Clonal analysis of functional differences among strains of human immunodeficiency virus (HIV)

Different isolates (HTLV-IIIB, LAV1 and ARV2) of human immunodeficiency virus (HIV) were cloned by a plaque-forming assay using MT-4 cells. The reverse transcriptase (RT) activity and plaque-forming unit (PFU) titers of all viral preparations were assayed. PFU/RT values, which indicate the relative proportions of incomplete and infectious viruses, were used for determination of viral infectivity. High values were obtained mainly for clones of HTLV-IIIB and LAV1, and low values for ARV2-derived clones, suggesting that ARV2 and its clones were genetically less infectious. For studies on cytocidal effects of the viruses, four clones of HTLV-IIIB, LAV1 and ARV2 were selected that had similar PFU/RT (infectivity) values for proliferation in infected MT-4 cells. When compared at the same dose (MOI), one clone (HTLV-IIIB-C-2) was found to be more cytocidal than the others. Furthermore, plaques induced by HTLV-IIIB-C-2 were larger than those induced by other clones, suggesting that the release of progeny from HTLV-IIIB-C-2-infected cell and their proliferation were the most efficient. Among the cloned viruses tested, three were found to induce strong cytopathic changes (fusion and ballooning) selectively in MT-4 cells. Thus, the infectivity, proliferation and cytopathic fusion-effects were proposed to be encoded by the viral genome and be separable by the plaque-cloning method.