Multiple mixed chimeras: reconstitution of lethally irradiated mice with syngeneic plus allogeneic bone marrow from...

Reconstitution of lethally irradiated B10 mice with a mixture of 5 x 10(6) B10 plus 15 x 10(6) B10.D2 T-cell-depleted (TCD) bone marrow (BM) cells has previously been shown to produce stable, mixed chimeras which are specifically tolerant to donor skin grafts; the inclusion of TCD syngeneic marrow in the inoculum leads to improved immunocompetence in the resulting chimeras. In order to determine whether this method of transplant tolerance induction could be extended to multiple simultaneous allogeneic donors, we have investigated the engraftment capacity of combinations containing syngeneic and more than one allogeneic source of bone marrow. B10 mice were lethally irradiated and reconstituted with a mixture of (B10 + B10.D2 + B10.BR) or (B10 + B10.RIII + B10.BR) TCD BM. Analysis of each group of animals by flow microfluorometry provided evidence for stable multiple mixed chimerism in the majority of animals. All animals which exhibited such multiple chimerism were also tolerant of skin grafts from both allogeneic donors and promptly rejected fourth party skin grafts. An attempt to produce chimerism with TCD marrow from 5 allogeneic plus syngeneic BM cells was less successful. When animals were given non-TCD allogeneic BM from 2 allogeneic donors along with TCD syngeneic BM, they reconstituted as fully allogeneic chimeras in which one or the other allogeneic donor prevailed. These results indicate that (1) multiple allogeneic donor BM cells can engraft simultaneously in the mixed marrow model, but there may be a limit to the number of marrow strains which can repopulate a single animal; (2) multiple allogeneic engraftment confers transplantation tolerance to multiple donors; and (3) TCD is essential to permit multiple mixed chimerism to develop.