined by their cytokine repertoire, regulate cell-mediated and humora~ immune responses. Protective responses to pathogens are dependent on activation of the appropriate T,., subset accompanied by its characteristic set of immure effector functions. Evidence to date suggesfs ihat the cytokines produced by the TH cells themselves are important regulafors of THsubset activation and differentiation. Fiona Powrie and Robert Coffman discuss how manipulation of the levels of these cytokines can be used to alter the balance of T,-cell subsets and illustrate some clinical situations where this may be beneficial. A successful immune response to an infectious agent is dependent on the activation of an appropriate set of immune effector functions. These can broadly be divided into two types, cell-mediated and humoral. Cell-mediated immune responses involve the activation of macrophages and the induction of cytotoxic CDS’ and CD4+ T cells, whereas humoral immunity is characterized by antibody production. Recently it has become clear that these two arms of the immune response are reguF. Powtie is a Postdoctoral Fellow nnd R. 1.

Coffman is Associate Director of r~~~~o~og~ at the DNAX Research lnsfifufe of Mokcuiar and CellularBjalogy, 902 Cnfi~a~iu Avenue, Palo Alto, CA 94304,USA.

lated by distinct subsets of CD4’ helper T cells, termed T,l and TJ cells, which secrete different patterns of cytokines. The distinct array of cytokines produced by each of these subsets both dictates their effector functions and also plays a major role in inhibiting the induction and effector functions of the reciprocal subset’. ht most situations, the immune systern is able to develop the TH response that is most effective for the particular type of antigen or pathogen. However, in some cases the wrong subset of T, cells is activated, often with dire consequence@. This review focuses on the role of cytokines in regulating 04’ T-cell function and specu-

Subsets of CD4+ T cells

T cells respond to antigenic stimulation with a transient burst of cytokine production. Analysis of a panel of murine CD/I+ T-cell clones has revealed distinct patterns of cytokine production*. The key differences are the expression of interferon gamma (IFN-y), tumour necrosis factor p (TNF-8) and interleukin 2 (IL-Z) by T,l clones, and IL-4 and IL-5 by T,2 clones (Table I). That these two subsets represent differentiation TABLE 1.Principal subsets of murine CD4+ Tcells

Functions

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Til’S -May 1993 fVol.141 states of T, cells in viva is shown by the highly polarized T,l and T,2 populations induced by a variety of pathogens2 and by sensitive single-cell analyses4. A third phenotype (T,O), which makes a combination of the cytokines characteristic of the other two subsets (Table I), has been reported and may dominate in the earliest stages of some responses’. The lineage relationships among these three subsets are unclear and other subsets with discrete cytokine profiles may exist. In humans, there is now considerable evidence for CD4+ T cells with cytokine patterns and functions that are comparable to murine T,O, T,l and T,2 cell@, although the expression of a few cytokines, such as IL-2 and IL-lo, may be less restricted7. As in the mouse, the T,l spectrum of cytokines is generally elevated in successful responses to a variety of intracellular pathogens’. Tn2 cytokines, on the other hand, are elevated in allergic diseases and helminth infections’,r’. In both man and mouse, most CDP T-cell populations and clones have a TJ-like cytokine pattern, but there is recent evidence that T,2like CDS+ T ceils occur in both speciesl’G1*. Nearly all of the regulatory and direct effector functions of T, cells are mediated by the cytokines they secrete. Not surprisingly then, T,l and T,2 clones and populations mediate a number of quite distinct functions. T,2 cells stimulate the production of three of the hallmark features of allergic diseases: mast cells, eosinophils and IgE antibodies, which mediate the degranulation of the two inflammatory cell typesl. The cytokines responsible for these activities are IL-4 for IgE productionX3, IL-5 for eosinophilia14, and the combination of IL-3, IL-4 and IL-10 for mast cell productions’. These TW2-specific responses are prominent in infections with metazoan parasites, although it is controversial whether these responses are always beneficial to the host2r3. The cytokines produced by T,.,l cells mediate a very different set of immune responses. Central to these is the activation of macrophages by IFN-y and, to some extent, by TNF and granulocytecolony-stimulating macrophage

