Transplantation of bone marrow from unrelated donors is limited by a lack of HLA-matched donors and the risk of graft-versus-host disease (GVHD). Placental blood from sibling donors can reconstitute hematopoiesis. We report preliminary results of transplantation using partially HLA-mismatched placental blood from unrelated donors.

Twenty-five consecutive patients, primarily children, with a variety of malignant and nonmalignant conditions received placental blood from unrelated donors and were evaluated for hematologic and immunologic reconstitution and GVHD. HLA matching was performed before transplantation by serologic typing for class I HLA antigens and low-resolution molecular typing for class II HLA alleles. In donor–recipient pairs who differed by no more than one HLA antigen or allele, high-resolution class II HLA typing was done retrospectively. For donor–recipient pairs who were mismatched for two HLA antigens or alleles, high-resolution typing was used prospectively to select the best match for HLA-DRB1.

Twenty-four of the 25 donor–recipient pairs were discordant for one to three HLA antigens. In 23 of the 25 transplant recipients, the infused hematopoietic stem cells engrafted. Acute grade III GVHD occurred in 2 of the 21 patients who could be evaluated, and 2 patients had chronic GVHD. In vitro proliferative responses of T cells and B cells to plant mitogens were detected 60 days after transplantation. With a median follow-up of 12¹ /2 months and a minimal follow-up of 100 days, the overall 100-day survival rate among these patients was 64 percent, and the overall event-free survival was 48 percent.

HLA-mismatched placental blood from unrelated donors is an alternative source of stem cells for hematopoietic reconstitution in children.