The investigator has discovered recently that a nucleoside analog- resistance mutation In RT exhibits increased fidelity of dNTP insertion. The prototype of such an enzyme is resistant to 3TC, and it has the genotype M184V. The investigator postulates that mutations resulting in increased fidelity could be beneficial in combination therapy by decreasing the frequency of RT resistance to other antiviral agents. The following 3 Specific Aims are proposed: 1) To identify other RT mutations that cause an increase in polymerase fidelity. A panel of selected mutants will be assessed in biochemical assays to measure errors by misinsertion, misextension and slippage. Error rates in RNA-dependent and DNA- dependent polymerization steps will be compared: 2) to compare the mutation rates in vitro and in a single-cycle HIV replication assay: and 3) to examine the influence of increased fidelity in clinical settings. In this Specific Aim, the investigator proposes to study the clinical significance of increased fidelity of 3TC- resistant HIV variants, which he postulates will reduce the frequency of mutations in patients receiving 3TC and other drugs. Samples will be obtained from a clinical trial, in which patients will be treated first with 3TC and given ritonavir as a second arm only after the appearance of 3TC-resistant RT is confirmed. The investigator plans to study the frequency at which ritonavir- resistance will emerge in such patients and attempt to correlate this with the in vivo mutation rate dictated by mutant RT.