165 factor. This results in enhanced antigen presentation, phagocytosis, Fe receptor expression and nitric oxide and superoxide produ:cL!an’6. These changes lead to substantial increases in the ability of macrophages to kill a wide variety of intracellular and extracellular pathogens and to enhance the development of immunity to those long-term organismsr’. T-1, but not T,Z cells, also mediate the complex cellular inflammatory response known as delayed-type hypersensitivity (DTH)r’. Furthermore, by secreting IFN-y and TNF they are also directly cytotoxic to some cell types l9 . Thus, each T, subset induces and regulates a coherent set of effector functions targeted at specific types of antigens and pathogens. Central regulatory pathways Given the very different consequences of immune responses dominated by T,l or T,2 subsets, an understanding of the regulation of the development and function of these cells becomes central to the understanding of immunoregulation. Control can occur at several levels, as summarized in Fig. 1. Diflerentiaficitz The emerging consensus is that the T,l and T&I subsets arise from a common precursor, which secretes high levels of IL-2 but little IL-4 or IFN-y, through a process of antigen-driven extramattiration5*20,21. The thymic alternative hypothesis, that these subsets exist as committed precursors in the thymus, has not been definitively excluded, but there is little evidence to support it. It has been postulated that many factors, such as antigen concentration, the nature of antigenpresenting cells and mi~en~ronmental factors, such as hormones can affect T, subset differentiation. However, the most definitive studies highlight a role for cytokines themselves. The presence of IL-4 in the early stages of T-cell stimulation (polyclonal or antigen specific) in z&o, ieads to strong polarization of the T cells towards the T,2 phenotype and the secretion of high levels of IL-4 upon restimuIation*‘. T,,l diffe~ntiation to the same stimuli can be induced by IFN-y or

TGF-l3, especially in the absence of IL-4 (Ref. 21). A role for IL-12 in inducing T,l responses has recently been proposed22. Studies in mice infected with the protozoan parasite Leishmania major confirm the importance of IFN-y and IL-4 for T,l and T,2 differentiation in viva Anti-IFN-y administered at the time of L. major infection ablates the healing associated with the normal T,l response of C3H mice23. Furthermore, early treatment of BALBlc mice with anti-IL-4 antibodies results in inhibition of the nonprotective T,2 response and establishment of a protective T,l population24*25. Manipulating cytokine levels at the early stages of antigen encounter may be very useful for vaccine strategies in a number of disease situations, discussed in detail below. Questions left unanswered include: what are the cellular sources of these cytokines produced so early in a primary response? immune Moreover, what triggers their production? Possible candidates include the non-antigen-specific cells of the immune system such as NK cells, macrophages and mast cells25~26or possibly the T cells themselves. Reciprocal regulation of TMsubsets A major challenge for successful immunotherapy directed at T, subsets is to convert an already established, but inapprop~ate, T, response into one that is beneficial, or at least not pathological. To do this requires a clear understanding of how growth and cytokine production by T,l and T,2 cells are regulated. Results from a number of recent studies, mainly in vitro, suggest that the cytokines produced by the T,l and T,2 subsets themselves reciprocally regulate the functions of each other. For exampfe, IFN-y inhibits the proliferation of T,2 but not T,l cells27 and It-lo, via an effect on the antigen-presenting cells, inhibits the synthesis of IFN-y and other cytokines by T,l clones28. IL-~ also inhibits the synthesis of IFN-y by human peripheral blood mononuclear cell.99 and mouse CD4” 1: cells (Powrie, F. and Coffman, R. L., unpublished). Cytokines produced by T,l and T,2 subsets also antagonize the

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Fig. 1. Diagram of the prominent regulatory interaclions behveen 1334’ T-cell subsets. The control of TNsubsets and fheir efff?cfor functions occurs at three distinct stages. Most of these interactions have been demonstrated in the mouse both in vitro and in viva, end many have been ~o~~~ in humans in vitro. DTH, dela~d-type hypemensjtivi~.

effector functions of one another. antagonizes a number of the IL-4-mediated effects on I3 cells such as induction of class II MHC antigens and CD23 ex-

IFNy

pression”*3 and isotype switching to IgE and IgGl (Ref. 32). The TJ cytokines IL-4 and IL-10 inhibit a number of T,l effector functions, notably the induction by IFN-y of cytokine production (IL-l, TNF-cu, IL-6)33,34 and reactive oxygen and nitrogen intermediates by macrophages and monocytes3. Recent evidence suggests that the inhibitory activities of IL-4 and IL-10 are complementary. IL-4 and IL-10 synergize with TGF-8 to inhibit macrophage cytotoxici~’ and a combination of IL-4 and IL-10 inhibits DTH responses in mice, more effectively than either cytokine alone (Powrie, F., Menon, S. and Coffman, R. L., unpublished~. Thus, the products of T,l and T,2 cells play a major role in mutual regulation of their differentiation and subsequent effector

