[Replicative properties of HIV-1 strains, resistant to 3'-azido-2'3'-dideoxythymidine]

The replicative activity of two strains of human immunodeficiency virus type I, 1974 and 1978, resistant to 3'-azido-2',3'-dideoxythymidine (AZT), was investigated. Assessment of AZT sensitivity by the standard method showed the 50% effective dose (ED50) for strain 1974 to be 0.1 mumole and for strain 1978, 1 mumole. Both strains had the slow/low. 3 phenotype. The level of virus-specific antigens in these strains was 3-7 times lower than in AZT-sensitive strain IIIB. In order to study the effects of AZT on virus replication, the strains were passaged in Jurkat-tat cells in the presence of 3.5 mumole of AZT. Virus activity was assessed from the level of intracellular (S-12) and extracellular (P-100) antigens, cell viability, and syncytium formation. Cell viability increased by 10%, syncytium formation dropped 5 times, and antigen accumulation increased 1.5-2 times in the culture with strain 1974. For strain 1978 these parameters were as follows: 17% decrease of cell viability, increase of syncytium formation by 1.7 times, and no changes in the level of viral antigen. After four serial passages in the presence of AZT ED50 for strain 1974 was 0.5 mumole and at least 1 mumole for strain 1978.