The haemopoietic and immunogenic capacities of living hybrid bone marrow cells tested in tumour allograft rejection.

In irradiated mice the capacity to reject allogenic tumours can be reconstituted with syngeneic lymphoid cells if the transferred cells are primed with the allogenicantigen. Living semi-allogeneic cells proved to be 30-100-times more acitve as priming antigen than cell membrane fractions. The tumour-suppressive activity of primed lymphoid cells increased in the following order: bone marrow less than Peyer's patches less than thymus less than spleen less than lymph node cells. Even bone marrowcells showed a considerable suppressing activity after priming with live antigen. It was a great advantage that 2 times 10-6 semi-allogeneic bone marrow cells could be used both for the restoration of the haemopoietic system after irradiation and for stimulation of the transferred parental lymphocytes. Priming with large numbers of semi-allogeneic spleen cells abolished the tumour-suppressive activity of the transferred lymphoid cells. This tolerogenic effect disappeared when the priming cells were pretreated with mitomycin. Tolerance could be induced when the cell donors were treated with cyclophosphamide in combination with the living cells. Cell membranes were not effective.