Elimination of T cells from human peripheral blood and bone marrow using a cocktail of three anti-T cell immunotoxins

Four anti-T cell monoclonal antibodies were coupled to ricin-A and tested for their ability to kill T cells in peripheral blood and bone marrow using a clonogenic assay to quantify T cell survival. The immunotoxins (IT) prepared from RFT11 (CD2) and WT1 (CD7) antibodies were the most toxic to peripheral blood T cells. The immunotoxin prepared from RFT1 (CD5) was the next most efficient toxin and the immunotoxin prepared from RFT8 (CD8) was the least toxic. When these reagents were applied to peripheral blood cells at 3 x 10^-8 M the number of T cell colonies was reduced by an average of 95%, 94%, 84% and 50%, respectively. Peripheral blood T cells from different donors showed marked variability in their sensitivity to ITs. However, a cocktail of three ITs prepared from RFT11, WT1 and RFT1 gave superior and consistent killing (mean 99.9%; range 99.8-100%) of peripheral blood T cells from six donors. When this cocktail was applied to bone marrow cells from six donors, an average of 99.6% (range 99.5-99.8%) of the T cells were killed. Under the same conditions there was little or no reduction in the number of normal haematopoietic progenitors (CFU-GM, CFU-GEMM, CFU-Meg and BFU-E).