functions

(Fig. 1). Regulation

can

occur at several levels, the results of which are complementary. For example, IL-4 acts on differentiation to stimulate T,2 development, whilst at the same time inhibiting “I’,1 effector function. The net result of this is a strong enhancement of T,2 activity at the expense of T,l ceils. A simifar but reciprocal scheme can be put forward for IFN-y (Fig. 1). T-cell subset manipulation in disease states These recent advances in our understanding of T-cell mediated immunoregulation suggest a number of potential therapeutic applications. Tools for cytokine manipulation Over the past decade, it has become clear that cytokines are integral components of the complex intercellular communication required to mount and control an immune response, Studies that have elucidated the activities of

individual cytokines have also identified many new strategies for possible therapeutic intervenfion in infectious and immunological diseases. Furthermore, many cytokines themselves {and sometimes their receptors) are potential therapeutic agents. Cytokine-receptor interactions are especially attractive targets for immune system modulation because of their exquisite specificity and accessibility in the extracellular environment. The central problem is how to apply what is known to the treatment of specific diseases. The similarities in the general features of T-cell regulation between mice and humans have made murine models exceptionally useful for sorting out the activities of cytokines and the consequences of modulating the levels o’ ii~dividual cytokines in vim. Several important tools are available for this work, including recombinant cytokines and neutralizing anti-cytokine antibodies. More recently, transgenic and

TiPS - May 1993 [Vol. 141 homologous recombinar,t (‘gene knockout’) mice, with surfeits or deficits of specific cytokines, have become available36,s7. In many instances, the removal of specific cytokines in viva has had more profound and informative effects than their addition2s*3s. This suggests that cytokine antagonists may often be more valuable in the clinic than the cytokines themselves. Neutralizing anti-cytokine antibodies constitute one class of cytokine antagonist. While they may have limited intrinsic therapeutic utility, they afford an opportunity to evaluate the benefits and side-effects of more ‘drug-like’ cytokine antagonists, before the latter are developed. Many other molecules are being evaluated for cytokine antagonist activity, including naturally occurring cytokine analogs with antagonist activity39, mutant cytokines40, soluble cytokine receptor fragments4r, along with other peptides and small molecular weight compounds. Interest has focused on three major classes of disease in which modulation of T-cell activities by cytokine agonists and antagonists may provide significant benefit. Znfectious diseases There is now considerable evidence that the failure to control or resolve infectious diseases often results from inappropriate rather than insufficient immune responses. A good example is nonhealing forms of leishmaniasis in mice and humans, which represent strong, but counterproductive T,2dominated responses2f42. Intervention in this situation could be aimed at expanding protective TJ cells or alternatively enhancing the key protective response macrophage activation by IFN-y. IFN-y has already proven its utility as an adjunct to drug therapy for the treatment of visceral leishmaniasis in humans43. For some infections, such as leprotomatous leprosy, it may be more useful to prevent the dominant, but inappropriate, T,2 response from actively inhibiting diseasecontrolling TJ response@. Experiments with animal models also show the usefulness of antagonizing cytokines that mediate pathologies, disease-associated such as granuIomas and cerebral malaria45.

167 autoimmune diseases In contrast to the benefits of ‘I,,1 inflammatory responses to many pathogenic microorganisms, such responses to self-antigens are usually deleterious. Several animal models of human inflammato~ autoimmune diseases suggest that preferential activation of T,l responses is central to the pathogenesis of these diseases. Experimental allergic encephalomyelitis (EAE) is a CD4+ T-cell mediated autoimmune, inflammatory disease of the CNS that can be induced in rodents by injection of myelin basic protein in complete Freund’s adjuvantd6. Some forms of EAE are thought to be good models of multiple sclerosis (MS) in humans. T-cell lines and clones that transfer EAE in the rat and the mouse produce the TJ cytokines IFN-y, IL-2, TNF-cu and TNF-S (Refs 47, 48) and these cytokines are present in the CNS of animals with active disease49. SP ontaneous recovery of rats and mice with EAE correlates with an expansion of T,2-like cells and cytokines49*50. Immunization with myelin basic protein under conditions that lead to enhanced antibody production5i or IL-4 and TGF-S production4’ also inhibits disease as does treatment with anti-TNF antibodysZ. It may be anticipated from these results that treatment of mice with IL-4 and/or IL-10 may ameliorate inflammatory responses in EAE by inhibiting T,l effector mechanisms and inducing protective T,2 cells. Such treatment may also be beneficial for patients with MS, although at present there is little information on cytokine production in MS. It is worth noting, however, that at least one ciinical trial of IFN-y in MS patients resulted in the exacerbation of symptoms in many patients? There is also evidence of T,l cell involvement in insulin-dependent diabetes mellitus (IDDM) in humans and animal models of the disease. IFN-y production correlates with diabetes in non-obese diabetic mice whereas anti-IFN-y prevents disease inductions4. A high frequency of IFN-y-containing lymphocytes (40%) infiltrating the islets was detected in autopsy pancreases from patients with IDDM55. Recently, an inverse relationship between autoanti-

