Resistance & Routine Testing

• Virco’s poster “Development of a Potency Weighted Sensitivity Score to Assess the Activity of Antiretroviral Drug Regimens” by Bart Winters et al was of high interest. This poster showed that a potency weighted PSS score was a more robust predictor of response at week 24 than the unweighted. In salvage patients, the wPSS remained highly accurate while accuracy declined for unweighted scores. Marc Mascolini from NATAP highlighted Virco’s poster on his Sunday ICAAC summary on their website (www.natap.org)
• Brendan Larder, Anton Pozniak, Jose Gatell, Richard Harrigan, Julio Montaner and others presented a poster titled “Computational Models Can Accurately Predict Response to Antiretroviral Therapy without a Genotype” which showed that two RF (random forest) models without genotypes predict virologic response only marginally less accurately than models with genotypes and both were superior to rules systems. This approach has potential clinical application in resource-poor settings.
• A poster from George Washington University ER in Washington, DC., M. Czarnogorski and colleagues showed that there was an almost 3x higher prevalence of HIV infection in patients who decline routine HIV testing than in those who accept it. Although there are various reasons to opt-out of HIV testing, 
  the most common reason documented was that patients felt they were not at risk for HIV infection.

Deep Sequencing

• Richard Harrigan and L.C. Swenson et al demonstrated that the evolution of transmitted drug resistant variants and revision to wild type was very dependent on particular mutation analyzed. Transmitted drug resistance was detected by standard drug resistance testing and confirmed with deep sequencing, which unveiled low-level resistance mutations not detected by standard sequencing including D30N in protease and G190E in RT. The deep sequencing approach also has the potential to assess reversion rates and linkage of resistance mutations within the diverse viral population in vivo. 
• The same authors also tested 1157 samples with matched population in deep sequencing and 450 with matched Trofile results. All three approaches to determining tropism gave concordant results in most cases, with discordant values driven by factors including the detection of minority species of X4 variants or CD4 count. 

Tropism

• Monogram Biosciences (L. Napolitano et al) showed that incorporating optimized primers into the Trofile assay improved determination of viral tropism in genetically diverse HIV subtypes, and Gilead 
  (R. Hluhanich et al) showed that HIV integrase inhibitors do not exert a post-antibiotic effect (PAE) despite slow dissociation from IN-DNA complexes in vitro.

• “A Potency Weighted Sensitivity Score Enables a Transparent and Accurate Prediction of the Activity of a Combination Therapy” by Bart Winters et al.
• “Rare HIV-1drug resistance mutations exert subtle synergistic and antagonistic effects in the context of the genetic background” by Margriet Van Houtte et al.
• “Validation of V3-loop based genotyping by direct comparison with 454 pyrosequencing in patients eligible for Maraviroc initiation”; a collaborative poster by Ina Vandenbroucke, Linos Vandekerckhove; Chris Verhofstede; and Anna Maria Geretti.

These posters will be available on the Virco.com web site after the Congress.