T-cell-depleted CD34+ cell transplantation from an HLA-mismatched donor in a low-birthweight infant with X-linked severe combined immunodeficiency.

The best strategy of hematopoietic stem cell (HSC) transplantation for low-birthweight (LBW) infants with severe combined immunodeficiency (SCID) remains to be determined. To avoid the toxicity of drugs used for the transplantation and the risk of graft-versus-host disease (GVHD), the authors performed allogeneic bone marrow HSC transplantation with a combination of CD34 selection and T-cell depletion in a LBW infant with X-linked SCID. The authors analyzed the process of T-cell reconstitution after the transplantation in this patient. The patient was born at 30 weeks and 2 days' gestational age via cesarean section. He was diagnosed as having SCID at birth. The patient received a transplant of 1 million CD34+ cells/kg body weight. Immunologic reconstitution was investigated by means of phenotypic analysis of T cells and genetic analysis of coding joint T-cell receptor rearrangement excision circle expression. Increases in donor-derived NK cells and T cells were observed 2 and 3 months after the transplantation, respectively. The patient had no infectious complications or GVHD despite the presence of SCID and prematurity-associated immunodeficiency. Analysis of T-cell regeneration pathways revealed that T cells reconstituted mainly via the thymus-dependent pathway. T-cell-depleted CD34+ cell transplantation would be a safe and useful therapy for LBW infants with SCID.