A new laboratory-developed test (LDT) from Quest Diagnostics (Madison, N.J.) can assist physicians in determining whether a patient with a history of HIV drug resistance will respond to the class of antiretroviral therapies known as CCR5 antagonist entry inhibitors.

Quest’s HIV-1 Coreceptor Tropism Test will compete with the market-leading Trofile assay developed and performed by Monogram Biosciences (South San Francisco, Calif.). The new LDT replaces SensiTrop, the HIV tropism test that Quest offered through a license with Pathway Diagnostics before acquiring the company in December 2008.

HIV coreceptor tropism refers to which chemokine co-receptor that a strain of HIV uses to enter healthy CD4 cells. Entry inhibitors, a new class of antiretroviral drugs, targets the tropism process involving one or both coreceptors, CCR5 or CXCR4, of CD4 cells. Depending on which co-receptor a particular virus uses to enter cells, a patient’s HIV infection can be categorized as R5 HIV (CCR5-tropic), X4 HIV (CXCR4-tropic), or D/M HIV (dual- or mixed- tropic).

Guidelines issued in January 2008 by the United States Department of Health and Human Services recommend tropism testing prior to the start of a CCR5 inhibitor, such as maraviroc (marketed by Pfizer as Selzentry in the U.S. and Celsentri elsewhere). Maraviroc has been approved by the U.S. Food and Drug Administration for use in combination with other HIV medications in treatment-experienced adult patients with CCR5-tropic HIV.

Quest expects to report results for its new HIV tropism test within seven days of receiving a patient’s specimen, compared to Monogram’s Trofile turnaround time of approximately 14 days.

For more on HIV tropism testing, see the special pharmacogenomics supplement included in the July issue of Diagnostic Testing and Technology Report.