In vivo T-cell dynamics during immune reconstitution after hematopoietic stem cell gene therapy in adenosine deaminase severe combined immune deficiency

Gene therapy for severe combined immunodeficiencies and beyond

This review describes how gene therapy of severe combined immunodeficiency became a reality, primarily based on the expected selective advantage conferred by transduction of hematopoietic progenitor cells. Thus, it resulted in a progressive extension to the treatment of other primary immunodeficiencies.

Ex vivo retrovirally mediated gene therapy has been shown within the last 20 yr to correct the T cell immunodeficiency caused by γc-deficiency (SCID X1) and adenosine deaminase (ADA) deficiency. The rationale was brought up by the observation of the revertant of SCIDX1 and ADA deficiency as a kind of natural gene therapy. Nevertheless, the first attempts of gene therapy for SCID X1 were associated with insertional mutagenesis causing leukemia, because the viral enhancer induced transactivation of oncogenes. Removal of this element and use of a promoter instead led to safer but still efficacious gene therapy. It was observed that a fully diversified T cell repertoire could be generated by a limited set (<1,000) of progenitor cells. Further advances in gene transfer technology, including the use of lentiviral vectors, has led to success in the treatment of Wiskott–Aldrich syndrome, while further applications are pending. Genome editing of the mutated gene may be envisaged as an alternative strategy to treat SCID diseases.

Consensus approach for the management of severe combined immune deficiency caused by adenosine deaminase deficiency

Inherited defects in adenosine deaminase (ADA) cause a subtype of severe combined immunodeficiency (SCID) known as severe combined immune deficiency caused by adenosine deaminase defects (ADA-SCID). Most affected infants can receive a diagnosis while still asymptomatic by using an SCID newborn screening test, allowing early initiation of therapy. We review the evidence currently available and propose a consensus management strategy. In addition to treatment of the immune deficiency seen in patients with ADA-SCID, patients should be followed for specific noninfectious respiratory, neurological, and biochemical complications associated with ADA deficiency. All patients should initially receive enzyme replacement therapy (ERT), followed by definitive treatment with either of 2 equal first-line options. If an HLA-matched sibling donor or HLA-matched family donor is available, allogeneic hematopoietic stem cell transplantation (HSCT) should be pursued. The excellent safety and efficacy observed in more than 100 patients with ADA-SCID who received gammaretrovirus- or lentivirus-mediated autologous hematopoietic stem cell gene therapy (HSC-GT) since 2000 now positions HSC-GT as an equal alternative. If HLA-matched sibling donor/HLA-matched family donor HSCT or HSC-GT are not available or have failed, ERT can be continued or reinstituted, and HSCT with alternative donors should be considered. The outcomes of novel HSCT, ERT, and HSC-GT strategies should be evaluated prospectively in "real-life" conditions to further inform these management guidelines.

Twenty-Five Years of Gene Therapy for ADA-SCID: From Bubble Babies to an Approved Drug

Twenty-five years have passed since first attempts of gene therapy (GT) in children affected by severe combined immunodeficiency (SCID) due to adenosine deaminase (ADA) defect, also known by the general public as bubble babies. ADA-SCID is fatal early in life if untreated. Unconditioned hematopoietic stem cell (HSC) transplant from matched sibling donor represents a curative treatment but is available for few patients. Enzyme replacement therapy can be life-saving, but its chronic use has many drawbacks. This review summarizes the history of ADA-SCID GT over the last 25 years, starting from first pioneering studies in the early 1990s using gamma-retroviral vectors, based on multiple infusions of genetically corrected autologous peripheral blood lymphocytes. HSC represented the ideal target for gene correction to guarantee production of engineered multi-lineage progeny, but it required a decade to achieve therapeutic benefit with this approach. Introduction of low-intensity conditioning represented a crucial step in achieving stable gene-corrected HSC engraftment and therapeutic levels of ADA-expressing cells. Recent clinical trials demonstrated that gamma-retroviral GT for ADA-SCID has a favorable safety profile and is effective in restoring normal purine metabolism and immune functions in patients >13 years after treatment. No abnormal clonal proliferation or leukemia development have been observed in >40 patients treated experimentally in five different centers worldwide. In 2016, the medicinal product Strimvelis™ received marketing approval in Europe for patients affected by ADA-SCID without a suitable human leukocyte antigen-matched related donor. Positive safety and efficacy results have been obtained in GT clinical trials using lentiviral vectors encoding ADA. The results obtained in last 25 years in ADA-SCID GT development fundamentally contributed to improve patients' prognosis, together with earlier diagnosis thanks to newborn screening. These advances open the way to further clinical development of GT as treatment for broader applications, from inherited diseases to cancer.

