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Human Vγ9Vδ2 T cell immune responses towards congenital Toxoplasma gondii infection and mistletoe extract drug stimulation

par Ma, Ling
Président du jury Fontaine, Véronique
Promoteur Vermijlen, David
Publication Non publié, 2020-10-21

Thèse de doctorat

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Résumé :

Vγ9Vδ2 T cells are the main circulating γδ T cells in human adult blood. They are known for their T cell receptor (TCR)-dependent recognition of microbe and endogenous-derived non-peptide pyrophosphate antigens (phosphoantigens, PAg). With the intrinsically biased type 1 immune responses, Vγ9Vδ2 T cells are an important force in the defense of infections and tumors. However, the immune responses of Vγ9Vδ2 T cells in early life infections and in immunotherapies are not clear yet. In this thesis, we explored Vγ9Vδ2 T cell immune responses in both aspects. Vγ9Vδ2 T cells are abundant in human fetal peripheral blood, but compared to their adult counterparts they have a distinct developmental origin, are hyporesponsive towards in vitro phosphoantigen exposure and they do not possess a cytotoxic effector phenotype. In order to obtain insight into the role of Vγ9Vδ2 T cells in the human fetus, we investigated in the first part of this thesis their responses upon in utero infection with the phosphoantigen-producing parasite Toxoplasma gondii (T. gondii). Most congenital infections are caused by viruses, T. gondii is one of the exceptions. The organelle apicoplast present in T. gondii can generate the most potent Vγ9Vδ2 T cell activator. Thus infection in utero with T. gondii makes it a good model to observe Vγ9Vδ2 T cell immune responses in early life. By comparing to age-matched controls, we found that fetal Vγ9Vδ2 T cells were highly expanded in congenital T. gondii infected newborns, and these expanded cells were highly differentiated towards potent cytotoxic effector cells. While the impact of congenital infection on Vγ9Vδ2 T cell expansion and function waned after birth, the Vγ9Vδ2 TCR repertoire of infected infants possessed a clear fetal footprint with public clonotypes, reflecting the Vγ9Vδ2 T cell response in utero. Indeed, verification of the antigen recognition related complementarity-determining region 3 (CDR3) of the TCR for γ and δ chain by high-throughput sequencing revealed the enrichment of three Vδ2 sequences in congenitally-infected infants that are already generated at 8 weeks of gestation. Vγ9Vδ2 T cells possess several characteristics, including MHC-independent recognition of tumor cells and potent killing potential, that make them attractive candidates for cancer immunotherapeutic approaches. In the second part of this thesis we investigated Vγ9Vδ2 T cell responses towards two kinds of hemiparasite plant Viscum album L. (European mistletoe) extract drugs in vitro. Mistletoe therapy is the most used complementary cancer therapy in European countries. Mistletoe extract drugs are considered to benefit for increasing the quality of life of cancer patients and modulate immune cells, but the mechanism of action is not clear. Here, we investigated in-depth the in vitro response of human T cells towards mistletoe extract drugs by analyzing their functional and TCR responses using flow cytometry and high-throughput sequencing respectively. Non-fermented mistletoe-extract drugs (AbnobaViscum), but not their fermented counterparts (Iscador), induced specific expansion of Vγ9Vδ2 T cells among T cells. Furthermore, AbnobaViscum rapidly induced the release of cytotoxic granules and the production of the cytokines IFNγ and TNFα in Vγ9Vδ2 T cells. This stimulation of anti-cancer Vγ9Vδ2 T cells was mediated by the butyrophilin BTN3A, did not depend on the accumulation of endogenous phosphoantigens and involved the same Vγ9Vδ2 TCR repertoire as those of phosphoantigen-reactive Vγ9Vδ2 T cells.In summary, in the first part of this thesis we showed that the human fetus intrinsically possesses a group of Vγ9Vδ2 T cells that are responding to congenital parasite infections that provide potential protective effects to the fetus. In the second part, we provided insight into the in vitro responses of Vγ9Vδ2 T cells towards mistletoe extract drugs, indicating that Vγ9Vδ2 T cells can be an important target in mistletoe therapy.