The presence of p53 mutation or deletion predicts for poor response to conventional therapy in chronic lymphocytic leukemia (CLL). We sought to determine whether the humanized anti-CD52 antibody alemtuzumab was effective in this patient group. Thirty-six patients with flu-

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BACKGROUND Red blood cell (RBC) alloimmunization occurs at a high frequency in sickle cell anemia (SCA) despite serologic matching for Rh (C/c, E/e) and K antigens. RBC minor antigen genotyping allows for prediction of antigens and RH variants that may lead to alloimmunization. STUDY DESIGN AND METHODS RBC antigen genotyping was performed on chronically transfused pediatric SCA patients, using PreciseType Human Erythrocyte Antigen (HEA), RHCE, and RHD BeadChip arrays. All patients received C/c, E/e, and K serologically matched units (category 1); patients with prior RBC antibodies were also matched for Fya, Jkb, and any antibodies (category 2). The RBC genotypes of all leukoreduced (LR) units transfused over a 12-month period were determined by the prototype HEA-LR BeadChip assay. RESULTS There were 2320 RBC units transfused to 90 patients in 1135 transfusion episodes. Thirty-five (38.9%) patients had homozygous or compound heterozygous RH variants. Seven new alloantibodies were detected, with alloantibody incidence of 0.706/100 units for category 2 transfusions and 0.068/100 units for category 1 (p=0.02). Three patients on category 2 transfusions formed new anti-Jsa and had a higher rate of exposure to Jsa than those who did not form anti-Jsa (20.4 vs. 8.33 exposures/100 units, p=0.02). The most frequent mismatches were S (43.9%), Doa (43.9%), Fya (29.2%), M (28.4%), Jkb (28.1%). CONCLUSIONS Alloimmunization incidence was higher in those with prior RBC antibodies, suggesting that past immunologic responders are at higher risk for future alloimmunization and therefore may benefit from more extensive antigen matching beyond C/c, E/e, K, Fya and Jkb.