The management of HIV positive patients using a CD8/38 flow cytometry assay as an alternative to viral load testing
Date
2011-09-19
Authors
Moodley, Keshendree
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
BACKGROUND: Human Immunodeficiency Virus (HIV) is a global epidemic with growing
numbers of people on highly active anti‐retroviral therapy (HAART) programmes.
Effectiveness of treatment needs to be monitored to ensure the uncompromised well
being of patients. This is currently done using both Viral Load (VL) and CD4 cell counts
for HAART initiation and follow‐up. Although VL is the best predictor of disease
progression it is often too expensive for monitoring patients in resource‐limited settings.
There is thus a need for a cheaper, more accessible alternative to monitor long term
patient response to therapy.
METHODS: This study evaluated the use of a recently described flow cytometric assay of
CD38 expression (previously developed at the Johannesburg Flow Cytometry Reference
Laboratory) in a cohort of HIV+ patients failing 1st line therapy, who were subsequently
enrolled onto 2nd line HAART. CD38 and CD8 were “piggy ‐backed” onto the PLG/CD4
protocol and mean fluorescence intensity (MFI) of the CD8/38 expression was
monitored longitudinally. Patterns of CD38 expression were compared to 1st line
treatment observations to establish equivalence in the predictive power of CD38
expression of fluctuation in viral load on 2nd line treatment patients. In addition, the
effect of sample age on assay accuracy was tested before implementation of the CD38
assay at a secondary testing site.
RESULTS: The patterns observed in the cohort of 2nd line therapy patients mirrored
patterns previously seen in 1st line therapy with 55% of patients showing a continuous
decline in CD38 MFI that mimicked changes in VL. The remaining 33% of patients had
non‐specific increases in CD38 MFI without concurrent increases in VL and one patient
showed irregular VL and CD38 MFI (non‐responder). The CD38 assay showed acceptable
accuracy and reproducibility up to 48 hours after venesection (%CV<5%).
Implementation at the secondary testing site was successful with 98% similarity
(%CV<5%) compared to the reference laboratory.
CONCLUSION: CD38 monitoring of 2nd line therapy patients showed comparable
patterns to observations in 1st line therapy patients. The assay proved stable over time
and easy to implement at another PLG/CD4 testing facility. As such, the CD38 assay
offers a cost‐effective, reliable real time supplementary test to long‐term VL monitoring
of HIV infected patients on the national ART programme.
Description
MSc (Med), Dept of Haematology, School of Pathology, Faculty of Health Sciences, University of the Witwatersrand
Keywords
flow cytometry, HIV testing, managing HIV, viral load monitoring