Effect of reverse transcriptase inhibitors and mutations on the low-cost Cavidi reverse transcriptase viral load assay

Assessment of the Cavidi ExaVir Load Assay for Monitoring Plasma Viral Load in HIV-2-Infected Patients

HIV plasma viral load is an established marker of disease progression and of response to antiretroviral therapy, but currently there is no commercial assay validated for the quantification of viral load in HIV-2-infected individuals. We sought to make the first clinical evaluation of Cavidi ExaVir Load (version 3) in HIV-2-infected patients. Samples were collected from a total of 102 individuals living in Cape Verde, and the HIV-2 viral load was quantified by both ExaVir Load and a reference in-house real-time quantitative PCR (qPCR) used in Portugal in 91 samples. The associations between viral load and clinical prognostic variables (CD4⁺ T cell counts and antiretroviral therapy status) were similar for measurements obtained using ExaVir Load and qPCR. There was no difference between the two methods in the capacity to discriminate between nonquantifiable and quantifiable HIV-2 in the plasma. In samples with an HIV-2 viral load quantifiable by both methods (n = 27), the measurements were highly correlated (Pearson r = 0.908), but the ExaVir Load values were systematically higher relative to those determined by qPCR (median difference, 0.942 log₁₀ copies/ml). A regression model was derived that enables the conversion of ExaVir Load results to those that would have been obtained by the reference qPCR. In conclusion, ExaVir Load version 3 is a reliable commercial assay to measure viral load in HIV-2-infected patients and therefore a valuable alternative to the in-house assays in current use.

Can HIV reverse transcriptase activity assay be a low-cost alternative for viral load monitoring in resource-limited settings?

OBJECTIVE

To evaluate the performance and cost of an HIV reverse transcriptase-enzyme activity (HIV-RT) assay in comparison to an HIV-1 RNA assay for routine viral load monitoring in resource limited settings.

DESIGN

A cohort-based longitudinal study.

SETTING

Two antiretroviral therapy (ART) centres in Karnataka state, South India, providing treatment under the Indian AIDS control programme.

PARTICIPANTS

A cohort of 327 HIV-1-infected Indian adult patients initiating first-line ART.

OUTCOME MEASURES

Performance and cost of an HIV-RT assay (ExaVir Load V3) in comparison to a gold standard HIV-1 RNA assay (Abbott m2000rt) in a cohort of 327 Indian patients before (WK00) and 4 weeks (WK04) after initiation of first-line therapy.

RESULTS

Plasma viral load was determined by an HIV-1 RNA assay and an HIV-RT assay in 629 samples (302 paired samples and 25 single time point samples at WK00) obtained from 327 patients. Overall, a strong correlation of r=0.96 was observed, with good correlation at WK00 (r=0.84) and at WK04 (r=0.77). Bland-Altman analysis of all samples showed a good level of agreement with a mean difference (bias) of 0.22 log10copies/mL. The performance of ExaVir Load V3 was not negatively affected by a nevirapine/efavirenz based antiretroviral regimen. The per test cost of measuring plasma viral load by the Abbott m2000rt and ExaVir Load V3 assays in a basic lab setting was $36.4 and $16.8, respectively.

CONCLUSIONS

The strong correlation between the HIV-RT and HIV-1 RNA assays suggests that the HIV-RT assay can be an affordable alternative option for monitoring patients on antiretroviral therapy in resource-limited settings.

TRIAL REGISTRATION NUMBER

ISRCTN79261738.

Performance characteristics of the Cavidi ExaVir viral load assay and the ultra-sensitive P24 assay relative to the Roche Monitor HIV-1 RNA assay

BACKGROUND

The Cavidi viral load assay and the ultra-sensitive p24 antigen assay (Up24 Ag) have been suggested as more feasible alternatives to PCR-based HIV viral load assays for use in monitoring patients infected with HIV-1 in resource-limited settings.

OBJECTIVES

To describe the performance of the Cavidi ExaVir Load™ assay (version 2.0) and two versions of the Up24 antigen assay and to characterize their agreement with the Roche Monitor HIV-1 RNA assay (version 1.5).

STUDY DESIGN

Observational study using a convenience sample of 342 plasma specimens from 108 patients enrolled in two ACTG clinical trials to evaluate the performance characteristics of the Up24 Ag assay using two different lysis buffers and the Cavidi ExaVir Load™ assay.

RESULTS

In analysis of agreement with the Roche assay, the Cavidi assay demonstrated superiority to the Up24 Ag assays in accuracy and precision, as well as sensitivity, specificity, and positive and negative predictive values for HIV-1 RNA ≥ 400, ≥ 1000 and ≥ 5000 copies/mL. Logistic performance curves indicated that the Cavidi assay was superior to the Up24 assays for viral loads greater than 650 copies/mL.

CONCLUSIONS

The results suggest that the Cavidi ExaVir Load assay could be used for monitoring HIV-1 viral load in resource-limited settings.