Selection of the patients from whom the mAbs were isolated was extremely assay dependent. The patients who gave the three interesting mAbs would not have been selected if any of the alternative assays had been used. The influence of target cells on neutralization has already been observed both by us and others [10, 20, 26, 27] . In particular, there is a three way interaction effect between the virus, antibody and target cells. Especially MPER specific Abs are more potent in PBMC based assays [4, 26, 27] . Since our data show that the HJ, HK and HGN patients are more potent in PBMC neutralization assays with an extended incubation phase it could be envisioned that these special patients could have a high proportion of gp41 specific Abs in their plasma.