Hypomorphic Janus kinase 3 mutations result in a spectrum of immune defects, including partial maternal T-cell engraftment

Abstract

Mutations in Janus kinase 3 (JAK3) are a cause of severe combined immunodeficiency, but hypomorphic JAK3 defects can result in a milder clinical phenotype, with residual development and function of autologous T cells. Maternal T-cell engraftment is a common finding in infants with severe combined immunodeficiency but is not typically observed in patients with residual T-cell development. We sought to study in detail the molecular, cellular, and humoral immune phenotype and function of 3 patients with hypomorphic JAK3 mutations. We analyzed the distribution and function of T and B lymphocytes in 3 patients and studied the invitro and invivo responses of maternal T lymphocytes in 1 patient with maternal T-cell engraftment and residual production of autologous Tlymphocytes. B cells were present in normal numbers but with abnormal distribution of marginal zone-like and memory Bcells. B-cell differentiation to plasmablasts invitro in response to CD40 ligand and IL-21 was abolished. In 2 patients the T-cell repertoire was moderately restricted. Surprisingly, 1 patient showed coexistence of maternal and autologous T lymphocytes. By using an mAb recognizing the maternal noninherited HLA-A2 antigen, we found that autologous cells progressively accumulated invivo but did not compete with maternal cells invitro. The study of 3 patients with hypomorphic JAK3 mutations suggests that terminal B-cell maturation/differentiation requires intact JAK3 function, even if partially functioning T lymphocytes are present. Maternal T-cell engraftment can occur in patients with JAK3 mutations despite the presence of autologous T cells.