Prevention of human T cell lymphotropic virus type I infection in Japanese macaques by passive immunization.

Prophylaxis against human T cell lymphotropic virus type I (HTLV-I) is of primary importance for the eradication of adult T cell leukemia and other diseases associated with this virus. Hyperimmune globulin (H-IgG) prepared from healthy blood donors with high antibody titers for HTLV-I was evaluated for its prophylactic effect against HTLV-I in Japanese macaques (Macaca fuscata). Normal IgG (N-IgG) prepared from seronegative healthy blood donors was used as control. Both preparations contained 50 mg/ml IgG and H-IgG had a neutralizing antibody titer of 1:7100 by vesicular stomatitis virus (HTLV-I) pseudotype neutralization assay. Two macaques were infused with 2 ml/kg N-IgG and three macaques were immunized with 2-0.5 ml/kg H-IgG. They were immediately challenged by inoculation of 8 x 10(6)/kg cells from an HTLV-I-producing rabbit lymphoid cell line (Ra-1). Another macaque was immunized with 1 ml/kg H-IgG 24h after inoculation of 8 x 10(6)/kg Ra-1 cells. HTLV-I infection, as determined by seroconversion and verified by polymerase chain reaction, occurred in both of the N-IgG-injected macaques but in none of the four H-IgG-injected macaques. These results demonstrate the protective efficacy of H-IgG against HTLV-I infection in a primate model and provide an experimental basis for passive immunization trials in humans.