Co-Receptor Tropism Assay Launched for HIV Patients

The human immunodeficiency virus (HIV) diagnostic co-receptor tropism assay has been launched for patients in the United States.

Called Trofile, the assay determines which co-receptor a patient's HIV strain or strains use for viral entry--CCR5, CXCR4, or a combination of CCR5 and CXCR4. The cellular gateways that a particular HIV strain uses to gain entry into a healthy CD4+ cell is known as the patient's tropism.

Trofile amplifies a patient's HIV genome (from his/her blood sample) to make HIV particles specific to that individual patient. The resultant HIV particles are then used to infect CCR5- and CXCR4- expressing cell lines. Once the virus infects the cell and undergoes its single round of replication, a reporter gene expresses its indicator gene (luciferase), giving a visible signal-thus identifying the patient's viral tropism. Viral load must be at least 1,000 copies/ml to determine a patient's viral tropism.

Monogram (San Francisco, CA, USA) announced the commercial introduction of its Trofile assay following the announcement that Pfizer
(New York, NY, USA) received US Food and Drug Administration (FDA) approval of a novel HIV therapy, Selzentry (maraviroc), a CCR% antagonist. Trofile was the test used for patient selection for Selzentry's clinical development program and the two companies are engaged in a collaboration agreement to make Monogram's assay available for patient use globally.

Selzentry has been approved for the combination antiretroviral treatment of adults infected with only CCR5-tropic HIV-1 who have evidence of viral replication and have HIV-1 strains resistant to multiple antiretroviral agents. The FDA-approved label requires that tropism testing to identify patients infected with R5 virus guide the use of Selzentry.

Trofile is a vital new tool that helps physicians make the most informed treatment decisions for their patients living with HIV. Combined with Pfizer's new therapy, this represents a major milestone in the treatment of HIV, said Monogram CEO Bill Young. [The] approval also marks an important landmark in personalized medicine as the healthcare community shifts to treat patients individually by combining powerful diagnostic tools with drug therapies to better predict an individual patient's response.


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