Effect of class-specific therapy interruption on persistence of HIV type 1 antiretroviral resistance

Interruption of all antiretroviral therapy for HIV-1 infection when therapy is failing and antiretroviral resistance has emerged is frequently associated with the disappearance of detectable resistance-associated protease and reverse transcriptase substitutions. However, the effect that discontinuation of treatment with a particular antiretroviral class has on resistance to that class when other antiretroviral therapy is continued is unknown. We investigated differences in detectable genotypic resistance to protease inhibitors (PI) and non-nucleoside reverse transcriptase inhibitors (NNRTI) among two populations: patients undergoing testing at the moment class-specific treatment failed (Group 1) and patients undergoing testing for varying periods after class-specific treatment failed and was discontinued but therapy with other antiretroviral classes continued with incomplete viral suppression (Group 2). We found that the prevalence of detectable resistance to the PI and NNRTI classes was similar in both groups despite the absence of class-specific selective pressure for lengthy periods of time in Group 2. We hypothesize that this finding may be due to nonspecific selective pressure (i.e., to nucleoside reverse transcriptase inhibitors) selecting out PI- and, to a lesser extent, NNRTI-resistant viral variants.