RBC alloimmunization remains a significant problem for many patients with SCD. To reduce alloimmunization some strategies have been implemented to provide limited (C/c, E/e, K) or extended antigen matched (C/c, E/e, K, Fya/b, Jka/b, S/s) RBC transfusions to patients with SCD who need chronic transfusion support. There is no consensus if prophylactic extended antigen matching significantly reduces the rate of RBC alloimmunization in patients with SCD compared to limited antigen matching. Based on this, the aim of this study was to evaluate the effects of prophylactic RBC transfusion with extended antigen matching on rate of alloimmunization in patients with SCD chronically transfused.

A retrospective study was conducted in the period from March 2000 to March 2020. Our study included 179 (73 male and 106 female) patients with SCD, homozygous for HbS, on chronic RBC transfusion therapy receiving prophylactic RBC transfusions with antigen matching. In this period, 91 patients received RBC units matched for ABO, Rh and K and 88 patients were matched with selected donors for ABO, Rh, K, Fya/Fy/b, Jka/Jkb and S/s antigens. Among the patients, 60 were alloimmunized against RBC antigens and 119 patients were not. Serological typing was performed in patients and donors by gel cards (Biorad). Molecular typing was performed in all patients who had recent transfusions or a positive direct antiglobulin test by Laboratory Developed Tests (LDT) and HEA BeadChip (Immucor) to predict their antigen profile. RH variant alleles were determined in patient's antigen-positive who developed Rh antibodies using RHD and RHCE BeadChips (Immucor). Adsorption onto autologous RBC was also performed to aid the differentiation of autoantibodies from alloantibodies

Alloimmunized patients received a range of 5–515 units while non-alloimmunized patients received a range of 5–289 units. The median age in the alloimmunized group is 38.4 and in non-alloimmunized is 41. Of the 60 alloimmunized patients, 27 (45%) were alloimmunized before they started receiving limited or extended antigen matched RBC transfusions. Of the 91 patients receiving Rh and K matched RBC units, 22 (24.2%) produced alloantibodies (3 Anti-Fya, 4 anti-Jkb, 6 anti-S, 1 anti-Dia, 1 anti-Cw, 4 anti-e, 1 anti-D, 2 anti-C) during these 20 years. Of the 88 patients receiving extended antigen matching, 11 (12.5%) were alloimmunized (1 anti-D, 1 anti-E, 3 anti-C, 4 anti-e, 1 anti-Jsa, 1 anti-Kpa). Thirteen patients who developed Rh antibodies had RH variant alleles. Autoantibodies were found in 8 patients (6 receiving limited antigen matching and 2 receiving extended antigen matched RBC units).

RBC transfusions with extended antigen matching had significant effects on autoimmunization and alloimmunization rates in chronically transfused patients with SCD over 20 years. SCD patients may benefit from receiving RBC transfusions with extended antigen matching as demonstrated by the lack of antigens on FY, JK and MNS systems. However, this strategy does not avoid alloimmunization to antigens against Rh antigens.