At the suggestion of Dr. Howard Shapiro, the workshop participants discussed the need for low cost cytometers in Third World countries, especially in Africa. These are needed particularly for AIDS monitoring, especially in conjunction with HIV vaccine trials. The discussion initially focused on identifying preliminary design requirements. Since the primary need is expected to be for enumerating T helper cells in whole blood as a diagnostic tool for AIDS progression, a primary requirement is the ability to provide counts from a known volume (i.e., number of cells of a particular type per ml of blood). For flow systems, another primary requirement is that the system be capable of handling large cells in whole blood. However, it may be difficult to build an inexpensive image cytometer that provides volumetric counts and such systems might require some type of preenrichment for white cells in order to get statistically-meaningful counts for lymphocytes. The plans of Mycometrix (which owns patent rights to the Caltech system) for blood cell counting are currently unkown.
The participants then discussed the possible development of inexpensive cytometers (both flow and image) taking advantage of recent advances in relevant technology. The possibility of producing a system without a microscope objective to measure fluorescence (e.g., using fiber-optics or microfabricated optics) was discussed and ruled out due to the high background obtained when fluorescence is not collected with focussing (using fiber optics without an objective lens, light is collected from a region on the order of 1,000 times larger than with a typical objective lens). The possibility of focusing engineering effort on improving cell preparation methods (e.g., using robots) rather than reducing cytometer cost was discussed.
Systems currently under development were then discussed. Both the Guava system being developed by Guava Technologies and the CellTracks system being developed by Immunocon were considered to have good potential. The microfluidic systems being developed in Dr. Steven Quake's group at the California Institute of Technology are likely to reduced cost and complexity of flow cytometers in general, but current versions use rectangular fluid channels of 1-30 mm that would clog when using whole blood. Whether microsystems using fluid channels with dimensions of 100 mm or more can be made is uncertain.
The discussion then shifted to current commercial systems that might be suitable. The systems discussed included the FACScount manufactured by Becton Dickinson Immunocytometry Systems (retail cost, $35,000), the CyFlow manufactured by Partec (retail cost of appropriately configured instrument, $25,000), and the ZBI Coulter Counter manufactured by Beckman Coulter (retail cost, $10,000). All are intended to be simple to use and can be run from a 12 volt battery. The first two are flow cytometers that use fluorescent-conjugated antibodies to identify cell types and fluorescent beads to provide conversion to cell concentrations. The latter counts known volumes and particular cell types can be identified by rosetting via specific antibodies. In all cases, there was concern that reagent costs would be high, especially for the fluorescence-based systems. The consensus of the group was that obtaining foundation or government support for purchasing existing instruments and reagents (at cost) may be more economical in the long run than the cost of efforts to design, manufacture and support a cytometer explicitly to meet the Third World need. Nonetheless there was considerable enthusiasm that an inexpensive system could be designed and built with collaboration between cytometry experts inside and outside of industry, and there was a good deal of willingness among the participants to assist in such efforts.