Background:  Neutralizing antibody responses are a major immunologic component during viral infection and of protective vaccinees. However, little is known about cross-clade neutralizing antibody responses in HIV-1-infected persons in countries where multiple subtypes, CRF, and URF are co-circulating. We investigated the patterns of cross-clade neutralizing antibody responses in HIV-1-infected Cameroonians.

Methods:  Between March 2004 and February 2005, we collected and tested plasma samples from 42 HIV-1-infected Cameroonian blood donors. Anti-HIV-1 neutralizing antibodies were measured by a recombinant virus assay. We included 8 HIV-1 Env-pseudotyped viruses:  3 were subtype C, 2 subtype B, and 1 each of subtype A, CRF01_AE, and CRF02_AG. Neutralizing antibody titers were defined as the plasma dilution that gave 50% reduction in single-round viral infectivity measured by luciferase activity from indicator cells.  

Results:  Median CD4 count for the 35 donors, for whom data were available, was 428 cells/mm³ (range 178 to 1532), and median log₁₀ viral load was 4.66 copies/mL (range 2.30 to 6.11). Of the 42 plasma samples, 28 (67%) had neutralizing antibodies against at least 1 of the 8 Env-pseudotyped viruses, and 14 (33%) had no detectable neutralizing antibodies. Neutralizing antibody titers against the Env-pseudotyped viruses ranged from 30 to 543. Of the 28 persons with neutralizing antibodies, 63% had neutralizing antibodies against pseudoviruses with subtype A env sequences, 57% with subtype C env sequences, and 16% with subtype B env sequences. Of the samples, 11 (39%) had broadly neutralizing antibodies to more than 4 of the Env-pseudotyped viruses tested, with median IC₅₀ titer 62, ranging from 30 to 543.

Conclusions:  Our preliminary analysis indicates that in Cameroon, a country where multiple HIV-1 subtypes and recombinants circulate, the majority of persons with HIV-1 infection produce cross-clade neutralizing antibodies with some degree of reactivity against diverse primary HIV-1 strains. Thus, comprehensive analyses of cross-clade neutralizing antibody responses may provide valuable information on vaccine design and effective strategies in HIV prevention.