The major complication after allogeneic bone marrow transplantation is the
occurrence of acute GvHD. This complication can be successfully prevented
when T lymphocytes are depleted from a bone marrow graft. The beneficial
effect of prevention of acute GvHD is counterbalanced by an increased frequency
of engraftment failures. In view of this problem several experiments
were planned to unravel whether the engraftment failures after T lymphocyte
depletion were attributable to the loss of the trophic function of T lymphocytes
or were attributable to the loss of the immunosuppressive action of donor Tlymphocytes.
When the latter option is valid, more immunosuppression of the
recipient would result in sustained engraftment ofT lymphocyte depleted bone
marrow grafts. With regard to T lymphocyte depletion, it was attempted to positively select
for stem cells and concomitantly negatively select for T lymphocytes. Stem cells
are the essential cells in a bone marrow graft since they are responsible for sustained
engraftment. A positive selection of these cells would yield an uniform
method for preparation of a bone marrow graft rich in stem cells and fully
depleted of T lymphocytes. A second approach was to investigate whether depletion of a subpopulation of T lymphocytes (helper/inducer or suppressor/
cytotoxic T lymphocytes) was sufficient to prevent acute GvHD