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Cancer immunotherapy is advancing rapidly and gene-modified T cells expressing chimeric antigen receptors (CARs) show particular promise. A challenge of CAR-T cell therapy is that the ex vivo-generated CAR-T cells become exhausted during expansion in culture, and do not persist when transferred back to patients. It has become clear that naive and memory CD8 T cells perform better than the total CD8 T-cell populations in CAR-T immunotherapy because of better expansion, antitumor activity, and persistence, which are necessary features for therapeutic success and prevention of disease relapse. However, memory CAR-T cells are rarely used in the clinic due to generation challenges. We previously reported that mouse CD8 T cells cultured with the S enantiomer of the immunometabolite 2-hydroxyglutarate (S-2HG) exhibit enhanced antitumor activity. Here, we show that clinical-grade human donor CAR-T cells can be generated from naive precursors after culture with S-2HG. S-2HG-treated CAR-T cells establish long-term memory cells in vivo and show superior antitumor responses when compared with CAR-T cells generated with standard clinical protocols. This study provides the basis for a phase 1 clinical trial evaluating the activity of S-2HG-treated CD19-CAR-T cells in patients with B-cell malignancies.

Retroviral gene transfer of T cell receptors (TCRs) or chimeric-antigen receptors has been successfully used to redirect T cell specificity to tumor antigens and has shown promising results in clinical trials for patients with melanoma and B cell malignancies. Successful therapy relies not only on the generation of an efficient effector response but also in the ability of T cells to engraft and persist during and after cancer rejection. Yet, both aspects can be compromised. On the one hand, effector T cells can be disarmed in vivo by the immunosuppressive environment of the tumor, where the depletion of key nutrients (glucose, arginine, etc.) and the predominance of inhibitory signals (TGF-β, PD-L1, etc.) dampen their functions. On the other hand, current retroviral gene transfer protocols require T cells to be activated and expanded ex vivo,driving terminal effector differentiation at the expense of the capacity for self-renewal (“stemness”). This may prevent the generation of long-term protective memory and compromise therapeutic success. The mechanistic target of rapamycin (mTOR) pathway has recently emerged as a driver of effector differentiation in CD8 T cells by acting as a signalling bridge between extracellular stimuli and effector differentiation. Whilst high doses of rapamycin are known to be immunosuppressive, a low dose regimen increases memory output after a viral challenge without impairing viral clearance. These and other studies suggest that mTOR can be used as a rheostat to regulate T cell differentiation to clinical advantage. Using a mouse model of TCR gene therapy we aimed to produce T cells in which the mTOR pathway is either hyperactive, in order to generate ‘super-effectors’ that can function in the tumor microenvironment, or hypoactive in order to preserve “stemness”, increase engraftment and produce better recall immunity. To this purpose we transferred genes into therapeutic T cells encoding either (1) an mTOR activator, RHEB (Ras homolog enriched in brain) or (2) an mTOR inhibitor, PRAS40 (proline-rich Akt substrate 40 kDa). Upon stimulation in vitro,the phosphorylation of ribosomal protein S6, an mTOR downstream target, was increased in RHEB-expressing cells and decreased in PRAS40-expressing cells. RHEB T cells demonstrated a greater propensity than controls for blast formation, lower expression of L-selectin, increased IFN-g production and resistance to TGF-b. In contrast, PRAS40 T cells were smaller in size, expressed higher surface levels of L-selectin and had reduced but not ablated production of IFN-g, IL-2 and TNF-a production. In vivo, RHEB T cells co-transduced with a tumor-specific TCR showed increased initial expansion that was associated with increased tumor protection. However, this was followed by a steep decrease in T cell numbers compared to control cells, with preliminary experiments indicating that RHEB cells produced a less robust re-call response upon antigenic re-challenge. In contrast, PRAS40 cells failed to expand in vivo or to infiltrate tumors, resulting in complete lack of protection. Yet, the few PRAS40 cells remaining in circulation were predominately high for L-selectin, IL-7Ra and Sca-1 (markers associated with ‘stemness’). These results demonstrated that constitutive suppression of mTOR was of no therapeutic advantage. To circumvent this, we developed a doxycycline (DOX)-inducible PRAS40 vector in which mTOR suppression in T cells can be temporally controlled in vivo. Unlike the constitutive vector used previously, with the DOX-ON system the level of mTOR suppression was lower and furthermore, could be applied only during the period of antigen exposure. Thus, when DOX was added during tumor challenge, PRAS40-expressing T cells could reject tumor as well as controls. However, after DOX was withdrawn and transgene expression turned off, increased numbers of therapeutic T cells were found in peripheral blood. When re-challenged, these T cells produced a stronger recall response relative to cells in which mTOR had not been suppressed initially. Thus, our results show that genetic manipulation of mTOR can be used to alter the intrinsic properties of T cells and direct either their effector or memory differentiation. This approach maybe useful in designing better therapeutic immunotherapeutic strategies according to the type of T cell response required in vivo. Disclosures: No relevant conflicts of interest to declare.

Adoptive transfer of antitumor cytotoxic T cells is an emerging form of cancer immunotherapy. A key challenge to expanding the utility of adoptive-cell therapies is how to enhance the survival and function of the transferred T cells. Immune-cell survival requires adaptation to different microenvironments, and particularly to the hypoxic milieu of solid tumors. The hypoxia-inducible factor (HIF) transcription factors are an essential aspect of this adaptation. In this study, we undertook experiments to define structural determinants of HIF that potentiate antitumor efficacy in cytotoxic T cells. We first created retroviral vectors to deliver ectopic expression of HIF1ɑ and HIF2ɑ in mouse CD8+ T cells, together or individually, and with or without sensitivity to the oxygen-dependent HIFɑ inhibitors Von Hippel Lindau (VHL) and Factor Inhibiting HIF (FIH). HIF2ɑ, but not HIF1ɑ, drove broad transcriptional changes in CD8+ T cells, resulting in increased cytotoxic differentiation and cytolytic function against tumor targets. A specific mutation replacing the hydroxyl group–acceptor site for FIH in HIF2ɑ gave rise to the most effective antitumor T cells after adoptive transfer in vivo. In addition, co-delivering an FIH-insensitive form of HIF2ɑ with an anti-CD19 chimeric antigen receptor greatly enhanced cytolytic function of human CD8+ T cells against lymphoma cells both in vitro and in a xenograft adoptive transfer model. These experiments point to a means to increase the antitumor efficacy of therapeutic CD8+ T cells via ectopic expression of the HIF transcription factor.

Exercise has a wide range of systemic effects. In animal models, repeated exertion reduces malignant tumor progression, and clinically, exercise can improve outcome for cancer patients. The etiology of the effects of exercise on tumor progression are unclear, as are the cellular actors involved. We show here that in mice, exercise-induced reduction in tumor growth is dependent on CD8+ T cells, and that metabolites produced in skeletal muscle and excreted into plasma at high levels during exertion in both mice and humans enhance the effector profile of CD8+ T-cells. We found that activated murine CD8+ T cells alter their central carbon metabolism in response to exertion in vivo, and that immune cells from trained mice are more potent anti-tumor effector cells when transferred into tumor-bearing untrained animals. These data demonstrate that CD8+ T cells are metabolically altered by exercise in a manner that acts to improve their anti-tumoral efficacy.