Link to Pubmed [PMID] – 15577536
AIDS 2004 Nov;18(17):2243-52
Despite multiple exposure to HIV-1, some individuals remain uninfected. This resistance has been associated with homozygosity for a 32 base pair deletion in the gene for the CCR5 receptor. This variant occurs frequently in Caucasians but is extremely rare in Asians or Africans.
http://www.ncbi.nlm.nih.gov/pubmed/15577536