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Immune response to bovine papillomavirus type 1 in equine sarcoid
The Veterinary Journal 216 (2016) 107–108
Contents lists available at ScienceDirect
The Veterinary Journal j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / t v j l
Guest Editorial
Immune response to bovine papillomavirus type 1 in equine sarcoid
The Papillomaviridae are a family of genetically heterogeneous DNA viruses which adhere to common biological principles. Papillomaviruses (PVs) are relatively small viruses that consist of a non-enveloped icosahedral capsid harbouring a circular double stranded DNA genome of ~8 kilobase pairs. The genome contains open reading frames encoding three early regulatory proteins (E1, E2, E4), up to three early transforming proteins (E5–E7), two late capsid proteins (L1, L2) and a non-coding long control region required for viral replication and transcription (Campo, 2006). PVs are usually highly species-specific. However, bovine papillomaviruses types 1 and 2 (BPV1, BPV2) are an exception to this rule, because of their ability to infect not only cattle and other ruminants, but also equids, i.e. horses, donkeys, zebras and mules. In the bovine host, BPV1/2 are the aetiological agents of papillomas that usually regress spontaneously. In equids, BPV1/2 are the causative agents of persistent, non-metastasising, yet locally aggressive skin tumours termed sarcoids. These constitute a significant veterinary problem because of their common occurrence, their resistance to therapy and their propensity to recrudesce in a more severe form following ineffective treatment (Hainisch and Brandt, 2015). Despite the high impact of sarcoids on the health and welfare of affected horses and other equid species, only limited information is available regarding the innate and adaptive immune responses to BPV1/2 infection and the mechanisms underlying the ability of the virus to escape immune surveillance, which entails the establishment of a permanent infection and the development of persistent sarcoids (Campo, 2006). In cattle, BPV1/2 infection is restricted to the epidermis and is productive in this skin layer. The viral life cycle is tightly linked to keratinocyte differentiation. Following initial infection of basal keratinocytes, which provide the surface molecules required for virus entry, early protein expression occurs in the basal and suprabasal epidermal layers. Replication of the viral genome is confined to the differentiating keratinocytes of the spinous and granular layers. Capsid protein expression and subsequent virion assembly are restricted to the squamous layer, from which infectious particles are ultimately released via desquamation (Campo, 2006). The antibody response to BPV1 infection is limited. Initially, infection is probably overlooked by the immune system because of its strict tropism for keratinocytes and a general lack of inflammation, which otherwise would alert the immune system. However, T and B cell responses to viral L1 and E7 antigens are observed at later stages of disease, thus giving a possible explanation for the usual transience of bovine papillomas (Campo, 2006). Spontaneous regression of BPV type 4-induced bovine papillomas has been associated with high densities of activated lymphocytes, notably CD4+ http://dx.doi.org/10.1016/j.tvjl.2016.07.012 1090-0233/© 2016 Elsevier Ltd. All rights reserved.
