CD4 Measurements in Patients with HIV: Are They Feasible for Poor Settings?

The lack of facilities to measure CD4 counts in poor countries impedes instituting rational and effective antiretroviral therapy in these countries. Can a new microchip counting technique help to solve the problem?

M easurement of peripheral blood CD4 T lymphocytes is probably the most important laboratory assay for evaluation and monitoring of patients with HIV. The CD4 count is critical for determining the clinical stage of HIV infection, for deciding when to start antiretroviral therapy (ART), for evaluating the effi cacy of treatment, and for changing the medications when necessary. Most HIV treatment decisions are therefore based upon the CD4 count [1][2][3].

Flow Cytometry
The most common technique for measuring CD4 counts in developed country settings is fl ow cytometry. Flow cytometers use lasers to excite fl uorescent antibody probes specifi c for various cell surface markers, such as CD3, CD4, and CD8, which distinguish one type of lymphocyte from another.
As Rodriguez et al. point out in their study in this issue of PLoS Medicine [4], the cost of a fl ow cytometer ranges from $30,000 to $150,000, and the reagents needed for determining the lymphocyte surface markers by this method are very costly. In addition, use of fl ow cytometry requires technical and operational expertise as well as a reliable electricity source. Considering all these factors together, it is no surprise that CD4 measurements cannot be widely applied in developing world settings.

Why CD4 Counts Matter in Developing Countries
This grim reality-the lack of facilities to measure CD4 counts in poor countries-stands in sharp contrast to the urgent need for instituting rational and effective ART in these countries. The absence of tools to measure CD4 counts clearly jeopardizes the success of the recently launched global campaigns to fi ght AIDS, such as those of the World Health Organization and the Global Fund to Fight AIDS, Tuberculosis, and Malaria. These campaigns aim to distribute ART to millions of people with HIV, mostly living in developing countries. Regretfully, it is highly likely that these major efforts will fail, unless improved and widely used means for counting CD4 cells become available and can be applied where they are most needed. Since at least 35 million people are infected with HIV, and several million of them are in need of urgent lifesaving ART, the issue of CD4 monitoring has become a crucial one.
Rodriguez et al. point out that several efforts have been made to develop alternative, affordable CD4 counting methods for resource-poor settings [4]. These include improved fl ow cytometric approaches and microbead capture/separation of CD4 cells followed by manual cell counting [5][6][7][8]. Also, new single-purpose fl ow cytometers have been designed that perform the test at a much lower price. Though all these assays are indeed cheaper than regular fl ow cytometry, they suffer from decreased accuracy and, most importantly, they are all of low throughput.

A New Method for Counting CD4
Rodriguez et al. describe a novel method for counting CD4 in resource-poor settings (Figure 1) [4]. The method is based on a novel microchip detection system for measuring various analytes in very small volumes. A series of chemical and immunological reactions carried out on microspheres are visualized and captured on a charge-coupled device (developed for digital camera technology). This method allows for accurate measurement of CD4, CD8, and CD4/CD8. The prototype used for demonstration of the new apparatus shows extremely good agreement with currently used fl ow cytometry. Most importantly, the investigators claim that the cost of each assay is much lower than that for fl ow cytometry.
There are, however, a number of unresolved issues in this study that need further clarifi cation before the assay can meet the expectations Perspectives Open access, freely available online The Perspectives section is for experts to discuss the clinical practice or public health implications of a published article that is freely available online. This is a digital image of whole blood from a fi ve-month-old male infant from Botswana with an absolute CD4 count of 2,098 cells/ ml and a CD4 percentage of T cells of 0.39, obtained using a prototype method for low-cost CD4 count monitoring. CD4 + T cells are yellow. Also visualized are monocytes (green) and CD8 + T cells (red). (Photo courtesy of the authors of [8].) for becoming a widely used tool in resource-poor settings. Firstly, the study was performed with a prototype apparatus, tailored to meet the requirements of the study, but not yet representing a commercially established and viable production line. Secondly, though the authors state that the price of each CD4 determination will become much cheaper, it is not clear how much each assay will cost in the end, and whether the fi nal cost is realistic in the context of developing countries. It is clear, though, that the actual price of the assay will change once it is widely and consistently used on a large scale. Thirdly, although a few children were tested (six infants in total), the results in this small group remain questionable, and therefore the application of the test to pediatric populations needs further testing. It may well be that application to pediatric patients will require an improved apparatus or improved handling.

Conclusion
Despite these reservations, the authors of this study should be commended for addressing an extremely important issue and developing this novel approach for counting CD4 in patients with HIV. Their study may lead to further development of such an apparatus, which is sorely needed for the global fi ght against AIDS. Such efforts will hopefully be noticed by public funding agencies, leading to the improvement of tools for measuring CD4 counts.