Susceptibility of MM23′s viruses to neutralization by autologous sera, sCD4 and MAbs.^a

aTiters are expressed as: (A) the reciprocal dilution of serum required to reduce infectivity by ≥90% (IC90) compared to pooled HIV ve- serum control; or (B) the concentration of sCD4 or MAb required to reduce infectivity by ≥50% (IC50) compared to medium only control. bMM23 serum samples collected from the indicated days after onset of symptoms characteristic of PHI. cClones indicated with an asterisk (*) displayed high sensitivity to neutralizzation by heterologous sera. d<10, less than 90% reduction of infection was observed at the highest serum input tested (1:10). ent, not tested. fViruses were assayed for neutralization by MAb 17b both in the presence (+sCD4) and absence (−sCD4) of sCD4. When sCD4 was included with 17b reduction in infection was calculated against virus assayed in the presence of sCD4 alone. The amount of sCD4 included varied between viruses, being equal to the IC50 for each virus. g>15, less than 50% reduction of infection was observed at the highest (15 µg/ml) concentration tested. hN/A, not assessed as the virus was resistant to neutralization by sCD4.