Non–T-cell–depleted HLA haploidentical stem cell transplantation in advanced hematologic malignancies based on the feto-maternal michrochimerism

Feto-maternal microchimerism suggests that immunologic tolerance exists between mother and fetus. Based on this hypothesis, we performed haploidentical stem cell transplantation (SCT) without T-cell depletion (TCD) in 5 patients with advanced hematologic malignancies. HLA incompatibilities for graft-versus-host disease (GVHD) direction included 3-loci mismatches in 4 patients, and 2-loci mismatches in one patient. Recipient chimeric cells were detected in all patients. The prophylaxis against GVHD was tacrolimus with minidose methotrexate. Engraftment was obtained in all patients. An acute GVHD of less than or equal to grade 2 developed in all patients except one who developed tacrolimus encephalopathy. Two patients died, 1 from fungal pneumonia and 1 from disease progression. The other 3 patients survived, with one patient in complete remission. These observations suggest that haploidentical SCT based on the feto-maternal microchimerism without TCD is possible.