FOXN1 Deficiency: from the Discovery to Novel Therapeutic Approaches

Multicellular bioprinted skin facilitates human-like skin architecture in vivo

Bioprinting is a promising alternative method to generate skin substitutes because it can replicate the structural organization of the skin into biomimetic layers in vitro. In this study, six primary human skin cell types were used to bioprint a trilayer skin construct consisting of epidermis, dermis, and hypodermis. Transplantation of the bioprinted skin with human cells onto full-thickness wounds of nu/nu mice promoted rapid vascularization and formation of epidermal rete ridges analogous to the native human epidermis, with a normal-looking extracellular matrix. Cell-specific staining confirmed the integration of the implanted cells into the regenerated skin. Using a similar approach, a 5 centimeter-by-5 centimeter bioprinted autologous porcine skin graft was transplanted onto full-thickness wounds in a porcine excisional wound model. The bioprinted skin graft improved epithelialization, reduced skin contraction, and supported normal collagen organization with reduced fibrosis. Differential gene expression demonstrated pro-remodeling protease activity in wounds transplanted with bioprinted autologous skin grafts. These results demonstrate that bioprinted skin can support skin regeneration to allow for nonfibrotic wound healing and suggest that the skin bioprinting technology may be applicable for human clinical use.

Cutaneous Findings in Inborn Errors of Immunity: An Immunologist's Perspective

Cutaneous manifestations are common in patients with inborn errors of immunity (IEI)/primary immunodeficiency and could be due to infections, immune dysregulation, or lymphoproliferative/malign diseases. Immunologists accept some as warning signs for underlying IEI. Herein, we include noninfectious/infectious cutaneous manifestations that we come across in rare IEI cases in our clinic and provide a comprehensive literature review. For several skin diseases, the diagnosis is challenging and differential diagnosis is necessary. Detailed disease history and examination play a vital role in reaching a diagnosis, especially if there is a potential underlying IEI. A skin biopsy is sometimes necessary, especially if we need to rule out inflammatory, infectious, lymphoproliferative, and malignant conditions. Specific and immunohistochemical stainings are particularly important when diagnosing granuloma, amyloidosis, malignancies, and infections like human herpes virus-6, human herpes virus-8, human papillomavirus, and orf. Elucidation of mechanisms of IEIs has improved our understanding of their relation to cutaneous findings. In challenging cases, the immunological evaluation may lead the approach when there is a specific primary immunodeficiency diagnosis or at least help to reduce the number of differential diagnoses. Conversely, the response to therapy may provide conclusive evidence for some conditions. This review raises awareness of concomitant lesions and expands the scope of the differential diagnosis of IEI and the spectrum of skin disease therapy by highlighting frequent forms of IEI-associated cutaneous manifestations. The manifestations given here will guide clinicians to plan for alternative use of diverse therapeutics in a multidisciplinary way for skin diseases.

Administration of recombinant FOXN1 protein attenuates Alzheimer's pathology in mice

BACKGROUND

Alzheimer's disease (AD) is the most common cause of dementia in older adults and characterized by progressive loss of memory and cognitive functions that are associated with amyloid-beta (Aβ) plaques and neurofibrillary tangles. Immune cells play an important role in the clearance of Aβ deposits and neurofibrillary tangles. T cells are the major component of the immune system. The thymus is the primary organ for T cell generation. T cell development in the thymus depends on thymic epithelial cells (TECs). However, TECs undergo both qualitative and quantitative loss over time. We have previously reported that a recombinant (r) protein containing FOXN1 and a protein transduction domain can increase the number of TECs and subsequently increases the number of T cells in mice. In this study we determined the ability of rFOXN1 to affect cognitive performance and AD pathology in mice.

METHODS

Aged 3xTg-AD and APP/PS1 AD mice were injected with rFOXN1 or control protein. Cognitive performance, AD pathology, the thymic microenvironment and immune cells were then analyzed.

RESULTS

Administration of rFOXN1 into AD mice improves cognitive performance and reduces Aβ plaque load and phosphorylated tau in the brain. This is related to rejuvenating the aged thymic microenvironment, which results in enhanced T cell generation in the thymus, leading to increased number of T cells, especially IFNγ-producing T cells, in the spleen and the choroid plexus (CP), enhanced expression of immune cell trafficking molecules in the CP, and increased migration of monocyte-derived macrophages into the brain. Furthermore, the production of anti-Aβ antibodies in the serum and the brain, and the macrophage phagocytosis of Aβ are enhanced in rFOXN1-treated AD mice.

