Transient suppression of high-prevalence Kell blood group antigens and concomitant development of a Kell-related antibody that appears to recognize a high-prevalence Kell antigen not previously defined.

A previously healthy 32-year-old male patient was admitted to hospital with malaise, dyspnea, anemia, thrombocytopenia, and leukopenia. Anemia and thrombocytopenia worsened during the third week. Considering the possible need for transfusion, routine ABO and D typing and an antibody detection test were performed. Antibody detection test was positive, necessitating fur ther immunohematologic investigation that revealed an antibody with Kell-related specificity and suppression/alteration of several high-prevalence Kell blood group system antigens. Autocontrols and direct antiglobulin tests (DATs) were negative in several samples during the disease course. Sequencing of the patient's KEL and XK genes did not reveal any mutations. Initial tentative diagnosis was myeloid neoplasm based on dyserythropoiesis in the bone marrow smear and no obvious biochemical signs of hemolysis. Azacitidine treatment was initiated, accordingly, but had to be interrupted when the patient's hemoglobin (Hb) dropped to 4.6 g/dL in 3 days, and he experienced more severe anemia symptoms (fatigue, nausea, and heart palpitations). Platelet concentrates, and 3 very rare Kell_null packed RBC concentrates, imported from abroad, were transfused. However, no increase in Hb was achieved. Platelet autoantibodies were not detected. Suspecting an autoimmune etiology, intravenous immunoglobulin and high-dose glucocorticoids were given. The patient responded to the latter treatment; he felt much better and regained his daily activity, and his Hb value and platelet count normalized on day 45. The steroid dose was tapered during the next 6 months until it was discontinued. His RBCs had normal Kell antigen expression, and the antibody was undetectable on day 105. Therefore, we concluded that an autoimmune etiology was the most plausible cause for the patient's condition despite a negative DAT. The immunohematologic investigation showed disease-related transient loss and/or alteration of several Kell system high-prevalence antigens and a Kell-related antibody that appeared to recognize a unique high-prevalence Kell antigen with a not-yet fully defined epitope.