Incomplete restoration of the bursa-dependent immune system after transplantation of allogeneic stem cells into immunodeficient chicks.

Transplantation of allogeneic cells from bursa of Fabricius into cyclophosphamide-treated, immunodeficient chicks resulted in immunological tolerance to donor line skin grafts; graft-versus-host disease did not occur. Allogeneic bursal stem cells taken from 3-day-old donors induced restoration of bursal morphology, of antibody formation to Brucella abortus and of occurrence of pyroninophilic cells and immunoglobulin-bearing cells in the peripheral lymphoid tissues. Secondary response to sheep red blood cells and production of germinal centers were not restored. Transplantation of histocompatible bursal stem cells resulted in a complete reconstitution of the bursa-dependent lymphoid system, both in function and in morphology. Allogeneic postbursal stem cells taken from the bursa of 10-week-old donors had a reconstitutive effect only on the production of antibodies to Brucella. Transplanted stem cells maintained their functional potential in the allogeneic environment, since, when transferred back to histocompatible hosts, they displayed normal function. These findings indicate that a complete functional and morphological restoration of the bursa-dependent immune system cannot be achieved without identity of the donor and recipient at loci near to or identical with those determining the major histocompatibility antigens, even though graft-versus-host disease is avoided. This identity permits a full cooperation of the donor and host cells.