Adoptively transferred TCR-engineered cytotoxic human T lymphocytes use TRAIL apoptotic pathway in killing melanomas: Pivotal role of DR5 and regulation of resistance by SAHA (P2124)

Abstract

Abstract Adoptive transfer of ex vivo engineered autologous lymphocytes encoding high-affinity MART-1/ A*0201-specific TCRα/β chains (F5 CTL), densely infiltrate into metastatic sites, mediating dramatic but partial responses in metastatic melanoma patients. We hypothesized that down-modulation of death receptors and aberrant apoptotic signaling confer resistance to F5 CTLs. To test this, we established a preclinical model of resistance from sensitive parental lines under serial F5 CTL-selective pressure. While surface peptide/MHC complex remains intact (F5 CTLs efficiently recognize and engage melanomas), R lines downregulate surface DR5 expression, exhibit constitutive NF-κB activation and overexpress resistant factors. The HDACi SAHA blocked antiapoptotic pathway, reduced expression of resistance factors, restored DR5 expression, and sensitized R lines to F5 CTL. At concentrations used, SAHA didn’t affect functionality and viability of F5 CTLs. Using blocking Abs, rhTRAIL and murine CTL hybridoma line, we found that TCR-engineered F5 CTLs mainly utilize TRAIL apoptosis pathway. Further, using Drozitumab (αDR5 mAb), pivotal role of DR5 and its regulation by SAHA was confirmed. These studies identify molecular determinants of resistance to TCR engineered CTL and suggest that adjuvant therapy with SAHA in immune-resistant tumors imposes a proapoptotic milieu by regulating apoptotic machinery and inducing death-receptor expression, thus, overcoming melanoma immunotherapy resistance.