Enhancement of mTORC1 Activity in Engineered Therapeutic CD4+ T Cells Amplifies Tumour Infiltration but Impairs Cytotoxicity

There is substantial interest in developing strategies to improve the intrinsic functions of engineered therapeutic T cells, for example by manipulating their metabolic fitness. Mammalian target of Rapamycin complex 1 (mTORC1) is a critical orchestrator of anabolic metabolism and effector functions in T cells. Our group has previously shown that overexpression of an mTORC1 positive regulator (Ras homologue enriched in brain; Rheb) in engineered CD8⁺ T cells increased anabolic metabolism, improved tumour infiltration and cytotoxicity, but reduced their long-term persistence (1). However, because of differences in baseline and activation-induced metabolism, it is less clear how manipulation of intrinsic mTORC1 activity might influence therapeutic CD4⁺ T cell function.

We therefore tested the consequence of overexpressing Rheb in a murine model of anti-tumour immunity that requires in vivo cytotoxic CD4⁺ T cell differentiation. As we have previously found for CD8⁺ T cells, Rheb overexpression in tumour-specific CD4⁺ T cells, engineered to express a class II restricted T cell receptor targeting melanoma antigen Tyrosinase-related protein- 1 (TRP-1), enhanced baseline and activated glycolysis and oxygen phosphorylation, promoted differentiation of T-bet high effector cells and significantly increased tumour infiltration in vivo. Conversely, mTORC1 inhibition using Proline-rich Akt substrate of 40kDa (PRAS40) produced a state of relative metabolic quiescence, rendered the cells in a less differentiated Th0 state and reduced tumour infiltration. Rheb-transduced tumour-specific CD4⁺ T cells showed reduced cytotoxic gene expression and failed to eliminate all tumours compared to control cells. Unlike CD8⁺ T cells, constitutive mTORC1 activation did not impair long-term persistence of CD4⁺ T cells, but the surviving cells expressed high levels of co-inhibitory receptors, especially Lymphocyte-activation gene 3 (LAG-3), and showed impaired proliferation in responses to antigenic re-challenge.

Together, these data highlight the need to address how engineering of intrinsic metabolic fitness might impact upon CD4⁺ versus CD8⁺ T cells in distinct ways and suggests the need for bespoke strategies to enhance their respective functions and survival.

References

1. Genetic Regulation of Fate Decisions in Therapeutic T Cells to Enhance Tumor Protection and Memory Formation. Veliça P, Zech M, Henson S, Holler A, Manzo T, Pike R, Santos E Sousa P, Zhang L, Heinz N, Schiedlmeier B, Pule M, Stauss H, Chakraverty R. 2015 Jul, Cancer Res. , pp. 1;75(13):2641-52.

Sillito:Kite, Gilead: Honoraria. Stauss:Quell Therapeutics: Consultancy, Current equity holder in private company, Honoraria, Research Funding. Chakraverty:Accelerating Clinical Trials Ltd.: Consultancy.