Selective depletion of alloreactive donor T cells leads to elimination of graft-versus-host reactivity and stimulates graft-versus-leukaemia/myeloma effect.

Graft-versus-host disease is a severe complication of allogeneic stem cell transplantation. The major role is played by alloreactive donor T-cell clones leading to host tissue damage. Selective depletion is a strategy to eliminate host-reactive donor T cells from haematopoietic stem cell allografts to prevent graft-versus-host disease while conserving useful donor immune functions. We have used irradiated peripheral blood mononuclear cells from cancer patients and healthy donor cells as responder cells in primary mixed leukocyte reaction. To prepare graft-versus leukaemia/myeloma-specific T cells, alloreactive T cells in primary mixed leukocyte reaction were depleted with anti-CD25 immunotoxin. The remaining T cells had insignificant alloreactivity in secondary mixed leukocyte reaction. Then, allodepleted donor T cells were repeatedly stimulated using purified leukaemia/tumour cells from the same cancer patient. Leukaemia/tumour-reactive donor T cells were purified using cell sorter on the basis of CD4 and CD8 activation. Their specificity was tested in nonradioactive cytotoxicity test. We performed 22 reactions (15 samples with leukemic and 7 samples with multiple myeloma cells). Selective depletion of alloreactive donor T cells with anti-CD25 immunotoxin led to significant depletion (99.2-100 %, median 99.7%). The effect of donor T cells was well preserved, while the graft-versus-host reactivation of donor cells was negligible, even after repeated stimulation with patient's non-tumour cells. Thus, it is possible to selectively deplete donor alloreactive T cells with anti-CD25 immunotoxin. In the cases of leukaemia patients, a strong graft-versus-leukaemia reactivity was noticed in allodepleted donor T cells; in myeloma patients, graft-versus-myeloma reactivity was less significant.