Increased engraftment and GVHD after in utero transplantation of MHC-mismatched bone marrow cells and CD80low, CD86- dendritic cells in a fetal mouse model

Background. Bone marrow transplantation (BMT) is the only known cure for a variety of inherited diseases and requires the administration of high doses of immunosuppressive and myeloablative therapy. Because the fetus is immunoincompetent early in gestation, in utero stem cell transplantation (IUT) could avoid the need for this toxic conditioning. A major limitation to date of IUT is the low level of engraftment and failure to induce tolerance. Dendritic cells (DC) are considered very potent antigen-presenting cells, but DC progenitors (pDC) are strongly tolerogenic. Methods. We examined the effect of donor pDC on the degree of engraftment and tolerance induction after IUT. Bone marrow-derived pDC (CD80(low), CD86(-)) from male C57BL/6 mice (H2(b)) were injected with and without donor bone marrow (BM) intraperitoneally into 13 to 15-day BALB/c (H2(d)) fetuses. Engraftment was determined by flow cytometry and quantitative polymerase chain reaction and tolerance by skin grafts and the mixed lymphocyte reaction. Results. At 1-month posttransplant, mice that received BM+pDC showed a higher degree of engraftment (29 +/- 46%) than mice that received pDC-enriched cells or BM cells alone (0.11 +/-0.70% and 1.71 +/-1.66%, respectively, P <0.001). However, 5/19 recipients of BM+pDC died within 6 weeks; 4/5 had significant donor cell engraftment in blood and/or tissues. Also, these mice had evidence of graft-versus-host disease (GVHD). Two mice out of 15 long-term survivors in the BM+pDC group had virtually complete replacement of host with donor hematopoietic cells. Skin grafts and mixed lymphocyte reaction studies showed no durable tolerance induction other than in the two fully engrafted recipients of BM+pDC. Conclusions. These results suggest that donor pDC, along with donor BM, can have a significant impact on engraftment of NMC-mismatched donor cells associated with an increased incidence of GVHD. However, marrow-derived pDC do not result in an increase in tolerance induction in utero even when microchimerism is present.