T helper cells accumulating in the dermis underlying the papilloma, and cytotoxic T lymphocytes (CTLs) and γδ T cells infiltrating the epidermal microenvironment. This infiltration pattern is generally encountered in spontaneously regressing PV-associated lesions (Campo, 2006). In human PV (HPV)-induced cervical tumours, lack of inflammation entails reduced viral/tumour antigen presentation by dendritic cells (DCs), particularly Langerhans cells. However, spontaneous regression of cervical intraepithelial lesions may occur and is commonly associated with infiltration by T helper cells, whilst invasive tumours harbour CTLs, but also recruit significant numbers of CD4+FoxP3+CD25+ regulatory T cells (Tregs), which promote cancer progression and metastasis by suppressing the activation and expansion of effector T cells (Patel and Chiplunkar, 2009). PV-induced cancer cells not only attract Tregs into their microenvironment, but by means of deregulated signalling pathways, also recruit protumoural M2 macrophages, myeloid-derived suppressor cells (MDSCs) and T helper 2 cells that directly suppress the antitumoural immune response. Moreover, these cell types can actively promote tumour growth and maintenance by providing cytokines and growth factors, such as interleukin 6 and vascular endothelial growth factor (Allen et al., 2015). In horses, the immune response to sarcoids remains largely unknown and systematic investigations are desperately needed to uncover the mechanisms underlying sarcoid persistence and progression. Intramuscular immunisation of horses with BPV1 L1 virus-like particles (VLPs) has been shown to elicit high titres of BPV1-neutralising serum antibodies (Hainisch et al., 2012, 2015). In contrast, natural or experimental infection of the skin by wildtype BPV1/2 does not induce a measurable antibody response (Hartl et al., 2011). This may be partly explained by several particular characteristics of BPV1/2 infection in equids: (1) infection mainly involves dermal fibroblasts, where it is abortive; (2) the viral genome resides in infected fibroblasts as multiple episomes that replicate in synchrony with the cell cycle; and (3) viral protein expression seems to be restricted to early regulatory and transforming proteins, the latter inducing excessive cell proliferation (Hainisch and Brandt, 2015). Importantly, the E5 oncoprotein is constitutively expressed in tumour cells throughout disease and down-regulates major histocompatibility (MHC) class I expression, thus abrogating MHC I-mediated antigen presentation to CD8+ T cells (Marchetti et al., 2009). In a recent issue of The Veterinary Journal, Dr Helena Geisshüsler and colleagues from the Swiss Institute of Equine Medicine, Agroscope Liebefeld-Posieux Research Station (ALP-Haras) and the Vetsuisse Faculty of the University of Berne, Switzerland, present the findings of a study focussing on histological analysis of equine
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Guest Editorial / The Veterinary Journal 216 (2016) 107–108
sarcoids for the presence and distribution of CD4+, CD8+, FoxP3+, RORγt-, CD206+ and CD14+ cells, along with BPV1 regulatory protein E2 expression, using immunofluorescent staining in combination with a high content analysis system (Geisshüsler et al., 2016). Recent evidence also suggests that sarcoids are infiltrated by a specific subset of Tregs, since large amounts of intralesional FoxP3+ and dual CD4+CD8+ T cells have been demonstrated. This interpretation is supported by the observation that the sarcoids analysed also lacked effector T cell cytokine expression (Wilson and Hicks, 2016). An increased presence of Tregs in equine sarcoids is further strengthened by a report on significantly elevated FoxP3 transcription in tumour tissue in comparison to intact skin (Mahlmann et al., 2014). Sabine Brandt Oncology Research Group, Equine Clinic, University of Veterinary Medicine, 1210 Vienna, Austria E-mail address: [email protected]
References Allen, C.T., Clavijo, P.E., Van Waes, C., Chen, Z., 2015. Anti-tumor immunity in head and neck cancer: Understanding the evidence, how tumors escape and immunotherapeutic approaches. Cancers 7, 2397–2414.
