Since it has been reported that HIV-1 neutralization is target cell type-sensitive [59, 60] , we next used TZM-bl as target cells and titrated the mAbs against a larger panel (n = 46) of predominantly (38/46) Tier-2 pseudoviruses (Table S2) . Generally the results obtained with the extended panel confirmed the previous results and showed that several mAbs had potent neutralizing activity, with IC 50 values ,20 ng/ml. A striking exception was HK20, which neutralized 17/20 pseudoviruses in the HOS-based assay, but only 3/46 pseudoviruses in the TZM-bl based assay.