Accurate counts of helper T cells and related lymphocytes are critical in decisions about HIV status and antiretroviral therapies. Flow cytometry is the standard method of cell counting, but the majority of the 30 to 40 million infected people worldwide are in resource-limited areas and do not have access to these measurements. As a direct alternative, this project is developing a compact, low cost imaging instrument for HIV-related cell counting with a projected instrument cost of approximately $100. Through the Phase I grant and related funding, a prototype instrument and disposable cartridge for CD4 cell counting have been developed. Demonstrations with labeled cells were successful, and completion of a low cost instrument for absolute counts of helper T cells (CD4+) is on schedule for late 2009 - early 2010. This Phase II proposal describes plans to improve and expand the capabilities of the progress already achieved. Simple cartridge mechanics will significantly increase the total field of view, resulting in more cells being counted and better statistical accuracy. In addition to identifying CD4+ T cells, reagents and methods for counting cytotoxic T cells, B cells, monocytes, and lymphocytes will be tested and demonstrated with clinical samples. Reagents and surface coatings will be developed to allow simple sample preparation, without the repeated centrifugation associated with current flow cytometer methods of cell lysis, washing and staining. Clinical characterization of the instrument will be performed, providing feedback on the design and performance. At the conclusion of Phase II, a fieldable prototype instrument, cartridge, and procedure will be available for HIV-related cell counting with results that are comparable to current flow cytometry methods, and with a capital cost that is reduced by approximately 100-fold or more. PUBLIC HEALTH RELEVANCE: Accurate counts of helper T cells and related lymphocytes are critical in decisions about HIV status and antiretroviral therapies. HIV-infected people in resource poor countries have little or no access to appropriate cell counting, significantly affecting the use of antiretroviral therapies. The overall goal of this project is to develop a low cost, accurate system for HIV-related blood cell counting that can improve healthcare in developing regions.