PROMIDISα: A T-cell receptor α signature associated with immunodeficiencies caused by V(D)J recombination defects

Background: V(D)J recombination ensures the diversity of the adaptive immune system. Although its complete defect causes severe combined immunodeficiency (ie, T⁻B⁻ severe combined immunodeficiency), its suboptimal activity is associated with a broad spectrum of immune manifestations, such as late-onset combined immunodeficiency and autoimmunity. The earliest molecular diagnosis of these patients is required to adopt the best therapy strategy, particularly when it involves a myeloablative conditioning regimen for hematopoietic stem cell transplantation. Objective: We aimed at developing biomarkers based on analysis of the T-cell receptor (TCR) α repertoire to assist in the diagnosis of patients with primary immunodeficiencies with V(D)J recombination and DNA repair deficiencies. Methods: We used flow cytometric (fluorescence-activated cell sorting) analysis to quantify TCR-Vα7.2–expressing T lymphocytes in peripheral blood and developed PROMIDISα a multiplex RT-PCR/next-generation sequencing assay, to evaluate a subset of the TCRα repertoire in T lymphocytes. Results: The combined fluorescence-activated cell sorting and PROMIDISα analyses revealed specific signatures in patients with V(D)J recombination–defective primary immunodeficiencies or ataxia telangiectasia/Nijmegen breakage syndromes. Conclusion: Analysis of the TCRα repertoire is particularly appropriate in a prospective way to identify patients with partial immune defects caused by suboptimal V(D)J recombination activity, a DNA repair defect, or both. It also constitutes a valuable tool for the retrospective in vivo functional validation of variants identified through exome or panel sequencing. Its broader implementation might be of interest to assist early diagnosis of patients presenting with hypomorphic DNA repair defects inclined to experience acute toxicity during prehematopoietic stem cell transplantation conditioning.