Enforcing mTORC1 activity in therapeutic CD4+ T cells promotes persistence but eventual immune exhaustion.

There is substantial interest in developing novel engineering strategies to promote the sustained metabolic fitness of therapeutic T cells. We previously showed that overexpression of RAS homologue enriched in brain (RHEB), a positive regulator of mammalian target of rapamycin complex 1 (mTORC1), promotes aerobic glycolysis and increases the anti-tumor functions of effector CD8+ T cells. To address whether these effects are conserved in CD4+ T cells, we have now examined how enforced activation of mTORC1 activity affects CD4+ T cell differentiation and function. Rheb overexpression induced a more balanced metabolic shift in CD4+ T cells than in CD8+ T cells, with increases in both oxidative phosphorylation and aerobic glycolysis. Although Rheb overexpression initially increased CD4+ T cell activation and proliferation in vitro, the underlying population architecture was complex, involving a shift to both more proliferative, cytotoxic-like cell states as well as more quiescent cell clusters characterised by counter-regulation of mTORC1 activity. Following adoptive transfer, tumor antigen-specific Rheb-transduced CD4+ T cells showed greater persistence but were less efficient than controls in eliminating tumor. This functional deficiency could be explained by a greater propensity of persisting Rheb-transduced CD4+ T cells to develop features of immune exhaustion, as evidenced by expression of multiple co-inhibitory receptors and impaired proliferation upon tumor rechallenge. Together, these data demonstrate the dynamic population response to tuning of T cell mTORC1 and the need to separately appraise cellular outputs of therapeutic CD4+ versus CD8+ T cells when metabolic pathways are manipulated by the same method.