An image cytometer for resource-poor settings to monitor disease progression in HIV infection

Background: For resource-poor countries, affordable methods are required for enumeration of CD4+ T lymphocytes of HIV-positive patients. For infants, additional determination of CD4/CD8 ratio is needed.

Methods: We determine the CD4+ and CD8+ T lymphocytes as the CD3+CD4+ and CD3+CD8+ population of blood cells. Target cells are CD3-immunomagnetically separated from the whole blood, and CD4-Phycoerythrin and CD8-PerCP immunofluorescently labeled. A point-of-care single platform image cytometer was developed to enumerate the target CD3+CD4+ and CD3+CD8+ populations. It has light-emitting diodes illumination, is fully computer-controlled, operates from a 12 V battery, and was designed to be cheap and easy-to-handle. Target cells are imaged on a CCD camera and enumerated by an image analysis algorithm. The cytometer outputs the absolute number of CD4+ and CD8+ T lymphocytes/l and CD4/CD8 ratio.

Results: The quality of the cell images obtained with the cytometer is sufficient for a reliable enumeration of target cells. The image cytometer achieves an accuracy of better than 10% in the range of 50-1700 cells/l. Analysis of blood samples from HIV patients yields a good agreement with the TruCount method for CD4 and CD8 count and CD4/CD8 ratio.

Conclusions: The image cytometer is affordable (component costs $3,000), compact (25 × 25 × 20 cm3), and uses disposable test materials, making it a good candidate to monitor progression of immunodeficiency disease in resource-poor settings.