TCRαß-Depleted Haploidentical Grafts Are a Safe Alternative to HLA-Matched Unrelated Donor Stem Cell Transplants for Infants with Severe Combined Immunodeficiency.

Hematopoietic stem cell transplantation and gene therapy are the only curative therapies for severe combined immunodeficiency (SCID). In patients lacking a matched donor, TCRαß/CD19-depleted haploidentical family donor transplant (TCRαß-HaploSCT) is a promising strategy. Conditioned transplant in SCID correlates to better myeloid chimerism and reduced immunoglobulin dependency. We studied transplant outcome in SCID infants according to donor type, specifically TCRαß-HaploSCT, and conditioning, through retrospective cohort analysis of 52 consecutive infants with SCID transplanted between 2013 and 2020. Median age at transplant was 5.1 months (range, 0.8-16.6). Donors were TCRαß-HaploSCT (n = 16, 31.4%), matched family donor (MFD, n = 15, 29.4%), matched unrelated donor (MUD, n = 9, 17.6%), and matched unrelated cord blood (CB, n = 11, 21.6%). Forty-one (80%) received fludarabine/treosulfan-based conditioning, 3 (6%) had alemtuzumab only, and 7 (14%) received unconditioned infusions. For conditioned transplants (n = 41), 3-year overall survival was 91% (95% confidence interval, 52-99%) for TCRαß-HaploSCT, 80% (41-98%) for MFD, 87% (36-98%) for MUD, and 89% (43-98%) for CB (p = 0.89). Cumulative incidence of grade II-IV acute graft-versus-host disease was 11% (2-79%) after TCRαß-HaploSCT, 0 after MFD, 29% (7-100%) after MUD, and 11% (2-79%) after CB (p = 0.10). 9/10 patients who received alemtuzumab-only or unconditioned transplants survived. Myeloid chimerism was higher following conditioning (median 47%, range 0-100%) versus unconditioned transplant (median 3%, 0-9%) (p < 0.001), as was the proportion of immunoglobulin-free long-term survivors (n = 29/36, 81% vs n = 4/9, 54%) (p < 0.001). TCRαß-HaploSCT has comparable outcome to MUD and is a promising alternative donor strategy for infants with SCID lacking MFD. This study confirms that conditioned transplant offers better myeloid chimerism and immunoglobulin freedom in long-term survivors.

Hematopoietic Cell Transplantation for Adenosine Deaminase Severe Combined Immunodeficiency-Improved Outcomes in the Modern Era.

Current treatment for adenosine deaminase (ADA)-deficient severe combined immunodeficiency (SCID) includes enzyme replacement therapy (ERT), allogeneic hematopoietic stem cell transplant (HSCT), or ex vivo corrected autologous hematopoietic stem cell gene therapy. Historic data show HSCT survival is superior using unconditioned matched sibling and family compared to matched unrelated and haploidentical donors. Recent improvement in HSCT outcomes prompted us to retrospectively examine HSCT survival and long-term graft function in ADA-SCID transplanted at our center. Thirty-three ADA-deficient patients received HSCT between 1989 and 2020, with follow-up data to January 2021. Chemotherapy conditioning regimens were defined as myeloablative (MAC-busulfan/cyclophosphamide), reduced-toxicity myeloablative (RT-MAC-treosulfan-based, since 2007), or no conditioning. Serotherapy used included alemtuzumab (with or without other conditioning agents) or antithymocyte globulin (ATG). ERT was introduced routinely in 2010 until commencement of conditioning. Median age at HSCT was 3.2 (0.8-99.8) months. Twenty-one (63.6%) received stem cells from unrelated or haploidentical donors. Seventeen (51.5%) received chemotherapy conditioning and 16 (48.5%) received alemtuzumab. Median follow-up was 7.5 (0.8-25.0) years. Overall survival (OS) and event-free survival (EFS) at 8 years were 90.9% (95% CI: 79.7-100.0%) and 79% (55-91%), respectively. OS after 2007 (n = 21) was 100% vs 75% before 2007 (n = 12) (p = 0.02). Three (9.1%) died after HSCT: two from multiorgan failure and one from unexplained encephalopathy. There were no deaths after 2007, among those who received ERT and treosulfan-based conditioning pre-HSCT. Ten (30.3%) developed acute GvDH (3 grade II, 2 grade III); no chronic GvHD was observed. In the modern era, conditioned HSCT with MUD has a favorable outcome for ADA-deficient patients.

