Genetic Engineering of T Cells to Target HERV-K, an Ancient Retrovirus on Melanoma

Abstract

Purpose The human endogenous retrovirus (HERV-K) envelope (env) protein is a tumor- associated antigen expressed on melanoma, but not normal cells. This study was designed to engineer a chimeric antigen receptor (CAR) on T cell surface, such that they target tumors in advanced stages of melanoma. Experimental Design Expression of HERV-K protein was analyzed in 220 melanoma samples (with various stages of disease) and 139 normal organ donor tissues using immuno-histochemical (IHC) analysis. HERV-K env-specific CAR derived from mouse monoclonal antibody was introduced into T cells using the transposon-based Sleeping Beauty (SB) system. HERV-K env-specific CAR+ T cells were expanded ex vivo on activating and propagating cells (AaPC), and characterized for CAR expression and specificity. This includes evaluating the HERV-K-specific CAR+ T cells for their ability to kill A375-SM metastasized tumors in a mouse xenograft model. Results We detected HERV-K env protein on melanoma, but not in normal tissues. After electroporation of T cells and selection on HERV-K+ AaPC, over 95% of genetically-modified T cells expressed the CAR with an effector memory phenotype and lysed HERV-K env+ tumor targets in an antigen specific manner. Even though there is apparent shedding of this TAA from tumor cells which can be recognized by HERV-K env-specific CAR+ T cells, we observed a significant anti-tumor effect. Conclusion Adoptive cellular immunotherapy with HERV-K env-specific CAR+ T cells represents a clinically-appealing treatment strategy for advanced-stage melanoma and provides an approach for targeting this TAA on other solid tumors.

Human endogenous retroviruses and cancer

“…The antigen HERV-K-MEL is expressed in 85% of malignant melanocytes from normal nevi and dysplastic lesions to metastatic melanoma. The expression of HERV-K Env in melanomas is higher than that in benign lesions, especially in metastatic tumors 19 . HERV-K Env is also found in other tumors, such as breast cancer, ovarian cancer, teratocarcinoma, sarcoma, and bladder cancer 20-24 .…”

“…HERV-K Env protein has been identified in melanoma by immunohistochemistry using HERV-K Env-specific monoclonal antibody 6H5 19 . The antigen HERV-K-MEL is expressed in 85% of malignant melanocytes from normal nevi and dysplastic lesions to metastatic melanoma.…”

Epigenetic control of retrotransposons in adult tissues: implications for immune regulation

“…In addition to innate immunity, ERVs can stimulate adaptive immunity too because their encoded gene products, which are necessary for their mobilization are subject to standard antigen processing and presentation pathways. For example, tumour-associated antigens (TAAs) can be derived from HERV-K envelope protein [75]. Such neo-antigens can evoke adaptive T cell and antibody responses [76], both of which have been demonstrated to regulate ERVs [15,75].…”

“…For example, tumour-associated antigens (TAAs) can be derived from HERV-K envelope protein [75]. Such neo-antigens can evoke adaptive T cell and antibody responses [76], both of which have been demonstrated to regulate ERVs [15,75].…”

Sleeping Beautytransposition: from biology to applications

“…Alternatively, the SB system is used to engineer cells ex vivo that are administered/transplanted to the patient to treat the disease. Remarkably, this approach has already has been approved for a Phase 1, 2 clinical trials to fight against cancer by using engineered T cells (Deniger et al, 2016;Krishnamurthy et al, 2015;Magnani et al, 2016;Singh et al, 2013;Singh et al, 2015), and to treat age-related macular degeneration (AMD, TargetAMD (http://www.targetamd.eu/)). In sum, SB combines the integrating abilities of viral gene therapy vectors needed for stable and long-lasting transgene expression with the advantageous properties of easy production, simpler handling and potentially safer chromosomal integration profiles.…”