Abstract:
HIV drug resistance genotyping, phenotyping, and replication capacity analyses of plasma derived HIV in patients with stable suppression of plasma viremia<50 copies/ml

Eoin Coakley, M.D.

Abstract

Current recommendations for HIV therapy aim to achieve a complete suppression of viral replication. This has been taken to be present when the plasma viral load is sustained <50 copies/mL. Current approved technologies limit the quantitation of the plasma viral load to 50 copies/mL and HIV drug resistance genotyping to 1,000 copies/mL. Limited date exist evaluating the virologic profiles in subjects with low level viremia. In the BIDUSI study we defined a population of subjects with stable on-treatment viral loads between 50-1,000 copies/mL. Using a novel in-house genotyping assay we described the drug resistance genotypes in this cohort. At a median viral load of 315 copies/mL, 67% of subjects were resistant to their antiretroviral therapy. This was after a median 23 months of stable viremia <1,000 copies/mL and was associated with stable CD4 counts. While there are no data evaluating the plasma HIV genotypes <50 copies/mL. We believe these data suggest that in a proportion of treated subjects with plasma viral loads <50 copies/mL a stable but extremely low-level viremia is likely to be present possibly associated with antiretroviral resistance.

1. We propose a pilot study to identify 20 treated HIV positive subjects with stable levels of viremia<50 copies/mL by a boosted form of the Roche Amplicor Monitor Assay.
   
2. We will focus on those with occasional transient viremic episodes or ‘blips’ in viral load, those with prior antiretroviral resistance and those on NRTI-only therapy.
   
3. With a boosted form of the RNA harvest-RTPCR assay used in the BIDUSI study we will define the plasma HIV drug resistance genotypes in these subjects.
   
4. We will follow individuals longitudinally to demonstrate evolution of HIV drug resistance over time and to determine if this is associated with subsequent virologic escape.
   
5. Phylogenetic comparisons of gag and pol sequences will be performed to attempt to determine if such replication represents a steady and sustained replication by related viruses or random replicatory events from less closely related viruses.
   
6. In collaboration with investigators at ViroLogic Inc and Esoterix Inc, we will attempt to define the drug resistance phenotypes and replication capacities, and to quantitate the lymphocyte HIV mRNA levels. We will relate these data to the viral load and drug resistance genotypes.