CONCLUSIONS

Our results suggest that rFOXN1 protein has the potential to provide a novel approach to treat AD patients.

Generation and molecular characterization of human pluripotent stem cell-derived pharyngeal foregut endoderm

Approaches to study human pharyngeal foregut endoderm-a developmental intermediate that is linked to various human syndromes involving pharynx development and organogenesis of tissues such as thymus, parathyroid, and thyroid-have been hampered by scarcity of tissue access and cellular models. We present an efficient stepwise differentiation method to generate human pharyngeal foregut endoderm from pluripotent stem cells. We determine dose and temporal requirements of signaling pathway engagement for optimized differentiation and characterize the differentiation products on cellular and integrated molecular level. We present a computational classification tool, "CellMatch," and transcriptomic classification of differentiation products on an integrated mouse scRNA-seq developmental roadmap confirms cellular maturation. Integrated transcriptomic and chromatin analyses infer differentiation stage-specific gene regulatory networks. Our work provides the method and integrated multiomic resource for the investigation of disease-relevant loci and gene regulatory networks and their role in developmental defects affecting the pharyngeal endoderm and its derivatives.

An Analysis of the Gene Expression Associated with Lymph Node Metastasis in Colorectal Cancer

Objective

This study aimed to explore the genes regulating lymph node metastasis in colorectal cancer (CRC) and to clarify their relationship with tumor immune cell infiltration and patient prognoses.

Methods

The data sets of CRC patients were collected through the Cancer Gene Atlas database; the differentially expressed genes (DEGs) associated with CRC lymph node metastasis were screened; a protein-protein interaction (PPI) network was constructed; the top 20 hub genes were selected; the Gene Ontology functions and the Kyoto Encyclopedia of Genes and Genomes pathways were enriched and analyzed. The Least Absolute Shrinkage and Selection Operator (LASSO) regression method was employed to further screen the characteristic genes associated with CRC lymph node metastasis in 20 hub genes, exploring the correlation between the characteristic genes and immune cell infiltration, conducting a univariate COX analysis on the characteristic genes, obtaining survival-related genes, constructing a risk score formula, conducting a Kaplan-Meier analysis based on the risk score formula, and performing a multivariate COX regression analysis on the clinical factors and risk scores.

Results

A total of 62 DEGs associated with CRC lymph node metastasis were obtained. Among the 20 hub genes identified via PPI, only calcium-activated chloride channel regulator 1 (CLCA1) expression was down-regulated in lymph node metastasis, and the rest were up-regulated. A total of nine characteristic genes associated with CRC lymph node metastasis (KIF1A, TMEM59L, CLCA1, COL9A3, GDF5, TUBB2B, STMN2, FOXN1, and SCN5A) were screened using the LASSO regression method. The nine characteristic genes were significantly related to different kinds of immune cell infiltration, from which three survival-related genes (TMEM59L, CLCA1, and TUBB2B) were screened. A multi-factor COX regression showed that the risk scores obtained from TMEM59L, CLCA1, and TUBB2B were independent prognostic factors. Immunohistochemical validation was performed in tissue samples from patients with rectal and colon cancer.

Conclusion

TMEM59L, CLCA1, and TUBB2B were independent prognostic factors associated with lymphatic metastasis of CRC.

FOXN Transcription Factors: Regulation and Significant Role in Cancer

A growing number of studies have demonstrated that cancer development is closely linked to abnormal gene expression, including alterations in the transcriptional activity of transcription factors. The Forkhead box class N (FOXN) proteins FOXN1-6 form a highly conserved class of transcription factors, which have been shown in recent years to be involved in the regulation of malignant progression in a variety of cancers. FOXNs mediate cell proliferation, cell-cycle progression, cell differentiation, metabolic homeostasis, embryonic development, DNA damage repair, tumor angiogenesis, and other critical biological processes. Therefore, transcriptional dysregulation of FOXNs can directly affect cellular physiology and promote cancer development. Numerous studies have demonstrated that the transcriptional activity of FOXNs is regulated by protein-protein interactions, microRNAs (miRNA), and posttranslational modifications (PTM). However, the mechanisms underlying the molecular regulation of FOXNs in cancer development are unclear. Here, we reviewed the molecular regulatory mechanisms of FOXNs expression and activity, their role in the malignant progression of tumors, and their value for clinical applications in cancer therapy. This review may help design experimental studies involving FOXN transcription factors, and enhance their therapeutic potential as antitumor targets.

