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 proinfl ammatory 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-NALP3infl ammasome-IL18 pathway in the antitumor activity mediated by CD39 enzyme blockade, rather than simply reducing adenosine as mechanism of action. Effi cacy 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 signifi cant expansion of intratumor effector T cells. More importantly, anti-CD39 facilitated infi ltration 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-specifi c 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-infl ammasome-IL18 axis that reduces intratumor macrophage number, enhances intratumor T-cell effector function, overcomes anti-PD-1 resistance, and potentially enhances the effi cacy of adoptive T-cell transfer.

Multiple non-redundant immunosuppressive pathways co-exist in the tumor microenvironment and their co-targeting can increase clinical responses. Indeed, concurrent blockade of CTLA-4 and PD-1 in patients with advanced melanoma increased clinical responses over monotherapy alone although the frequency and severity of immune related adverse events (irAEs) also increased. Nevertheless, a substantial number of patients still display an innate resistance phenotype and are unresponsive to current approved immunotherapies even when utilized in combination. In this study, we generated and mice to investigate how loss of CD96 in combination with PD-1 or TIGIT impacts on immune homeostasis and hence the potential of inducing immune related toxicities following co-targeting of these pairs of receptors. The ability of and mice to suppress primary tumor growth was also assessed using the MC38 colon carcinoma and SM1WT1 BRAF-mutated melanoma tumor models. Both or mice displayed no overt perturbations in immune homeostasis over what was previously reported with or mice even when aged for 22 months. Interestingly, increased suppression of subcutaneous tumor growth and complete responses was seen in mice compared to or mice depending upon the tumor model. In contrast, in these models, growth suppression in were similar to or . This enhanced anti-tumor efficacy of appeared to be due to favorable changes in the ratio of CD8 T cells to T regulatory cells or CD11bGR-1 myeloid cells in the tumor microenvironment. Co-targeting CD96 and PD-1 may increase anti-tumor immunity over targeting PD-1 alone and potentially not induce serious immune-related toxicities and thus appears a promising strategy for clinical development.