Role of reduced intensity conditioning in T-cell and B-cell immune reconstitution after HLA-identical bone marrow transplantation in ADA-SCID

Assessment of non-myelotoxic agents as a preparatory regimen for hematopoietic stem cell gene therapy

RAG2 deficiency is characterized by a lack of B and T lymphocytes, causing severe lethal infections. Currently, RAG2 deficiency is treated with a Hematopoietic Stem Cell transplantation (HSCT). Most conditioning regimens used before HSCT consist of alkylating myelotoxic agents with or without irradiation and affect growth and development of pediatric patients. Here, we developed a non-myelotoxic regimen using G-CSF, VLA-4I or AMD3100. These agents are known HSC mobilizers or affect bone marrow (BM) permeability and may support the homing of HSCs to the BM, without inducing major side effects. Female Rag2-/- mice were pre-treated with Busulfan (BU), G-CSF, VLA-4I or AMD3100 and transplanted with male BM cells transduced with a lentiviral vector carrying codon optimized human RAG2 (RAG2co). Peripheral blood cell counts increased significantly after G-CSF, VLA-4I and AMD3100 treatment, but not after BU. Reconstitution of PB lymphocytes was comparable for all groups with full immune reconstitution at 6 months post transplantation, despite different methods of conditioning. Survival of mice pre-treated with non-myelotoxic agents was significantly higher than after BU treatment. Here, we show that the non-myelotoxic agents G-CSF, VLA-4I, and AMD3100 are highly effective as conditioning regimen before HSC gene therapy and can be used as an alternative to BU.

Stem Cells, Hematopoiesis and Lineage Tracing: Transplantation-Centric Views and Beyond

An appropriate production of mature blood cells, or hematopoiesis, is essential for organismal health and homeostasis. In this developmental cascade, hematopoietic stem cells (HSCs) differentiate into intermediate progenitor types, that subsequently give rise to the many distinct blood cell lineages. Here, we describe tools and methods that permit for temporal and native clonal-level HSC lineage tracing in the mouse, and that can now be combined with emerging single-cell molecular analyses. We integrate new insights derived from such experimental paradigms with past knowledge, which has predominantly been derived from transplantation-based approaches. Finally, we outline current knowledge and novel strategies derived from studies aimed to trace human HSC-derived hematopoiesis.

Long-Term Immune Recovery After Hematopoietic Stem Cell Transplantation for ADA Deficiency: a Single-Center Experience

Unconditioned hematopoietic stem cell transplantation (HSCT) is the recommended treatment for patients with adenosine deaminase (ADA)-deficient severe combined immunodeficiency with an HLA-matched sibling donor (MSD) or family donor (MFD). Improved overall survival (OS) has been reported compared to the use of unrelated donors, and previous studies have demonstrated that adequate cellular and humoral immune recovery can be achieved even in the absence of conditioning. Detailed insight of the long-term outcome is still limited. We aim to address this by studying a large single-center cohort of 28 adenosine deaminase-deficient patients who underwent a total of 31 HSCT procedures, of which more than half were unconditioned. We report an OS of 85.7% and event-free survival of 71% for the entire cohort, with no statistically significant differences after procedures using related or unrelated HLA-matched donors. We find that donor engraftment in the myeloid compartment is significantly diminished in unconditioned procedures, which typically use a MSD or MFD. This is associated with poor metabolic correction and more frequent failure to discontinue immunoglobulin replacement therapy. Approximately one in four patients receiving an unconditioned procedure required a second procedure, whereas the use of reduced intensity conditioning (RIC) prior to allogeneic transplantation improves the long-term outcome by achieving better myeloid engraftment, humoral immune recovery, and metabolic correction. Further longitudinal studies are needed to optimize future management and guidelines, but our findings support a potential role for the routine use of RIC in most ADA-deficient patients receiving an HLA-identical hematopoietic stem cell transplant, even when a MSD or MFD is available.

Successful engraftment of haploidentical stem cell transplant with post-transplantation cyclophosphamide in a patient with adenosine deaminase deficiency

BACKGROUND

SCID are characterized by an imbalance in cellular and humoral immunity. Enzyme ADA deficiency represents from 10% to 15% of the SCID. This generates diminished maturation of the cell precursors. Treatments include enzyme replacement therapy, allogenic, or autologous HSCT with gene therapy, with HSCT being of choice when an identical HLA donor exists.

CASE REPORT

Male patient, without relevant family antecedents or consanguinity. The patient had multiple infections during the first months of life, evidencing low immunoglobulin levels, with absence of T and B lymphocytes, and natural killer cells. Severe combined immunodeficiencies are considered due to ADA deficiency; management was begun and is derived to our hospital. Admission at 8 months of life, with chronic malnutrition and psychomotor retardation. The HLA studies were conducted without finding an identical donor, taken to HSCT with haploidentical donor. Conditioning regimen with cyclophosphamide, fludarabine, melphalan, and thymoglobulin. This patient received prophylaxis for graft-versus-host disease with cyclophosphamide, cyclosporine, and methotrexate. A 22 months post-transplant, the patient was without immunosuppressants or immunoglobulin, without evidence of graft-versus-host disease or new infections.

