Our qPCR experiments based on the primers for the ERVK3-1 locus in the A172 adherent line and GBM neurosphere lines (GBM28 and GBM43) confirmed robust expression of the HML-6 locus (A172 > GBM43 > GBM28) and support our bioinformatics findings (Fig. 3). Here, ERVK3-1 is linked to glioblastoma.