A CONVENIENT AND RELIABLE IL-2 BIOASSAY USING FROZEN CTLL-2 TO IMPROVE THE DETECTION OF HELPER T-LYMPHOCYTE PRECURSORS

The helper T lymphocyte precursor (HTLp) frequency detected in HLA mat ched sibling donors is directed against alloantigens and this frequenc y has been shown to correlate with the development of graft-versus-hos t disease in the patient after bone marrow transplantation. Using limi ting dilution analysis the HTLp frequency is determined by measuring I L-2 using the IL-2-dependent murine cell line CTLL-2. An important fac tor associated with the successful performance of any bioassay is the reliability of the indicator cell line used. When maintained in contin uous culture, however, the overall sensitivity of this cell line is hi ghly variable. To overcome this problem, large batches of CTLL-2 were grown, frozen and tested for their ability to detect low levels of IL- 2 (0.01 IU) in dose-response assays. Batches meeting this criterion we re stored in liquid nitrogen until required. In this study, we investi gated the effect of freezing and storing large batches of this cell li ne, thereby assuring a plentiful supply of sensitive indicator cells.