ERVW-1 and monocytic leukemia: We also generated HERV-K119 env KO U937 human monocytic leukemia cells to support the results of HERV-K119 env KO in THP-1 cells and confirmed that the HERV-K119 env gene was knocked out in U937 cells using genomic PCR, RT-PCR, and Western blotting (Supplementary Figure S1A–C).