Thymic Epithelial Cell Alterations and Defective Thymopoiesis Lead to Central and Peripheral Tolerance Perturbation in MHCII Deficiency.

Major Histocompatibility Complex (MHC) class II (MHCII) deficiency (MHCII-D), also known as Bare Lymphocyte Syndrome (BLS), is a rare combined immunodeficiency due to mutations in genes regulating expression of MHCII molecules. MHCII deficiency results in impaired cellular and humoral immune responses, leading to severe infections and autoimmunity. Abnormal cross-talk with developing T cells due to the absence of MHCII expression likely leads to defects in thymic epithelial cells (TEC). However, the contribution of TEC alterations to the pathogenesis of this primary immunodeficiency has not been well characterized to date, in particular in regard to immune dysregulation. To this aim, we have performed an in-depth cellular and molecular characterization of TEC in this disease. We observed an overall perturbation of thymic structure and function in both MHCII-/- mice and patients. Transcriptomic and proteomic profiling of murine TEC revealed several alterations. In particular, we demonstrated that impairment of lymphostromal cross-talk in the thymus of MHCII-/- mice affects mTEC maturation and promiscuous gene expression and causes defects of central tolerance. Furthermore, we observed peripheral tolerance impairment, likely due to defective Treg cell generation and/or function and B cell tolerance breakdown. Overall, our findings reveal disease-specific TEC defects resulting in perturbation of central tolerance and limiting the potential benefits of hematopoietic stem cell transplantation in MHCII deficiency.

Case Report: Unmanipulated Matched Sibling Donor Hematopoietic Cell Transplantation In TBX1 Congenital Athymia: A Lifesaving Therapeutic Approach When Facing a Systemic Viral Infection.

Congenital athymia can present with severe T cell lymphopenia (TCL) in the newborn period, which can be detected by decreased T cell receptor excision circles (TRECs) on newborn screening (NBS). The most common thymic stromal defect causing selective TCL is 22q11.2 deletion syndrome (22q11.2DS). T-box transcription factor 1 (TBX1), present on chromosome 22, is responsible for thymic epithelial development. Single variants in TBX1 causing haploinsufficiency cause a clinical syndrome that mimics 22q11.2DS. Definitive therapy for congenital athymia is allogeneic thymic transplantation. However, universal availability of such therapy is limited. We present a patient with early diagnosis of congenital athymia due to TBX1 haploinsufficiency. While evaluating for thymic transplantation, she developed Omenn Syndrome (OS) and life-threatening adenoviremia. Despite treatment with anti-virals and cytotoxic T lymphocytes (CTLs), life threatening adenoviremia persisted. Given the imminent need for rapid establishment of T cell immunity and viral clearance, the patient underwent an unmanipulated matched sibling donor (MSD) hematopoietic cell transplant (HCT), ultimately achieving post-thymic donor-derived engraftment, viral clearance, and immune reconstitution. This case illustrates that because of the slower immune recovery that occurs following thymus transplantation and the restricted availability of thymus transplantation globally, clinicians may consider CTL therapy and HCT to treat congenital athymia patients with severe infections.

Innovative Cell-Based Therapies and Conditioning to Cure RAG Deficiency.

