Background and objectives: In utero transplantation of hematopoietic stem cells allows immune reconstitution of fetuses with severe combined immunodeficiency. The objective of this work was to study the quality of T-cell reconstitution following this procedure.
Design and methods: We evaluated the kinetics and extent of T-cell reconstitution in five infants with severe combined immune deficiency (SCID), three with a B+ and two with a B- phenotype, who received haploidentical stem cell transplantation before birth. To this end, we measured the frequency of T-cell receptor excision circles (TREC) and the diversity of the T-cell repertoire.
Results: In utero transplantation led to engraftment of donor-derived T lymphocytes which attained normal numbers in four infants, who are in good health. In the three patients with a B+ phenotype, generation of a heterogeneous T-cell repertoire was associated with development of TREC levels comparable to those of SCID patients treated by post-natal transplantation and of healthy babies. Of the two patients with a B- phenotype, one developed mixed T-cell chimerism and a substantial number of circulating T cells, associated with a variable heterogeneity of the T-cell repertoire; TREC levels were normal soon after birth, but declined thereafter. The remaining B- patient remained lymphopenic with a skewed T-cell repertoire and very low TREC levels. This patient eventually required transplantation from a matched unrelated donor at 5 years of age, but died of EBV-related lymphoproliferative disease.
Interpretation and conclusions: These data indicate that in utero transplantation of fetuses with B+ SCID allows generation of newly diversified T lymphocytes and ensures long-term reconstitution of cell-mediated immunity.