Overall, the data suggest that a broader range of HIV-1 peptides are recognized by HLA heterozygous individuals resulting in more efficient-specific cytotoxic T lymphocyte responses againt the pathogen. It may also take the virus a longer time to accumulate escape mutations in HLA heterozygous individuals relative to homozygous individuals. An alternative interpretation of the data is based on a model of frequency-dependent selection (or rare allele advantage), which argues that HIV adapts to HLA alleles that are common in the population. This alleles are most likely to be observed in HLA homozygotes. HLA heterozygoous individuals on the other hand are more likely to carry rare alleles (in combination with common alleles), to which the virus has not adapted as well, and therefore, individuals with these alleles are better able to contain the virus.