Clinical, Immunological Features, Treatments, and Outcomes of Autoimmune Hemolytic Anemia in Patients with RAG Deficiency

Background: The clinical features of patients with recombination activating gene (RAG1 and 2) deficiency are diverse, ranging from severe combined immunodeficiency to combined immunodeficiency with granulomatous disease and/or autoimmunity (CID-G/AI). The latter phenotype has been typically associated with hypomorphic mutations, resulting in residual RAG enzymatic activity and frequent autoimmune manifestations. Autoimmune hemolytic anemia (AIHA) is most common, and its development is thought to be due to the breakdown of T/B-cell tolerance, usually triggered by an environmental factor (e.g., viral infection). Its therapeutic response to standard treatment is often unsatisfactory. However, our understanding of this condition is still limited to case reports and small series. Herein, we systematically present clinical, immunological features, treatments, and outcomes of the largest case series of AIHA in RAG deficiency.

Methods: To assemble a highly annotated and curated patient database, we retrospectively collected detailed clinical information of AIHA in patients with RAG deficiency through multi-national collaboration and reviewed all published cases with RAG deficiency and concurrent AIHA from PubMed between 2001 and 2021.

Results: We identified 74 patients with RAG deficiency who developed AIHA during their disease course, and characteristics of the cohort are shown in the Table. Of our own case series (n = 20), the median age at clinical and molecular diagnosis was 1.6 and 2.3 years, respectively. There was a slight predominance of female patients (53.7%). RAG1 mutations were found in 75.0% of cases, and CID-G/AI (55.0%) was the predominant clinical phenotype with a median RAG1 activity of 19.3%. AIHA was typically preceded by viral infections (55.0%) and presented with severe symptomatic anemia (median hemoglobin 6.4 g/dL), with recurrent episodes (median 2), and required multiple units of transfusion support (median 5 units). Most cases were warm AIHA with IgG autoantibodies (92.9%) detected by Coombs tests. In parallel, anti-cytokine autoantibodies against IFNα (85.7%), IFNω (57.1%), and IL12 (28.6%) were frequently found in these patients. Despite the use of high-dose corticosteroid (85.0%) and intravenous immunoglobulin (68.8%), more than half of them required additional immunosuppressive treatment (52.6%), and ultimately, 15 (75%) patients underwent allogeneic stem cell transplant. Among them, refractory cytopenias were the indication of transplant in seven patients. Cases reported in the literature (n = 54) had a similar clinical profile to our cohort; therefore, they were combined for further analysis (n = 74). We found a unique immunological profile of patients fulfilled the diagnosis of Evans syndrome (n = 34, 45.9%), including a trend of more female patients (65.5 vs. 42.9%, p = 0.062), a higher frequency of positive Coombs test (96.7 vs. 75.0%, p = 0.023), lower total lymphocyte (median 1009 vs. 2120/µL, p = 0.015), CD8⁺ (median 102 vs. 226/µL, p = 0.004), CD56⁺ cell counts (median 209 vs. 382/µL, p = 0.005), and more cases underwent allogeneic stem cell transplant (75.0 vs. 45.9%, p = 0.014). In the combined cohort, the 10-year overall survival was 55.4%, and allogeneic stem cell transplant was associated with reduced mortality (31.7 vs. 57.1%, p = 0.036).

Conclusion: Patients with RAG deficiency often experience severe, recurrent, and treatment-refractory cytopenias, including AIHA during their disease course. Those with Evans syndrome demonstrated a unique immunological profile with reduced numbers of cytotoxic cells, which required further mechanistic investigations. Multiple lines of AIHA-directed therapies are typically required, and allogeneic stem cell transplant, if indicated, may improve the long-term outcomes in this population.