Regulatory T cells (Treg) play a crucial role in controlling immune homeostasis. Several inflammatory diseases including multiple sclerosis and inflammatory bowel disease have been associated with dysfunctional and/or reduced numbers of Treg. While several mechanisms of action have been discovered by which Treg can exert their function, disease-specific Treg requirements remain unknown. The Treg pool consists of highly diverse subpopulations, indicating that there is a potential to optimise Treg-targeted therapies if disease-relevant mechanisms can be established. Microarray data from our lab suggests a marked upregulation of the integrin αv as well as the IL-33 receptor ST2 in Treg retrieved from the inflamed central nervous system (CNS) during experimental autoimmune encephalomyelitis compared to peripheral lymphoid organs. These two molecules were further investigated within this PhD project with the aim to understand their role in Treg function during chronic inflammatory disease. αvβ integrins have been reported to be needed for effector T cell migration to inflamed sites through binding of extracellular matrix components and are involved in TGF-β activation by a variety of cell types. Conditional knockout mice lacking the integrin αv specifically in Foxpγ+ Treg were generated to address the role of αv integrins on regulatory T cells in inflammatory disease. αv-/- Treg showed a deficiency in activating latent TGF-β, but were able to suppress responder T cell proliferation in vitro as well as in vivo. αv-/- Treg were also able to migrate to the inflamed CNS during EAE and resolve disease. However, αv-/- Treg were detected at significantly lower numbers and proportions in the inflamed gut during a curative T cell transfer model of colitis; this led to a quantitative impairment in the ability of αv-/- Treg to cure colitis when compared to wild-type (WT) Treg. Whether this is a deficit in migration, survival, proliferation, or Foxp3 stability, remains to be investigated. IL-33 acts as an alarmin and is best studied as a cytokine released upon tissue damage that induces a potent type 2 immune response by acting on a multitude of immune cells. Expression of the IL-33 receptor ST2 on Treg has recently been associated with positive metabolic parameters in visceral adipose tissue, protection from gut inflammation, and tissue-restorative function in other inflamed tissues such as injured muscle or lung. This project showed that in steady state, ST2+ Treg expressed high levels of several markers which have been associated with potent regulatory function. When stimulated in vitro, ST2+ Treg showed a better survival and expansion rate compared to their ST2- counterparts, even more so in the presence of IL-33. T-bet deficiency in Treg resulted in an increased ST2+ Treg pool, and T-bet-associated cytokine IFN-γ was found to antagonise IL-33-induced expansion of the ST2+ Treg pool in a T-bet-independent manner. When ST2+ and ST2- Treg were tested for their respective suppressive capacity in vivo, ST2+ Treg were able to suppress responder T cell expansion despite being found only at low numbers in secondary lymphoid organs compared to ST2- Treg. However, in a curative model of T cell transfer colitis, ST2+ Treg were less capable of controlling the ongoing immune response than ST2- Treg. A possible explanation for the superiority of ST2- Treg in this setting can be found in the fact that injected ST2- Treg acquired a distribution of ST2 expression reminiscent of WT Treg over the course of disease. On the other hand, an increased starting pool of ST2+ Treg as occurs in T-bet-/- Treg significantly enhanced the capacity of Treg to control colitis compared to WT Treg. In conclusion, both ST2- and ST2+ Treg are likely to have a distinct, non-redundant role in suppressing T cell activation in secondary lymphoid organs and controlling ongoing inflammation in peripheral tissue, respectively.

O carcinoma espinocelular (CEC) é um dos cânceres humanos mais incidentes. A despeito do entendimento da fisiopatologia do CEC, as opções terapêuticas ainda são limitadas e o(s) exato(s) mecanismo(s) envolvido(s) na progressão deste tipo de tumor ainda não foi descrito. Estudos recentes mostram a existência de uma associação direta entre a resposta imune TH1 e um melhor prognóstico em pacientes com CEC. Aumento da expressão de componentes do eixo IL-33/ST2 foi demonstrado contribuir para transformação neoplásica em diversos modelos tumorais, incluindo cânceres de estômago e de mama. Trabalho recente do nosso e de outros laboratórios indicam que IL-33 pode impedir a resposta imune TH1 . Baseado nessas observações, a hipótese testada foi que o impedimento da resposta imune pela interação IL-33/ST2 pode contribuir para iniciação e progressão do CEC. Utilizando modelo de carcinogênese química em camundongos WT e deficientes de ST2 (ST2KO), os resultados mostram que a deficiência de ST2 leva a uma notável redução da severidade das lesões 20 semanas após a carcinogênese química, sugerindo que a sinalização ST2 é necessária para o desenvolvimento tumoral neste modelo. Análises do infiltrado inflamatório presente nas lesões em camundongos WT e ST2KO revelaram redução significativa nas percentagens de macrófagos, células T CD4+ e células dendríticas, mas não em células T CD8+, células B e células natural killer (NK) no microambiente tumoral de camundongos ST2KO. Além