Modulating Immunometabolism to Reinvigorate T-Cell Effector Function and Antitumor Immunity in the Mantle Cell Lymphoma Microenvironment

Background: The mantle cell lymphoma (MCL) tumor microenvironment (TME) induces immunosuppressive signaling that compromises antitumor immunity. Specifically, tumor-imposed restrictions create a barrier to immune cells in the TME, especially tumor-infiltrating lymphocytes (TILs), which undergo metabolic and/or functional exhaustion inhibiting effector T cell function while regulatory T cell suppressive activity is promoted. In fact, T-cell exhaustion is a major challenge leading to relapse following chimeric antigen receptor (CAR) T cell therapy of MCL even though CD19-directed CAR T therapy achieved impressive efficacy initially in patients with relapsed/recurrent disease. Thus, novel approaches are needed to overcome the metabolic barrier of the immunosuppressive TME and enhance immune cell fitness to bolster the efficacy of MCL immunotherapies.

Methods: Human primary pan-T cells were isolated from peripheral blood mononuclear cells derived from normal human donors or patients with MCL and cultured in lymphocyte growth medium supplemented with 5% human serum AB and 50 IU/ml IL-2. Activated T cells were transduced with lentivirus expressing CD19-directed CAR. Bispecific T cell engagers were generated using synthetic sequences encoding single chain variant fragments of the antibodies specific for tumor antigens, and CD3ε. T cell effector function was determined by T cell activation and cell-dependent cytotoxicity assays. Mitochondrial metabolism was evaluated through glucose uptake, respiration, mitochondrial mass, and mitochondria membrane potential (ΔΨm) assays.

Results: Transcriptomic analysis of MCL clinical specimens revealed immune function genes were dysregulated, particularly those responsible for INFγ-mediated anti-tumor immunity. T cells from the patients predominantly displayed exhaustion phenotypes as indicated by decreased expression of T cell activation markers (CD25, CD28, CD38, and CD71) and increased immune checkpoint molecules including PD-1. Moreover, T cell receptor stimulation failed to induce the expression of IFNγ and TNFα in these T cells compared to those from healthy donors. Mitochondrial respiration was also impaired in MCL-derived T cells, as shown by decreased glucose uptake and ΔΨm, suggesting diminished T cell metabolic fitness was associated with exhaustion.

To recapitulate the interplay between T cells and TME, MCL cells were cultured on CD40L-expressing lymph node stromal HK cells in the presence of IL-4, with which we examined the effect of metabolic modulators on T cell activation and effector functions. Glutamine metabolism was upregulated in MCL cells, which may negatively regulate CD8⁺ T cells. Indeed, CD19-CAR T cells cultured in glutamine-limited media, or treated with a glutamine inhibitor (BPTES), induced the expression of the activation markers and diminished expression of exhausted signatures. Co-culture of the T cells with MCL cell lines further increased cytotoxicity and granzyme B secretion compared to untreated cells.

Inactivation of T cell autophagy may also enhance metabolic fitness and anti-tumor immunity. We found that pre-treatment of the T cells with the autophagy inhibitor SBI-02026965 led to T cell activation and elevated cytokine secretion. PGC1α sustains mitochondrial biogenesis but may be repressed in MCL. Induced expression of PGC1α stimulates mitochondria biogenesis, and we observed that treatment of T-cells cultured under the TME-mimicking conditions with the PPARδ agonist GW501516 increased mitochondria mass, reserve respiratory capacity, and ATP production. Importantly, pre-treatment of the CAR T cells with GW501516 enhanced their effector functions and anti-tumor immunity. Bispecific T-cell engagers (BiTEs) may activate exhausted T cells induced by long-term exposure to tumor antigens. Consistently, co-culture of T cells with MCL cell lines exhibited modest cytotoxicity. However, incubation of both cells with ROR1- or CD20-directed BiTE markedly increased the cytolytic effect on MCL cells in this model.

Conclusions: In summary, we found that MCL cells suppress immune cell function by upregulating immunosuppressive signaling and forging a metabolic barrier to effector T cells and immunotherapy. Tailored metabolic modulation of T cells in culture enhanced their metabolic fitness and antitumor immunity in the TME may ultimately bolster T cell therapy.

Wang:Meeting Minds Experts: Honoraria; Studio ER Congressi: Honoraria; Lilly: Consultancy, Research Funding; Pharmacyclics: Consultancy, Honoraria, Research Funding; Molecular Templates: Research Funding; Loxo Oncology: Research Funding; OncLive: Honoraria; Moffit Cancer Center: Honoraria; Oncternal: Consultancy, Research Funding; Physicians Education Resources (PER): Honoraria; Practice Point Communications (PPC): Honoraria; Vinverx: Research Funding; Dava Oncology: Honoraria; Pepromene Bio: Consultancy; Juno Therapeutics: Consultancy, Research Funding; IDEOlogy Health: Honoraria; MJH Life Sciences: Honoraria; Medscape: Honoraria; Milken Institute: Consultancy; Merck: Honoraria; Genentech: Consultancy, Research Funding; Eastern Virginia Medical School: Honoraria; Celgene: Research Funding; Oncology Specialty Group: Honoraria; Genmab: Research Funding; LLC TS Oncology: Honoraria; Kite Pharma: Consultancy, Honoraria, Research Funding; VelosBio: Consultancy, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Leukemia & Lymphoma Society: Consultancy, Honoraria; InnoCare: Consultancy, Research Funding; Deciphera: Consultancy; BioInvent: Consultancy, Honoraria, Research Funding; BeiGene: Consultancy, Honoraria, Research Funding; AstraZeneca: Consultancy, Honoraria, Research Funding; Acerta Pharma: Honoraria, Research Funding; AbbVie: Consultancy.