Bone Marrow Transplantation Using HLA-Matched Unrelated Donors for Patients Suffering from Severe Combined Immunodeficiency

Targeted genome editing for the correction or alleviation of primary Immunodeficiencies

Primary immunodeficiencies (PID) are a growing list of unique disorders that result in a failure of the innate/adaptive immune systems to fully respond to disease or infection. PIDs are classified into five broad categories; B cell disorders, combined B and T cell disorders, phagocytic disorders, complement disorders, and disorders with recurrent fevers and inflammation. Many of these disorders, such as X-SCID, WAS, and CGD lead to early death in children if intervention is not implemented. At present, the predominant method of curative therapy remains an allogeneic transplant from a healthy donor, however many complications and limitations exist with his therapy such as availability of donors, graft vs host disease, graft rejection, and infection. More recently, gene therapy using viral based complementation vectors have successfully been implemented to functionally correct patient cells in an autologous transplant, but these methods carry significant risks, including insertional mutagenesis, and provide non-physiological gene expression. For these reasons, gene-editing reagents such as targeted nucleases, base editors (BE), and prime editors (PE) are being explored. The BE and PE tools, sometimes referred to as digital editors, are of very high interest as they provide both enhanced molecular specificity and do not rely on DNA repair pathways after DSBs to change individual base pairs or directly replace DNA sequences responsible for pathogenic phenotypes. With this in mind the purpose of this chapter is to highlight some of the most common PIDs found within the human population, discuss successes and shortcomings of previous intervention strategies, and highlight how the next generation of gene-editing tools may be deployed to directly repair the underlying genetic causes of this class of disease.

Hematopoietic Stem Cell Transplantations for Primary Immune Deficiencies: 3 Decades of Experience From a Tertiary Medical Center

Hematopoietic stem cell transplantation (HSCT) remains the leading treatment for the majority of severe primary immune deficiency (PID). This study aims to analyze changes in outcome over time. We conducted a retrospective analysis of HSCT in children with PID in a tertiary medical center over the period of 1983 to 2012. We identified 93 children with PID with a median follow-up of 3.6 years (range, 29 d to 21.2 y) after HSCT. The 2-year survival rates after HSCT for children with severe combined immune deficiency, hemophagocytic lymphohistiocytosis/lymphoproliferative disease, Wiskott-Aldrich syndrome, granulocyte defect, and undefined PID were 65.7%±6.8%, 80%±10.3%, 83.3%±15.2%, 75%±12.5%, and 25%±21.7%, respectively. Survival was associated with year of HSCT and matching. The hazard ratio (HR) (95% CI) for HSCT done in 1983 to 1999 compared with 2000 to 2012 and for matched (related and unrelated) compared with mismatched donor were 2.14 (0.99 to 4.653) and 3.07 (1.46 to 6.4), respectively. Survival was not associated with age, sex of the recipient, underlying PID, conditioning regimen, and presence of acute graft-versus-host disease. After adjustment to the underlying PID, donor and use of fludarabine-based conditioning, the HR (95% CI) for HSCT from the year 2000 was 4.69 (range, 1.4 to 15.45). Advances in HSCT over time have improved the survival of children with PID.

Cord blood transplants for SCID: better B-cell engraftment?

Hematopoietic stem-cell transplantation is the treatment of choice for severe combined immunodeficiency (SCID). Despite successful T-cell engraftment in transplanted patients, B-cell function is not always achieved; up to 58% of patients require immunoglobulin therapy after receiving haploidentical transplants. We report 2 half-sibling males with X-linked γ-chain SCID treated with different sources of stem cells. Sibling 1 was transplanted with T-cell-depleted haploidentical maternal bone marrow and sibling 2 was transplanted with 7/8 human leukocyte antigen-matched unrelated umbilical cord blood. Both patients received pretransplant conditioning and posttransplant graft-versus-host-disease prophylaxis. B-cell engraftment and function was achieved in sibling 1 but not in sibling 2. This disparate result is consistent with a review of 19 other SCID children who received cord blood transplants. B-cell function, as indicated by no need for immunoglobulin therapy, was restored in 42% of patients given haploidentical transplants and in 68% of patients given matched unrelated donor transplants compared with 80% of patients given cord blood transplants. Cord blood is an alternative source of stem cells for transplantation in children with SCID and has a higher likelihood of B-cell reconstitution.