Inflammatory

body production and T-cell proliferative responses to the islet cell autoantigen, glutamic acid decarboxyIase, has been described in prediabetic individuals. It has therefore been suggested that those at high risk of developing IDDM mount a T,l and not a T,2 response to the antigen56. A T,2 response may be protective in this situation. Spontaneous diabetes in rats that are rendered lymphopoenic by adult thymectomy and sublethal irradiation can be prevented by transfer of a subpopulation of CD4’ T cells (~D45R~1~w) from normal donors. These have been shown to produce IL-4 upon polyclonal stimulation57. As with EAE, a combination of T,l antagonists iind T,2 agonists may be useful to reset the T-cell subset balance in IDDM. A number of factors have been linked to genetic predisposition to IDDI@ and it may be possible to use IL-4 and IL-10 together with relevant antigens in high risk individuals to alter the qualitative nature of the immune response to a less pathogenic one. Allergic disease Most allergic diseases appear to represent T,2-like responses to single or multiple environmental antigens. Although the degree to which IgE, mast cells and eosinophils are involved differs arnong specific diseases, much of the available evidence suggests the involvement of T,2-specific cytokines in each of these responses58c59. Thus, strategies similar to those outlined above could be aimed at allergen-specific reAlready, IFN-(u, which sponses. shares many activities with IFN-y, has been used to reduce IgE and eosinophil levels in patients with hyper-IgE and hypereosinophil syndromes60~6’. Recently, substantial alteration of the allergenspecific TH subset balance has been accomplished i?z vitro by antigen stimulation of T, cells in the presence of IFN-Y or IFN-o and/or anti-IL-4 antibodies“‘. cl

•J

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The complex web of cytokine regulation of T-cell function is gradually being untangled. Major players have emerged and immunotherapy aimed at manipulating these has already shown

TiPS - May 2993 Wol. 241

168 success. On the basis of these Fromising results it is a possibility that in the next decade cytokine therapy for certain diseases will be commonplace. some

Acknowledgement We are grateful to Dann Finn for help with graphics. DNAX Research Institute is supported by the Schering Plough Corporation. References 1 Mosmann, T. R. and Coffman, R. L. (1989) Annu. Rev. Z~~zz~no~.7,14S-173 2 Sher, A. and Coffman, R. L. (1992) Armu. Rev. Itxmunol. 10.385-409 3 Sher, A. ef al. (1992) Immunol. Rev. 127, 183-204 4 Carding. S. R., ?Vest, J., Woods, A. and Bottomly,K. (1989) Eur. J. ~~~~?ro~. 19, 231-238 5 Mosmann, T. R. et al. (1991) Immwrol. Rev. 123,209-229 6 Romagnani. S. (1991) Zmmunol. Today 12,2x-257 7 Yssei, H. et al. (1992) I. Immunof. 149, 2378-2384 8 Yamamura, M. ef al. (1991) Science 254, 277-279 9 Limaye, A. I’., Abrams, J. S,, Silver, J. E., Ottesen, E. A. and Nutman, T. 8. (1990) 1. Exp. Med. 172. 399-402 10 Maggi, E. et al. (1992) J. ilmmw,ml. 148, 2142-2147 11 Salgame, P. et al. (1991) Science 254, 379-287 _. -_12 Seder, R. A. et at. (1992) I. Inmmnol. 148, lbS2-1656 13 Coffman, R. L. and Cart), J. (1986) J. Immunol. 136, 949-954 14 Sanderson, C. j., O’Garra, A. O., Warren, D. J. and Klaus, G. G. (1986) Proc. Nafi Acaci. Sci. USA 83, 437-440 15 Thompson-Snipes, L. et al. (1991) j. Exp. Med. 173,507-510 16 Murray, H. W. (1990) Diugn. Microbial. Infect. Dis. 13,411-421 17 Murray, H. W., Spitalny, G. L. and

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de Vries,

61 Zielinski, R. M. and Lawrence, W. D. (1990) Ann. Intern. Med. 113, 7X-718

in ~rnrn~~~~~gy Today Viral i~~~~ol~~

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