STANDARD CONDITIONS OF VIRUS ISOLATION REVEAL BIOLOGICAL VARIABILITY OF HIV TYPE-1 IN DIFFERENT REGIONS OF THE WORLD

HIV-1 isolates were obtained from four countries within the framework of the WHO Network for HIV Isolation and Characterization. The use of standard HIV isolation procedures allowed us to compare the biological properties of 126 HIV-1 isolates spanning five genetic subtypes. In p rimary isolation cultures, viruses from Uganda and Brazil appeared ear ly and replicated without delay, whereas the replication of Thai virus es was delayed by several weeks. Regardless of genetic subtype or coun try of origin, blood samples collected more than 2 years after serocon version yielded virus that replicated efficiently in the primary isola tion cultures. None of the isolates obtained from Thailand or Rwanda r eplicated in cell lines, whereas 5 of the 13 Brazilian isolates and 7 of the 11 Ugandan isolates replicated and induced syncytia in MT-2 cel ls. As expected for virus isolates obtained early in HIV-1 infection ( within 2 years of seroconversion), all viruses from Brazil, Rwanda, an d Thailand showed a slow/low replicative pattern. For the Ugandan samp les, the time from seroconversion was known precisely for a few of the samples and only in one case was less than 2 years. This may explain why the five viruses that were able to replicate in all cell lines, an d thus classified as rapid/high, were of Ugandan origin. Viruses able to induce syncytia in MT-2 cells, also induced syncytia in PBMC. Howev er, 8 slow/low viruses (out of 27) gave discordant results, inducing s yncytia in PBMC but not in MT-2 cells. Furthermore, using syncytium in duction as a marker, changes in virus populations during early in vitr o passage in PBMC could be observed. The results indicate that biologi cal variation is a general property of HIV-1 in different regions of t he world. Moreover, the time from HIV-1 infection, rather than genetic subtype, seems to be linked to viral phenotype.