Background: HIV-1 viruses readily evolve in response to host immunity. More rapid adaptation of the virus presumably accounts for the documented increased likelihood of viral transmission from a seropositive (index) to a seronegative (recipient) sexual partner in the presence of greater HLA allele concordance. We searched for a replicative advantage of HIV-1 isolates in hosts who shared alleles at the 3 most polymorphic HLA class I (A, B) and class II (DRB1) loci.

Methods: Co-habiting HIV-1-discordant Zambian couples were closely monitored for HIV-1 transmission. Presence of genetically similar viruses in the suspected index and newly seroconverted recipient partners defined intra-couple (linked) HIV-1 transmission. HLA-A, HLA-B, and HLA-DRB1 alleles in all linked pairs were typed by PCR-based techniques. The difference in mean plasma virus load (HIV-1 RNA copies/ml) relatively early in infection was compared between index and recipient partners with varying degrees of HLA allele sharing. All statistics in general linear regression models were adjusted for index partner age, gender, and virus load.

Results: Between 1995–2002, 115 cases of linked HIV-1C transmission were identified and included in the final analyses. The frequencies of HLA allele sharing ranged from 28%–37%. A linear correlation (adjusted r = 0.33, p = 0.002) was detected between virus load in index and recipient partners. However, the degree of sharing HLA alleles (1, 2, or 3 loci) made little difference in the recipients’ virus loads (+ 0.05 to + 0.22 log₁₀, p > 0.13).

Conclusions: HLA allele sharing is common in Zambian couples with HIV-1C infection. At the population level, sharing of HLA alleles did not confer a survival advantage for the genetically-related viruses in the early months of infection. Further longitudinal data from these virologically linked couples may provide additional insights into the dynamics of virus-host equilibration.