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Education > Clinical Updates

Clinical Update #3 - News from the 23^rd Clinical Virology Symposium

Clearwater Beach, Florida
April 29 to May 2, 2007

Karam Mounzer and colleagues from The Jonathan Lax Treatment Center, in collaboration with Virco, presented a poster at the 23^rd Annual Clinical Virology Symposium evaluating concordance of drug-specific resistance in PhenoSense GTTM (PGT) and virco^®TYPE HIV-1 (virtual phenotype, VP) and estimated the cost savings associated with introduction of VP assays into a community-based clinic.

This retrospective, single-center study included all patients on a failing antiretroviral drug regimen who had a PGT assay conducted over 1 year (July 1, 2004 and June 30, 2005). For study inclusion, results from the PhenoSenseTM phenotype (PT) assay had to provide additional informational value to the GeneSeq^™ HIV genotype (GT) assay. Added value was defined as: 1) discordance between PT and GT where in the net assessment the PT overruled the GT, 2) concordance between PT and GT where the PT showed possible residual activity of a drug, or 3) assays with >2 mixtures where PT drove the net assessment. Complete mutation/polymorphism lists derived from PGT assay reports were used to generate a corresponding VP. Pearson correlation (PC) and Kendall tau b (Ktb) were used to evaluate drug-specific measures of agreement for predictions based on the VP and PGT assays for 13 nucleoside reverse transcriptase inhibitor (NRTI) and protease inhibitor (PI) agents.

The primary objectives of the study were to determine 1) the concordance between fold change (FC) per drug in each sample as measured by the PGT and VP assays, and 2) the level of agreement in antiretroviral regimen selection between the two assay reports for patients who achieved a >=1 log10 reduction in HIV RNA at 3 months (+1 month) after initiation of the new regimen. A secondary objective was to establish parameters for a cost-benefit analysis between PGT and VP resistance testing in a community-based clinic setting.

Of the 51 PGT assays conducted during the 1-year study, 21 (42%) met the inclusion criteria and 17 had 3-month follow-up HIV RNA data. Patients with eligible assay results had a median of 8 prior antiretroviral agents. Resistance predictions based on the VP assay were correlated highly with the PGT assay net assessment. Composite correlation scores were:

• NRTI: Pearson correlation 0.75 (Ktb=0.51)
• PI: Pearson correlation 0.97 (Ktb=0.94)
• Combined NRTI/PI scores: Pearson correlation 0.92 (Ktb=0.66)

Among patients with follow-up data, 76% achieved an HIV RNA reduction of >=1 log10 copies/mL at 3 months on the new regimen guided by the PGT assay. These patients had highly-concordant VP for PGT and all active drugs maintained or added based on PGT net assessment could have been selected by the VP prediction, except for abacavir in one patient. VP predicted resistance to drugs defined by PGT in all 21 samples. VP results were obtained 7 days quicker.

In this study, ordering virco^®TYPE HIV-1 in place of the more expensive PhenoSense GTTM would have resulted in an estimated cost savings of $25,500 and would have provided the clinicians at the Jonathan LAX Center with information that resulted in the same treatment decisions. These data underscore the relative value of a virco^®TYPE HIV-1 resistance interpretation in optimizing antiretroviral regimens. If you are interested in viewing the complete poster, please click here.

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