ERVW-1 and infection: To map the exact Env recognition sites of the RV144 vaccine-induced mAbs CH54 and CH55 and assess if these differ from the epitopes of cluster A antibodies A32 and C11 induced in the course of natural infection or from those induced in the RV305 trial (28), we determined crystal structures of complexes of their Fabs with CD4-triggered gp120 antigen.