Endogenous Retrovirus-Targeted Immunotherapy for Non-Small Cell Lung Cancer Supported by Cellular HERV-K Expression, Dependency and Efficacy of ERV Therapy in a Murine Model

Human endogenous retrovirus-K (HERV-K/HML-2) has been associated with non-small cell lung cancer (NSCLC), but its functional relevance and the potential for HERV-directed immunotherapy remains unresolved. Here, we characterized HERV-K expression across 207 advanced NSCLC patient biopsies by total RNA-seq observing widespread expression of HERV-K Gag and Env antigen encoding sequences. The Env-ORF that disrupted HERV-K102 was strongly associated with interferon and antigen-presenting programs, identifying it as a marker of an immune-activated tumor state. shRNA-mediated knockdown of HERV-K in five NSCLC cell lines with distinct driver mutations impaired proliferation and survival. In separate experiments, exposure of these cell lines to treatment-related stressors, including cytokines (TNF-α and IFN-γ) and chemotherapy, revealed dynamic patterns of HERV-K protein accumulation with antigen expression retained, and in some cases increased. Immunotherapeutic targeting was performed using the ASB-XIV mouse NSCLC cell line and a murine ERV surrogate antigen using adenovirus to express murine leukemia virus (MLV) antigen on a mouse β-retroviral particle structurally related to HERV-K. This immunization was able to elicit significant protection against tumor challenge and additive benefit with anti-PD-L1 in therapeutic treatment, establishing proof-of-concept for ERV-targeted immunotherapy in a murine surrogate system rather than direct evidence of HERV-K-targeted efficacy. Our findings suggest an important role of HERV-K in NSCLC immunobiology and that adaptive immunity targeting HERV-K should be explored in the treatment of NSCLC patients.