Dr. Puck leads the Immunologic Genetics Section in the Genetics and Molecular Biology Branch. This Laboratory has been involved in the mapping and characterization of human disorders of the immune system, with the combined aims of better understanding normal development of immunologic responses and developing methods for treatment of patients with immunologic dysfunction.

This group initially mapped human X-linked severe combined immunodeficiency (XSCID) to Xq13.1, assisted by a new carrier test based on the finding that lymphocytes, but not other cell lineages, from female carriers of XSCID had skewed X chromosome inactivation rather than random Lyonization. Dr. Puck hypothesized that this lineage-specific X inactivation pattern arose from selection against maturing lymphocyte progenitors with an XSCID mutation on the active X chromosome. Her group has performed other linkage and carrier detection studies for genetic immunodeficiencies, including studies on Wiskott-Aldrich syndrome, X-linked agammaglobulinemia, hyper-IgM syndrome, and X-linked lymphoproliferative syndrome.

In the spring of 1993, this laboratory was one of two that independently identified the gene for XSCID to be the gamma chain of the lymphocyte IL-2 receptor IL-2RG. This lab sequenced the complete gene, which has eight exons encoding a 1.8 kb mRNA and a genomic span of 4.2 kb. The IL2RG gene product is a protein found not only in IL-2 receptors, but also in receptors for IL-4, IL-7, IL-9, and IL-15; it is now known as the common gamma chain, c. It is a membrane-spanning protein with cytokine receptor features, including four conserved cysteines and a WSXWS motif in its extracellular domain, and a kinase-interacting SH2 related region in the cytoplasmic portion. Single-strand conformation polymorphism (SSCP), dideoxy fingerprinting (DDF) and limited sequencing are currently being employed to define the mutations.

A large number of mutations defined by Dr. Puck's group and other laboratories have been collected into a database, called IL2RGbase. Five mutation hot spots account for about a quarter of the mutations, while the majority of mutations causing XSCID are unique to a particular family. Protocols leading to future gene therapy for XSCID are under development.

Dr. Puck is investigating the functional consequences of these mutations on cytokine binding, downstream interactions and association with the other cytokine receptor chains. Moreover, a variety of gene transfer studies are being carried out with retroviral constructs to investigate gene therapy. These studies involve cells from boys affected with XSCID as well as a canine XSCID model. Previous findings of skewed X inactivation in female carriers - who because of Lyonization are effectively chimeras with mutant and normal lymphocyte progenitors -indicate that a normal gamma chain confers a strong selective advantage for cell survival and proliferation over lymphoid precursors expressing a mutant gene. This biological selection in favor of lymphocytes with corrected c will be an important advantage for the development of stem cell gene therapy for XSCID with retroviral vectors.

Other areas of focus for the laboratory are the human autoimmune lymphoproliferative syndrome (ALPS) and Hyper IgE syndrome studied in collaboration with groups at the National Institute of Allergy and Infectious Diseases. ALPS patients with adenopathy, elevated numbers of CD4- CD8- T cells and autoimmune disease have been found to have impaired lymphocyte apoptosis (programmed cell death) because of harmful mutations in the gene encoding FAS, a cell surface apoptosis receptor. The spectrum and cellular abnormalities of this syndrome, as well as its relationship to mutations in FAS pathway genes, can now be defined. A positional cloning project to find the basis of Hyper IgE syndrome is ongoing.