Ordered accumulation of mutations in HIV protease confers resistance to ritonavir

Analysis of the HIV protease gene from the plasma of HIV-infected patients revealed substitutions at nine different codons selected in response to monotherapy with the protease inhibitor ritonavir. Mutants at valine-82, although insufficient to confer resistance, appeared first in most patients. Significant phenotypic resistance required multiple mutations in HIV protease, which emerged subsequently in an ordered, stepwise fashion. The appearance of resistance mutations was delayed in patients with higher plasma levels of ritonavir. Early mutants retained susceptibility to structurally diverse protease inhibitors, suggesting that dual protease inhibitor therapy might increase the duration of viral suppression.

Sequential determination of viral load and phenotype in human immunodeficiency virus type 1 infection

Detailed studies of HIV viral load and phenotype were performed on sequentially cryopreserved peripheral blood mononuclear cells (PBMCs) from eight infected individuals followed in the Los Angeles Multicenter AIDS Cohort Study. Three individuals remained clinically and immunologically stable over a 5- to 8-year period, three demonstrated precipitous and two gradual declines in CD4+ T lymphocytes. Viral load in PBMCs was quantitated by limiting dilution culture and DNA PCR, while minimally passaged viral isolates were studied for their ability to induce syncytium formation in vitro and, when relevant, sensitivity to zidovudine (ZDV). Viral burden remained relatively low in those who remained clinically and immunologically stable, while increasing substantially in all five individuals who experienced a decline in CD4+ T lymphocytes. Two subjects were noted to have a switch from non-syncytium-inducing (NSI) to syncytium-inducing (SI) isolates immediately preceding a precipitous decline in CD4+ T lymphocytes, while the third individual who experienced such a decline and the two who had gradual declines did not develop SI isolates. Moreover, of the three subjects who experienced a decrease in CD4+ T lymphocyte number and were given ZDV during the study period, none were noted to develop resistance to this agent. In summary, the virology in clinically and immunologically stable individuals was characterized by relatively low viral burden in PBMCs and a predominance of NSI isolates.(ABSTRACT TRUNCATED AT 250 WORDS)