Targeting Complement Inhibition in Cold Hemolysis; A Multifaceted Approach Using Sutimlimab and Washed Red Cell Transfusions

^{Introduction:Cold agglutinin syndrome (CAS) is a transient disorder mediated by autoantibodies that cause red cell agglutination at cold temperatures. CAS is often associated with infections rather than malignant or autoimmune conditions. Sutimlimab, a monoclonal antibody directed against the complement component C1s, was previously shown to improve anemia and fatigue in cold agglutinin disease (CAD) in single-arm studies. However, its use in CAS has not yet been elucidated. Here, we describe a case where complement inhibition using the novel C1s inhibitor, as well as washed and warmed red cell transfusions, were used to treat CAS in the setting of a rare autoantibody directed toward the Pr antigen}

^{Case report: A healthy 46-year-old woman presented with severe acute hemolytic anemia: with nadir hemoglobin of 4.7, hematocrit of 13.4%, 0.2% of reticulocytes, total bilirubin of 9.8 mg/dL, and unconjugated bilirubin of 8.4 mg/dL. A peripheral blood smear review revealed severe anemia with agglutination of red blood cells. An extensive infectious workup was negative including COVID-19, Parvovirus B19, CMV, EBV, CMV, and HIV. Over a period of two weeks, she received three doses of IVIG, prednisone, and 17 transfusions units of warmed red blood cells in the setting of persistent hemolytic anemia.}

^{Despite the evidence of severe hemolysis, her reticulocyte count remained very low (<0.5%). A bone marrow biopsy showed trilineage hematopoiesis with erythroid hypoplasia and maturation arrest. A direct Coombs test was intermittently positive but probably confused by IgG infusions, with anti-I and anti-i titers of 1:64, and positive for C3. Thermal amplitude studies showed agglutination at 30°C, 37°C, and room temperature. Red blood cell antibodies were not identified in the eluate. The indirect antiglobulin test was negative for ficin-treated RBCs showing no agglutination. This led the reference laboratory to report that the cold agglutination was directed against the anti-pr antigen and that this patient had clinically significant anti-Pr antibodies.}

^{The patient was kept warm and started on Danazol and Sutimlimab. However, the patient continued to have hemolysis after transfusions. After receiving her second dose of Sutimlimab and in the context of persistent hemolytic anemia, she underwent another bone marrow biopsy on day 34 after presentation. The biopsy showed hypercellular bone marrow with erythroid hyperplasia and complete maturation. However, this was not reflected in reticulocytosis until day 44.}

^{The patient received her third dose of Sutimlimab, and red blood cell transfusions were washed in addition to being warmed, which resolved hemolysis after transfusion reactions. She received a total of 30 red blood cell transfusions since presentation. The patient's anemia improved, with a hemoglobin level of 8.8 mg/dL and a reticulocyte count of 13%, and she was discharged on Day 51 after presentation (figure 1). She received one more dose of Sutimlimab (total of four doses) with complete resolution of her anemia, a normal reticulocyte count, normal LDH, negative Coombs study, and negative cold agglutinin titers.}

^{Conclusion: Here, we describe a challenging case of CAS caused by a rare Pr autoantibody, with a failure of first-line treatments for CAS. This report is the first to describe the use of Sutimlimab as a treatment for CAS. After initiating Sutimlimab, the patient continued to experience significant hemolysis shortly after transfusions, exhibiting hemoglobinuria and an inadequate increase in hematocrit. Only when the red blood cell transfusions were washed to remove complement, the hemolytic reactions ceased and significant increases in hematocrit occurred. This finding may be a consideration in other cases of cold agglutinin anemia. As CAS is a transient disorder, Sutimlimab could ultimately be discontinued once the hemolysis resolved. This case illustrates the role of complement inhibition in CAS and the potential need to warm and wash red blood cells in severe cases of CAS.}