Immune Reconstitution Inflammatory Syndrome After Hematopoietic Stem Cell Transplantation in a FOXN1 -deficient Patient

The FOXN1 gene mutation is a unique disorder that causes the nude severe combined immunodeficiency phenotype. In patients with severe combined immunodeficiency, hematopoietic stem cell transplantation (HSCT) is life-saving if performed earlier. Thymic transplantation is the curative treatment for FOXN1 deficiency because the main pathology is thymic stromal changes. In this report, we describe the clinical features of a Turkish patient with a homozygous FOXN1 mutation treated with HSCT from his human leukocyte antigen-matched sibling. On follow-up, he showed Bacille Calmette Guerin adenitis and was evaluated as having immune reconstitution inflammatory syndrome. By presenting our patient, we aimed to draw attention to the development of HSCT and subsequent immune reconstitution inflammatory syndrome as a treatment option in patients with FOXN1 deficiency.

Congenital Athymia: Unmet Needs and Practical Guidance

Inborn errors of thymic stromal cell development and function which are associated with congenital athymia result in life-threatening immunodeficiency with susceptibility to infections and autoimmunity. Athymic patients can be treated by thymus transplantation using cultured donor thymus tissue. Outcomes in patients treated at Duke University Medical Center and Great Ormond Street Hospital (GOSH) over the past three decades have shown that sufficient T-cell immunity can be recovered to clear and prevent infections, but post-treatment autoimmune manifestations are relatively common. Whilst thymus transplantation offers the chance of long-term survival, significant challenges remain to optimise the outcomes for the patients. In this review, we will discuss unmet needs and offer practical guidance based on the experience of the European Thymus Transplantation programme at GOSH. Newborn screening (NBS) for severe combined immunodeficiency (SCID) and routine use of next-generation sequencing (NGS) platforms have improved early recognition of congenital athymia and increasing numbers of patients are being referred for thymus transplantation. Nevertheless, there remain delays in diagnosis, in particular when the cause is genetically undefined, and treatment accessibility needs to be improved. The majority of athymic patients have syndromic features with acute and chronic complex health issues, requiring life-long multidisciplinary and multicentre collaboration to optimise their medical and social care. Comprehensive follow up after thymus transplantation including monitoring of immunological results, management of co-morbidities and patient and family quality-of-life experience, is vital to understanding long-term outcomes for this rare cohort of patients. Alongside translational research into improving strategies for thymus replacement therapy, patient-focused clinical research will facilitate the design of strategies to improve the overall care for athymic patients.

Morbidity, Mortality, and Therapeutics in Combined Immunodeficiency: Data From the USIDNET Registry

BACKGROUND

Optimal management of patients with combined immunodeficiency, especially pertaining to hematopoietic stem cell transplantation (HSCT), remains unclear.

OBJECTIVE

To identify factors influencing HSCT and mortality in the population with combined immunodeficiency in North America.

METHODS

We identified 337 participants in the United States Immunodeficiency Network database with diverse forms of combined immunodeficiency and their characteristics, including demographic characteristics, laboratory values, infectious history, comorbidities, and treatment strategies. Univariate analysis was performed using logistic regression, whereas multivariate analysis was performed using multiple Cox proportional hazards.

RESULTS

On univariate analysis, disseminated invasive viral infections and variants in STAT3, GATA2, and, DOCK8 were associated with increased odds of HSCT. Mucocutaneous fungal infections and variants in STAT3 were associated with increased odds of survival, whereas disseminated/invasive fungal infections, disseminated/invasive viral infections, and parasitic infections were associated with decreased odds of survival. On multiple variable Cox proportional hazards analysis, variants in ZAP70, nonspecific bacterial, and disseminated/invasive viral infections were associated with increased hazards of transplantation, whereas variants in multiple genes (RMRP, NEMO, DOCK8, CD40L, and CARD9), disseminated/invasive viral infections, autoimmune disease, and higher absolute lymphocyte count were associated with increased hazards of death. Importantly, demographic characteristics, basic lymphocyte subset counts, and absence of genetic diagnosis were not associated with HSCT or mortality.

