THE CONSEQUENCE OF PASSIVE ADMINISTRATION OF AN ANTI-HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 NEUTRALIZING MONOCLONAL-ANTIBODY BEFORE CHALLENGE OF CHIMPANZEES WITH A PRIMARY VIRUS ISOLATE

The anti-gp41 virus neutralizing monoclonal antibody 2F5 was infused i nto chimpanzees, which were then given an intravenous challenge with a primary human immunodeficiency virus type 1 (HIV-1) isolate. In two c ontrol animals, the infection was established immediately, as evidence d by positive cell-associated DNA PCR and serum RNA PCR tests within 1 week, seroconversion by 4 weeks, and development of lymphadenopathy i n this acute phase, Serum RNA PCR tests were negative in one of the tw o antibody-infused animals until week 8 and in the other antibody-infu sed animal until week 12; both animals seroconverted at week 14. The p eak of measurable virus-specific serum RNA was delayed until week 16 i n one antibody-infused animal. Virus-specific RNA in the other animal did not reach levels comparable to those in the other animals through 1 year of follow-up studies, Virus was isolated from the week 16 blood sample from one infused animal, Virus was not isolated from periphera l blood of the second animal but was isolated from lymph node cells ta ken at week 36, The infection of untreated chimpanzees with this prima ry isolate appears robust. Use of this isolate should widen the scope of possible experiments in the chimpanzee model. This antibody infusio n study indicates that neutralizing antibody, when present at the time of challenge, affects the timing and level of infection and remains i nfluential after it can no longer be detected in the peripheral circul ation, It is possible that preexisting, neutralizing antibodies (passi vely administered or actively elicited) affect the course of acute-pha se virus replication in humans. It remains to be established whether t hese immunologically mediated early effects will influence the course of HIV-1 disease.