Update on the safety and efficacy of retroviral gene therapy for immunodeficiency due to adenosine deaminase deficiency

Adenosine deaminase (ADA) deficiency is a rare, autosomal-recessive systemic metabolic disease characterized by severe combined immunodeficiency (SCID). The treatment of choice for ADA-deficient SCID (ADA-SCID) is hematopoietic stem cell transplant from an HLA-matched sibling donor, although <25% of patients have such a donor available. Enzyme replacement therapy (ERT) partially and temporarily relieves immunodeficiency. We investigated the medium-term outcome of gene therapy (GT) in 18 patients with ADA-SCID for whom an HLA-identical family donor was not available; most were not responding well to ERT. Patients were treated with an autologous CD34(+)-enriched cell fraction that contained CD34(+) cells transduced with a retroviral vector encoding the human ADA complementary DNA sequence (GSK2696273) as part of single-arm, open-label studies or compassionate use programs. Overall survival was 100% over 2.3 to 13.4 years (median, 6.9 years). Gene-modified cells were stably present in multiple lineages throughout follow up. GT resulted in a sustained reduction in the severe infection rate from 1.17 events per person-year to 0.17 events per person-year (n = 17, patient 1 data not available). Immune reconstitution was demonstrated by normalization of T-cell subsets (CD3(+), CD4(+), and CD8(+)), evidence of thymopoiesis, and sustained T-cell proliferative capacity. B-cell function was evidenced by immunoglobulin production, decreased intravenous immunoglobulin use, and antibody response after vaccination. All 18 patients reported infections as adverse events; infections of respiratory and gastrointestinal tracts were reported most frequently. No events indicative of leukemic transformation were reported. Trial details were registered at www.clinicaltrials.gov as #NCT00598481.

B-cell development and functions and therapeutic options in adenosine deaminase-deficient patients

BACKGROUND

Adenosine deaminase (ADA) deficiency causes severe cellular and humoral immune defects and dysregulation because of metabolic toxicity. Alterations in B-cell development and function have been poorly studied. Enzyme replacement therapy (ERT) and hematopoietic stem cell (HSC) gene therapy (GT) are therapeutic options for patients lacking a suitable bone marrow (BM) transplant donor.

OBJECTIVE

We sought to study alterations in B-cell development in ADA-deficient patients and investigate the ability of ERT and HSC-GT to restore normal B-cell differentiation and function.

METHODS

Flow cytometry was used to characterize B-cell development in BM and the periphery. The percentage of gene-corrected B cells was measured by using quantitative PCR. B cells were assessed for their capacity to proliferate and release IgM after stimulation.

RESULTS

Despite the severe peripheral B-cell lymphopenia, patients with ADA-deficient severe combined immunodeficiency showed a partial block in central BM development. Treatment with ERT or HSC-GT reverted most BM alterations, but ERT led to immature B-cell expansion. In the periphery transitional B cells accumulated under ERT, and the defect in maturation persisted long-term. HSC-GT led to a progressive improvement in B-cell numbers and development, along with increased levels of gene correction. The strongest selective advantage for ADA-transduced cells occurred at the transition from immature to naive cells. B-cell proliferative responses and differentiation to immunoglobulin secreting IgM after B-cell receptor and Toll-like receptor triggering were severely impaired after ERT and improved significantly after HSC-GT.

CONCLUSIONS

ADA-deficient patients show specific defects in B-cell development and functions that are differently corrected after ERT and HSC-GT.