CONCLUSIONS

We determined that specific genetic diagnoses and infection burden impacts the decision to undergo HSCT in this cohort. In addition, certain genetic diagnoses and invasive viral infections carry an increased risk of mortality.

P63 targeted deletion under the FOXN1 promoter disrupts pre-and post-natal thymus development, function and maintenance as well as induces severe hair loss

Progressive immune deficiency of aging is characterized by severe thymic atrophy, contracted T cell repertoire, and poor immune function. p63 is critical for the proliferative potential of embryonic and adult stem cells, as well as thymic epithelial cells (TECs). Because p63 null mice experience rapid post-natal lethality due to epidermal and limb morphogenesis defects, studies to define a role for p63 expression in TEC biology focused on embryonic thymus development and in vitro experiments. Since post-natal thymic stromal development and function differs from that of the embryo, we assessed the impact of lineage-restricted p63 loss on pre- and post-natal murine TEC function by generating mice with a loss of p63 function targeted to TEC, termed p63TECko mice. In adult p63TECko mice, severe thymic hypoplasia was observed with a lack in a discernable segregation into medullary and cortical compartments and peripheral T cell lymphopenia. This profound thymic defect was seen in both neonatal as well as embryonic p63TECko mice. In addition to TECs, p63 also plays in important role in the development of stratified epithelium of the skin; lack of p63 results in defects in skin epidermal stratification and differentiation. Interestingly, all adult p63TECko mice lacked hair follicles despite having normal p63 expression in the skin. Together our results show a critical role of TEC p63 in thymic development and maintenance and show that p63 expression is critical for hair follicle formation.

NFAT5 Controls the Integrity of Epidermis

The skin protects the human body against dehydration and harmful challenges. Keratinocytes (KCs) are the most abundant epidermal cells, and it is anticipated that KC-mediated transport of Na⁺ ions creates a physiological barrier of high osmolality against the external environment. Here, we studied the role of NFAT5, a transcription factor whose activity is controlled by osmotic stress in KCs. Cultured KCs from adult mice were found to secrete more than 300 proteins, and upon NFAT5 ablation, the secretion of several matrix proteinases, including metalloproteinase-3 (Mmp3) and kallikrein-related peptidase 7 (Klk7), was markedly enhanced. An increase in Mmp3 and Klk7 RNA levels was also detected in transcriptomes of Nfat5^-/- KCs, along with increases of numerous members of the 'Epidermal Differentiation Complex' (EDC), such as small proline-rich (Sprr) and S100 proteins. NFAT5 and Mmp3 as well as NFAT5 and Klk7 are co-expressed in the basal KCs of fetal and adult epidermis but not in basal KCs of newborn (NB) mice. The poor NFAT5 expression in NB KCs is correlated with a strong increase in Mmp3 and Klk7 expression in KCs of NB mice. These data suggests that, along with the fragile epidermis of adult Nfat5^-/- mice, NFAT5 keeps in check the expression of matrix proteases in epidermis. The NFAT5-mediated control of matrix proteases in epidermis contributes to the manifold changes in skin development in embryos before and during birth, and to the integrity of epidermis in adults.

Generation and Evaluation of Novel Biomaterials Based on Decellularized Sturgeon Cartilage for Use in Tissue Engineering

Because cartilage has limited regenerative capability, a fully efficient advanced therapy medicinal product is needed to treat severe cartilage damage. We evaluated a novel biomaterial obtained by decellularizing sturgeon chondral endoskeleton tissue for use in cartilage tissue engineering. In silico analysis suggested high homology between human and sturgeon collagen proteins, and ultra-performance liquid chromatography confirmed that both types of cartilage consisted mainly of the same amino acids. Decellularized sturgeon cartilage was recellularized with human chondrocytes and four types of human mesenchymal stem cells (MSC) and their suitability for generating a cartilage substitute was assessed ex vivo and in vivo. The results supported the biocompatibility of the novel scaffold, as well as its ability to sustain cell adhesion, proliferation and differentiation. In vivo assays showed that the MSC cells in grafted cartilage disks were biosynthetically active and able to remodel the extracellular matrix of cartilage substitutes, with the production of type II collagen and other relevant components, especially when adipose tissue MSC were used. In addition, these cartilage substitutes triggered a pro-regenerative reaction mediated by CD206-positive M2 macrophages. These preliminary results warrant further research to characterize in greater detail the potential clinical translation of these novel cartilage substitutes.

