What is Tropism?

Coreceptor tropism is defined as the ability of a particular HIV-1 virus to infect a target cell using a specific coreceptor. HIV requires two binding events to enter into a cell. It must first bind CD4 and then, secondly, a chemokine receptor. Tropism is a label given to the virus that describes which chemokine receptor the virus is using.

Tropism 101

The HIV-1 viruses can be characterized into four broad classifications based on their tropism status.

RS-tripic R5-tropic: Viruses or virus populations that can use only the CCR5 chemokine coreceptor to infect CD4+ cells.
X4-tropic: X4-tropic: Viruses or virus populations that can use only the CXCR4 chemokine coreceptor to infect CD4+ cells.
Dual (D)-tropicDual (D)-tropic: Viruses or virus populations that can use either the CCR5 or CXCR4 coreceptors to infect CD4+ cells.
Mixed (M)-tropic: Virus populations that may contain various combinations of R5 virus, X4 virus, and/or dual-tropic viruses.

Trofile® Assays Determine Viral Tropism

Monogram currently offers two tests for tropism determination for both suppressed and nonsuppressed patients.

More than 100,000 samples have been tested using Monogram’s Trofile® assays. All 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.

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

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/inline-files/AdultandAdolescentGL.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; ciaa1391, https://doi.org/10.1093/cid/ciaa1391
trofile

For patients with detectable viral loads ≥ 1000 copies/mL

trofileDNA

For patients with undetectable viral loads

Trofile Select

For patients with unknown viral load. Determines HIV-1 coreceptor tropism by selection of the appropriate assay, Trofile or Trofile DNA, through an initial prescreening viral assessment.