CONCLUSIONS

The ADA deficiency is an infrequent pathology that can be potentially fatal if adequate treatment is not started. Haploidentical HSCT, using post-transplantation cyclophosphamide, emerges as a viable option with which good results can be achieved and improve the quality of life in patients with no other therapeutic alternatives.

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.

Lymphocytes are a major source of circulating soluble dipeptidyl peptidase 4

Dipeptidyl peptidase 4 (DPP4, CD26) is a serine protease that is expressed constitutively by many haematopoietic and non-haematopoietic tissues. It exists as a membrane-associated protein, as well as in an active, soluble form (herein called sDPP4), present at high concentrations in bodily fluids. Despite the proposed use of sDPP4 as a biomarker for multiple diseases, its cellular sources are not well defined. Here, we report that individuals with congenital lymphocyte immunodeficiency had markedly lower serum concentrations of sDPP4, which were restored upon successful treatment and restoration of lymphocyte haematopoiesis. Using irradiated lymphopenic mice and wild-type to Dpp4-/- reciprocal bone marrow chimeric animals, we found that haematopoietic cells were a major source of circulating sDPP4. Furthermore, activation of human and mouse T lymphocytes resulted in increased sDPP4, providing a mechanistic link between immune system activation and sDPP4 concentration. Finally, we observed that acute viral infection induced a transient increase in sDPP4, which correlated with the expansion of antigen-specific CD8+ T cell responses. Our study demonstrates that sDPP4 concentrations are determined by the frequency and activation state of lymphocyte populations. Insights from these studies will support the use of sDPP4 concentration as a biomarker for inflammatory and infectious diseases.

Gene Therapy for Adenosine Deaminase Deficiency: A Comprehensive Evaluation of Short- and Medium-Term Safety

Loss of adenosine deaminase activity leads to severe combined immunodeficiency (ADA-SCID); production and function of T, B, and natural killer (NK) cells are impaired. Gene therapy (GT) with an autologous CD34⁺-enriched cell fraction that contains CD34⁺ cells transduced with a retroviral vector encoding the human ADA cDNA sequence leads to immune reconstitution in most patients. Here, we report short- and medium-term safety analyses from 18 patients enrolled as part of single-arm, open-label studies or compassionate use programs. Survival was 100% with a median of 6.9 years follow-up (range, 2.3 to 13.4 years). Adverse events were mostly grade 1 or grade 2 and were reported by all 18 patients following GT. Thirty-nine serious adverse events (SAEs) were reported by 15 of 18 patients; no SAEs were considered related to GT. The most common adverse events reported post-GT include upper respiratory tract infection, gastroenteritis, rhinitis, bronchitis, oral candidiasis, cough, neutropenia, diarrhea, and pyrexia. Incidence rates for all of these events were highest during pre-treatment, treatment, and/or 3-month follow-up and then declined over medium-term follow-up. GT did not impact the incidence of neurologic/hearing impairments. No event indicative of leukemic transformation was reported.

In vivo tracking of T cells in humans unveils decade-long survival and activity of genetically modified T memory stem cells

A definitive understanding of survival and differentiation potential in humans of T cell subpopulations is of paramount importance for the development of effective T cell therapies. In particular, uncovering the dynamics in vivo in humans of the recently described T memory stem cells (TSCM) would be crucial for therapeutic approaches that aim at taking advantage of a stable cellular vehicle with precursor potential. We exploited data derived from two gene therapy clinical trials for an inherited immunodeficiency, using either retrovirally engineered hematopoietic stem cells or mature lymphocytes to trace individual T cell clones directly in vivo in humans. We compared healthy donors and bone marrow-transplanted patients, studied long-term in vivo T cell composition under different clinical conditions, and specifically examined TSCM contribution according to age, conditioning regimen, disease background, cell source, long-term reconstitution, and ex vivo gene correction processing. High-throughput sequencing of retroviral vector integration sites (ISs) allowed tracing the fate of more than 1700 individual T cell clones in gene therapy patients after infusion of gene-corrected hematopoietic stem cells or mature lymphocytes. We shed light on long-term in vivo clonal relationships among different T cell subtypes, and we unveiled that TSCM are able to persist and to preserve their precursor potential in humans for up to 12 years after infusion of gene-corrected lymphocytes. Overall, this work provides high-resolution tracking of T cell fate and activity and validates, in humans, the safe and functional decade-long survival of engineered TSCM, paving the way for their future application in clinical settings.

Longitudinal Evaluation of Immune Reconstitution and B-cell Function After Hematopoietic Cell Transplantation for Primary Immunodeficiency

PURPOSE

Hematopoietic cell transplantation (HCT) provides a curative therapy for severe forms of primary immunodeficiencies (PID). While the timing and extent of T-cell reconstitution following transplant for PID has been studied in depth, less is known about the kinetics of B-cell development and long-term restoration of humoral functions, which been often reported to be suboptimal after HCT.