Genetic defects in recombination activating genes (RAG) 1 and 2 cause a broad spectrum of severe immune defects ranging from early severe and repeated infections to inflammation and autoimmune manifestations. A correlation between in vitro recombination activity and immune phenotype has been described. Hematopoietic cell transplantation is the treatment of care; however, the availability of next generation sequencing and whole genome sequencing has allowed the identification of novel genetic RAG variants in immunodeficient patients at various ages, raising therapeutic questions. This review addresses the recent advances of novel therapeutic approaches for RAG deficiency. As conventional myeloablative conditioning regimens are associated with acute toxicities and transplanted-related mortality, innovative minimal conditioning regimens based on the use of monoclonal antibodies are now emerging and show promising results. To overcome shortage of compatible donors, gene therapy has been developed in various RAG preclinical models. Overall, the transplantation of autologous gene corrected hematopoietic precursors and the use of non-genotoxic conditioning will open a new era, offering a cure to an increasing number of RAG patients regardless of donor availability and severity of clinical conditions.

Asymptomatic Infant With Atypical SCID and Novel Hypomorphic RAG Variant Identified by Newborn Screening: A Diagnostic and Treatment Dilemma.

The T-cell receptor excision circle (TREC) assay detects T-cell lymphopenia (TCL) in newborns and is especially important to identify severe combined immunodeficiency (SCID). A spectrum of SCID variants and non-SCID conditions that present with TCL are being discovered with increasing frequency by newborn screening (NBS). Recombination-activating gene (RAG) deficiency is one the most common causes of classical and atypical SCID and other conditions with immune dysregulation. We present the case of an asymptomatic male with undetectable TRECs on NBS at 1 week of age. The asymptomatic newborn was found to have severe TCL, but normal B cell quantities and lymphocyte proliferation upon mitogen stimulation. Next generation sequencing revealed compound heterozygous hypomorphic RAG variants, one of which was novel. The moderately decreased recombinase activity of the RAG variants (16 and 40%) resulted in abnormal T and B-cell receptor repertoires, decreased fraction of CD3+ TCRVα7.2+ T cells and an immune phenotype consistent with the RAG hypomorphic variants. The patient underwent successful treatment with hematopoietic stem cell transplantation (HSCT) at 5 months of age. This case illustrates how after identification of a novel RAG variant, in vitro studies are important to confirm the pathogenicity of the variant. This confirmation allows the clinician to expedite definitive treatment with HSCT in an asymptomatic phase, mitigating the risk of serious infectious and non-infectious complications.

Clinical, Immunological, and Genetic Features in 49 Patients With ZAP-70 Deficiency: A Systematic Review.

Background: Zeta-Chain Associated Protein Kinase 70 kDa (ZAP-70) deficiency is a rare combined immunodeficiency (CID) caused by recessive homozygous/compound heterozygous loss-of-function mutations in the ZAP70 gene. Patients with ZAP-70 deficiency present with a variety of clinical manifestations, particularly recurrent respiratory infections and cutaneous involvements. Therefore, a systematic review of ZAP-70 deficiency is helpful to achieve a comprehensive view of this disease. Methods: We searched PubMed, Web of Science, and Scopus databases for all reported ZAP-70 deficient patients and screened against the described eligibility criteria. A total of 49 ZAP-70 deficient patients were identified from 33 articles. For all patients, demographic, clinical, immunologic, and molecular data were collected. Results: ZAP-70 deficient patients have been reported in the literature with a broad spectrum of clinical manifestations including recurrent respiratory infections (81.8%), cutaneous involvement (57.9%), lymphoproliferation (32.4%), autoimmunity (19.4%), enteropathy (18.4%), and increased risk of malignancies (8.1%). The predominant immunologic phenotype was low CD8+ T cell counts (97.9%). Immunologic profiling showed defective antibody production (57%) and decreased lymphocyte responses to mitogenic stimuli such as phytohemagglutinin (PHA) (95%). Mutations of the ZAP70 gene were located throughout the gene, and there was no mutational hotspot. However, most of the mutations were located in the kinase domain. Hematopoietic stem cell transplantation (HSCT) was applied as the major curative treatment in 25 (51%) of the patients, 18 patients survived transplantation, while two patients died and three required a second transplant in order to achieve full remission. Conclusion: Newborns with consanguineous parents, positive family history of CID, and low CD8+ T cell counts should be considered for ZAP-70 deficiency screening, since early diagnosis and treatment with HSCT can lead to a more favorable outcome. Based on the current evidence, there is no genotype-phenotype correlation in ZAP-70 deficient patients.

