Optimising a limiting dilution culture system for quantitating frequencies of alloreactive cytotoxic T lymphocyte...

We have developed a limiting dilution assay for estimating the frequencies of allo-MHC reactive cytotoxic T lymphocyte precursors (CTL-p) in peripheral blood. The culture conditions were optimised in order to give maximum sensitivity while at the same time maintaining a high degree of specificity. While the addition of filler cells, interleukin-1 and interleukin-4 were unnecessary, the addition of interleukin-2 (IL-2) was crucial for optimal expansion of the CTL-ps. However, excess exogenous IL-2 was found to give rise to nonspecific cytotoxicity, and 5 U/ml final concentration of recombinant IL-2 added on Days 3 and 6 was optimal. The establishment of baseline control cultures for determining positivity and negativity of the test cultures is discussed. Using this modified assay system, we demonstrated that the culture conditions fulfil "single hit" criteria and that the assay is highly specific.