A CELL-SAVING NONRADIOACTIVE LIMITING DILUTION ANALYSIS-ASSAY FOR THECOMBINED DETERMINATION OF HELPER AND CYTOTOXIC T-LYMPHOCYTE PRECURSORFREQUENCIES

We have developed a limiting dilution analysis-assay which makes the d etermination of both helper and cytotoxic T lymphocyte precursor frequ encies possible. The way in which T helper precursor frequencies are d etermined in this combined assay is essentially the same as the method published previously, Experimental conditions for the combined assay have been optimized to obtain cytotoxic T lymphocyte precursor frequen cies that are comparable to those determined in the assay routinely us ed in our laboratory. For all situations where the amount of available cell material is a limiting factor, it will be an advantage that with the same number of cells needed for a standard cytotoxic T lymphocyte precursor frequency determination, in the combined assay both helper and cytotoxic T lymphocyte precursor frequencies can be determined. Th is is especially convenient in the case of bone marrow transplantation , where evidence is accumulating that low or negative cytotoxic T lymp hocyte and/or T helper precursor frequencies may be a prerequisite for a successful transplantation with a minimal risk of graft-versus-host disease.