Composition of CD4 T cell subsets and impact on tumor growth control across mouse syngeneic tumor models

CD4 T cells include multiple sublineages orchestrating a broad range of effector activities during the initiation, promotion, and progression of carcinogenesis. Although regulatory T cells (Tregs) are well-characterized to promote tumor progression, the impact of effector CD4+ T cell subsets (Teff) in anti-tumor immunity is less well known. Further, the relative contribution of Teff and Treg cell subsets in different syngeneic tumor models has not been characterized. We observed that CD4 depletion had significantly different impact of tumor growth across different syngeneic tumor models: no effect on MC38 tumor growth; enhanced tumor growth in CT26.KSA tumor model; while almost complete tumor regression in the EMT-6 tumor model. We hypothesized that each tumor model has a vastly different composition in the CD4 T cell compartment. To test this, we characterized expression of activation and CD4 T cell differentiation markers as well as cytokine production from CD4 TILs in each of the syngeneic tumor models. We found that while effector CD4 TILs (FoxP3⁻CD4⁺) from MC38 and CT26.KSA tumors expressed high levels activation and differentiation markers, Teff from EMT-6 tumors expressed very low levels of T cell activation and differentiation markers, suggesting the Teff in EMT-6 tumors are largely dysfunctional. Ex vivo restimulation of tumor samples with anti-CD3/anti-CD28 promoted IFNγ production in CD4 TILs from MC38 and CT26.KSA tumor models, but not from EMT-6 tumor models, further supporting that Teff from MC38 and CT26.KSA tumors remain highly active, while CD4 TILs from EMT-6 tumors are dysfunctional. When looking at the Treg compartment, the frequency of Tregs in CT26.KSA tumors was reduced compared to MC38 and EMT-6 tumors. Further, Tregs in MC38 and EMT-6 tumors expressed very high levels of CD69, a marker of highly immunosuppressive Tregs, while Tregs in CT26.KSA tumors expressed lower levels of CD69, suggesting that these Tregs may be less immunosuppressive. In summary, the CD4 T cell compartment is vastly different across CT26.KSA, MC38 and EMT-6 syngeneic tumor models, resulting in very different impact of tumor growth control. Citation Format: Chunxiao Xu, Lindsay Webb, Sireesha Yalavarthi, Clotilde Bourin, Jacques Moisan. Composition of CD4 T cell subsets and impact on tumor growth control across mouse syngeneic tumor models [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P077.