V3 LOOP SEQUENCE-ANALYSIS OF 7 HIV TYPE-1 GROUP-O ISOLATES PHENOTYPEDIN PERIPHERAL-BLOOD MONONUCLEAR-CELLS AND MT-2 CELLS

HIV-1-infected individuals from which syncytium-inducing (SI) viruses are isolated most often progress more rapidly to AIDS than individuals carrying only non-syncytium-inducing (NSI) viruses. The syncytium-ind ucing capacity of virus isolates is commonly determined in conjunction to replication in MT-2 cells. Comparison of HIV-1 env sequences and a site-directed mutagenesis study have indicated that the presence of a positively charged amino acid at position 11 or 25 in the V3 loop is minimally required for the SI capacity of HIV-1 subtype B viruses. Stu dies have also shown a similar correlation between positively charged signature amino acids in the V3 loop and syncytium formation in MT-2 c ells for HIV-1 subtypes A, D, and E. In the present study virus phenot ype was determined and compared to the V3 loop sequence of seven HIV-1 group O isolates. Three of the HIV-1 group O isolates showed the NSI/ non-MT-2 tropic phenotype and two showed the SI/MT-2 tropic phenotype, whereas two isolates presented an uncommon NSI/MT-2 tropic phenotype. The V3 loop of the two SI/MT-2 tropic isolates had a high net positiv e charge and contained a positively charged amino acid at position 11 or 25. The V3 loop of the two NSI/MT-2 tropic isolates had a low net p ositive charge and contained a single positively charged amino acid at position 37.