IL-7 and IL-15 instruct the generation of human memory stem T cells from naive precursors

Long-living memory stem T cells (T(SCM)) with the ability to self-renew and the plasticity to differentiate into potent effectors could be valuable weapons in adoptive T-cell therapy against cancer. Nonetheless, procedures to specifically target this T-cell population remain elusive. Here, we show that it is possible to differentiate in vitro, expand, and gene modify in clinically compliant conditions CD8(+) T(SCM) lymphocytes starting from naive precursors. Requirements for the generation of this T-cell subset, described as CD62L(+)CCR7(+)CD45RA(+)CD45R0(+)IL-7Rα(+)CD95(+), are CD3/CD28 engagement and culture with IL-7 and IL-15. Accordingly, T(SCM) accumulates early after hematopoietic stem cell transplantation. The gene expression signature and functional phenotype define this population as a distinct memory T-lymphocyte subset, intermediate between naive and central memory cells. When transplanted in immunodeficient mice, gene-modified naive-derived T(SCM) prove superior to other memory lymphocytes for the ability to expand and differentiate into effectors able to mediate a potent xenogeneic GVHD. Furthermore, gene-modified T(SCM) are the only T-cell subset able to expand and mediate GVHD on serial transplantation, suggesting self-renewal capacity in a clinically relevant setting. These findings provide novel insights into the origin and requirements for T(SCM) generation and pave the way for their clinical rapid exploitation in adoptive cell therapy.

Gene therapy for primary immunodeficiencies: Part 1

Over 60 patients affected by SCID due to IL2RG deficiency (SCID-X1) or adenosine deaminase (ADA)-SCID have received hematopoietic stem cell gene therapy in the past 15 years using gammaretroviral vectors, resulting in immune reconstitution and clinical benefit in the majority of them. However, the occurrence of insertional oncogenesis in the SCID-X1 trials has led to the development of new clinical trials based on integrating vectors with improved safety design as well as investigation on new technologies for highly efficient gene targeting and site-specific gene editing. Here we will present the experience and perspectives of gene therapy for SCID-X1 and ADA-SCID and discuss the pros and cons of gene therapy in comparison to allogeneic transplantation.

T-cell suicide gene therapy prompts thymic renewal in adults after hematopoietic stem cell transplantation

The genetic modification of T cells with a suicide gene grants a mechanism of control of adverse reactions, allowing safe infusion after partially incompatible hematopoietic stem cell transplantation (HSCT). In the TK007 clinical trial, 22 adults with hematologic malignancies experienced a rapid and sustained immune recovery after T cell-depleted HSCT and serial infusions of purified donor T cells expressing the HSV thymidine kinase suicide gene (TK+ cells). After a first wave of circulating TK+ cells, the majority of T cells supporting long-term immune reconstitution did not carry the suicide gene and displayed high numbers of naive lymphocytes, suggesting the thymus-dependent development of T cells, occurring only upon TK+ -cell engraftment. Accordingly, after the infusions, we documented an increase in circulating TCR excision circles and CD31+ recent thymic emigrants and a substantial expansion of the active thymic tissue as shown by chest tomography scans. Interestingly, a peak in the serum level of IL-7 was observed after each infusion of TK+ cells, anticipating the appearance of newly generated T cells. The results of the present study show that the infusion of genetically modified donor T cells after HSCT can drive the recovery of thymic activity in adults, leading to immune reconstitution.

Advances in basic and clinical immunology in 2011

Investigations of basic immunologic mechanisms and clinical studies of primary immunodeficiencies were most prevalent in 2011. Significant progress was achieved in the characterization of T(H)17 cell differentiation and associated cytokines in the setting of inflammatory disorders, HIV infection, and immunodysregulation disorders. The role of transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) mutations in the pathogenesis of CVID was further described and reported to be likely mediated by impaired TACI expression affecting B-cell function. The frequency of autoimmunity in patients with partial DiGeorge syndrome was estimated at 8.5%, predominantly resulting in blood cytopenias and hypothyroidism. Several reports emphasized the presentation of neoplasias, most often lymphomas, as the first manifestation of several primary immunodeficiencies. Novel strategies for newborn screening of B-cell lymphopenia by measuring immunoglobulin κ chain-deletion recombinant excision circles and for adenosine deaminase deficiency using tandem mass spectrometry were demonstrated to be feasible at a large scale. Progress in the treatment of primary immunodeficiencies included increased success with unrelated HLA-compatible donors for hematopoietic stem cell transplantation and the development of new gene therapy approaches with improved safety features. Induced pluripotent stem cells were developed from patients with primary immunodeficiencies, providing a virtually unlimited resource for pathophysiology and gene correction studies. New findings in several of the uncommon immunodeficiencies, such as the increased susceptibility to severe viral infections caused by defects in the activation of the Toll-like receptor 3 pathway, overall contributed to the understanding of their immunologic basis and provided for the design of effective diagnostic and therapeutic strategies.