Sodium chloride in the tumor microenvironment enhances T cell metabolic fitness and cytotoxicity.

The efficacy of antitumor immunity is associated with the metabolic state of cytotoxic T cells, which is sensitive to the tumor microenvironment. Whether ionic signals affect adaptive antitumor immune responses is unclear. In the present study, we show that there is an enrichment of sodium in solid tumors from patients with breast cancer. Sodium chloride (NaCl) enhances the activation state and effector functions of human CD8+ T cells, which is associated with enhanced metabolic fitness. These NaCl-induced effects translate into increased tumor cell killing in vitro and in vivo. Mechanistically, NaCl-induced changes in CD8+ T cells are linked to sodium-induced upregulation of Na+/K+-ATPase activity, followed by membrane hyperpolarization, which magnifies the electromotive force for T cell receptor (TCR)-induced calcium influx and downstream TCR signaling. We therefore propose that NaCl is a positive regulator of acute antitumor immunity that might be modulated for ex vivo conditioning of therapeutic T cells, such as CAR T cells.

Dissecting the metabolic signaling pathways by which microbial molecules drive the differentiation of regulatory B cells.

The host-microbiome axis has been implicated in promoting anti-inflammatory immune responses. Yet, the underlying molecular mechanisms of commensal-mediated IL-10 production by regulatory B cells (Bregs) are not fully elucidated. Here, we demonstrate that bacterial CpG motifs trigger the signaling downstream of TLR9 promoting IκBNS-mediated expression of Blimp-1, a transcription regulator of IL-10. Surprisingly, this effect was counteracted by the NF-κB transcription factor c-Rel. A functional screen for intestinal bacterial species identified the commensal Clostridium sporogenes, secreting high amounts of short-chain fatty acids (SCFAs) and branched-chain fatty acids (BCFAs), as an amplifier of IL-10 production by promoting sustained mTOR signaling in B cells. Consequently, enhanced Breg functionality was achieved by combining CpG with the SCFA butyrate or the BCFA isovalerate thereby synergizing TLR- and mTOR-mediated pathways. Collectively, Bregs required two bacterial signals (butyrate and CpG) to elicit their full suppressive capacity and ameliorate T cell-mediated intestinal inflammation. Our study has dissected the molecular pathways induced by bacterial factors, which might contribute not only to better understanding of host-microbiome interactions, but also to exploration of new strategies for improvement of anti-inflammatory cellular therapy.

Microbial metabolite-guided CAR T cell engineering enhances anti-tumor immunity via epigenetic-metabolic crosstalk.

Emerging data have highlighted a correlation between microbiome composition and cancer immunotherapy outcome. While commensal bacteria and their metabolites are known to modulate the host environment, contradictory effects and a lack of mechanistic understanding impede the translation of microbiome-based therapies into the clinic. In this study, we demonstrate that abundance of the commensal metabolite pentanoate is predictive for survival of chimeric antigen receptor (CAR) T cell patients in two independent cohorts. Its implementation in the CAR T cell manufacturing workflow overcomes solid tumor microenvironments in immunocompetent cancer models by hijacking the epigenetic-metabolic crosstalk, reducing exhaustion and promoting naive-like differentiation. While synergy of clinically relevant drugs mimicked the phenotype of pentanoate-engineered CAR T cells in vitro, in vivo challenge showed inferior tumor control. Metabolic tracing of 13C-pentanoate revealed citrate generation in the TCA cycle via the acetyl- and succinyl-CoA entry points as a unique feature of the C5 aliphatic chain. Inhibition of the ATP-citrate lyase, which links metabolic output and histone acetylation, led to accumulation of pentanoate-derived citrate from the succinyl-CoA route and decreased functionality of SCFA-engineered CAR T cells. Our data demonstrate that microbial metabolites are incorporated as epigenetic imprints and implementation into CAR T cell production might serve as embodiment of the microbiome-host axis benefits for clinical applications.

Learning from the microbes: exploiting the microbiome to enforce T cell immunotherapy.

The opportunities genetic engineering has created in the field of adoptive cellular therapy for cancer are accelerating the development of novel treatment strategies using chimeric antigen receptor (CAR) and T cell receptor (TCR) T cells. The great success in the context of hematologic malignancies has made especially CAR T cell therapy a promising approach capable of achieving long-lasting remission. However, the causalities involved in mediating resistance to treatment or relapse are still barely investigated. Research on T cell exhaustion and dysfunction has drawn attention to host-derived factors that define both the immune and tumor microenvironment (TME) crucially influencing efficacy and toxicity of cellular immunotherapy. The microbiome, as one of the most complex host factors, has become a central topic of investigations due to its ability to impact on health and disease. Recent findings support the hypothesis that commensal bacteria and particularly microbiota-derived metabolites educate and modulate host immunity and TME, thereby contributing to the response to cancer immunotherapy. Hence, the composition of microbial strains as well as their soluble messengers are considered to have predictive value regarding CAR T cell efficacy and toxicity. The diversity of mechanisms underlying both beneficial and detrimental effects of microbiota comprise various epigenetic, metabolic and signaling-related pathways that have the potential to be exploited for the improvement of CAR T cell function. In this review, we will discuss the recent findings in the field of microbiome-cancer interaction, especially with respect to new trajectories that commensal factors can offer to advance cellular immunotherapy.