1. Adult males and females e" 18 years of age at Screening 2. Confirmed diagnosis of primary CAgD based on the following criteria: a. Chronic hemolysis, b. Polyspecific direct antiglobulin test (DAT) positive, c. Monospecific DAT strongly positive for C3d, d. Cold agglutinin titer e" 64 at 4Ë%C, e. IgG DAT d" 1+, and f. No overt malignant disease 3. History of blood transfusion within 6 months of the Screening visit 4. Hemoglobin level d" 10.0 g/dL at the Screening visit 5. Bilirubin level above the normal reference range at the Screening visit 6. B12, ferritin, and folate levels within the normal reference ranges at Screening unless deemed not clinically significant by the Investigator (or designee) 7. Presence of one or more of the following CAgD-related signs or symptoms within 3 months of Screening: a. Symptomatic anemia b. Fatigue c. Acrocyanosis d. Hemoglobinuria e. Disabling circulatory symptoms, and/or f. History of a major adverse vascular event (including thrombosis) 8. Patients on iron supplementation must be on a stable dose for at least 4 weeks prior to enrollment. 9. Bone marrow biopsy within 6 months of Screening with no overt evidence of lymphoproliferative disease or other hematological malignancy. An additional bone marrow biopsy will be required if the prior bone marrow is deemed unsuitable for analysis by the Sponsor. 10. Up-to-date vaccinations against encapsulated bacterial pathogens (Neisseria meningitis, Meningitis B, Haemophilus influenzae, and Streptococcus pneumoniae) in accordance with 2016 Centers for Disease Control and Prevention (CDC) recommendations or applicable local guidelines, OR willing to undergo vaccination or take antibiotic prophylaxis as prescribed by Investigator (or designee) 11. Adequate IV access 12. If female, must be post-menopausal, surgically sterile, or be established on (e" 3 months prior to Screening) and agree to continue to use the same highly effective methods of birth control throughout the study and for 90 days after the EOT/ET visit 13. Males must be surgically sterile for at least 90 days or when sexually-active with female partners of child-bearing potential will agree to use highly effective contraception from Day 0 until 90 days following the EOT/ET visit 14. Able to comprehend and give informed consent 15. Able to comply with the requirements of the study and to complete the full sequence of protocol-related procedures

Patients who meet any of the following criteria will be excluded from the study: 1. Cold agglutinin syndrome secondary to infection, rheumatologic disease, or active hematologic malignancy 2. Clinically significant infection (eg, HIV, active hepatitis C, pneumonia) 3. Clinical diagnosis of systemic lupus erythematosus (SLE) 4. Treatment with rituximab monotherapy within 3 months or rituximab combination therapies (eg, with bendamustine, fludarabine, ibrutinib, or cytotoxic drugs) within 6 months prior to enrollment 5. Concurrent treatment with corticosteroids other than a stable daily dose equivalent to d" 10 mg/day prednisone for previous 3 months 6. Erythropoietin deficiency. Concurrent treatment with erythropoietin is permitted if the patient has been on a stable dose for the previous 3 months. 7. Clinically significant medical history or ongoing chronic illness that would jeopardize the safety of the patient or compromise the quality of the data derived from his/her participation in this study (as determined by the Investigator [or designee]) at Screening 8. Concurrent treatment with other experimental drugs or participation in another clinical trial with any investigational drug within 30 days or 5 half-lives, whichever is greater, prior to treatment start 9. Females who are pregnant, lactating, or, if having reproductive potential, are considered potentially unreliable with respect to contraceptive practice