Campo, M.S. (Ed.), 2006. Papillomavirus Research: From Natural History to Vaccines and Beyond. Caister Academic Press, Norfolk, UK. 424 pp. Geisshüsler, H., Marti, E., Stoffel, M.H., Kühni, K., Stojiljkovic, A., von Tscharner, C., Vidondo, B., Gerber, V., Koch, C., 2016. Quantitative analysis of infiltrating immune cells and bovine papillomavirus type 1 E2-positive cells in equine sarcoids. The Veterinary Journal doi:10.1016/j.tvjl.2016.06.016. Hainisch, E.K., Brandt, S., 2015. Equine sarcoids. In: Robinson, N.E., Sprayberry, K.A. (Eds.), Robinson’s Current Therapy in Equine Medicine. Saunders Elsevier, St Louis, Missouri, USA, pp. 424–427. Hainisch, E.K., Brandt, S., Shafti-Keramat, S., Van den Hoven, R., Kirnbauer, R., 2012. Safety and immunogenicity of BPV-1 L1 virus-like particles in a dose-escalation vaccination trial in horses. Equine Veterinary Journal 44, 107–111. Hainisch, E.K., Abel, H., Harnacker, J., Wetzig, M., Shafti-Keramat, S., Kirnbauer, R., Brandt, S., 2015. BPV1 L1 VLP vaccination shows high potential to protect horses from equine sarcoids. In: Proceedings of the 24th Annual Scientific Meeting of the European College of Veterinary Surgeons, Berlin, Germany, 2–4 July 2015. Hartl, B., Hainisch, E.K., Shafti-Keramat, S., Kirnbauer, R., Corteggio, A., Borzacchiello, G., Tober, R., Kainzbauer, C., Pratscher, B., Brandt, S., 2011. Inoculation of young horses with bovine papillomavirus type 1 virions leads to early infection of PBMCs prior to pseudo-sarcoid formation. The Journal of General Virology 92, 2437–2445. Mahlmann, K., Hamza, E., Marti, E., Dolf, G., Klukowska, J., Gerber, V., Koch, C., 2014. Increased FOXP3 expression in tumour-associated tissues of horses affected with equine sarcoid disease. The Veterinary Journal 202, 516–521. Marchetti, B., Gault, E.A., Cortese, M.S., Yuan, Z., Ellis, S.A., Nasir, L., Campo, M.S., 2009. Bovine papillomavirus type 1 oncoprotein E5 inhibits equine MHC class I and interacts with equine MHC I heavy chain. Journal of General Virology 90, 2865–2870. Patel, S., Chiplunkar, S., 2009. Host immune responses to cervical cancer. Current Opinion in Obstetrics and Gynecology 21, 54–59. Wilson, A.D., Hicks, C., 2016. Both tumour cells and infiltrating T-cells in equine sarcoids express FOXP3 associated with an immune-supressed cytokine microenvironment. Veterinary Research 47, 55.
Contents lists available at ScienceDirect
The Veterinary Journal j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / t v j l
Guest Editorial
Immune response to bovine papillomavirus type 1 in equine sarcoid
The Papillomaviridae are a family of genetically heterogeneous DNA viruses which adhere to common biological principles. Papillomaviruses (PVs) are relatively small viruses that consist of a non-enveloped icosahedral capsid harbouring a circular double stranded DNA genome of ~8 kilobase pairs. The genome contains open reading frames encoding three early regulatory proteins (E1, E2, E4), up to three early transforming proteins (E5–E7), two late capsid proteins (L1, L2) and a non-coding long control region required for viral replication and transcription (Campo, 2006). PVs are usually highly species-specific. However, bovine papillomaviruses types 1 and 2 (BPV1, BPV2) are an exception to this rule, because of their ability to infect not only cattle and other ruminants, but also equids, i.e. horses, donkeys, zebras and mules. In the bovine host, BPV1/2 are the aetiological agents of papillomas that usually regress spontaneously. In equids, BPV1/2 are the causative agents of persistent, non-metastasising, yet locally aggressive skin tumours termed sarcoids. These constitute a significant veterinary problem because of their common occurrence, their resistance to therapy and their propensity to recrudesce in a more severe form following ineffective treatment (Hainisch and Brandt, 2015). Despite the high impact of sarcoids on the health and welfare of affected horses and other equid species, only limited information is available regarding the innate and adaptive immune responses to BPV1/2 infection and the mechanisms underlying the ability of the virus to escape immune surveillance, which entails the establishment of a permanent infection and the development of persistent sarcoids (Campo, 2006). In cattle, BPV1/2 infection is restricted to the epidermis and is productive in this skin layer. The viral life cycle is tightly linked to keratinocyte differentiation. Following initial infection of basal keratinocytes, which provide the surface molecules required for virus entry, early protein expression occurs in the basal and suprabasal epidermal layers. Replication of the viral genome is confined to the differentiating keratinocytes of the spinous and granular layers. Capsid protein expression and subsequent virion assembly are restricted to the squamous layer, from which infectious particles are ultimately released via desquamation (Campo, 2006). The antibody response to BPV1 infection is limited. Initially, infection is probably overlooked by the immune system because of its strict tropism for keratinocytes and a general lack of inflammation, which otherwise would alert the immune system. However, T and B cell responses to viral L1 and E7 antigens are observed at later stages of disease, thus giving a possible explanation for the usual transience of bovine papillomas (Campo, 2006). Spontaneous regression of BPV type 4-induced bovine papillomas has been associated with high densities of activated lymphocytes, notably CD4+ http://dx.doi.org/10.1016/j.tvjl.2016.07.012 1090-0233/© 2016 Elsevier Ltd. All rights reserved.
