NON-SYNCYTIUM-INDUCING HIV TYPE-1 ISOLATED FROM INFECTED INDIVIDUALS REPLICATES IN MT-2 CELLS

Human immunodeficiency virus type 1 (HIV-1) isolates from six infected individuals less then 4 years of age were phenotyped for their syncyt ium-inducing (SI) ability in MT-2 cells. Three viral isolates that ind uced syncytia were detected. One SI isolate was from an individual who was in disease stage P2A,B,C and two SI isolates were recovered seque ntially from another individual who switched from disease stage P1B to P2F. Non-syncytium-inducing (NSI) isolates were detected in two indiv iduals who were in stage P1B of disease, and in a third individual who was in stage P2A of disease. Three sequential isolates obtained over a 2-year period from a fourth individual who progressed from disease s tage P1B to P2A,B,C and subsequently died of AIDS-related disease were also found to have the NSI phenotype. To test whether NSI isolates ca n replicate in the absence of syncytium formation, we analyzed NSI-inf ected MT-2 cells for production of viral p24 antigen and expression of viral RNA by in situ hybridization. By day 12 postinfection, 6 of 7 N SI viral isolates produced 7- to 36-fold increases in p24 antigen comp ared to day 6, and expressed viral RNA in 13-20% of cells. A single NS I isolate that did not replicate in MT-2 cells was obtained from an in dividual who was asymptomatic (stage P1B). The individual rapidly prog ressed to symptomatic stage P2F and two sequential SI viruses were iso lated. These SI isolates replicated in MT-2 cells and induced cytopath ic effects. These results suggest that some cytopathic viral isolates replicate in MT-2 cells in the absence of syncytium induction and repl ication in MT-2 cells may serve as an indicator for disease progressio n in certain HIV-infected individuals.