Correction of X-Linked Hyper-IgM Syndrome by Allogeneic Bone Marrow Transplantation

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Abstract
The X-linked hyper-IgM syndrome is a rare immunodeficiency disease in which the ability of B cells to switch immunoglobulin production from IgM to IgG, IgA, and IgE is defective.1 A variety of mutations of the gene encoding the CD40 ligand cause the immunodeficiency.2-6 The functional effect of the mutation is that the CD40 ligand on T cells cannot interact with the CD40 glycoprotein on the surface of B cells. This interaction normally mediates immunoglobulin class switching by B cells. The deficiency of IgG and IgA leads to recurrent infections of the respiratory tract that can be prevented by intravenous immune globulin.1 Patients with the X-linked hyper-IgM syndrome are also prone to neutropenia, autoimmune disorders, and lymphomas.1,7 Some are susceptible to infection with opportunistic microorganisms such as Pneumocystis carinii, Histoplasma capsulatum, and cryptosporidium.1,8-13 Cryptosporidium causes unremitting diarrhea and is associated with cholangitis and cirrhosis. Although cellular immunity is normal in the X-linked hyper-IgM syndrome, the occurrence of these kinds of infections suggests a T-cell defect, possibly related to impaired interactions between T cells and macrophages14 and epithelial cells mediated by the CD40 glycoprotein and the CD40 ligand.15