Graft hyporeactivity induced by donor-specific bone marrow

Much interest has recently focused on administration of donor cells with organ transplantation to improve graft outcome. However, whether donor cell administration actually confers donor-specific (DS) hyporeactivity is unknown. The intra-graft events after DS bone marrow (BM) infusion were therefore examined in an in vivo sponge matrix allograft model. Recipient C57BL/6J (B6,H2b) mice (five per group) received either media alone, 10(7) syngeneic (B6), or allogeneic (DBA/2J,H2d) BM cells intravenously. Seven days later, a sponge matrix allograft containing 10(7) allogeneic (DBA) splenocytes was implanted. On various days after grafting, graft-infiltrating cells were tested for in vitro cytotoxicity by 51Cr release assay. Previous DSBM infusion significantly reduced intragraft allospecific cytolytic T-cell (CTL) activity compared with mice receiving syngeneic BM or media alone (3.5 +/- 5.1% vs. 46.2 +/- 13.3% and 47.9 +/- 13.5% at 100:1 E:T, respectively, P < 0.001). Time course studies showed that DSBM impaired allospecific CTL activity whether given on day -10 (3.3% at 100:1 E:T), day -7 (2.2%), day -2(7.7%), or day 0 (6.5%), but was not as effective when given on day +7 (27.1%). Flow cytometry of graft-infiltrating cells on day +12 showed a decreased percentage of CD8+ cells after DSBM, compared with syngeneic BM or media alone (13.1% vs. 38.0% and 36% respectively, P = 0.01), but the percentage of CD4+ cells was similar in all groups (5.5%, 6.9%, and 4%, respectively). Thus, (1) DSBM inhibits allospecific CTL development in the allograft, (2) decreased intra-graft CTL activity after DSBM correlates with a decreased percentage of intragraft CD8+ cells, and (3) DSBM induces hyporeactivity up until the day of the allograft placement, but not thereafter. DSBM may, thus, induce graft hyporeactivity by impairing intragraft immune activation.