The epidemiology of HIV coreceptor tropism.

According to their cellular coreceptor tropism, HIV variants are termed R5 if they use CCR5 as a coreceptor, whereas viruses with a preference for CXCR4 are termed X4. The prevalence of R5, X4 and dual/mixed (D/M) strains shows considerable variation in different patient populations. In treatment naive patients, R5 strains are found in 80-90%, compared to only 50-55% in patients with antiretroviral exposure. The most important predictor of R5 tropism seems to be a higher CD4 T-cell count in both naive and antiretrovirally pretreated patients. A low HIV plasma viremia seems to be associated with R5 tropism only in untreated patients. As the benefit of the new antiretroviral drug class of the CCR5 coreceptor antagonists will be probably limited to the HIV-infected patients harbouring R5 strains, determination of viral coreceptor tropism has become an important diagnostic prerequisite for the treatment of HIV infection. This review will focus on current knowledge of the epidemiology of HIV coreceptor tropism.