Unexpected and variable phenotypes in a family with JAK3 deficiency

Area of Science:

• Immunology
• Genetics

Background:

• Mutations in Janus kinase 3 (JAK3) typically cause severe combined immunodeficiency (SCID) with T and NK cell absence.
• Previous understanding linked JAK3 deficiency to T-B+SCID, characterized by low T and NK cells but normal B cells.

Purpose of the Study:

• To report novel JAK3 mutations associated with unusual clinical presentations of immunodeficiency.
• To investigate the molecular mechanisms underlying these varied presentations, including T cell accumulation.

Main Methods:

• Genetic analysis of a family with JAK3 mutations.
• Assessment of T cell phenotype, cytokine signaling, and Fas ligand (FasL) expression.
• Analysis of T cell receptor (TcR) Vbeta family distribution.

Main Results:

• Identified compound heterozygous JAK3 mutations (A96G and G2775(+3)C) in siblings with distinct clinical outcomes.
• Observed minimal functional JAK3 expression, leading to defective IL-2 signaling and impaired FasL expression on activated T cells.
• Found evidence of T cell accumulation with activated phenotypes and skewed TcR Vbeta distribution in patients.

Conclusions:

• JAK3 deficiency presents a broader clinical spectrum than previously recognized, including T cell accumulation.
• Residual JAK3 activity may allow thymocyte maturation but is insufficient for peripheral T cell homeostasis via IL-2/FasL pathways.
• JAK3 plays a critical role in maintaining peripheral T cell homeostasis in humans.