The Effects of Stimulation with PMA/Ionomycin on CD4+ T cell Proliferation and Surface CD4 Molecule Modulation of Patients with LRBA Deficiency and CVID with the Unsolved Genetic Defect

Background: Common variable immunodeficiency (CVID) is the most prevalent symptomatic primary immunodeficiencies. LPS-responsive beige-like anchor protein (LRBA) deficiency is a combined immunodeficiency characterized by a CVID-like phenotype. Affected patients by LRBA and CVID present a wide range of clinical manifestations, including hypogammaglobulinemia, recurrent infections, autoimmunity, as well as T cell abnormality. Methods: The study population comprised of patients with CVID (n=10), LRBA deficiency (n=11), and healthy controls (n=12). CD4+ T cell frequency and CD4 MFI (mean fluorescence intensity) were evaluated using flow cytometry before and after stimulation with PMA/ION. Results: The frequencies of CD4+ T cells were significantly lower in patients with LRBA deficiency than in HCs before and after treatment. In the unstimulated state, the CD4+ T cells frequency in CVID patients was significantly lower than in HCs. There were no statistically significant differences between patients and healthy individuals in CD4+ T cell proliferation. Compared to HCs, LRBA and CVID patients showed a lower CD4 MFI in unstimulated conditions. Furthermore, CD4 MFI decreased in both patients and the control group following activation. Conclusion : Despite the reported decrease in CD4+ T cell frequency in patients with CVID and LRBA deficiency, our findings demonstrated that their CD4+ T cells have a normal proliferative response to stimuli similar to healthy individuals.

Different Apples, Same Tree: Visualizing Current Biological and Clinical Insights into CTLA-4 Insufficiency and LRBA and DEF6 Deficiencies

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.

Case Report: Infantile-Onset Fulminant Type 1 Diabetes Mellitus Caused by Novel Compound Heterozygous LRBA Variants

Lipopolysaccharide-responsive beige-like anchor (LRBA) deficiency is a subtype of common variable immune deficiency (CVID). Numerous case reports and cohort studies have described a broad spectrum of clinical manifestations and variable disease phenotypes, including immune dysregulation, enteropathy, and recurrent infections. Although LRBA deficiency is an autosomal recessive primary immunodeficiency resulting in a phenotype similar to CVID, it is a monogenic disease and separate from CVID. Recently, in a report of monogenic primary immunodeficiency disorder associated with CVID and autoimmunity, the most common mutated gene was LRBA. We report the case of a girl who presented with fulminant type 1 diabetes at age 7 months. She later experienced recurrent bacterial infections with neutropenia and idiopathic thrombocytopenic purpura. Clinical genome sequencing revealed compound heterozygosity of the LRBA gene, which bore two novel mutations. A genetic basis should be considered in the differential diagnosis for very young patients with fulminant autoimmunity, and the diagnostic work-up should include evaluation of markers of immunodeficiency.

DEFICIENCY OF LRBA: BIBLIOGRAPHICAL REVIEW AND CASE REPORT

Since the description of the first primary immunodeficiencies (PIDs) in the 50–60s of the last century, they have been the subject of intensive research aimed at elucidating their etiology and finding effective treatments. The development of next-generation sequencing (NGS) methods made it possible to reveal the genetic basis of many new forms of PID, which were previously attributed to various syndromes due to their clinical and immunological characteristics. An example of such a PID is the LRBA (the lipopolysaccharide-responsive and beige-like anchor protein) deficiency, sometimes called LATAIE [LRBA deficiency with autoantibodies, regulatory T (Treg) cell defects, autoimmune infiltration, and enteropathy]. The article provides information on the main role of the LRBA molecule in the functions of immunocompetent cells, describes immunological disorders and clinical manifestations of LRBA deficiency and the principles of treatment of diseases. Two own observations of LRBA deficiency are presented.

Autoimmune Cytopenias in Nonmalignant Lymphoproliferative Disorders: Thinking Beyond ALPS(Autoimmune Lymphoproliferative Syndrome)

