Fenoglio D, et al. - This study was undertaken to assess HIV-infected patients for the frequency of CD8⁺CD28^-CD127^loCD39⁺ Treg (regulatory T) cells in their circulation. A remarkable expansion of CD8⁺CD28^-CD127^loCD39⁺ Treg cells was noted in the circulation of HIV-infected patients, the frequency of which correlated with both clinical disease and signs of chronic immune cell activation. Data indicated that monitoring their frequency in the circulation represents a new marker of response to antiretroviral therapy when impacts on viremia and clinical response are not met.