IL-7 receptor α (IL-7Rα) deficiency is a rare form of SCID that usually presents in the first months of life with severe and opportunistic infections, failure to thrive and high risk of mortality unless treated.
Signaling mediated by the cytokine interleukin-7 is essential for the differentiation of T cells from lymphoid progenitors, and mutations of either the interleukin-7 receptor alpha chain (IL-7Ralpha) or its associated cytokine receptor chain, the common gamma chain (gammac), result in SCID.
The essential non-redundant role of this cytokine for T cell development in vivo is indicated by the phenotype of murine knockout models as well as by humans with a T-B+NK+ form of severe combined immunodeficiency (SCID) resulting from mutations in IL-7 receptor alpha chain.
Analysis of gene-targeted mice and patients with severe combined immunodeficiency due to mutations of the alpha chain of the interleukin-7 receptor (IL-7Ralpha) has shown important differences between mice and humans in the role played by IL-7 in lymphoid development.
Mutation of the gamma c chain common to interleukin-2 (IL-2), IL-4, IL-7, IL-9, and IL-15 receptors has been shown to be responsible for the X chromosome-linked severe combined immune deficiency (SCIDX1).
Following retroviral-mediated gene transfer of gamma c into SCID X1 bone marrow progenitors, it was possible to reproduce a similar pattern of NK cell differentiation in two SCID-X1 patients with SCF + IL-2 + IL-7 and more efficiently in one of them with SCF + IL-15.
Mutations in the common gamma-chain (gamma c), which is part of several cytokine receptors including those for interleukin (IL)-2, IL-4, IL-7, IL-9 and IL-15, are responsible for X-linked SCID, which is usually associated with a lack of circulating T cells and the presence of B lymphocytes (T- B+ SCID).