isolates while the HK20 mAb is effective against only one of the three tier 1 strains and one of the 11 tier 2 isolates. The proportion of isolates neutralized by an individual plasma was also markedly dependent on the panel of HIV isolates used. The patients' plasma were initially selected in 24/1/14 PBMC assays and the ITM panel of 14 primary infectious HIV-1 isolates (Table 4 ). In the smaller, modified panel of PV used in Antwerp (Table 5) 