Pathobiology and treatment of patients with inborn errors of immunity

Division Of Basic Sciences - Nci

Investigators

Linked publications & trials

Abstract

Our projects in the area of inborn errors of immunity (IEI) are focused on understanding each disease's pathogenesis, and using that knowledge to design and test tailored cellular therapies. While severe combined immunodeficiency (SCID) is a group of disorders that abrogate T cell development, the vast majority of the >400 genetically defined IEI are non-SCID disorders. Severe forms of non-SCID IEI commonly compromise the function and/or regulation of T cells, B cells, myeloid cells, and other immune cells, predisposing patients to life-threatening infection, immune dysregulation, and/or autoimmunity. These diseases may be treated with standard cellular therapy i.e. allogeneic hematopoietic stem cell transplantation (HSCT) or experimental and promising gene therapy (GT) approaches using autologous cells. For either approach, myeloablation targeting recipient HSC must be given to promote engraftment. While immunoablation is strictly required for HSCT to prevent rejection of allogeneic cells, in the autologous GT setting, immunoablation may sometimes be used to eliminate dysregulated recipient immune cells and control autoimmunity. Gene transfer using integrating viral vectors, most commonly now lentiviral vectors, has been tested in human clinical trials since the 1990s. Gene transfer with viral vectors has varying efficacy based on transduction efficiency, the promoter used to drive transgene expression, and level and kinetics of cell-type specific expression achieved. In addition, the location and pattern of integration is not controlled, and depends on the insertional tendencies of the backbone used. Gene editing is a promising technology that aims to correct or replace the gene of interest in situ, in order to achieve expression that mimics natural expression, driven by the endogenous regulatory elements. Both HSCT and GT are intended to be one-time definitive treatments, and when successfully performed in children or young adults, could lead to decades of health and quality living, free of infection, immune dysregulation, and malignancy. We have focused this year on projects related to cellular therapy for Wiskott-Aldrich syndrome and DOCK8 deficiency. WAS is an X-linked disease, caused by mutations in the WAS gene, resulting in combined immunodeficiency, infections, eczema, microthrombocytopenia, infections, autoimmunity, and predisposition to lymphoma. We published the results of a trial of lentiviral-based gene therapy for WAS, enrolling 5 patients in Boston, completed an analysis of clinical outcome, immune and hematologic reconstitution, efficiency of gene transfer, and insertion site analysis. The lentiviral GT trial for WAS used a vector in which the transgene was not codon optimized, and was driven by a 1.6kB fragment of the endogenous WAS promoter. We and others using this vector have shown that expression of the WAS protein is subnormal, particularly when the vector copy number is low. Our analysis suggests strongly that more than 1 vector copy per cell in HSC is needed for correction of the thrombocytopenia that characterizes WAS. Our collaborators at ImmunoVec have developed and tested a next generation vector, that has a codon optimized transgene and a novel promoter designed to drive better expression in the platelet lineage. We have a clinical protocol in development and cell manufacturing and preclinical data being generated will be submitted to the FDA to support IND approval. DOCK8 deficiency is an autosomal recessive disease, caused by mutations in the DOCK8 gene, resulting in a combined immunodeficiency, eczema, food allergies, hyper-IgE, autoimmunity, and predisposition to malignancy, predominantly virally driven. Both WAS and DOCK8 proteins are critical for actin cytoskeletal rearrangement in multiple immune cells, and in fact the proteins interact in a complex. The DOCK8 transgene is very large, 6.2kB, and it is technically challenging to generate high titer vector. We have therefore designed several vectors, using alternate promoters that restrict expression to mature cell lineages, to avoid potential toxicity of expression in HSC. We have been exploring two novel strategies, 1) expressing the protein in two vectors, fused to split intein proteins, which when co-expressed in the same cell would result in trans-splicing and expression of the full-length protein and 2) expressing the protein using splicing at the mRNA level. These vectors are being tested in several different cellular models including T cells, NK cells, and monocytic cells to determine which vectors reconstitute function. We published the results of a clinical protocol of transplant for DOCK8 deficiency and a follow-on protocol is under development.