METHODS

We studied longitudinally B-cell development and function in a cohort of 13 PID patients transplanted between 1997 and 2010, with a follow-up ranging from 0.7 to 15 years. Flow cytometric analysis of naïve and antigen-experienced B-cell subsets and in vitro functional responses to CpG were compared with data from healthy children and correlated with the degree of B-cell chimerism and in vivo antibody production.

RESULTS

We found that total memory B-cells count remained below normal levels for the first 2 years of follow up and progressively normalized. Switched memory B-cells (CD19+CD27+IgD-IgM-) were restored early and better than IgM memory B-cells (CD19+CD27+IgD+IgM+), which remained significantly reduced long-term. The recovery of memory B-cells correlated with good in vivo humoral function and normalization of CpG-response. A complete B-cell reconstitution was usually associated with donor B-cells chimerism and pre-transplant conditioning. Donor source and the underlying genetic defect represented also important variables.

CONCLUSION

Monitoring of phenotypic and functional changes on B-cells following HCT may prove clinically relevant to tailor patients' care. In particular the analysis of IgM memory and switched memory B-cells in addition to in vitro B-cells stimulation are recommended before Ig replacement therapy (IgRT) discontinuation.

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.

Successful bone marrow transplantation with reduced intensity conditioning in a patient with delayed-onset adenosine deaminase deficiency

In this case report, we describe successful BMT with RIC in a patient with delayed-onset ADA deficiency. A three-yr-old Japanese boy was diagnosed with delayed-onset ADA deficiency because of recurrent bronchitis, bronchiectasia, and lymphopenia. In addition, autoimmune thyroiditis and neutropenia were present. At four yr of age, he underwent BMT with a RIC regimen, including busulfan and fludarabine, from an HLA-identical healthy sister. Engraftment after BMT was uneventful without GVHD. Decreased ADA levels in blood immediately increased following BMT, and the patient was disease-free 13 months after BMT. These results suggest that BMT with RIC may sufficiently restore immune regulation in delayed-onset ADA deficiency. A longer follow-up period is needed to confirm these observations.

In vivo selection of autologous MGMT gene-modified cells following reduced-intensity conditioning with BCNU and temozolomide in the dog model

Chemotherapy with 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU) and temozolomide (TMZ) is commonly used for the treatment of glioblastoma multiforme (GBM) and other cancers. In preparation for a clinical gene therapy study in patients with glioblastoma, we wished to study whether these reagents could be used as a reduced-intensity conditioning regimen for autologous transplantation of gene-modified cells. We used an MGMT(P140K)-expressing lentivirus vector to modify dog CD34(+) cells and tested in four dogs whether these autologous cells engraft and provide chemoprotection after transplantation. Treatment with O(6)-benzylguanine (O6BG)/TMZ after transplantation resulted in gene marking levels up to 75%, without significant hematopoietic cytopenia, which is consistent with hematopoietic chemoprotection. Retrovirus integration analysis showed that multiple clones contribute to hematopoiesis. These studies demonstrate the ability to achieve stable engraftment of MGMT(P140K)-modified autologous hematopoietic stem cells (HSCs) after a novel reduced-intensity conditioning protocol using a combination of BCNU and TMZ. Furthermore, we show that MGMT(P140K)-HSC engraftment provides chemoprotection during TMZ dose escalation. Clinically, chemoconditioning with BCNU and TMZ should facilitate engraftment of MGMT(P140K)-modified cells while providing antitumor activity for patients with poor prognosis glioblastoma or alkylating agent-sensitive tumors, thereby supporting dose-intensified chemotherapy regimens.

Autoimmune dysregulation and purine metabolism in adenosine deaminase deficiency

Genetic defects in the adenosine deaminase (ADA) gene are among the most common causes for severe combined immunodeficiency (SCID). ADA-SCID patients suffer from lymphopenia, severely impaired cellular and humoral immunity, failure to thrive, and recurrent infections. Currently available therapeutic options for this otherwise fatal disorder include bone marrow transplantation (BMT), enzyme replacement therapy with bovine ADA (PEG-ADA), or hematopoietic stem cell gene therapy (HSC-GT). Although varying degrees of immune reconstitution can be achieved by these treatments, breakdown of tolerance is a major concern in ADA-SCID. Immune dysregulation such as autoimmune hypothyroidism, diabetes mellitus, hemolytic anemia, and immune thrombocytopenia are frequently observed in milder forms of the disease. However, several reports document similar complications also in patients on long-term PEG-ADA and after BMT or GT treatment. A skewed repertoire and decreased immune functions have been implicated in autoimmunity observed in certain B-cell and/or T-cell immunodeficiencies, but it remains unclear to what extent specific mechanisms of tolerance are affected in ADA deficiency. Herein we provide an overview about ADA-SCID and the autoimmune manifestations reported in these patients before and after treatment. We also assess the value of the ADA-deficient mouse model as a useful tool to study both immune and metabolic disease mechanisms. With focus on regulatory T- and B-cells we discuss the lymphocyte subpopulations particularly prone to contribute to the loss of self-tolerance and onset of autoimmunity in ADA deficiency. Moreover we address which aspects of immune dysregulation are specifically related to alterations in purine metabolism caused by the lack of ADA and the subsequent accumulation of metabolites with immunomodulatory properties.