MYC inhibition reprograms tumor immune microenvironment by recruiting T lymphocytes and activating the CD40/CD40L system in osteosarcoma

The efficacy of immune checkpoint blockade (ICB) therapy depends on sufficient infiltration and activation of primed tumor-specific cytotoxic T lymphocytes (CTLs) in the tumor microenvironment. However, many tumor types, including osteosarcoma, mainly display immune-desert or immune-excluded phenotypes, which are characterized by a lack of tumor-infiltrating lymphocytes and a poor response to ICB monotherapy. Thus, novel therapeutic strategies are urgently needed to surmount these obstacles. In this study, we found that the expression of the c-Myc oncogene is negatively correlated with the T cell infiltration rate in osteosarcoma. Pharmacological inhibition of c-Myc with JQ-1 significantly reduced tumor burden and improved overall survival in an immunocompetent syngeneic murine model of osteosarcoma (K7M2). A mechanistic study revealed that JQ-1 administration dramatically reprogrammed the tumor immune microenvironment (TIME) within K7M2 tumors. On the one hand, JQ-1 can promote T cell trafficking into tumors by increasing the expression and secretion of T cell-recruiting chemokines. On the other hand, JQ-1 is capable of facilitating crosstalk between antigen-presenting dendritic cells and T cells through the CD40/CD40L costimulatory pathway, leading to activation of tumor-specific CTLs. Combined treatment with anti-PD-1 antibody and JQ-1 resulted in more pronounced tumor regression than either monotherapy, showing an obvious synergistic effect. These findings uncover for the first time that c-Myc inhibition can promote T cell infiltration and activation in osteosarcoma in multiple ways, delivering a one-two punch for modulating TIME. The present work also provides the basis for establishing c-Myc inhibitor and ICB coadministration as a novel therapeutic regimen for patients with osteosarcoma.