Patients were selected for inclusion into the study on the basis of the clade of their infecting virus (predominantly non-B clade) and on the ability of their plasma to neutralize a panel of HIV-1 primary isolates using two differerent assays. At the Institute for Tropical Medicine a panel of 4 primary A strains (VI191, 92UG37, VI820, VI 1031), 4 primary C strains (VI829, VI882, VI1144, VI1358) and 6 primary CRF02 strains (VI1090, VI2680, CI20, CA18, VI1380, VI2727) was used to select patients with .80% neutralization was measured at a 1/20 dilution of plasma. The plasma dilution was mixed with virus for 24 hours and absorbed to PHA/IL-2 stimulated freshly isolated PBMC for 1 hour. Virus-antibody mixture was then removed by extensive washing and p24 ELISA was performed after 14 days of culture to determine neutralization. At Queen Mary University of London, the TZMbl-based recombinant pseudovirus assay was employed with a selected panel of Tier 2-type clade A, B, C, CRF02_AG, _AE, F and BF viruses to measure .50% neutralization at a 1/20 dilution. MAbs were isolated using a previously described improved EBV immortalization method [41] . Culture supernatants were harvested 14 days after immortalization and assayed in parallel for binding to trimeric gp140 proteins (UG37, clade A and CN54, clade CRF07_BC) [48] , monomeric gp120 (CN54, CRF07_BC and IIIB, clade B) and gp41 recombinant ectodomain (HxB2, clade B). Those that were positive were then subcloned and grown up on a large scale for supernatant purification. The purity of all mAb preparations was assessed using a chromogenic LAL endotoxin assay (Genscript) and endotoxin levels were always ,0.05 EU/ml.