Survey of Infection Control Precautions for Patients with Severe Combined Immune Deficiency.

Severe combined immune deficiency (SCID) is caused by an array of genetic disorders resulting in a diminished adaptive immune system due to impaired T lymphocytes. In these patients, active infection at the time of hematopoietic transplantation has been shown to increase morbidity and mortality. To prevent transmission of infections in SCID patients, standardized infection control precautions should be implemented. An online survey regarding SCID-specific protocols was distributed through several immunodeficiency organizations. Seventy-three responses were obtained, with the majority (55%) of responses from the USA, 15% from Canada, and the remainder from 12 other countries. Only 50% of respondents had a SCID-specific infection control protocol at their center, and while a majority of these centers had training for physicians, a small minority had training for other healthcare workers such as nursing and housekeeping staff. Significant variability of infection control practices, such as in-patient precautions, required personal protective equipment (PPE), diet restrictions, visitor precautions and discharge criteria, was found between different treatment centers. There is a paucity of evidence-based data regarding the safest environment to prevent infection in SCID patients. Institutional protocols may have significant impact on infection risk, survival, family well-being, child development and cost of care. From these results, it is evident that further multi-center research is required to determine the safest and healthiest environment for these children, so that evidence-based infection control protocols for patients with SCID can be developed.

Prominent dermal Langerhans cells in an Omenn syndrome patient with a novel mutation in the IL2RG gene.

Prominent dermal infiltration by Langerhans cells (LC) is a rare finding in patients with Omenn syndrome (OS). Here, we report the case study of a 7-month-old boy with OS and with prominent dermal infiltration by LC, which is a rare histological manifestation of the skin. Striking erythroderma appeared in the patient 2 weeks after birth. We also noted alopecia, lymphadenopathy, hepatosplenomegaly, eosinophilia and an elevated serum immunoglobulin E level with hypogammaglobulinemia. Peripheral blood flow cytometry showed the Tlow NK+ B+ immunophenotype and genetic analysis, a novel mutation in the IL2RG gene (c.337_339delTCT, p.Ser113del). The final diagnosis was that of OS. He responded well to an allograft umbilical cord blood transplantation that was performed when the patient was 8 months of age. We speculate that the LC accumulated in the dermis will eventually migrate to the regional lymph node, then stimulate autoreactive T cells by overpresenting antigens, thus causing OS-specific skin symptoms.

Survival of human cadaver skin on severe combined immune deficiency pigs: Proof of concept.

Transplantation of human xenografts onto immunocompromised mice is a powerful research tool for studying wound healing. However, differences in healing between humans and mice and their small size limit this model. We determined whether human cadaver skin xenografts transplanted onto pigs with severe combined immune deficiency (SCID) would survive and not be rejected. Meshed (1:1.5), cryopreserved human cadaver skin was transplanted onto 10 partial thickness dermatome wounds in each of two normal domestic pigs and two SCID pigs. Autografts (n = 2/animal) from the four animals were used as controls. In normal pigs, all autografts were engrafted and healed with a minimal, if any, inflammation and scarring. All human xenografts were rejected by the normal pigs within 5-11 days and associated with an intense T-cell inflammatory response. In contrast, both autografts and xenografts were engrafted and survived the 28-day study in the SCID pigs with a minimal inflammation and no gross scarring.

Tandem Orthotopic Living Donor Liver Transplantation Followed by Same Donor Haploidentical Hematopoietic Stem Cell Transplantation for DOCK8 Deficiency.

