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Lab21 Conducting Tropism Testing for HIV Drug Selzentry in UK

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Lab21 announced last week that it will be the first commercial laboratory in the UK to provide the companion diagnostic test for Selzentry, Pfizer's CCR5-tropism drug for the treatment of HIV.

The Cambridge, UK-based company said that it will offer the service from its UK operations "with immediate effect and will be able to receive samples from all parts of the world." Eventually, Lab21 also plans to offer the test as part of its comprehensive HIV service at its US facility in Greenville, SC.

Selzentry, marketed under the brand name Celsentri in Europe, is marketed by ViiV Healthcare, which is facilitating companion testing for the HIV drug as part of its coverage agreement with UK's National Health Service.

ViiV Healthcare is Pfizer and GlaxoSmithKline's spin-off venture to market HIV treatments developed by both firms. The establishment of ViiV last November resulted in the transfer of two personalized medicine HIV drugs: Pfizer's Selzentry and GSK's Epizicom, which combines abacavir and lamivudine (PGx Reporter 11/11/09).

Selzentry is indicated for CCR5-tropic HIV-1 patients. The drug's label instructs doctors to establish a patient’s tropism status prior to administering the drug.

Pfizer and Monogram last year extended their existing deal to globally market Monogram's Trofile assay to support Selzentry access (PGx Reporter 05/18/09). However, Pfizer and Monogram have a non-exclusive agreement.

It appears that Lab21 will be conducting tropism testing using a test other than Trofile. On its website, Lab21 describes a test called HIV-1 Tropism by Genotype, which utilizes the geno2pheno algorithm developed by the Max Planck Institute to gauge the HIV-1 gp120 V3 genotype and determine the coreceptor being used by HIV virus to enter cells.

“The addition of this service to Lab21’s portfolio means that we can offer a fully comprehensive menu of tests for HIV clinicians to use including viral load and resistance analysis, CD4 counts, and serology," Berwyn Clarke, Lab21 chief scientific officer, said in a statement.

Although Trofile was validated in clinical trials for Selzentry, a head-to-head comparison of the geno2pheno method against the enhanced version of Trofile, presented last year at the European HIV Drug Resistance Workshop in Stockholm, suggests that the positive predictive value for virologic response is similar for the two tests.

Comparisons of the two platforms came from a study involving more than 100 patients at London's Royal Free Hospital and University College Medical School. According to the study, in 87 samples, the results between enhanced Trofile and geno2pheno agreed 91 percent of the time when geno2pheno had a false-positive setting of 10 percent and 90 percent of the time with a false-positive setting of 15 percent.

However, in the same study, when geno2pheno had a false-positive setting of 10 percent, its sensitivity was 69 percent. This led some reviewers at the workshop last year to assert that the geno2pehono method may not be ready for use in routine clinical testing.

Lab21 promises on its website to return results from its tropism test in 14 days.

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