The ALPS Clinic at NIH has studied autoimmune lymphoproliferative disorders for over 30 years elucidating the genetic underpinnings and natural history of Autoimmune Lymphoproliferative Syndrome (ALPS) due to FAS gene defects (Blood 2014). Over the years, we continue to receive and work-up numerous referrals for diseases that masquerade like ALPS-FAS, presenting with multi-lineage cytopenias due to autoimmune peripheral destruction and splenic sequestration in the setting of non-malignant lymphoproliferation. In a review of 259 cases evaluated by our team, there were 150 ALPS-FAS, 54 Activated PI3K-delta Syndrome (APDS), 31 CTLA-4 Haploinsufficiency (CTLA4), 7 LRBA deficiency (LRBA), and 17 MAGT-1 deficiency (XMEN) patients. Non-malignant lymphadenopathy and splenomegaly occurred on average in 83% and 71% of all patients, respectively. Anemia, thrombocytopenia, and neutropenia were seen in 65%, 58%, and 46%, respectively. Thus, autoimmune cytopenias in the setting of non-malignant lymphoproliferation in themselves are not adequate to rule in or rule out a presumptive diagnosis of ALPS-FAS. Timely and accurate genetic diagnosis of ALPS-like conditions will improve the morbidity and mortality associated with these disease processes. Rapamycin, an m-TOR inhibitor provides salutary benefits for many of these conditions by restoring the TREG function and reversing immune-dysregulation. For example, in addition to lymphadenopathy and splenomegaly associated with an increased risk of malignant lymphoma like ALPS-FAS patients, APDS patients usually present with recurrent sinopulmonary and ear infections. Their serum IgM tends to be elevated with low IgG levels. Unlike for ALPS-FAS patients, a potential targeted treatment for APDS exists: Leniolisib, a targeted PI3Kinase p-110 delta inhibitor is currently undergoing clinical trials (Blood 2016). CTLA-4 is critical for T-cell activation and immune check-point regulation by tempering regulatory T cell function. Patients affected by CTLA4 and LRBA variants present with symptoms of lymphocytic infiltration of the bone marrow (often leading to hypoplastic anemia), gut (colitis, bowel obstruction), lungs (bronchiectasis, restrictive airway disease), and central nervous system (seizures and neurological deficits due to brain and spinal cord lesions). They also tend to have B cell lymphopenia, low IgG and IgM levels. CTLA4 and LRBA patients share pathophysiology as well as clinical phenotype because LRBA gene regulates intracellular lysosomal trafficking and recycling of CTLA-4 protein. Hence CTLA-4 haploinsufficiency or LRBA deficiency renders both patient types CTLA-4 deficient. This can be directly addressed with abatacept infusions, a CTLA-4 hybridized immunoglobulin given as a combination immunosuppressive therapy with rapamycin. Abatacept replaces the CTLA-4 molecule and reverses some of the immune dysregulation and thus morbidity associated with both CTLA4 and LRBA deficiency. Like APDS patients, XMEN patients are also prone to recurrent ear and sinopulmonary infection, but key differentiating features of this X-linked disorder are that only males are affected, these patients are unable to clear Epstein-Barr virus (EBV) once exposed, and they have a propensity to develop EBV-driven lymphomas. These patients also usually have a strong family history of multiple lymphomas in males. Even though a targeted treatment does not yet exist, steroid-sparing measures such as rituximab, rapamycin and mycophenolate mofetil are the first-line treatments often used in managing their refractory autoimmune cytopenias. Hence accurate early genetic diagnosis is key to accessing the appropriate treatment, thus decreasing the morbidity and mortality associated with these childhood onset ALPS-like rare inherited disorders (table). Table Disclosures No relevant conflicts of interest to declare. OffLabel Disclosure: Rapamycin, Abatacept, Mycophenolate Mofetil.

Modern view on LRBA deficiency

Facilities of molecular genetic methods allow to distinguish several monogenic deficiencies in the general group of primary immunodeficiencies, including common variable immune deficiency (CVID), which have peculiarities of the natural course, therapy, and prognosis. One of these nosologies is LRBA deficiency. In this article a number of foreign sources were reviewed, systematized and classified to define a comprehensive understanding of the LRBA deficiency phenomenon . The most relevant scientific studies of North America and Europe and publications from various ranking medical journals were analyzed. LRBA deficiency is a PID caused by mutations inLRBAgene that disrupt the immune system regulation. It is characterized by lymphoproliferation, autoaggression, hypogammaglobulinemia and recurrent infections. Sometimes LRBA deficiency is called LATAIE disease (LRBA deficiency with autoantibodies, regulatory T-cell defects, autoimmune infiltration, and enteropathy). Special attention was given to the mutation ofLRBAgene and the connection to the defects caused in T- and B-lymphocytes, the clinical picture and diagnostics. It was suggested that LRBA protein reduces the level of autophagy, leading to increased apoptosis, impared T- and B-cell immune response, lymphoproliferation and autoimmune disorders. LRBA protein is especially expressed in the immune cells, its deficiency leads to defects of B-cells differentiation. However, LRBA deficiency does not affect T-regulatory cells differentiation. Main approaches to the treatment of patients with LRBA deficiency are presented in the article. Methods of systemic and content analysis of Russian and foreign sources were used when writing the article.