Inborn errors of immunity associated with defects of thymic development

Thymic inborn errors of immunity

The thymus is crucial for optimal T-cell development by facilitating the generation and selection of a diverse repertoire of T cells that can recognize foreign antigens while promoting tolerance to self-antigens. A number of inborn errors of immunity causing complete or partial defects in thymic development (athymia) and/or impaired thymic function have been increasingly recognized that manifest clinically with a combination of life-threatening infections, severe multiorgan autoimmunity, and/or cardiac, craniofacial, ectodermal, and endocrine abnormalities. The introduction of newborn screening programs and the advent of thymic transplantation show promise for early detection and improving the outcomes of patients with certain thymic inborn errors of immunity. We discuss our current understanding of the genetics, immunopathogenesis, diagnosis, and treatment of inborn errors of immunity that impair thymic development and/or function.

Rediscovering the human thymus through cutting-edge technologies

Recent technological advances have transformed our understanding of the human thymus. Innovations such as high-resolution imaging, single-cell omics, and organoid cultures, including thymic epithelial cell (TEC) differentiation and culture, and improvements in biomaterials, have further elucidated the thymus architecture, cellular dynamics, and molecular mechanisms underlying T cell development, and have unraveled previously unrecognized levels of stromal cell heterogeneity. These advancements offer unprecedented insights into thymic biology and hold promise for the development of novel therapeutic strategies for immune-related disorders.

IL-7-dependent and -independent lineages of IL-7R-dependent human T cells

Infants with biallelic IL7R loss-of-function variants have severe combined immune deficiency (SCID) characterized by the absence of autologous T lymphocytes, but normal counts of circulating B and NK cells (T-B+NK+ SCID). We report 6 adults (aged 22 to 59 years) from 4 kindreds and 3 ancestries (Colombian, Israeli Arab, Japanese) carrying homozygous IL7 loss-of-function variants resulting in combined immunodeficiency (CID). Deep immunophenotyping revealed relatively normal counts and/or proportions of myeloid, B, NK, and innate lymphoid cells. By contrast, the patients had profound T cell lymphopenia, with low proportions of innate-like adaptive mucosal-associated invariant T and invariant NK T cells. They also had low blood counts of T cell receptor (TCR) excision circles, recent thymic emigrant T cells and naive CD4+ T cells, and low overall TCR repertoire diversity, collectively indicating impaired thymic output. The proportions of effector memory CD4+ and CD8+ T cells were high, indicating IL-7-independent homeostatic T cell proliferation in the periphery. Intriguingly, the proportions of other T cell subsets, including TCRγδ+ T cells and some TCRαβ+ T cell subsets (including Th1, Tfh, and Treg) were little affected. Peripheral CD4+ T cells displayed poor proliferation, but normal cytokine production upon stimulation with mitogens in vitro. Thus, inherited IL-7 deficiency impairs T cell development less severely and in a more subset-specific manner than IL-7R deficiency. These findings suggest that another IL-7R-binding cytokine, possibly thymic stromal lymphopoietin, governs an IL-7-independent pathway of human T cell development.

Health-related quality of life in patients with inborn errors of immunity: A systematic review and meta-analysis

BACKGROUND

Inborn Errors of Immunity (IEI) significantly affect patients' health-related quality of life (HRQOL), presenting greater challenges than those faced by the healthy population and other chronic disease sufferers. Current research lacks comprehensive integration of this critical issue.

OBJECTIVE

This study explores HRQOL in IEI patients, identifies impacting factors, and advocates for increased research focus on their quality of life.

METHODS

Following systematic review and meta-analysis guidelines, a search of Scopus and PubMed until November 15, 2023, yielded 1633 publications. We evaluated the literature, assessed study quality, and compared the HRQOL of IEI patients to that of healthy individuals and other chronic disease patients.

RESULTS

Of 90 articles and 10,971 IEI patients analyzed, study quality varied (nine good, 63 moderate, and 18 poor). The Short Form-36 (SF-36) and Pediatric Quality of Life Inventory generic core scales (PedsQL) were the primary generic instruments used among adults and children, respectively, with 12 studies each using the disease-specific instruments. Meta-analysis showed IEI patients have significantly lower scores in general health, physical and mental health, and social and emotional roles compared to healthy populations. We noted significant differences between self and proxy reports, indicating caregiver anxiety and perception disparities.

CONCLUSION

Despite limitations like small sample sizes and reliance on generic instruments, this research underscores the substantially lower HRQOL among IEI patients, emphasizing the need for a patient-centered, multidisciplinary approach to improve their life quality and calling for more focused attention on IEI patients and their caregivers' HRQOL.

Health-related quality of life in patients with inborn errors of immunity: a bibliometric analysis

Background

Inborn Errors of Immunity (IEI) are characterized by a heightened susceptibility to infections, allergies, and various other health complications. Health-Related Quality of Life (HRQOL) in patients with IEI is a critical area of research that demands attention due to the impact of IEI on patients' lives. This study utilized bibliometric methods, aiming to comprehensively explore the research content and hotspots in the field of HRQOL in patients with IEI.