T helper cells accumulating in the dermis underlying the papilloma, and cytotoxic T lymphocytes (CTLs) and γδ T cells infiltrating the epidermal microenvironment. This infiltration pattern is generally encountered in spontaneously regressing PV-associated lesions (Campo, 2006). In human PV (HPV)-induced cervical tumours, lack of inflammation entails reduced viral/tumour antigen presentation by dendritic cells (DCs), particularly Langerhans cells. However, spontaneous regression of cervical intraepithelial lesions may occur and is commonly associated with infiltration by T helper cells, whilst invasive tumours harbour CTLs, but also recruit significant numbers of CD4+FoxP3+CD25+ regulatory T cells (Tregs), which promote cancer progression and metastasis by suppressing the activation and expansion of effector T cells (Patel and Chiplunkar, 2009). PV-induced cancer cells not only attract Tregs into their microenvironment, but by means of deregulated signalling pathways, also recruit protumoural M2 macrophages, myeloid-derived suppressor cells (MDSCs) and T helper 2 cells that directly suppress the antitumoural immune response. Moreover, these cell types can actively promote tumour growth and maintenance by providing cytokines and growth factors, such as interleukin 6 and vascular endothelial growth factor (Allen et al., 2015). In horses, the immune response to sarcoids remains largely unknown and systematic investigations are desperately needed to uncover the mechanisms underlying sarcoid persistence and progression. Intramuscular immunisation of horses with BPV1 L1 virus-like particles (VLPs) has been shown to elicit high titres of BPV1-neutralising serum antibodies (Hainisch et al., 2012, 2015). In contrast, natural or experimental infection of the skin by wildtype BPV1/2 does not induce a measurable antibody response (Hartl et al., 2011). This may be partly explained by several particular characteristics of BPV1/2 infection in equids: (1) infection mainly involves dermal fibroblasts, where it is abortive; (2) the viral genome resides in infected fibroblasts as multiple episomes that replicate in synchrony with the cell cycle; and (3) viral protein expression seems to be restricted to early regulatory and transforming proteins, the latter inducing excessive cell proliferation (Hainisch and Brandt, 2015). Importantly, the E5 oncoprotein is constitutively expressed in tumour cells throughout disease and down-regulates major histocompatibility (MHC) class I expression, thus abrogating MHC I-mediated antigen presentation to CD8+ T cells (Marchetti et al., 2009). In a recent issue of The Veterinary Journal, Dr Helena Geisshüsler and colleagues from the Swiss Institute of Equine Medicine, Agroscope Liebefeld-Posieux Research Station (ALP-Haras) and the Vetsuisse Faculty of the University of Berne, Switzerland, present the findings of a study focussing on histological analysis of equine
108
Guest Editorial / The Veterinary Journal 216 (2016) 107–108
sarcoids for the presence and distribution of CD4+, CD8+, FoxP3+, RORγt-, CD206+ and CD14+ cells, along with BPV1 regulatory protein E2 expression, using immunofluorescent staining in combination with a high content analysis system (Geisshüsler et al., 2016). Recent evidence also suggests that sarcoids are infiltrated by a specific subset of Tregs, since large amounts of intralesional FoxP3+ and dual CD4+CD8+ T cells have been demonstrated. This interpretation is supported by the observation that the sarcoids analysed also lacked effector T cell cytokine expression (Wilson and Hicks, 2016). An increased presence of Tregs in equine sarcoids is further strengthened by a report on significantly elevated FoxP3 transcription in tumour tissue in comparison to intact skin (Mahlmann et al., 2014). Sabine Brandt Oncology Research Group, Equine Clinic, University of Veterinary Medicine, 1210 Vienna, Austria E-mail address: [email protected]
References Allen, C.T., Clavijo, P.E., Van Waes, C., Chen, Z., 2015. Anti-tumor immunity in head and neck cancer: Understanding the evidence, how tumors escape and immunotherapeutic approaches. Cancers 7, 2397–2414.
