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 into chimpanzees, which were then given an intravenous challenge with a primary human immunodeficiency virus type I (HIV-1) isolate. In two control animals, the infection was established immediately, as evidenced by positive cell-associated DNA PCR and serum RNA PCR tests within 1 week, seroconversion by 4 weeks, and development of lymphadenopathy in this acute phase. Serum RNA PCR tests were negative in one of the two antibody-infused animals until week 8 and in the other antibody-infused animal until week 12; both animals seroconverted at week 14. The peak of measurable virus-specific serum RNA was delayed until week 16 in 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 peripheral blood of the second animal but was isolated from lymph node cells taken at week 36. The infection of untreated chimpanzees with this primary isolate appears robust. Use of this isolate should widen the scope of possible experiments in the chimpanzee model. This antibody infusion study indicates that neutralizing antibody, when present at the time of challenge, affects the timing and level of infection and remains influential after it can no longer be detected in the peripheral circulation. It is possible that preexisting, neutralizing antibodies (passively administered or actively elicited) affect the course of acute-phase virus replication in humans. It remains to be established whether these immunologically mediated early effects will influence the course of HIV-1 disease.

Correlates of protective immunity against HIV-1 infection in immunized chimpanzees.

Several experimental vaccination strategies have been developed to prevent primary infection with human immunodeficiency virus (HIV), and as immunotherapeutics for infected individuals. Many of the putative vaccines have been tested in chimpanzees (p. troglodytes) to determine their safety, efficacy, and to delineate immune correlates of protection. To date, approximately 25 candidate vaccines representing active or passive strategies have been evaluated in chimpanzees, and efficacy has been based on protection against primary infection following intravenous or mucosal challenge with cell-free or cell-associated virus. Active immunization has been attempted with whole inactivated virus, envelope depleted viral preparation, vaccinia vector expressing gp 160 in combination with other viral gene products, and subunit vaccines containing recombinant gp 120 derived from different isolates. Polyclonal and monoclonal antibodies with neutralizing activity have been utilized for pre- and post-exposure passive immunization to block primary infection with HIV.