Immune-based therapies hold promise for the treatment of multiple myeloma (MM), but so far immune checkpoint blockade targeting programmed cell death protein 1 (PD-1) has not proven effective as single agent in this disease. T cell immunoglobulin and ITIM domains (TIGIT) is another immune checkpoint receptor known to negatively regulate T cell functions. In this study, we investigated the therapeutic potential of TIGIT blockade to unleash immune responses against MM. We observed that, in both mice and humans, MM progression was associated with high levels of TIGIT expression on CD8⁺ T cells. TIGIT⁺ CD8⁺ T cells from MM patients exhibited a dysfunctional phenotype, characterized by decreased proliferation and inability to produce cytokines in response to anti-CD3/CD28/CD2 or myeloma antigen stimulation. Moreover, when challenged with Vk*MYC mouse MM cells, TIGIT-deficient mice showed decreased serum M-protein levels associated with reduced tumor burden and prolonged survival, indicating that TIGIT limits anti-myeloma immune responses. Importantly, blocking TIGIT using monoclonal antibodies (mAbs) increased the effector function of MM patient CD8⁺ T cells and suppressed MM development. Altogether our data provide evidence for an immune-inhibitory role of TIGIT in MM and support the development of TIGIT-blocking strategies for the treatment of MM patients. Key points TIGIT expression is up-regulated on CD8⁺ T cells during MM progression and is associated with impaired effector functions. TIGIT-deficiency or -blockade protects mice against multiple myeloma and improves effector functions of myeloma patient CD8⁺ T cells.

We explored the mechanism of action of CD39 antibodies that inhibit ectoenzyme CD39 conversion of extracellular ATP (eATP) to AMP and thus potentially augment eATP–P2-mediated proinflammatory responses. Using syngeneic and humanized tumor models, we contrast the potency and mechanism of anti-CD39 mAbs with other agents targeting the adenosinergic pathway. We demonstrate the critical importance of an eATP–P2X7–ASC–NALP3-inflammasome–IL18 pathway in the antitumor activity mediated by CD39 enzyme blockade, rather than simply reducing adenosine as mechanism of action. Efficacy of anti-CD39 activity was underpinned by CD39 and P2X7 coexpression on intratumor myeloid subsets, an early signature of macrophage depletion, and active IL18 release that facilitated the significant expansion of intratumor effector T cells. More importantly, anti-CD39 facilitated infiltration into T cell–poor tumors and rescued anti–PD-1 resistance. Anti-human CD39 enhanced human T-cell proliferation and Th1 cytokine production and suppressed human B-cell lymphoma in the context of autologous Epstein–Barr virus–specific T-cell transfer. Significance: Overall, these data describe a potent and novel mechanism of action of antibodies that block mouse or human CD39, triggering an eATP–P2X7–inflammasome–IL18 axis that reduces intratumor macrophage number, enhances intratumor T-cell effector function, overcomes anti–PD-1 resistance, and potentially enhances the efficacy of adoptive T-cell transfer. This article is highlighted in the In This Issue feature, p. 1631