HIV-infected long-term nonprogressors: epidemiology, mechanisms of delayed progression, and clinical and research implications.

Long-term nonprogressors (LTNPs) should be defined as untreated HIV-infected persons without AIDS and with high CD4(+) counts and low plasma viral loads 10 or more years after infection. Although no demographic or behavioral variables distinguish LTNPs, studies should be expanded to include geographically and ethnically diverse groups. Underlying mechanisms for delayed progression appear to include strong CD8(+) cytotoxic T-lymphocyte and noncytolytic suppressive activity, host genetic factors including chemokine receptor polymorphisms, and infection with attenuated viral strains.