Dosage effects of resveratrol on thymus involution in D-galactose-treated mice

The thymus regulates a specific microenvironment for the growth and maturation of naive T cells. Involution of immune function was an important factor during body aging. Preventing the senescence of immune organs has become a major medical issue. Resveratrol (RSV) has been proved to delay the aging of many organs including the thymus. However, the underlying mechanism remains indefinite and the dosages of RSV on thymus involution need to be further clarified. In the current study, the senescence-accelerated mice were produced using d-galactose for two months. RSV at different dosages (25, 50, 100 mg kg^-1  day^-1 ) was then administered. The alteration of the thymic morphological structure was observed. It showed that three dosages of RSV significantly decreased cellular senescence of the thymus and no dosage difference was detected. For cellular proliferation and apoptosis of the thymus, 50 and 25 mg/kg per day of RSV displayed the best effects on cellular proliferation and apoptosis in the thymus, respectively. Furthermore, 50 mg/kg per day of RSV increased the expression of FoxN1 both at transcription and translation levels. These findings indicated that RSV could delay thymus atrophy in a dosage-dependent pattern and FoxN1 might involve in the beneficial mechanism of RSV, which was of great significance for the enhancement of thymic health and organic immunity. PRACTICAL APPLICATIONS: Resveratrol has been proved to delay aging of many organs including of thymus. In the present study, we explored the dosage of resveratrol on thymus involution and the expression of transcription factors forkhead box protein N1 (FoxN1) in the senescenceaccelerated mice induced by D-galactose. The results indicated that resveratrol could delay thymus atrophy in a dosage-dependent pattern within a certain dose range, and higher RSV concentration may have drug toxicity, which suggests that the dosage of RSV requires attention, And FoxN1 might involve in the beneficial mechanism of resveratrol supplement, which was of great significance to explore the mechanism for the enhancement of thymus immunity.

Development of the Nude Rabbit Model

Loss-of-function mutations in the forkhead box N1 (FOXN1) gene lead to nude severe combined immunodeficiency, a rare inherited syndrome characterized by athymia, severe T cell immunodeficiency, congenital alopecia, and nail dystrophy. We recently produced FOXN1 mutant nude rabbits (NuRabbits) by using CRISPR-Cas9. Here we report the establishment and maintenance of the NuRabbit colony. NuRabbits, like nude mice, are hairless, lack thymic development, and are immunodeficient. To demonstrate the functional applications of NuRabbits in biomedical research, we show that they can successfully serve as the recipient animals in xenotransplantation experiments using human induced pluripotent stem cells or tissue-engineered blood vessels. Our work presents the NuRabbit as a new member of the immunodeficient animal model family. The relatively large size and long lifespan of NuRabbits offer unique applications in regenerative medicine, cancer research, and the study of a variety of other human conditions, including immunodeficiency.

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NuRabbit colony is established and available for the research community

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NuRabbits are nude and immunodeficient due to a mutation(s) in the FOXN1 gene

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NuRabbits support iPSC teratoma assay

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NuRabbits support xenotransplant of tissue-engineered blood vessels

When Screening for Severe Combined Immunodeficiency (SCID) with T Cell Receptor Excision Circles Is Not SCID: a Case-Based Review

Newborn screening efforts focusing on the quantification of T cell receptor excision circles (TRECs), as a biomarker for abnormal thymic production of T cells, have allowed for the identification and definitive treatment of severe combined immunodeficiency (SCID) in asymptomatic neonates. With the adoption of TREC quantification in Guthrie cards across the USA and abroad, typical, and atypical SCID constitutes only ~ 10% of cases identified with abnormal TRECs associated with T cell lymphopenia. Several other non-SCID-related conditions may be identified by newborn screening in a term infant. Thus, it is important for physicians to recognize that other factors, such as prematurity, are often associated with low TRECs initially, but often improve with age. This paper focuses on a challenge that immunologists face: the diagnostic evaluation and management of cases in which abnormal TRECs are associated with variants of T cell lymphopenia in the absence of a genetically defined form of typical or atypical SCID. Various syndromes associated with T cell impairment, secondary forms of T cell lymphopenia, and idiopathic T cell lymphopenia are identified using this screening approach. Yet there is no consensus or guidelines to assist in the evaluation and management of these newborns, despite representing 90% of the patients identified, resulting in significant work for the clinical teams until a diagnosis is made. Using a case-based approach, we review pearls relevant to the evaluation of these newborns, as well as the management dilemmas for the families and team related to the resolution of genetic ambiguities.