BACKGROUND: An 11-year-old girl with dedicator of cytokinesis 8 (DOCK8) deficiency was proposed for potentially curative hematopoietic stem cell transplantation (HSCT), the donor being her haploidentical mother. However, end-stage liver disease caused by chronic Cryptosporidium infection required liver transplantation before HSCT. METHODS: Consequently, a staged approach of a sequential liver transplant followed by a HSCT was planned with her mother as the donor for both liver and HSCT. RESULTS: The patient successfully underwent a left-lobe orthotopic liver transplant; however, she developed a biliary leak delaying the HSCT. Notably, the recipient demonstrated 3% donor lymphocyte chimerism in her peripheral blood immediately before HSCT. Haploidentical-related donor HSCT performed 2 months after liver transplantation was complicated by the development of acyclovir-resistant herpes simplex virus viremia, primary graft failure, and sinusoidal obstruction syndrome. The patient died from sinusoidal obstruction syndrome-associated multiorgan failure with Candida sepsis on day +40 following HSCT. CONCLUSIONS: We discuss the many considerations inherent to planning for HSCT preceded by liver transplant in patients with primary immunodeficiencies, including the role of prolonged immunosuppression and the risk of infection before immune reconstitution. We also discuss the implications of potential recipient sensitization against donor stem cells precipitated by exposure of the recipient to the donor lymphocytes from the transplanted organ.

Haematopoietic stem cell transplantation for severe combined immunodeficiency: Long-term health outcomes and patient perspectives.

AIM: To examine the long-term follow-up and health outcomes of patients who have undergone haematopoietic stem cell transplant (HSCT) for severe combined immunodeficiency (SCID). METHODS: Through a structured questionnaire, we examined follow-up arrangements and long-term health outcomes in 22 children who have had a successful HSCT for SCID during the period of 1984-2012 at the Sydney Children's Hospital, Sydney, Australia. RESULTS: Most children considered themselves healthy and 'cured' from SCID. Whilst many children enjoy relatively good bio-social health outcomes, specific negative health outcomes and absenteeism from school were perceived negatively. Two-thirds of children see their general practitioner or specialist regularly; however, there did not appear to be consistency with the nature of this follow-up. CONCLUSION: The findings from our study highlight the complex bio-psychosocial health needs of post-HSCT SCID children and encourage SCID centres to consider a multidisciplinary approach to their follow-up. Further studies into the determinants of patients' perceptions of their health are needed.

Outcomes of pediatric identical living-donor liver and hematopoietic stem cell transplantation.

Chronic IS is associated with significant morbidity in transplant recipients. Moreover, IS does not prevent chronic graft failure frequently. Allograft immune tolerance in LT can be induced by complete donor chimerism through allogenic HSCT combined with identical LDLT. This approach may exempt patients from chronic lifelong IS. However, it is unclear whether its benefits justify its risks. Here, we present three cases from our institution and analyze seven additional reports of children treated with HSCT/LDLT, all receiving HSCT due to hemato-oncological indications. In eight of 10 cases, donor macrochimerism resulted in allograft tolerance. Nine patients survived. One patient died due to fulminant ADV infection. Further complications were GvHD (n = 3) and bone marrow failure (n = 2). In conclusion, donor-specific allograft tolerance can be achieved by identical-donor HSCT/LDLT. However, at present, this approach should generally be limited to selected indications due to a potentially unfavorable risk-benefit ratio. Novel toxicity-reduced conditioning protocols for HSCT/LDLT in the absence of malignant or non-hepatic disease may prove to be a sufficiently safe approach for inducing graft tolerance in children receiving a LDLT in the future. This concept may reduce the burden of lifelong IS.

Can Parents Refuse a Potentially Lifesaving Transplant for Severe Combined Immunodeficiency?

If untreated, most children with severe combined immunodeficiency disorder (SCID) will die of complications of infection within the first 2 years of life. Early hematopoietic stem cell transplant (HSCT) is the current standard of care for this disease. Although potentially lifesaving, prognosis of HSCT in SCID is variable depending on a number of host and donor factors. Of the survivors, many develop secondary problems such as chronic graft-versus-host disease or even second malignancies. Posttransplant care is complex and requires great effort from parents to adhere to difficult treatment regimens. In this article, we address the difficult ethical question of what to do if parents choose not to have their child with SCID undergo HSCT but prefer palliative care.