VIRUS LOAD IN CHIMPANZEES INFECTED WITH HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 - EFFECT OF PREEXPOSURE VACCINATION

Many reports indicate that a long-term asymptomatic state following hu man immunodeficiency virus type I (HIV-1) infection is associated with a low amount of circulating virus. To evaluate the possible effect of stabilizing a low virus load by non-sterilizing preexposure vaccinati on, a quantitative virus isolation method was developed and evaluated in four chronically infected chimpanzees infected with a variety of HI V-1 related isolates. This assay was then used to monitor a group of c himpanzees (n = 6) challenged with HIV-1 following vaccination with gp 120 or gp160. Data indicated that of the three vaccinated animals whic h became infected after challenge, the animal with the lowest neutrali zing titre at the time of challenge acquired a virus load similar to t he control animals, whereas the two other chimpanzees had reduced numb ers of virus producing cells in their peripheral circulation. One anim al became virus isolation negative, developed an indeterminant PCR sig nal on lymph node DNA and subsequently became negative for HIV-1 DNA a s determined by PCR on PBMC (peripheral blood mononuclear cells) and b one marrow DNA. Recently, the second animal has also become PCR negati ve. To confirm observations from quantitative virus isolations, quanti fication of HIV-1 DNA in PBMC and virus RNA in serum was performed by PCR on serially diluted samples at two different time points. Comparis on of virus load as determined by these three methods confirmed that t here was an effect of vaccination in reducing virus load and demonstra ted a correlation between decreased numbers of virus producing cells, HIV-1 DNA containing cells and virus RNA molecules in serum.