Il est maintenant acquis que le système immunitaire occupe une place importante dans l’évolution les cancers (Hanahan et al., 2011). La compréhension actuelle de la réponse immunitaire adaptative en fait une cible de choix dans ce contexte. Il est apparu que les lymphocytes T CD4+, acteurs majeurs de la composante adaptative du système immunitaire, présentent des actions distinctes sur le contrôle de la croissance tumorale. Ainsi, les lymphocytes Th2 et Tfh, tous deux activateurs des lymphocytes B dans des conditions de lutte contre des infections pathogéniques, présentent des rôles ambivalents dans un contexte de cancer. En effet, de nombreuses études montrent que la présence de Th2 est corrélée à une progression de la maladie (notamment via l’action de l’IL-4 qu’ils sécrètent) (Koller et al., 2010 ; Roca et al., 2012) alors que les Tfh, seraient plutôt associés à un bon pronostic pour les patients (Gu-Trantien et al., 2013, 2017).Nos investigations actuelles nous ont permis de mettre en avant une caractéristique nouvelle de la biologie des lymphocytes Tfh. En effet, les Tfh expriment l’Hemathopoietic Prostaglandin D2 synthase (HPGDS). Cette enzyme de la voie de biosynthèse des eicosanoïdes est responsable de la production de Prostaglandine D2 (PGD2). Plusieurs travaux montrent que les cellules Th2 expriment le récepteur CRTH2, spécifique de la PGD2. Cette molécule agit sur ces cellules comme chemoattractant et permet également une augmentation de leur production cytokinique. Ainsi, nous posons l’hypothèse d’une communication potentielle entre lymphocytes Tfh et Th2 via la PGD2. Le projet présenté ici est alors axé sur la compréhension des mécanismes moléculaires et cellulaires sous-jacent à cette communication au sein des deux sous-types ainsi que sur son impact dans un contexte de cancer. Ce projet ayant également pour but de mettre en avant la PGD2 comme nouvelle cible thérapeutique dans le cancer. / It is now accepted that the immune system plays a critical role in cancers evolution (Hanahan et al., 2011). In this context, current understanding of the adaptive immune response made it a prime target. T CD4 cells, the main players of the adaptive immune system component, are known to possess distinct roles in the control of tumour growth. Thereby, Th2 and Tfh cells, both known to activate B cells in pathogenic infections, present antagonistic roles in cancer. Indeed, numerous studies demonstrate that Th2 cells are correlated with disease progression (especially via IL-4 secretion) (Koller et al., 2010 ; Roca et al., 2012), whereas Tfh cells are associated with a good prognosis for the patients (Gu-Trantien et al., 2013, 2017) despite the actual limited amount of available data.Our current researches highlighted a new property of the biology of Tfh cells. We found that Tfh cells are able to express the Hemathopoietic Prostaglandin D2 synthase (HPGDS), an eicosanoid pathway enzyme involved in Prostaglandin D2 (PGD2) production. Moreover, different studies revealed that Th2 cells expressed CRTH2, the specific PGD2 receptor. PGD2 is known as a chemoattractant molecule for Th2 cells and lead to the increase of their cytokine secretion. We hypothesized that Tfh communicate with Th2 cells via PGD2 signalling. The present project is focused on the understanding of the underlying molecular and cellular mechanisms involved in this cross-talk and their impact in cancer. The last aim of this work is to favor the development of PGD2 as a new cancer therapeutic target.

Glutathione transferases (GSTs, EC.2.5.1.18) are multifunctional enzymes that are universally distributed in all cellular life forms. They play important roles in metabolism and detoxication of endogenously produced toxic compounds and xenobiotics. GSTs have gained considerable interest over the years for biomedical and biotechnological applications due to their involvement in the conjugation of glutathione (GSH) to a vast array of chemical species. Additionally, the emergence of non-detoxifying functions of GSTs has further increased their biological significance. The present work encompasses four scientific studies aimed at investigating human as well as fruit fly Drosophila melanogaster GSTs. Paper I presents the immobilization of GSTs on nanoporous alumina membranes. Kinetic analyses with 1-chloro-2,4-dinitrobenzene followed by specificity screening with alternative substrates showed a good correlation between the data obtained from immobilized enzymes and the enzymes in solution. Furthermore, immobilization showed no adverse effects on the stability of the enzymes. Paper II presents inhibition studies of human hematopoietic prostaglandin D2 synthase (HPGDS), a promising therapeutic target for anti-allergic and anti-inflammatory drugs. Our screening results with an FDA-approved drug library revealed a number of effective inhibitors of HPGDS with IC50 values in the low micromolar range. Paper III concerns the toxicity of organic isothiocyanates (ITCs) that showed high catalytic activities with GSTE7 in vitro. The in vivo results showed that phenethyl isothiocyanate (PEITC) and allyl isothiocyanate in millimolar dietary concentrations conferred toxicity to the adult fruit flies leading to death or shortened life-span. The transgenic female flies overexpressing GSTE7 showed increased tolerance against PEITC toxicity compared to the wild-type. However, the effect was opposite in male flies overexpressing GSTE7 after one week exposure. Notably, the transgene enhanced the oviposition activity of flies with and without ITCs exposure. Paper IV highlights Drosophila GSTs as efficient catalysts of the environmental pollutant and explosive 2,4,6-trinitrotoluene and the related 2,4-dinitrotoluene degradation. This result suggests the potential of GST transgenes in plants for biotransformation and phytoremediation of these persistent environmental pollutants.