Differentiation pathways of tumor-reactive CD4 ⁺ T cells. (A) Within tumor-draining lymph nodes, Tregs can inhibit effective CD4⁺ T cell priming, leading to the induction of anergic CD4⁺ T cells. TGFβ produced by Tregs and other immunosuppressive cells can also promote the differentiation of naïve and anergic CD4⁺ T cells into induced Tregs. In contrast, efficient priming generates stem-like CD4⁺ T cells that are imprinted with features of either effector or exhausted T cells, depending on the strength of priming. The strength of this priming is influenced by variables such as clone size and TCR affinity. (B) Within tumors, TGFβ can induce anergic CD4⁺ T cells and drive the differentiation into Tregs. The propensity of stem-like CD4⁺ T cells to differentiate into either effector or exhausted CD4⁺ T cells is likely shaped by their initial imprinting in the lymph node. Whether these differentiation pathways are mutually exclusive—i.e., whether stem-like exhausted CD4⁺ T cells can become effector CD4⁺ T cells, or whether exhausted CD4⁺ T cells can re-differentiate into effectors—remains unknown. Additionally, factors within the tumor microenvironment (TME) can suppress CD4⁺ T cell effector function through mechanisms that are independent of classical T cell exhaustion. Created with BioRender. https://BioRender.com/ekcyog8. p-MHC, peptide-MHC; EOMES, eomesodermin.