Different Apples, Same Tree: Visualizing Current Biological and Clinical Insights into CTLA-4 Insufficiency and LRBA
Laura Gámez-Díaz1, Markus G Seidel2,3
1Faculty of Medicine, Center for Chronic Immunodeficiency, Institute for Immunodeficiency, Medical Center, Albert-Ludwigs-University of Freiburg, Freiburg, Germany.
Abstract:
Cytotoxic T lymphocyte antigen-4 (CTLA-4) is a crucial immune checkpoint that is constitutively expressed in regulatory T (Treg) cells. Following T-cell activation, CTLA-4 is rapidly mobilized from its intracellular vesicle pool to the cell surface to control the availability of co-stimulatory B7 molecules, thereby maintaining immune homeostasis. Heterozygous mutations in CTLA-4 lead to defects in (i) CTLA-4 ligand binding, (ii) homo-dimerization, (iii) B7-transendocytosis, and (iv) CTLA-4 vesicle trafficking, resulting in an inborn error of immunity with predominant autoimmunity. CTLA-4 vesicle trafficking impairment is also observed in patients with lipopolysaccharide-responsive beige-like anchor protein (LRBA) deficiency or the differentially expressed in FDCP6 homolog (DEF6) deficiency, caused by biallelic mutations in LRBA and DEF6, respectively. Therefore, patients with CTLA-4 insufficiency, LRBA deficiency, and-most recently reported-DEF6 deficiency present an overlapping clinical phenotype mainly attributed to a defective suppressive activity of Tregs, as all three diseases reduce overall surface expression of CTLA-4. In this paper, we describe the clinical phenotypes of these immune checkpoint defects, their patho-mechanisms, and visually compare them to other immune regulatory disorders (IPEX syndrome, CD27, and CD70 deficiencies) by using the immune deficiency and dysregulation (IDDA version 2.1) "kaleidoscope" score. This illustrates the variability of the degrees and manifestations of immune deficiency and dysregulation. Patients characteristically present with an increased risk of infections, autoimmune cytopenias, multi-organ autoimmunity, and inflammation, which are often severe and life-threatening. Furthermore, these patients suffer an increased risk of developing malignancies, especially Non-Hodgkin's lymphoma. Successful treatment options include regular administration of soluble CTLA-4-Ig fusion protein, Treg cell-sparing immune suppressants like sirolimus or mycophenolate mofetil, and hematopoietic stem cell transplantation. This mini-review highlights the most relevant biological and clinical features as well as treatment options for CTLA-4 insufficiency and LRBA and DEF6 deficiencies.
Insights
Defects in Cytotoxic T lymphocyte antigen-4 (CTLA-4), LRBA, and DEF6 cause immune dysregulation, leading to autoimmunity and infections. Treatment involves CTLA-4-Ig, immunosuppressants, or stem cell transplant.
Area of Science:
- Immunology
- Genetics
- Clinical Medicine
Background:
- Cytotoxic T lymphocyte antigen-4 (CTLA-4) is a key immune checkpoint on regulatory T (Treg) cells, crucial for immune homeostasis.
- Mutations in CTLA-4, LRBA, and DEF6 impair Treg function, leading to overlapping immune dysregulation phenotypes.
- These conditions result in reduced CTLA-4 surface expression, impacting immune suppression.
Purpose of the Study:
- To describe the clinical phenotypes and pathomechanisms of CTLA-4, LRBA, and DEF6 deficiencies.
- To compare these immune checkpoint defects with other immune regulatory disorders using a novel scoring system.
- To highlight current and potential treatment strategies for these conditions.
Main Methods:
- Review of clinical phenotypes and genetic defects associated with CTLA-4, LRBA, and DEF6 deficiencies.
- Utilizing the Immune Deficiency and Dysregulation (IDDA version 2.1) 'kaleidoscope' score for comparative analysis.
- Summarizing established and emerging treatment options.
Main Results:
- Patients exhibit severe infections, cytopenias, multi-organ autoimmunity, and inflammation.
- An increased risk of malignancies, particularly Non-Hodgkin's lymphoma, is observed.
- CTLA-4 insufficiency, LRBA deficiency, and DEF6 deficiency share overlapping clinical features due to impaired Treg suppressive activity.
Conclusions:
- CTLA-4, LRBA, and DEF6 deficiencies represent a spectrum of immune dysregulation with significant clinical impact.
- Early diagnosis and intervention are critical for managing these life-threatening conditions.
- Treatment strategies including CTLA-4-Ig, Treg-sparing immunosuppressants, and HSCT offer therapeutic options.
