Summary
Immunodeficient non‐obese diabetic (NOD)‐severe combined immune‐deficient (scid) mice bearing a targeted mutation in the gene encoding the interleukin (IL)‐2 receptor gamma chain gene ...(IL2rγnull) engraft readily with human peripheral blood mononuclear cells (PBMC). Here, we report a robust model of xenogeneic graft‐versus‐host‐like disease (GVHD) based on intravenous injection of human PBMC into 2 Gy conditioned NOD‐scid IL2rγnull mice. These mice develop xenogeneic GVHD consistently (100%) following injection of as few as 5 × 106 PBMC, regardless of the PBMC donor used. As in human disease, the development of xenogeneic GVHD is highly dependent on expression of host major histocompatibility complex class I and class II molecules and is associated with severely depressed haematopoiesis. Interrupting the tumour necrosis factor‐α signalling cascade with etanercept, a therapeutic drug in clinical trials for the treatment of human GVHD, delays the onset and progression of disease. This model now provides the opportunity to investigate in vivo mechanisms of xenogeneic GVHD as well as to assess the efficacy of therapeutic agents rapidly.
Deleterious mutations in the common gamma chain (γC, CD132) are associated with X-linked severe combined immunodeficiency (X-SCID) characterized by a T-B+NK- phenotype. Hypomorphic variants in the ...IL2RG gene have also been associated with a milder or atypical SCID phenotype. Milder phenotypes can also occur when somatic genetic rescue occurs in the setting of severe IL2RG mutations. Spontaneous somatic variants particularly in hematologic disorders can occur particularly in genes with known selection pressure including IL2RG.
Here, we report the clinical and molecular findings from two brothers with atypical X-SCID phenotype including hypogammaglobulinemia, elevated IgM, T cell lymphopenia and extensive verruca plana. One brother required splenectomy secondary to a benign vascular tumor and had recurrent pancreatitis consistent with primary sclerosing cholangitis. Both brothers developed recurrent suppurative pneumonia resulting in early bronchiectasis in their first decade. Next generation sequencing initially was negative, yet reanalysis found a large duplication event in exon 3 of IL2RG gene with somatic genetic rescue events that occurred twice in two brothers. Functional studies revealed a unique mosaic pattern in each affected sibling when stimulating peripheral blood mononuclear cells with IL-2 or IL-21 resulting in bimodal phospho-STAT5 or phospho-STAT3 respectively. The genetic analysis revealed the maternal allele was heterozygous as expected, although the ratio of these events and clonal analysis revealed cell type skewing.
Our data demonstrate an atypical SCID phenotype in two brothers secondary to the combination of a large duplication event in the IL-2RG gene partially rescued by somatic genetic rescue. Although previous somatic reversion cases have been reported involving the IL2RG genetic locus, our cases demonstrate a large duplication reversion event with recurrence. Our case highlights the unique selection pressure to amplify rare genetic events at the IL2RG locus.
"Humanized" mice are a promising translational model for studying human hematopoiesis and immunity. Their utility has been enhanced by the development of new stocks of immunodeficient hosts, most ...notably mouse strains such as NOD-scid IL2rgamma(null) mice that lack the IL-2 receptor common gamma chain. These stocks of mice lack adaptive immune function, display multiple defects in innate immunity, and support heightened levels of human hematolymphoid engraftment. Humanized mice can support studies in many areas of immunology, including autoimmunity, transplantation, infectious diseases, and cancer. These models are particularly valuable in experimentation where there is no appropriate small animal model of the human disease, as in the case of certain viral infections. This unit details the creation of humanized mice by engraftment of immunodeficient mice with hematopoietic stem cells or peripheral blood mononuclear cells, provides methods for evaluating engraftment, and discusses considerations for choosing the appropriate model system to meet specific goals.
Shearer et al in 2014 articulated well-defined criteria for the diagnosis and classification of severe combined immunodeficiency (SCID) as part of the Primary Immune Deficiency Treatment Consortium’s ...(PIDTC’s) prospective and retrospective studies of SCID.
Because of the advent of newborn screening for SCID and expanded availability of genetic sequencing, revision of the PIDTC 2014 Criteria was needed.
We developed and tested updated PIDTC 2022 SCID Definitions by analyzing 379 patients proposed for prospective enrollment into Protocol 6901, focusing on the ability to distinguish patients with various SCID subtypes.
