Identifying Primary Immune Deficiencies in Patients with Autoimmune Cytopenias

Objective: The purpose of this study is to increase awareness and improve diagnosis of primary immune deficiency (PID) in the heterogenous group of patients with autoimmune cytopenia (AIC) by identifying clinical characteristics and laboratory biomarkers that distinguish PID patients from patients with AIC alone. This is especially relevant in genetically-defined PIDs which may be resistant to conventional therapy and mechanism-based treatment approach is required. Evans syndrome, defined by multi-lineage autoantibodies (two or more positive anti-platelet, anti-neutrophil, or direct Coombs test) is a known risk factor for PID; therefore we also investigate the incidence of PID in a broad cohort of AIC patients with single and multi-lineage cytopenias.

Methods: Patients with autoimmune cytopenias (autoimmune hemolytic anemia (AIHA), immune thrombocytopenia (ITP), or autoimmune neutropenia (AIN)) were referred to our Immune Dysregulation clinical team and prospectively enrolled in the study period of 2016-2019. Detailed immune phenotyping (IgG, IgA, IgM, lymphocyte subsets, vaccine titers, lymphocyte proliferation to mitogens/antigens), serum lipopolysaccharide (LPS) and autoantibodies were measured and/or collected by chart review and genetic testing for PID was pursued.

Results: From 2016 to 2019, 78 patients were enrolled to our study. The patients were predominantly children (ages 1-82 years, average age 16.82 years). Of 78 patients with AIC, 48 (61%) were diagnosed with underlying PID based on immune phenotyping and/or genetic testing. Of 39 patients with genetic testing to date, 19 (49%) have been diagnosed with genetically-defined PID (pathogenic variants in CTLA-4, NFKB1, ALPS-related genes, WAS, POLE-1, PI3K, CYBB, or 22q11 [partial DiGeorge syndrome]); the remainder were classified as combined immune deficiency or common variable immune deficiency based on immune phenotyping; an additional two patients were classified as ALPS based on clinical history/flow cytometry/family history of ALPS. Lymphocyte subsets (CD4+ T, CD8+ T, CD19+ B, CD56+ NK) and immune globulins (IgG, IgA, IgM) tended to be lower in AIC-PID patients vs AIC-only (p<0.05). Evans syndrome was more commonly found in AIC-PID patients (13/31, 42%) compared to AIC-only (4/42, 10%). LPS was significantly elevated in the serum of AIC patients compared to healthy controls (mean 719 vs 87 pg/mL, p<0.001). Excluding partial DiGeorge syndrome patients (average LPS 222pg/mL), LPS levels were significantly higher in genetically-defined untreated PID patients (average 1463 pg/mL) vs. other PID (average 444 pg/mL) (p=0.02) or patients with AIC alone (average 667 pg/mL) (p=0.03). Studies are ongoing on specific subsets that are linked to immune dysregulation (T-regulatory cells, double negative T cells, T follicular helper cells).

Conclusions: An unexpectedly high fraction of patients with AIC were identified with underlying PID in our Immune Dysregulation program. Routine basic immune evaluation with immunoglobulin levels and lymphocyte subsets expedited diagnosis of PID. Genetic evaluation distinguished a group of patients with AIC-PID and highly elevated LPS level, reflecting high bacterial load, and this may distinguish them from the rest of patients with AIC. The source of bacterial LPS can be multifactorial and is yet to be determined. Our studies continue focusing on biomarkers that can be applied to the heterogenous group of patients with AIC. This will allow early detection and timely initiation of targeted therapies.