Expanding the Nude SCID/CID Phenotype Associated with FOXN1 Homozygous, Compound Heterozygous, or Heterozygous Mutations

Human nude SCID is a rare autosomal recessive inborn error of immunity (IEI) characterized by congenital athymia, alopecia, and nail dystrophy. Few cases have been reported to date. However, the recent introduction of newborn screening for IEIs and high-throughput sequencing has led to the identification of novel and atypical cases. Moreover, immunological alterations have been recently described in patients carrying heterozygous mutations. The aim of this paper is to describe the extended phenotype associated with FOXN1 homozygous, compound heterozygous, or heterozygous mutations. We collected clinical and laboratory information of a cohort of 11 homozygous, 2 compound heterozygous, and 5 heterozygous patients with recurrent severe infections. All, except one heterozygous patient, had signs of CID or SCID. Nail dystrophy and alopecia, that represent the hallmarks of the syndrome, were not always present, while almost 50% of the patients developed Omenn syndrome. One patient with hypomorphic compound heterozygous mutations had a late-onset atypical phenotype. A SCID-like phenotype was observed in 4 heterozygous patients coming from the same family. A spectrum of clinical manifestations may be associated with different mutations. The severity of the clinical phenotype likely depends on the amount of residual activity of the gene product, as previously observed for other SCID-related genes. The severity of the manifestations in this heterozygous family may suggest a mechanism of negative dominance of the specific mutation or the presence of additional mutations in noncoding regions.

The humanized mouse: Emerging translational potential

The humanized mouse (HM) has emerged as a valuable animal model in cancer research. Engrafted with components of a human immune system and subsequently implanted with tumor tissue from cell lines or in the form of patient-derived xenografts, the HM provides a unique platform in which the tumor microenvironment (TME) can be evaluated in vivo. This model may also be beneficial in the assessment of potential cancer treatments including immune checkpoint inhibitors. However, to maximize its utility, researchers need to understand the critical factors necessary to ensure that the tumor immune interactions in the HM are representative of those within cancer patients. In most current HM models, the human T cells residing in the HM are educated in a murine thymus, allogeneic to implanted tumor tissue, and/or alloreactive to mouse tissues, making their interaction and reactivity with tumor cells suspect. There are several strategies underway to harmonize the immune-tumor environment in the HM. Once the essential components of the HM-tumor TME interface have been identified and understood, the HM model will permit not only the discovery of effective immunotherapy treatments, but it can be used to predict patient responses to great clinical benefit.

Heterozygous FOXN1 Variants Cause Low TRECs and Severe T Cell Lymphopenia, Revealing a Crucial Role of FOXN1 in Supporting Early Thymopoiesis

FOXN1 is the master regulatory gene of thymic epithelium development. FOXN1 deficiency leads to thymic aplasia, alopecia, and nail dystrophy, accounting for the nude/severe combined immunodeficiency (nu/SCID) phenotype in humans and mice. We identified several newborns with low levels of T cell receptor excision circles (TRECs) and T cell lymphopenia at birth, who carried heterozygous loss-of-function FOXN1 variants. Longitudinal analysis showed persistent T cell lymphopenia during infancy, often associated with nail dystrophy. Adult individuals with heterozygous FOXN1 variants had in most cases normal CD4+ but lower than normal CD8+ cell counts. We hypothesized a FOXN1 gene dosage effect on the function of thymic epithelial cells (TECs) and thymopoiesis and postulated that these effects would be more prominent early in life. To test this hypothesis, we analyzed TEC subset frequency and phenotype, early thymic progenitor (ETP) cell count, and expression of FOXN1 target genes (Ccl25, Cxcl12, Dll4, Scf, Psmb11, Prss16, and Cd83) in Foxn1nu/+ (nu/+) mice and age-matched wild-type (+/+) littermate controls. Both the frequency and the absolute count of ETP were significantly reduced in nu/+ mice up to 3 weeks of age. Analysis of the TEC compartment showed reduced expression of FOXN1 target genes and delayed maturation of the medullary TEC compartment in nu/+ mice. These observations establish a FOXN1 gene dosage effect on thymic function and identify FOXN1 haploinsufficiency as an important genetic determinant of T cell lymphopenia at birth.