disso, células NK esplênicas isoladas de camundongos ST2KO exibiram atividade citotóxica aumentada contra células YAC quando comparado com células de camundongos do grupo controle (WT). Os resultados indicam que a via IL-33/ST2 contribui para o desenvolvimento de carcinoma espinocelular recrutando células T CD4+, macrófagos e células dendríticas e reduzindo a citotoxicidade de células NK. / Squamous cell carcinoma (SCC) is the second most common form of skin cancer and is most commonly observed in photo-exposed areas of the body. The mechanism(s) involved in the progression of this tumor are unknown. Recent studies have shown that there is a direct association between a TH1-related immune response and a better prognosis in patients with SCC. Increased expression of the IL33/ST2 axis components has been demonstrated to contribute to neoplastic transformation in several tumor models, including gastric and breast cancer. Recent work from ours and other laboratories indicate that can IL-33 impair TH1-type immune responses. Based on these observations, we hypothesized that TH1-type immune response impairment by IL33/ST2 could contribute to the initiation and progress SCC. We found that ST2 deficiency led to a marked decreased in severity of skin lesions at 20 weeks post-DMBA, suggesting that ST2 signaling is necessary for tumor development in this model. Analysis of tumor lesions in WT and ST2KO mice revealed that lack of ST2 led to a specific and significant reduction in the frequency of macrophages, T CD4+ and dendritic cells, but not CD8+, B and NK cells. In addition, splenic NK cells isolated from DMBA-treated ST2KO mice exhibited increased cytotoxicity activity against YAC cells targets when compared with WT splenic NK cells in the same cytotoxic assay. Altogether, our findings indicate that IL-33/ST2 pathway contributes to the SCC development by recruitment T CD4+ cells, macrophages, and dendritic cells and impairing NK cytotoxicity.

O carcinoma espinocelular (CEC) é um dos cânceres humanos mais incidentes. A despeito do entendimento da fisiopatologia do CEC, as opções terapêuticas ainda são limitadas e o(s) exato(s) mecanismo(s) envolvido(s) na progressão deste tipo de tumor ainda não foi descrito. Estudos recentes mostram a existência de uma associação direta entre a resposta imune TH1 e um melhor prognóstico em pacientes com CEC. Aumento da expressão de componentes do eixo IL-33/ST2 foi demonstrado contribuir para transformação neoplásica em diversos modelos tumorais, incluindo cânceres de estômago e de mama. Trabalho recente do nosso e de outros laboratórios indicam que IL-33 pode impedir a resposta imune TH1 . Baseado nessas observações, a hipótese testada foi que o impedimento da resposta imune pela interação IL-33/ST2 pode contribuir para iniciação e progressão do CEC. Utilizando modelo de carcinogênese química em camundongos WT e deficientes de ST2 (ST2KO), os resultados mostram que a deficiência de ST2 leva a uma notável redução da severidade das lesões 20 semanas após a carcinogênese química, sugerindo que a sinalização ST2 é necessária para o desenvolvimento tumoral neste modelo. Análises do infiltrado inflamatório presente nas lesões em camundongos WT e ST2KO revelaram redução significativa nas percentagens de macrófagos, células T CD4+ e células dendríticas, mas não em células T CD8+, células B e células natural killer (NK) no microambiente tumoral de camundongos ST2KO. Além disso, células NK esplênicas isoladas de camundongos ST2KO exibiram atividade citotóxica aumentada contra células YAC quando comparado com células de camundongos do grupo controle (WT). Os resultados indicam que a via IL-33/ST2 contribui para o desenvolvimento de carcinoma espinocelular recrutando células T CD4+, macrófagos e células dendríticas e reduzindo a citotoxicidade de células NK. / Squamous cell carcinoma (SCC) is the second most common form of skin cancer and is most commonly observed in photo-exposed areas of the body. The mechanism(s) involved in the progression of this tumor are unknown. Recent studies have shown that there is a direct association between a TH1-related immune response and a better prognosis in patients with SCC. Increased expression of the IL33/ST2 axis components has been demonstrated to contribute to neoplastic transformation in several tumor models, including gastric and breast cancer. Recent work from ours and other laboratories indicate that can IL-33 impair TH1-type immune responses. Based on these observations, we hypothesized that TH1-type immune response impairment by IL33/ST2 could contribute to the initiation and progress SCC. We found that ST2 deficiency led to a marked decreased in severity of skin lesions at 20 weeks post-DMBA, suggesting that ST2 signaling is necessary for tumor development in this model. Analysis of tumor lesions in WT and ST2KO mice revealed that lack of ST2 led to a specific and significant reduction in the frequency of macrophages, T CD4+ and dendritic cells, but not CD8+, B and NK cells. In addition, splenic NK cells isolated from DMBA-treated ST2KO mice exhibited increased cytotoxicity activity against YAC cells targets when compared with WT splenic NK cells in the same cytotoxic assay. Altogether, our findings indicate that IL-33/ST2 pathway contributes to the SCC development by recruitment T CD4+ cells, macrophages, and dendritic cells and impairing NK cytotoxicity.