Aberrant expression of HERV-K envelope in lymphoma represents an opportunity for novel treatments.

PURPOSE: Human endogenous retrovirus K (HERV-K/HML-2) is a human-specific endogenous retrovirus family that maintains intact open reading frames and is aberrantly expressed in multiple cancers. We tested whether HERV-K, specifically its envelope (Env) protein, marks clinically relevant diffuse large B-cell lymphoma (DLBCL) states and serves as a tractable immunotherapeutic target. EXPERIMENTAL DESIGN: Locus-level transposable element (TE) and HERV expression was quantified in two independent DLBCL RNA-seq cohorts using curated TE annotation and a uniform alignment/counting workflow. Env transcript and protein expression (including cell-surface localization) was validated in lymphoma cell lines using RT-qPCR, immunoblotting, and flow cytometry. Functional relevance was assessed by siRNA-mediated Env knockdown. Candidate extracellular linear epitopes were predicted in silico and synthesized for serological and phage display assays. Anti-Env camelid VHHs were isolated, humanized, and tested for binding, antibody-dependent cellular cytotoxicity (ADCC), and antigen-dependent internalization. RESULTS: TE transcripts stratified DLBCL into clinically distinct subgroups, and high HERV-K expression associated with an interferon/viral-mimicry program. Env RNA was detected in patient tumors and cell lines, and the protein was detected on the surface of a subset of lymphoma cell lines, in which Env knockdown reduced proliferation. A humanized heavy-chain antibody (FF-01) bound surface Env, induced selective ADCC in Env-positive models (reporter and primary NK-cell assays), and underwent rapid antigen-dependent internalization. CONCLUSIONS: HERV-K activity identifies biologically meaningful DLBCL states and exposes a targetable surface antigen. FF-01 provides proof of principle for antibody-based strategies against HERV-K Env, including ADCC- and ADC-oriented approaches.