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Tropism Assays

Co-receptor tropism refers to HIV-1 entry into a target cell utilizing a specific co-receptor located on the surface of the target cell. HIV-1 requires two binding events to enter a cell. Viral particles first bind to CD4 receptors and, thereafter, to a chemokine receptor or co-receptor, both of which are located on the target cell surface. Tropism describes the specific chemokine receptor the virus utilizes, CCR5 or CXCR4.

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HIV-1 viruses are classified based on their tropism status.

R5-tropic 
Viruses or viral populations that use only the CCR5 chemokine receptor to infect CD4+ cells.

X4-tropic 
Viruses or viral populations that use only the CXCR4 chemokine receptor to infect CD4+ cells.

Dual (D)-tropic 
Viruses or viral populations that use either the CCR5 or CXCR4 coreceptors to infect CD4+ cells.

Mixed-tropic 
Viral populations that may contain various combinations of R5-using virus, X4-using virus and/or dual-tropic viruses.

Trofile® Assays Determine Viral Tropism

More than 100,000 samples have been tested using Labcorp’s Trofile® assays.  All investigational trials of coreceptor antagonists have used Trofile® in their clinical development.  Trofile® has been shown to be accurate, precise, sensitive, reproducible and robust in the measurement of HIV-1 coreceptor tropism.

Department of Health and Human Services (DHHS) and Infectious Diseases Society of America (IDSA) guidelines recommend that a coreceptor tropism test be performed whenever the use of a CCR5 antagonist is being considered for HIV treatment.1,2  Coreceptor tropism testing might also be considered for patients who exhibit virologic failure while taking a CCR5 inhibitor.

Labcorp offers two assays for determining tropism for patients based on viral load:  one for patients with viremia and the other for patients with viral suppression.

Order Code 553100

Trofile

Determines viral tropism in patients with viral loads > 1000 copies/mL.

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Trofile DNA (829670)

Order Code 829670

Trofile DNA

Determines viral tropism in patients with suppressed virus or viral loads < 1000 copies/mL.

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Trofile Select

Order Code 553355

Trofile Select

Determines viral tropism when a clinician has a question about whether Trofile® or Trofile® DNA is the more appropriate assay. Assay selection is guided by viral load testing performed at Labcorp. When the viral load is > 1000 copies/mL, Trofile® is performed. When the viral load is < 1000 copies/mL, Trofile® DNA is performed.

Trofile® Select testing requires plasma for viral load testing and Trofile®, if appropriate, and whole blood for Trofile® DNA, if appropriate.

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References

  1. Panel on Antiretroviral Guidelines for Adults and Adolescents. Guidelines for the Use of Antiretroviral Agents in Adults and Adolescents with HIV. Department of Health and Human Services. Available at https://clinicalinfo.hiv.gov/sites/default/files/guidelines/archive/AdultandAdolescentGL_2021_08_16.pdf. Accessed April 30, 2021.
  2. IDSA guidelines: Thompson M, Horberg M, Agwu A, et al. Primary Care Guidance for Persons with Human Immunodeficiency Virus: 2020 Update by the HIV Medicine Association of the Infectious Diseases Society of America. Clin Infect Dis. 2020; 73(11): e3572-e3605. https://doi.org/10.1093/cid/ciaa1391