Effect of 3'-azido-2',3'-dideoxythymidine (AZT) and neutralizing antibody on human immunodeficiency virus (HIV)-induced cytopathic effects: implication of giant cell formation for the spread of virus in vivo.

The effect of 3'-azido-2',3'-dideoxythymidine (AZT) on the human immunodeficiency virus (HIV)-associated giant cell formation was studied in vitro. For this purpose we developed a coculture system using Molt-4 and its virus-producing cell, Molt-4/HTLV-III, which induced syncytia very efficiently. Treatment of the cocultures with 1 and 5 microM of AZT did not inhibit induction of multinucleated giant cells, although only 0.1 microM AZT resulted in almost complete inhibition of HIV replication in Molt-4 cells by cell-free virus infection. This was also evidenced by the assays for viral antigen-positive cells, reverse transcriptase activity, and virus particles released from cell cultures after AZT treatment. When the cocultures were treated with 1% neutralizing antibody (NA) from HIV-infected individuals alone, giant cell formation was inhibited to some extent. However, the concomitant treatment of culture with AZT and NA resulted in much stronger inhibition of giant cell formation. The amount of CD4 antigens on the surface of cells was reduced greatly in the HIV producer cells (Molt-4, H9, and MT-4 cells) as compared to their HIV-free counterparts. These data suggest that (1) both CD4 antigen and viral antigens on the surface of cells play central roles in the induction of multinucleated giant cells and (2) AZT is more effective in inhibition of viral spread in patients with higher NA, probably at an earlier stage of the disease than in patients with lower NA titer.