Sunitinib Mediates Reversal of Myeloid-Derived Suppressor Cell Accumulation in Renal Cell Carcinoma Patients

TLDR: Sunitinib-based therapy has the potential to modulate antitumor immunity by reversing MDSC-mediated tumor-induced immunosuppression and is correlated with reversal of type 1 T-cell suppression.

Abstract: Purpose: Immune dysfunction reported in renal cell carcinoma (RCC) patients may contribute to tumor progression. Myeloid-derived suppressor cells (MDSC) represent one mechanism by which tumors induce T-cell suppression. Several factors pivotal to the accumulation of MDSC are targeted by the tyrosine kinase inhibitor, sunitinib. The effect of sunitinib on MDSC-mediated immunosuppression in RCC patients has been investigated. Experimental Design: Patient peripheral blood levels of MDSC and regulatory T-cell (Treg) and T-cell production of IFN-γ were evaluated before and after sunitinib treatment. Correlations between MDSC and Treg normalization as well as T-cell production of IFN-γ were examined. The in vitro effect of sunitinib on patient MDSC was evaluated. Results: Metastatic RCC patients had elevated levels of CD33 + HLA-DR − and CD15 + CD14 − MDSC, and these were partially overlapping populations. Treatment with sunitinib resulted in significant reduction in MDSC measured by several criteria. Sunitinib-mediated reduction in MDSC was correlated with reversal of type 1 T-cell suppression, an effect that could be reproduced by the depletion of MDSC in vitro . MDSC reduction in response to sunitinib correlated with a reversal of CD3 + CD4 + CD25 hi Foxp3 + Treg cell elevation. No correlation existed between a change in tumor burden and a change in MDSC, Treg, or T-cell production of IFN-γ. In vitro addition of sunitinib reduced MDSC viability and suppressive effect when used at ≥1.0 μg/mL. Sunitinib did not induce MDSC maturation in vitro . Conclusions: Sunitinib-based therapy has the potential to modulate antitumor immunity by reversing MDSC-mediated tumor-induced immunosuppression.