A considerable proportion of
cancer patients are resistant or only partially responsive to
immune checkpoint blockade immunotherapy. Tumor-Associated Macrophages (TAMs) infiltrating the
tumor stroma suppress the adaptive immune responses and, hence, promote tumor immune evasion. Depletion of TAMs or modulation of their protumoral functions is actively pursued, with the purpose of relieving this state of immunesuppression. We previously reported that
trabectedin, a registered antitumor compound, selectively reduces monocytes and TAMs in treated
tumors. However, its putative effects on the adaptive immunity are still unclear. In this study, we investigated whether treatment of
tumor-bearing mice with
trabectedin modulates the presence and functional activity of T-lymphocytes. In treated
tumors, there was a significant upregulation of T cell-associated genes, including CD3, CD8,
perforin, granzyme B, and IFN-responsive genes (MX1, CXCL10, and PD-1), indicating that T lymphocytes were activated
after treatment. Notably, the
mRNA levels of the Pdcd1 gene, coding for PD-1, were strongly increased. Using a
fibrosarcoma model poorly responsive to PD-1-immunotherapy, treatment with
trabectedin prior to anti-PD-1 resulted in improved antitumor efficacy. In conclusion, pretreatment with
trabectedin enhances the therapeutic response to checkpoint inhibitor-based
immunotherapy. These findings provide a good rational for the combination of
trabectedin with
immunotherapy regimens.