[Ectopic thymic tissue and ectopic thymic tumors]

Ectopic thymic tissue outside its core position in the antero-superior mediastinum is quite common owing to the complexity of embryonal thymus development, whereby reported prevalence values (1 to 90%) are heavily dependent on the method of investigation and the intensity of the workup. The debated prevalence and relevance of ectopic thymic tissue and its accessibility underlie the ongoing discussion whether modern, minimally invasive thymectomy strategies can match the proven benefit of the radical transsternal thymectomy procedure for the treatment of Myasthenia gravis. In this context, the following article covers the etiology, prevalence, and location of normal-looking, reactive, and neoplastic ectopic thymic tissue. Furthermore, ectopic tissues and tumors inside or adjacent to the thymus are mentioned.

Clinical, Immunological, and Molecular Features of Typical and Atypical Severe Combined Immunodeficiency: Report of the Italian Primary Immunodeficiency Network

Severe combined immunodeficiencies (SCIDs) are a group of inborn errors of the immune system, usually associated with severe or life-threatening infections. Due to the variability of clinical phenotypes, the diagnostic complexity and the heterogeneity of the genetic basis, they are often difficult to recognize, leading to a significant diagnostic delay (DD). Aim of this study is to define presenting signs and natural history of SCID in a large cohort of patients, prior to hematopoietic stem cell or gene therapies. To this purpose, we conducted a 30-year retro-prospective multicenter study within the Italian Primary Immunodeficiency Network. One hundred eleven patients, diagnosed as typical or atypical SCID according to the European Society for Immune Deficiencies criteria, were included. Patients were subsequently classified based on the genetic alteration, pathogenic mechanism and immunological classification. A positive relationship between the age at onset and the DD was found. SCID patients with later onset were identified only in the last decade of observation. Syndromic SCIDs represented 28% of the cohort. Eight percent of the subjects were diagnosed in Intensive Care Units. Fifty-three percent had an atypical phenotype and most of them exhibited a discordant genotype-immunophenotype. Pre-treatment mortality was higher in atypical and syndromic patients. Our study broadens the knowledge of clinical and laboratory manifestations and genotype/phenotype correlation in patients with SCID and may facilitate the diagnosis of both typical and atypical forms of the disease in countries where newborn screening programs have not yet been implemented.

Epstein-Barr virus associated with high-grade B-cell lymphoma in nude severe combined immunodeficiency

Severe combined immunodeficiency (SCID) is an extremely rare disease caused by a disruption in the forkhead box N1 (FOXN1) gene, with an incidence of <1 per 1 000 000 live births. We report a boy aged 4 months who presented with a history of fever for 3 weeks and enlarged lymph nodes. The fever was associated with dry cough and runny nose. On physical examination, we noted oral thrush, generalised lymphadenopathy, nail dystrophy and alopecia. Flow cytometry of lymph node biopsy showed high-grade B-cell lymphoma. In addition, Epstein-Barr virus (EBV) infection was documented by PCR. The diagnosis of SCID was made by genetic testing, which revealed a homozygous variant of the FOXN1 gene. The variant was confirmed with Sanger sequencing. Management of EBV infection and lymphoma was initiated; unfortunately, the patient passed away on day 45 of hospitalisation.

Thymic stromal cells: Roles in atrophy and age-associated dysfunction of the thymus

Atrophy of the thymus, the primary site of T lymphocyte generation, is a hallmark of the aging immune system. Age-associated thymic atrophy results in diminished output of new, naïve T cells, with immune sequelae that include diminished responses to novel pathogenic challenge and vaccines, as well as diminished tumor surveillance. Although a variety of stimuli are known to regulate transient thymic atrophy, mechanisms governing progressive age-associated atrophy have been difficult to resolve. This has been due in part to the fact that one of the primary targets of age-associated thymic atrophy is a relatively rare population, thymic stromal cells. This review focuses on changes in thymic stromal cells during aging and on the contributions of periodic, stochastic, and progressive causes of thymic atrophy.