p21(WAF1/CIP1) RNA expression in highly HIV-1 exposed, uninfected individuals

Abstract

Some individuals remain HIV-1 antibody and PCR negative after repeated exposures to the virus, and are referred to as HIV-exposed seronegatives (HESN). However, the causes of resistance to HIV-1 infection in cases other than those with a homozygous CCR5Δ32 deletion are unclear. We hypothesized that human p21WAF1/CIP1 (a cyclin-dependent kinase inhibitor) could play a role in resistance to HIV-1 infection in HESN, as p21 expression has been associated with suppression of HIV-1 in elite controllers and reported to block HIV-1 integration in cell culture. We measured p21 RNA expression in PBMC from 40 HESN and 40 low exposure HIV-1 seroconverters (LESC) prior to their infection using a real-time PCR assay. Comparing the 20 HESN with the highest exposure risk (median = 111 partners/2.5 years prior to the 20 LESC with the lowest exposure risk (median = 1 partner/2.5 years prior), p21 expression trended higher in HESN in only one of two experiments (P = 0.11 vs. P = 0.80). Additionally, comparison of p21 expression in the top 40 HESN (median = 73 partners/year) and lowest 40 LESC (median = 2 partners/year) showed no difference between the groups (P = 0.84). There was a weak linear trend between risk of infection after exposure and increasing p21 gene expression (R2 = 0.02, P = 0.12), but again only in one experiment. Hence, if p21 expression contributes to the resistance to viral infection in HESN, it likely plays a minor role evident only in those with extremely high levels of exposure to HIV-1.

Fig 1. p21 expression in HESN and LESC.

Shown are comparisons of p21 expression between: A) the top 20 ranking HIV-uninfected individuals with the greatest risk exposure (HESN) and the top 20 ranking HIV-infected individuals with the lowest risk exposure (LESC) (sampled prior to HIV infection); and B) the top 40 ranking HESN and LESC. All individuals were of European ancestry and none possessed a CCR5Δ32 deletion. p21 count refers to the number of p21 transcripts per ng of cDNA derived from total PBMC RNA.

Fig 2. Linear regression comparisons of p21 expression in HESN and LESC.

A) Linear regression of log10-transformed p21 count (number of p21 transcripts per ng of cDNA derived from total PBMC RNA) on individual pscores (the partner score, determined by the number of self-reported different sexual partners and the proportion of those partners with whom the individual had unprotected anal-receptive intercourse in the previous 2.5 years) for the top 20 ranking HESN and LESC. Shown are initial (black) and replicate (red) experiments. All individuals were of Caucasian ancestry and none possessed the CCR5Δ32 deletion. B) Plot of linear regression of p21 expression data on individual pscores for the top 40 ranking HESN and LESC, with initial (black) and replicate (red) experiments shown.