A Microchip CD4 Counting Method for HIV Monitoring in Resource-Poor Settings

William R Rodriguez is with Massachusetts General Hospital, Harvard Medical School, and Brigham and Women's Hospital; Nicolaos Christodoulides is with UT Austin; Pierre N Floriano is with UT Austin; Susan Graham is with Brigham and Women's Hospital; Sanghamitra Mohanty is with UT Austin; Meredith Dixon is with Massachusetts General Hospital; Mina Hsiang is with Massachusetts General Hospital; Trevor Peter is with Princess Marina Hospital; Shabnam Zavahir is with Princess Marina Hospital; Ibou Thior is with Princess Marina Hospital; Dwight Romanovicz is with UT Austin; Bruce Bernard is with UT Austin; Adrian P Goodey is with UT Austin; Bruce D Walker is with Massachusetts General Hospital, Harvard Medical School; John T McDevitt is with UT Austin.Background -- More than 35 million people in developing countries are living with HIV infection. An enormous global effort is now underway to bring antiretroviral treatment to at least 3 million of those infected. While drug prices have dropped considerably, the cost and technical complexity of laboratory tests essential for the management of HIV disease, such as CD4 cell counts, remain prohibitive. New, simple, and affordable methods for measuring CD4 cells that can be implemented in resource-scarce settings are urgently needed. Methods and Findings -- Here we describe the development of a prototype for a simple, rapid, and affordable method for counting CD4 lymphocytes. Microliter volumes of blood without further sample preparation are stained with fluorescent antibodies, captured on a membrane within a miniaturized flow cell and imaged through microscope optics with the type of charge-coupled device developed for digital camera technology. An associated computer algorithm converts the raw digital image into absolute CD4 counts and CD4 percentages in real time. The accuracy of this prototype system was validated through testing in the United States and Botswana, and showed close agreement with standard flow cytometry (r = 0.95) over a range of absolute CD4 counts, and the ability to discriminate clinically relevant CD4 count thresholds with high sensitivity and specificity. Conclusion -- Advances in the adaptation of new technologies to biomedical detection systems, such as the one described here, promise to make complex diagnostics for HIV and other infectious diseases a practical global reality.Biochemistr