Severe combined immunodeficiency. A model disease for molecular immunology and therapy

Cytokine-mediated signalling and early defects in lymphoid development

PURPOSE OF REVIEW

The aim of the review is to report on recent advances in cytokine-mediated signalling, as illustrated by the study of natural human mutants. In particular, the role of cytokines and cytokine-mediated signalling in human T-cell development is analysed in detail, and currently available forms of treatment including experimental trials are described.

RECENT FINDINGS

Defects of the cytokine/JAK/STAT axis have been recently described as responsible for human Severe Combined Immune Deficiency. In particular, defects in gammac, JAK3 and IL7RA have been analysed in terms of development of novel diagnostic tools as well as of new therapeutic agents for the treatment of autoimmune diseases and graft-versus-host disease.

SUMMARY

Dissection of the genetic defects underlying the various forms of Severe Combined Immune Deficiency has helped develop new and more accurate diagnostic assays and novel forms of treatment.

CD3 deficiencies

PURPOSE OF REVIEW

The molecular characterization of inherited T-cell immunodeficiencies has contributed to delineating key factors in human T-cell development. This review reports on the recent description of deleterious mutations in the genes encoding CD3 subunits expressed at the T-lymphocyte membrane in association with the T-cell receptor.

RECENT FINDINGS

Homozygous mutations in CD3D and CD3E genes lead to a complete block in T-cell development and thus to an early-onset severe combined immunodeficiency phenotype. Thymic studies have shown that the defect in T-cell development occurs at the transition between 'double-negative' and 'double-positive' thymocytes. These results contrast with the partial T-cell immunodeficiency caused by a deficiency in CD3G.

SUMMARY

Two new severe combined immunodeficiency conditions have been reported as a consequence of either CD3D or CD3E deficiency. The distinct phenotype of CD3G deficiency sheds light on the differential roles of CD3 subunits in T-lymphocyte development.