According to PIDTC 2022 Definitions, 18 of 353 patients eligible per 2014 Criteria were considered not to have SCID, whereas 11 of 26 patients ineligible per 2014 Criteria were determined to have SCID. Of note, very low numbers of autologous T cells (<0.05 × 109/L) characterized typical SCID under the 2022 Definitions. Pathogenic variant(s) in SCID-associated genes was identified in 93% of patients, with 7 genes (IL2RG, RAG1, ADA, IL7R, DCLRE1C, JAK3, and RAG2) accounting for 89% of typical SCID. Three genotypes (RAG1, ADA, and RMRP) accounted for 57% of cases of leaky/atypical SCID; there were 13 other rare genotypes. Patients with leaky/atypical SCID were more likely to be diagnosed at more than age 1 year than those with typical SCID lacking maternal T cells: 20% versus 1% (P < .001). Although repeat testing proved important, an initial CD3 T-cell count of less than 0.05 × 109/L differentiated cases of typical SCID lacking maternal cells from leaky/atypical SCID: 97% versus 7% (P < .001).
The PIDTC 2022 Definitions describe SCID and its subtypes more precisely than before, facilitating analyses of SCID characteristics and outcomes.
Severe combined immunodeficiency (SCID) results from defects in the differentiation of hematopoietic stem cells into mature T lymphocytes, with additional lymphoid lineages affected in particular ...genotypes. In 2014, the Primary Immune Deficiency Treatment Consortium published criteria for diagnosing SCID, which are now revised to incorporate contemporary approaches. Patients with typical SCID must have less than 0.05 × 109 autologous T cells/L on repetitive testing, with either pathogenic variant(s) in a SCID-associated gene, very low/undetectable T-cell receptor excision circles or less than 20% of CD4 T cells expressing naive markers, and/or transplacental maternally engrafted T cells. Patients with less profoundly impaired autologous T-cell differentiation are designated as having leaky/atypical SCID, with 2 or more of these: low T-cell numbers, oligoclonal T cells, low T-cell receptor excision circles, and less than 20% of CD4 T cells expressing naive markers. These patients must also have either pathogenic variant(s) in a SCID-associated gene or reduced T-cell proliferation to certain mitogens. Omenn syndrome requires a generalized erythematous rash, absent transplacentally acquired maternal engraftment, and 2 or more of these: eosinophilia, elevated IgE, lymphadenopathy, hepatosplenomegaly. Thymic stromal defects and other causes of secondary T-cell deficiency are excluded from the definition of SCID. Application of these revised Primary Immune Deficiency Treatment Consortium 2022 Definitions permits precise categorization of patients with T-cell defects but does not imply a preferred treatment strategy.
The Irish Travellers are an ethnically distinct minority community originating from Ireland, with substantial immigration to the U. S. resulting in a current subpopulation estimated around 20,000. ...Given the history of cultural endogamy in this community, there are known increased rates of severe combined immunodeficiency (SCID), with two recombinase activating gene 1 pathogenic variants (RAG1; p.Arg897*and p.Ser259Alafs*5) and one novel non-homologous end-joining 1 gene variant (NHEJ1; p.Gln224Argfs*27) detected in the US community. However, knowledge of rare genetic disorders, including how they are passed and the value of carrier testing, is limited among some members of this population.
A multi-institutional collaboration developed an outreach project for SCID patients and their relatives in the U.S.-based Irish Traveller community. SCID patients were identified through newborn screening and pedigree interviews. Genetic testing for SCID variants was offered to kindred members, prioritizing members of child-bearing age. An online educational program was designed to identify knowledge gaps and disseminate information on SCID and implications of carrier status.
Baseline knowledge and attitude assessments prior to educational intervention were obtained from 28 kindred members, all of whom were female and the majority (n = 23) were of child bearing age. Similar to their counterparts in Ireland, the majority (n = 21) had less than a high school diploma. 12 respondents identified three or more family members diagnosed with SCID. The majority of respondents (n ≥17) strongly agreed on the importance of knowing what diseases run in their family. However, only a minority (n ≤8) were able to correctly identify how autosomal dominant, autosomal recessive, and X-linked diseases were passed down. Open ended discussions with key members of this kindred also helped identify religious and cultural barriers which contributed to hesitancy around genetic testing in this underserved community. Early diagnosis of affected members, enabled by educational sessions and carrier screening within this high-risk population, is vital to increase preparedness for the birth of a child with SCID. This is especially important in the case of SCID caused by NHEJ1, as the radiosensitivity caused by this mutation necessitates treatment and conditioning protocols which differ from that of SCID caused by RAG1 mutations.
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