Data from BRAF Inhibition Increases Tumor Infiltration by T cells and Enhances the Antitumor Activity of Adoptive Immunotherapy in Mice

Abstract

<div>Abstract<p><b>Purpose:</b> Treatment of melanoma patients with selective BRAF inhibitors results in objective clinical responses in the majority of patients with <i>BRAF</i>-mutant tumors. However, resistance to these inhibitors develops within a few months. In this study, we test the hypothesis that BRAF inhibition in combination with adoptive T-cell transfer (ACT) will be more effective at inducing long-term clinical regressions of <i>BRAF</i>-mutant tumors.</p><p><b>Experimental Design:</b><i>BRAF</i>-mutated human melanoma tumor cell lines transduced to express gp100 and H-2D<sup>b</sup> to allow recognition by gp100-specific pmel-1 T cells were used as xenograft models to assess melanocyte differentiation antigen–independent enhancement of immune responses by BRAF inhibitor PLX4720. Luciferase-expressing pmel-1 T cells were generated to monitor T-cell migration <i>in vivo</i>. The expression of VEGF was determined by ELISA, protein array, and immunohistochemistry. Importantly, VEGF expression after BRAF inhibition was tested in a set of patient samples.</p><p><b>Results:</b> We found that administration of PLX4720 significantly increased tumor infiltration of adoptively transferred T cells <i>in vivo</i> and enhanced the antitumor activity of ACT. This increased T-cell infiltration was primarily mediated by the ability of PLX4720 to inhibit melanoma tumor cell production of VEGF by reducing the binding of c-myc to the VEGF promoter. Furthermore, analysis of human melanoma patient tumor biopsies before and during BRAF inhibitor treatment showed downregulation of VEGF consistent with the preclinical murine model.</p><p><b>Conclusion:</b> These findings provide a strong rationale to evaluate the potential clinical application of combining BRAF inhibition with T-cell–based immunotherapy for the treatment of patients with melanoma. <i>Clin Cancer Res; 19(2); 393–403. ©2012 AACR</i>.</p></div>