Background: T follicular helper cells (Tfh) are essential to shape B cell response during germinal center formation. Tfh accumulation has been reported in various human cancers, with positive or negative prognostic roles. However, the mechanisms explaining the accumulation of Tfh and their role in cancer remain obscure. Methods: In vitro differentiated and mouse cell sorted Tfh phenotype was evaluated by flow cytometry and quantitative PCR (qPCR). Antitumor effect of Tfh was evaluated by adoptive transfer in different tumor-bearing mice models. The involvement of immune cells, cytokines and chemokines was evaluated, using depleting antibodies. Chemokines and cytokines expression and production were evaluated by qPCR and ELISA. In human, the impact of immune cells and chemokines on survival was evaluated by analyzing transcriptomic data from public databases and from our own patient cohorts. Results: In this study, we show that Tfh exert an antitumor immune effect in a CD8⁺-dependent manner. Tfh produce interleukin-21, which sustains proliferation, viability, cytokine production and cytotoxic functions of exhausted T cells. The presence of Tfh is required for efficacy of antiprogrammed cell death ligand-1 therapy. Tfh accumulate in the tumor bed and draining lymph nodes in different mouse cancer models. This recruitment is due to the capacity of transforming growth factor β to drive Chemokine (C-X-C motif) Ligand 13 expression, a chemoattractant of Tfh, by intratumor CD8⁺ T cells. Accumulation of Tfh and exhausted CD8⁺ T cells predicts cancer outcome in various cancer types. In patients treated with anti-programmed cell death-1 mAb, accumulation of Tfh and CD8⁺ at the tumor site is associated with outcome. Conclusion: This study provides evidence that CD8⁺/Tfh crosstalk is important in shaping antitumor immune response generated by immunotherapy.

Polycythemia vera belongs to myeloproliferative neoplasms, essentially by affecting the erythroblastic lineage. JAK2 alterations have emerged as major driver mutations triggering PV-phenotype with the V617F mutation detected in nearly 98% of cases. That’s why JAK2 targeting therapeutic strategies have rapidly emerged to counter the aggravation of the disease. Over decades of research, to go further in the understanding of the disease and its evolution, a wide panel of genetic alterations affecting multiple genes has been highlighted. These are mainly involved in alternative splicing, epigenetic, miRNA regulation, intracellular signaling, and transcription factors expression. If JAK2 mutation, irrespective of the nature of the alteration, is known to be a crucial event for the disease to initiate, additional mutations seem to be markers of progression and poor prognosis. These discoveries have helped to characterize the complex genomic landscape of PV, resulting in potentially new adapted therapeutic strategies for patients concerning all the genetic interferences.

T follicular helper (Tfh) cells are a subset of CD4+ T cells essential in immunity and have a role in helping B cells produce antibodies against pathogens. However, their role during cancer progression remains unknown. The mechanism of action of Tfh cells remains elusive because contradictory data have been reported on their protumor or antitumor responses in human and murine tumors. Like Tfh cells, Th2 cells are also involved in humoral immunity and are regularly associated with tumor progression and poor prognosis, mainly through their secretion of IL4. Here, we showed that Tfh cells expressed hematopoietic prostaglandin D2 (PGD2) synthase in a pSTAT1/pSTAT3-dependent manner. Tfh cells produced PGD2, which led to recruitment of Th2 cells via the PGD2 receptor chemoattractant receptor homologous molecule expressed on Th type 2 cells (CRTH2) and increased their effector functions. This cross-talk between Tfh and Th2 cells promoted IL4-dependent tumor growth. Correlation between Th2 cells, Tfh cells, and hematopoietic PGD2 synthase was observed in different human cancers and associated with outcome. This study provides evidence that Tfh/Th2 cross-talk through PGD2 limits the antitumor effects of Tfh cells and, therefore, could serve as a therapeutic target.

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.

Supplementary Figure from Hematopoietic Prostaglandin D2 Synthase Controls Tfh/Th2 Communication and Limits Tfh Antitumor Effects

T follicular helper (Tfh) cells are a subset of CD4+ T cells essential in immunity and have a role in helping B cells produce antibodies against pathogens. However, their role during cancer progression remains unknown. The mechanism of action of Tfh cells remains elusive because contradictory data have been reported on their protumor or antitumor responses in human and murine tumors. Like Tfh cells, Th2 cells are also involved in humoral immunity and are regularly associated with tumor progression and poor prognosis, mainly through their secretion of IL4. Here, we showed that Tfh cells expressed hematopoietic prostaglandin D2 (PGD2) synthase in a pSTAT1/pSTAT3-dependent manner. Tfh cells produced PGD2, which led to recruitment of Th2 cells via the PGD2 receptor chemoattractant receptor homologous molecule expressed on Th type 2 cells (CRTH2) and increased their effector functions. This cross-talk between Tfh and Th2 cells promoted IL4-dependent tumor growth. Correlation between Th2 cells, Tfh cells, and hematopoietic PGD2 synthase was observed in different human cancers and associated with outcome. This study provides evidence that Tfh/Th2 cross-talk through PGD2 limits the antitumor effects of Tfh cells and, therefore, could serve as a therapeutic target.