Homozygous and heterozygous CCR5-Delta 32 genotypes are associated with resistance to HIV infection

Objective: To investigate evidence for resistance to HIV-1 infection associ ated with the heterozygous genotype CCR5-+/Delta 32 and with the homozygous genotype CCR5-Delta 32/Delta 32, which results in a nonfunctional CCR5 rec eptor. Design: Cohort study of initially HIV-seronegative high-risk individuals fr om eight different cities. Enrollment data were analyzed to investigate the association of demographic factors and risk behaviors with CCR5 genotypes on the assumption that increased genotype prevalence among persons with his tories of longer or more intensive exposure to HIV would indicate HIV resis tance associated with that genotype. Longitudinal data were analyzed to inv estigate the association of HIV seroincidence with CCR5 genotypes. The coho rt of 2996 individuals included 1892 men who have sex With men (MSM), 474 m ale injection drug users (IDUs), 347 women at heterosexual risk, and 283 fe male IDU. Measurements: CCR5 genotype, FEV serostatus, demographic factors, and risk behaviors during the 6 months before enrollment, followed by measurement of MV seroincidence during the subsequent IS months (for men) and 24 months ( for women). Results: Forty (1.3%) subjects were homozygous. CCR5-Delta 32/Delta 32 and 387 (12.9%) were heterozygous CCR5-+/Delta 32. All but 1 CCR5-Delta 32/Delt a 32 individuals and 51 CCR5-+/Delta 32 individuals were Caucasian. Among 1 531 Caucasian MSM, CCR5-+/Delta 32 individuals were present more frequently (22.3%) among those reporting unprotected receptive anal intercourse than among those not reporting this risk (15.9%) (p = .002), suggesting a select ive advantage of the heterozygous genotype. CCR5-+/Delta 32 individuals als o had a significantly reduced relative risk of HIV seroconversion adjusted for unprotected receptive anal intercourse compared with CCR5-+/+ individua ls (relative risk = 0.30, 95% confidence interval [CI]: 0.08-0.97). CCR5-De lta 32/Delta 32 prevalence among Caucasian MSM was significantly associated with age among subjects recruited from high HIV seroprevalence cities (New York City and San Francisco) (odds ratio [OR] for each decade increase in age = 2.57, Cl: 1.56-4.21) but not among those recruited from lower HIV pre valence sites (Boston, Chicago, Philadelphia, Seattle, and Providence/Pawtu cket, Rhode Island) (OR = 1.20 Cl: 0.75-1.89). Conclusions: Cross-sectional and longitudinal analyses indicated that among highrisk HIV seronegative MSM, CCR5-+/Delta 32 and CCR5-Delta 32/Delta 32 are associated with protection against HIV infection. These findings imply that strategies aimed at reducing susceptibility to MV infection by blockin g CCR5 receptor sites need not seek blockage of all receptor sites to achie ve an imperfect but substantial degree of protection.