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Sickle cell disease (SCD) is an inherited blood disorder which can be complicated by stroke in infancy and childhood. The primary and secondary prevention of stroke in this patient population is regular RBC transfusion therapy at least every three weeks, but there is no consensus on the ideal RBC transfusion therapy. The Charles Drew Program, a partnership among a blood center and several hospitals affiliated with academic medical centers in Missouri, provides RBCs for the care of patients with SCD. There are three basic aims: the RBC components are phenotypically matched on three minor RBC antigens, the units are less than 7 days old, and each patient has a limited number of dedicated donors, so that the donor exposure is minimized. This report describes the operational phases of this program and summarizes its performance with respect to each of these aims.
Xenograft recipients produce large amounts of high-affinity anti-Gal IgG in response to Galalpha1-3Galbeta1- 4GlcNAc-R (alpha-gal) epitopes on the graft. In contrast, ABO-mismatched allograft recipients undergo "accommodation," a state of very weak immune response to ABO antigens. These differences in anti-carbohydrate immune response were studied in alpha1,3galactosyltransferase knock-out mice. Pig kidney membranes administered to these mice elicited extensive production of anti-Gal IgG, whereas allogeneic kidney membranes expressing alpha-gal epitopes elicited only a weak anti-Gal IgM response. Anti-Gal IgG response to xenograft membranes depended on helper T cell activation and was inhibited by anti-CD40L antibody. These T cells were activated by xenopeptides and not by alpha-gal epitopes. Moreover, allogeneic cell membranes manipulated to express xenoproteins also induced anti-Gal IgG response. Xenoglycoproteins with alpha-gal epitopes are processed by anti-Gal B cells. Xenopeptides presented by these cells activate a large repertoire of helper T cells required for the differentiation of anti-Gal B cells into cells secreting anti-Gal IgG. Alloglycoproteins with alpha- gal epitopes have very few immunogenic peptides and fail to activate helper T cells. Similarly, ineffective helper T-cell activation prevents a strong immune response to blood group antigens in ABO-mismatched allograft recipients, thus enabling the development of accommodation.