CD163(+) M2-type Tumor-associated Macrophage Support the Suppression of Tumor-infiltrating T Cells in Osteosarcoma

Osteosarcoma is one of the most common childhood cancers with high numbers of cancer-related deaths. Progress in conventional therapies is showing limited improvement. An adaptive T cell-based immunotherapy represents a promising new therapeutic option, but to improve its efficacy, regulatory mechanisms in osteosarcoma need further elucidation. Here, to evaluate the regulatory effect of tumor microenvironment of T cells in osteosarcoma, we examined the peripheral blood (PB) and tumor infiltrating (TI) T cells, and their correlations with PB and tumor immune characteristics. We found that TI T cells contained significantly higher levels of TIM-3(+)PD-1(-) and TIM-3(+)PD-1(+) cells than their PB counterparts. Similar to that in chronic HIV and HCV infections, these TIM-3(+)PD-1(-) and TIM-3(+)PD-1(+) T cells presented reduced proliferation and proinflammatory cytokine secretion in response to stimulation. Presence of M2-type (CD163(+)) macrophages exacerbated T cell immunosuppression, since frequencies of CD163(+) tumor-associated macrophages were directly correlated with the frequencies of suppressed TIM-3(+)PD-1(+) T cells. Moreover, depletion of CD163(+) macrophages significantly improved T cell proliferation and proinflammatory cytokine production. Overall, our data presented an intratumoral T cell-specific immunosuppression that was amplified by M2-type tumor-associated macrophages.