Acquisition of syncytium-inducing HIV-1 strains during therapy with zidovudine alone or combined with alpha interferon or didanosine.

The effect of antiretroviral treatment on HIV-1 phenotype was studied in a group of 83 nucleoside-naive patients. These initially nonsyncytium-inducing HIV-1 positive patients were followed prospectively for their HIV-1 phenotype. Syncytium-inducing variants were detected by cocultivation of peripheral blood mononuclear cells with the MT-2 T-cell line. Overall, 16 of 83 (19%) patients underwent a shift to syncytium-inducing phenotype: 11 of 67 during zidovudine treatment, 3 of 10 during zidovudine plus alpha interferon treatment, and 2 of 6 under initial zidovudine plus didanosine therapy. The results of this study demonstrate that neither zidovudine therapy alone nor combined with interferon or didanosine prevents the acquisition of syncytium-inducing strains.