Background:  Comparisons of highly exposed seronegative individuals (HESN) and low-exposure seroconverters (LESC) have the potential to reveal host genetic mechanisms of HIV-1 susceptibility and resistance. We hypothesize that host factors associated with HIV-1 resistance will be reflected in differences in gene expression patterns. Recent work has indicated that the human protein p21/WAF1 (a cyclin-dependent kinase inhibitor encoded by the gene CDKN1A) is a potent inhibitor of HIV-1 DNA integration, and is responsible for resistance of primitive hematopoietic cells and macrophages to HIV-1 infection. In addition, p21/WAF1 has been implicated in virological control in both elite and viremic controllers. As such, p21/WAF1 is a candidate host protein that could contribute to resistance to HIV-1 infection.

Methods:  We identified HESN and LESC in the Multicenter AIDS Cohort Study (MACS) by ranking individuals by the number of different anal intercourse partners reported in the 2.5 years before MACS semiannual visit 2. We chose the top-ranked 20 HESN and LESC, selecting only individuals of Caucasian ancestry, individuals with no CCR5∆32 alleles, and LESC samples obtained prior to the estimated dates of seroconversion. We used a highly sensitive real-time PCR assay to measure CDKN1A expression. RNA was extracted from cryopreserved peripheral blood mononuclear cells of each individual, and then reverse transcribed using a primer specific for CDKN1A. Quantitative real-time PCR was performed in triplicate using primers and hydrolysis probes that were specific to CDKN1A.

Results:  The mean level of CDKN1A expression was higher in the 20 HESN individuals than in the 20 LRSC individuals (p = 0.04, Mann-Whitney U test; HESN mean/median copy number = 22,370/4130, range 420 to 178,700; LESC mean/median copy number = 3582/2144, range 162 to 27,130). We are currently evaluating RNA expression levels in a second set of HESN and LESC.

Conclusions:  This result reveals a novel biological pathway that is associated with resistance to HIV-1 infection, and which could have profound implications for our understanding of natural protection against HIV-1 infection.