Common Variable Immunodeficiency Caused by FANC Mutations

Common variable immunodeficiency (CVID) is the most common adult-onset primary antibody deficiency disease due to various causative genes. Several genes, which are known to be the cause of different diseases, have recently been reported as the cause of CVID in patients by performing whole exome sequencing (WES) analysis. Here, we found FANC gene mutations as a cause of adult-onset CVID in two patients. B cells were absent and CD4⁺ T cells were skewed toward CD45RO⁺ memory T cells. T-cell receptor excision circles (TRECs) and signal joint kappa-deleting recombination excision circles (sjKRECs) were undetectable in both patients. Both patients had no anemia, neutropenia, or thrombocytopenia. Using WES, we identified compound heterozygous mutations of FANCE in one patient and homozygous mutation of FANCA in another patient. The impaired function of FANC protein complex was confirmed by a monoubiquitination assay and by chromosome fragility test. We then performed several immunological evaluations including quantitative lymphocyte analysis and TRECs/sjKRECs analysis for 32 individuals with Fanconi anemia (FA). In total, 22 FA patients (68.8%) were found to have immunological abnormalities, suggesting that such immunological findings may be common in FA patients. These data indicate that FANC mutations are involved in impaired lymphogenesis probably by the accumulation of DNA replication stress, leading to CVID. It is important to diagnose FA because it drastically changes clinical management. We propose that FANC mutations can cause isolated immunodeficiency in addition to bone marrow failure and malignancy.

Loss of Fancc Impairs Antibody-Secreting Cell Differentiation in Mice through Deregulating the Wnt Signaling Pathway

Fanconi anemia (FA) is characterized by a progressive bone marrow failure and an increased incidence of cancer. FA patients have high susceptibility to immune-related complications such as infection and posttransplant graft-versus-host disease. In this study, we investigated the effect of FA deficiency in B cell function using the Fancc mouse model. Fancc(-/-) B cells show a specific defect in IgG2a switch and impaired Ab-secreting cell (ASC) differentiation. Global transcriptome analysis of naive B cells by mRNA sequencing demonstrates that FA deficiency deregulates a network of genes involved in immune function. Significantly, many genes implicated in Wnt signaling were aberrantly expressed in Fancc(-/-) B cells. Consistently, Fancc(-/-) B cells accumulate high levels of β-catenin under both resting and stimulated conditions, suggesting hyperactive Wnt signaling. Using an in vivo Wnt GFP reporter assay, we verified the upregulation of Wnt signaling as a potential mechanism responsible for the impaired Fancc(-/-) B cell differentiation. Furthermore, we showed that Wnt signaling inhibits ASC differentiation possibly through repression of Blimp1 and that Fancc(-/-) B cells are hypersensitive to Wnt activation during ASC differentiation. Our findings identify Wnt signaling as a physiological regulator of ASC differentiation and establish a role for the Wnt pathway in normal B cell function and FA immune deficiency.

Immunological profile of Fanconi anemia: a multicentric retrospective analysis of 61 patients

In this study, the immunological status of 61 patients with Fanconi anemia (FA) with advanced marrow failure before hematopoietic stem cell transplantation was analyzed by assessing the phenotype of peripheral blood lymphocytes, serum immunoglobulin (Ig) levels, and inflammatory cytokines. In patients with FA, total absolute lymphocytes (P < 0.0001), B cells (P < 0.0001), and NK cells (P = 0.003) were reduced when compared with normal controls. T cells (CD3), that is, cytotoxic T cells, naïve T cells, and regulatory T cells, showed a relative increase when compared with controls. Serum levels of IgG (P < 0.0001) and IgM (P = 0.004) were significantly lower, whereas IgA level was higher (P < 0.0001) than in normal controls. TGF-β (P = 0.007) and interleukin (IL)-6 (P = 0.0007) levels were increased in the serum of patients when compared with controls, whereas sCD40L level decreases (P < 0.0001). No differences were noted in the serum levels of IL-1β, IL-2, IL-4, IL-10, IL-13, IL-17, and IL-23 between FA subjects and controls. This comprehensive immunological study shows that patients with FA with advanced marrow failure have an altered immune status. This is in accordance with some characteristics of FA such as the proinflammatory and proapoptotic status. In addition, B lymphocyte failure may make tight and early immunological monitoring advisable.