Abstract 3946: Tumor checkpoint inhibitor profiling for an optimal clinical response

The last three decades have seen a steady rise in melanoma, the most aggressive form of skin cancer. The discovery of checkpoint inhibitors has revolutionized the treatment landscape for melanoma; anti-CTLA4 and anti-PD1 showing great successes in clinic. While checkpoint molecules and co-stimulatory molecules are traditionally present on cells involved in immune activation, mounting evidence suggests that tumor cells also express these molecules. Our laboratory has characterized five patient-derived melanoma cell lines, MEL-2, MEL-V, 3MM, KFM, and GLM-2 and screened them for the expression of a comprehensive list of 29 co-stimulatory and co-inhibitory molecules compared to normal adult melanocytes. We see a differential mRNA expression of many of these immune-regulatory molecules, including BTLA, HVEM, CD160, CD226 and TIM1. Western blots and immunofluorescence confirmed the presence of these molecules at the protein level. A flow cytometry analysis demonstrated that BTLA, HVEM, CD160, TIM1 and CD226 are present on the membrane of these patient derived melanoma cells; implying that they are capable of engaging their respective ligands and exerting a functional role in immunomodulation. These findings were additionally validated in melanoma tissues, obtained from patients, by immunohistochemistry. Interestingly, treatment of MEL-2, MEL-V, KFM and GLM-2, our BRAFV600E containing patient derived cells, with BRAFV600E inhibitor PLX4032 led to the upregulation of these molecules. This upregulation was coupled with an increase in transcription factor MITF, a binding site for which is present in the promoter region of all the upregulated molecules. Co-culture experiments with immune cells, demonstrate a modulatory role played by the HVEM/BTLA/CD160 axis molecules that are present on tumor cells. The presence of these additional immune-regulatory molecules signify the existence of a robust tolerance mechanism induced by these checkpoint inhibitors. Our studies underscore the importance of characterizing tumor profiles to enable the selection of an optimal treatment regimen combining targeted small molecule inhibitors, and checkpoint inhibitors to maximize T cell killing, and tumor clearance. Citation Format: Rachana R. Maniyar, Sanjukta Chakraborty, Ghada Ben Rahoma, John J. Degliuomini, Marc Wallack, Jan Geliebter, Raj K. Tiwari. Tumor checkpoint inhibitor profiling for an optimal clinical response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3946.