Neutralization of HTLV-III/LAV Replication by Antiserum to Thymosin $\alpha _{1}

An antiserum prepared against thymosin $\alpha _{1}$, a hormone secreted by the thymus gland, effectively neutralized the AIDS-associated virus [HTLV-III/LAV (clone BH-10)] and blocked its replication in H9 cells. Reverse transcriptase activity and expression of the HTLV-III/LAV antigens p15 and p24 were inhibited by purified immunoglobulin G preparations of antisera to thymosin $\alpha _{1}$. The antiviral activity of the antiserum was found to be due to a region of homology between thymosin $\alpha _{1}$ and p17, a product of the gag gene of HTLV-III/LAV. Comparison of the primary sequences of thymosin $\alpha _{1}$ and the gag protein revealed a 44% to 50% homology in an 18--amino acid region, between positions 11 and 28 on thymosin $\alpha _{1}$ and 92 and 109 on the gag protein. The effectiveness of the thymosin $\alpha _{1}$ antiserum and of immunoglobulin G--enriched preparations in blocking replication of HTLV-III (BH-10) in H9 cells suggests a novel approach to the development of an AIDS vaccine. A vaccine directed against the gag protein might overcome the problem of genetic drift in the envelope region of the virus and be useful against all genetic variants of HTLV-III/LAV.