Virtual Phenotyping Is Helpful in HIV Drug Resistance Testing

By David Douglas

Real and virtual phenotyping appear to provide similar outcomes when used to guide HIV treatment in patients failing highly active antiretroviral therapy (HAART), according to Italian researchers. The virtual approach is also simpler and cheaper.

Virtual phenotyping aims to overcome drawbacks in other means of genotyping, Dr. Giampiero Carosi of the University of Brescia, and colleagues note in the March 1st issue of the Journal of Acquired Immune Deficiency Syndromes. A probabilistic estimate of the real phenotype is obtained by matching the patient's HIV genotype with those in a large database of samples.

To compare immunological responses after using real and virtual phenotyping, the researchers randomized 201 patients who were failing HAART to one of these approaches. All had had at least 2 years of exposure to antiretrovirals, had used more than six drugs and had a plasma HIV-1 RNA load greater than 1000 copies/mL.

Over 48 weeks of follow-up, between-group differences were not significant. For example, using intention-to-treat analysis, 20% of the real group and 24% of the virtual group showed a plasma viral load of less than 400 copies/mL. On-treatment analyses gave similar results.

Moreover, co-researcher Dr. Carlo Torti told Reuters Health that "patients' adherence to antiretroviral treatment and the baseline CD4+ T-cell count are of crucial importance for the virological success of salvage treatment. In particular, the association between higher CD4+ T-cell count and virological success suggests that resistance testing should not be delayed in those failing HAART."

Altogether, the researchers conclude that virtual phenotype testing is less expensive, easier to perform and less time consuming than the real method, and, as such, is a valuable surrogate. However, they also point out that "additional factors have to be integrated in salvage strategies to take better advantage of resistance testing in clinical practice."

04/25/03

J Acquir Immune Defic Syndr 2003;32:268-279.