Campo, M.S. (Ed.), 2006. Papillomavirus Research: From Natural History to Vaccines and Beyond. Caister Academic Press, Norfolk, UK. 424 pp. Geisshüsler, H., Marti, E., Stoffel, M.H., Kühni, K., Stojiljkovic, A., von Tscharner, C., Vidondo, B., Gerber, V., Koch, C., 2016. Quantitative analysis of infiltrating immune cells and bovine papillomavirus type 1 E2-positive cells in equine sarcoids. The Veterinary Journal doi:10.1016/j.tvjl.2016.06.016. Hainisch, E.K., Brandt, S., 2015. Equine sarcoids. In: Robinson, N.E., Sprayberry, K.A. (Eds.), Robinson’s Current Therapy in Equine Medicine. Saunders Elsevier, St Louis, Missouri, USA, pp. 424–427. Hainisch, E.K., Brandt, S., Shafti-Keramat, S., Van den Hoven, R., Kirnbauer, R., 2012. Safety and immunogenicity of BPV-1 L1 virus-like particles in a dose-escalation vaccination trial in horses. Equine Veterinary Journal 44, 107–111. Hainisch, E.K., Abel, H., Harnacker, J., Wetzig, M., Shafti-Keramat, S., Kirnbauer, R., Brandt, S., 2015. BPV1 L1 VLP vaccination shows high potential to protect horses from equine sarcoids. In: Proceedings of the 24th Annual Scientific Meeting of the European College of Veterinary Surgeons, Berlin, Germany, 2–4 July 2015. Hartl, B., Hainisch, E.K., Shafti-Keramat, S., Kirnbauer, R., Corteggio, A., Borzacchiello, G., Tober, R., Kainzbauer, C., Pratscher, B., Brandt, S., 2011. Inoculation of young horses with bovine papillomavirus type 1 virions leads to early infection of PBMCs prior to pseudo-sarcoid formation. The Journal of General Virology 92, 2437–2445. Mahlmann, K., Hamza, E., Marti, E., Dolf, G., Klukowska, J., Gerber, V., Koch, C., 2014. Increased FOXP3 expression in tumour-associated tissues of horses affected with equine sarcoid disease. The Veterinary Journal 202, 516–521. Marchetti, B., Gault, E.A., Cortese, M.S., Yuan, Z., Ellis, S.A., Nasir, L., Campo, M.S., 2009. Bovine papillomavirus type 1 oncoprotein E5 inhibits equine MHC class I and interacts with equine MHC I heavy chain. Journal of General Virology 90, 2865–2870. Patel, S., Chiplunkar, S., 2009. Host immune responses to cervical cancer. Current Opinion in Obstetrics and Gynecology 21, 54–59. Wilson, A.D., Hicks, C., 2016. Both tumour cells and infiltrating T-cells in equine sarcoids express FOXP3 associated with an immune-supressed cytokine microenvironment. Veterinary Research 47, 55.