Methods

This bibliometric analysis utilized data from the Science Citation Index Expanded (SCIE) and Social Sciences Citation Index (SSCI) within the Web of Science core datasets up to January 1, 2024. The study focused on literature that addressed HRQOL in IEI patients, involving a total of 1,807 authors and 309 articles published across 112 journals. The analysis included publication volume and growth trends, country and institutional contributions, authorship, and journal analysis.

Results

The research found that despite the importance of HRQOL in IEI, the volume of publications in this field remains consistently low, with no significant increase in trend. The USA leads in publication and citation volumes, reflecting a geographical imbalance in research contributions. Key journals in this field include the Journal of Clinical Immunology, Frontiers in Immunology, and the Journal of Allergy and Clinical Immunology. The study highlights that while treatments like hematopoietic stem cell transplants and gene therapy have improved patient IEI survival rates, they still often come with significant side effects impacting HRQOL. The analysis underlines the need for comprehensive HRQOL assessments in IEI, considering the physical and psychological impacts of treatments.

Conclusions

This study represents a bibliometric analysis focusing on HRQOL in patients with. It underscores the need for more extensive and systematic research in this area, emphasizing the importance of a multidisciplinary approach. Despite advancements in medical treatments for IEI, there is a crucial need to focus on HRQOL to enhance patient satisfaction and overall well-being. The findings advocate for more personalized treatment plans and a better understanding of the psychosocial needs of patients with IEI to improve their quality of life.

Primary and secondary defects of the thymus

The thymus is the primary site of T-cell development, enabling generation, and selection of a diverse repertoire of T cells that recognize non-self, whilst remaining tolerant to self- antigens. Severe congenital disorders of thymic development (athymia) can be fatal if left untreated due to infections, and thymic tissue implantation is the only cure. While newborn screening for severe combined immune deficiency has allowed improved detection at birth of congenital athymia, thymic disorders acquired later in life are still underrecognized and assessing the quality of thymic function in such conditions remains a challenge. The thymus is sensitive to injury elicited from a variety of endogenous and exogenous factors, and its self-renewal capacity decreases with age. Secondary and age-related forms of thymic dysfunction may lead to an increased risk of infections, malignancy, and autoimmunity. Promising results have been obtained in preclinical models and clinical trials upon administration of soluble factors promoting thymic regeneration, but to date no therapy is approved for clinical use. In this review we provide a background on thymus development, function, and age-related involution. We discuss disease mechanisms, diagnostic, and therapeutic approaches for primary and secondary thymic defects.

Thymic Atrophy and Immune Dysregulation in Infants with Complex Congenital Heart Disease

Congenital heart disease (CHD) is the most common birth defect, and up to 50% of infants with CHD require cardiovascular surgery early in life. Current clinical practice often involves thymus resection during cardiac surgery, detrimentally affecting T-cell immunity. However, epidemiological data indicate that CHD patients face an elevated risk for infections and immune-mediated diseases, independent of thymectomy. Hence, we examined whether the cardiac defect impacts thymus function in individuals with CHD. We investigated thymocyte development in 58 infants categorized by CHD complexity. To assess the relationship between CHD complexity and thymic function, we analyzed T-cell development, thymic output, and biomarkers linked to cardiac defects, stress, or inflammation. Patients with highly complex CHD exhibit thymic atrophy, resulting in low frequencies of recent thymic emigrants in peripheral blood, even prior to thymectomy. Elevated plasma cortisol levels were detected in all CHD patients, while high NT-proBNP and IL-6 levels were associated with thymic atrophy. Our findings reveal an association between complex CHD and thymic atrophy, resulting in reduced thymic output. Consequently, thymus preservation during cardiovascular surgery could significantly enhance immune function and the long-term health of CHD patients.

A guide to thymic selection of T cells

The thymus is an evolutionarily conserved organ that supports the development of T cells. Not only does the thymic environment support the rearrangement and expression of diverse T cell receptors but also provides a unique niche for the selection of appropriate T cell clones. Thymic selection ensures that the repertoire of available T cells is both useful (being MHC-restricted) and safe (being self-tolerant). The unique antigen-presentation features of the thymus ensure that the display of self-antigens is optimal to induce tolerance to all types of self-tissue. MHC class-specific functions of CD4+ T helper cells, CD8+ killer T cells and CD4+ regulatory T cells are also established in the thymus. Finally, the thymus provides signals for the development of several minor T cell subsets that promote immune and tissue homeostasis. This Review provides an introductory-level overview of our current understanding of the sophisticated thymic selection mechanisms that ensure T cells are useful and safe.

Early Is the Key for Treatment of Severe Combined Immunodeficiency

This Pillars of Immunology article is a commentary on “Hematopoietic stem cell transplantation for severe combined immunodeficiency in the neonatal period leads to superior thymic output and improved survival,” a pivotal article written by L. A. Myers, D. D. Patel, J. M. Puck, and R. H. Buckley, and published in Blood, in 2002. https://pubmed.ncbi.nlm.nih.gov/11806989/.