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HIV-1 Coreceptor Tropism, Proviral DNATest code(s) 91299
This is an outdated version of this FAQ. It was effective 12/11/2012 to 10/26/2016.
The current version is available here.
Question 1. What is HIV tropism?
Tropism refers to the type of cytokine coreceptor used by HIV-1 when infecting the host cell. The viruses in most (>80%) treatment-naïve patients use the CCR5 (R5) coreceptor.1 Conversely, the viruses in up to 50% of treatment-experienced patients use either the CXCR4 (X4) coreceptor or both coreceptors (ie, R5 and X4).2 Viruses that use both coreceptors are called dual-mixed (D/M) viruses.
Question 2. What is a coreceptor tropism test, and when should I order one?
A coreceptor tropism test determines whether a patient exclusively harbors R5-tropic virus or has X4-tropic or D/M virus. Patients who exclusively harbor R5-tropic virus can be treated with CCR5 antagonists such as maraviroc (Selzentry®). CCR5 antagonists block R5 viruses from binding to the CCR5 coreceptor and infecting cells. They are ineffective in patients with X4 or D/M virus. Thus, coreceptor tropism testing can help determine patient eligibility for CCR5 antagonist therapy.
A coreceptor tropism test should be performed when the use of a CCR5 antagonist is being considered.3,4 Coreceptor tropism testing might also be considered for patients who exhibit virologic failure while taking a CCR5 inhibitor.3,4 See also Question 6.
Question 3. What tests are available for tropism testing?
We offer two tests for tropism testing:
HIV-1 Coreceptor Tropism with Reflex to Ultradeep Sequencing (test codes 90666, 90954or 90955): determines tropism of HIV-1 RNA; used when the plasma viral load is >1000 copies/mL
For more information, go to http://education.questdiagnostics.com/faq/FAQ86v1.
- HIV-1 Coreceptor Tropism, Proviral DNA (test code 91299): used when the plasma viral load is <1000 copies/mL
Question 4. What is a proviral DNA tropism test?
A proviral DNA tropism test determines the tropism of HIV-1 DNA that has integrated into the host genome of infected T-lymphocytes. Proviral DNA persists despite suppressive antiviral therapy and therefore is present when plasma viral RNA is low or undetectable. Whole blood or peripheral blood mononuclear cells (PBMC), rather than plasma, should be submitted for this test.
Question 5. How reliable is proviral DNA tropism testing compared to RNA tropism testing?
Although X4 sequences are more commonly found in proviral DNA than RNA, several studies have found a high degree of correlation between proviral DNA tropism and RNA tropism. For example:
- Soulie et al determined proviral DNA tropism in a genotype assay and compared results to archived RNA tropism data from treatment-experienced patients with undetectable plasma viral loads. The authors saw no change in viral tropism over a median of four years in 92.9% (119/128) of these patients and concluded genotypic proviral DNA tropism could be used to determine viral tropism.5
- Verhofstede et al found a concordance of 95.2% when comparing proviral PBMC DNA tropism to plasma RNA tropism determined from simultaneously collected sample types (n=165 patients). Similarly, concordance was 88.1% when current proviral DNA tropism was compared to pretreatment RNA tropism data from 126 patients.6
Question 6. When should I order a proviral DNA tropism test?
U.S. guidelines indicate that proviral testing can be used to determine tropism in patients with undetectable plasma viral load, but they note that the clinical utility of this approach has not yet been determined.3 The European tropism testing guidelines recommend proviral DNA tropism testing for patients with a low (<1000 copies/mL) or undetectable plasma viral load when they are being considered for maraviroc therapy.7
Proviral DNA tropism testing may be appropriate for successfully treated patients seeking to switch to a new regimen that includes a CCR5 antagonist.
Question 7. How do you perform a genotypic proviral DNA tropism test?
We first extract DNA from whole blood. PCR amplification of DNA in the V3 loop region of the envelope gene is performed in triplicate and the replicates are sequenced by Sanger sequencing. Tropism is then determined by bioinformatic analysis of the V3 loop sequence. Ultradeep sequencing (UDS) is not required for the proviral DNA assay.
Question 8. What is the turnaround time for the proviral DNA tropism test?
The turnaround time is approximately one week.
Question 9. How are results from the proviral DNA tropism test reported?
When X4 virus is detected
CXCR4 (X4) DETECTED Net Tropism Assessment DM/X4 MVC Activity Anticipated NO
When X4 virus is not detected
CXCR4 (X4) NOT DETECTED Net Tropism Assessment R5 MVC Activity Anticipated YES
- Clotet B. CCR5 inhibitors: promising yet challenging. J Infect Dis. 2007;196:178-180.
- Poveda E, Briz V, de Mendoza C, et al. Prevalence of X4 tropic HIV-1 variants in patients with differences in disease stage and exposure to antiretroviral therapy. J Med Virol. 2007;79:1040-1046.
- Panel on Antiretroviral Guidelines for Adults and Adolescents. Guidelines for the use of antiretroviral agents in HIV-1–infected adults and adolescents. Department of Health and Human Services. March 27, 2012. Available at: http://www.aidsinfo.nih.gov/contentfiles/lvguidelines/adultandadolescentgl.pdf. Accessed November 2, 2012.
- Thompson MA, Aberg JA, Hoy JF, et al. Antiretroviral treatment of adult HIV infection: 2012 recommendations of the International Antiviral Society-USA panel. JAMA. 2012;308:387-402.
- Soulie C, Lambert-Niclot S, Wirden M, et al. Low frequency of HIV-1 tropism evolution in patients successfully treated for at least 2 years. AIDS. 2011;25:537-539.
- Verhofstede C, Brudney D, Reynaerts J, et al. Concordance between HIV-1 genotypic coreceptor tropism predictions based on plasma RNA and proviral DNA. HIV Med. 2011;12:544-552.
- Vandekerckhove LP, Wensing AM, Kaiser R, et al. European guidelines on the clinical management of HIV-1 tropism testing. Lancet Infect Dis. 2011;11:394-407.
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