The production of group O cells

Transfusion to blood group A and O patients of group B RBCs that have been enzymatically converted to group O

BACKGROUND

The transfusion of ABO-incompatible RBCs is the leading cause of fatal transfusion reactions. Group O RBCs, lacking terminal immunodominant A and B sugars to which humans are immunized, are safe for transfusion to persons of any ABO blood group. With the use of a recombinant alpha-galactosidase to remove terminal galactose from group B RBCs, the safety and efficacy of enzyme-converted group-B-to-group-O (ECO) RBC components were studied in transfusion-dependent patients.

STUDY DESIGN AND METHODS

Twenty-four patients (blood groups A and O) were randomly assigned to receive transfusion(s) of either ECO or control group O RBCs. If a second transfusion was given, the other blood component was administered.

RESULTS

Twenty-one patients were given ECO RBCs; 18 also underwent control transfusions. One patient received only a small aliquot for RBC survival studies, instead of a full-unit transfusion, because his serum was incompatible with ECO RBCs. No adverse events occurred. Both ECO and control transfusions resulted in appropriate Hb increments and comparable (51)Cr-labeled RBC survival studies. One patient developed a transient, weak-positive DAT, without hemolysis. Two weeks after transfusion, 5 of 19 evaluable ECO RBC recipients had increases in anti-B titers.

CONCLUSION

ECO RBCs were comparable to group O cells for safety and efficacy in this study. The clinical significance of the increase in anti-B and of occasional serologic incompatibilities with ECO RBCs is unclear. If strategies can be developed to remove A epitopes, enzymatic conversion could be used to create a universal (group O) donor blood supply.

Blood group A antigen is a coreceptor in Plasmodium falciparum rosetting

The malaria parasite Plasmodium falciparum utilizes molecules present on the surface of uninfected red blood cells (RBC) for rosette formation, and a dependency on ABO antigens has been previously shown. In this study, the antirosetting effect of immune sera was related to the blood group of the infected human host. Sera from malaria-immune blood group A (or B) individuals were less prone to disrupt rosettes from clinical isolates of blood group A (or B) patients than to disrupt rosettes from isolates of blood group O patients. All fresh clinical isolates and laboratory strains exhibited distinct ABO blood group preferences, indicating that utilization of blood group antigens is a general feature of P. falciparum rosetting. Soluble A antigen strongly inhibited rosette formation when the parasite was cultivated in A RBC, while inhibition by glycosaminoglycans decreased. Furthermore, a soluble A antigen conjugate bound to the cell surface of parasitized RBC. Selective enzymatic digestion of blood group A antigen from the uninfected RBC surfaces totally abolished the preference of the parasite to form rosettes with these RBC, but rosettes could still form. Altogether, present data suggest an important role for A and B antigens as coreceptors in P. falciparum rosetting.

Cloning, functional expression and purification of endo-beta-galactosidase from Flavobacterium keratolyticus

Endo-beta-galactosidase (EC 3.2.1.103) is an enzyme that hydrolyzes internal endo-beta-galactosyl linkages in keratan sulfate, and glycoconjugates with N-acetyl-lactosamine repeating units. Here, we report the cloning of the endo-beta-galactosidase-encoding gene from Flavobacterium keratolyticus, its expression in Escherichia coli and the purification of the enzyme. The enzyme was purified over 15000-fold to apparent homogeneity. The purified endo-beta-galactosidase consists of a single band of about 43kDa on SDS-PAGE and has a specific activity of 148micro/mg. Based on peptide sequences derived from the purified enzyme, a full-length clone encoding endo-beta-galactosidase was isolated from F. keratolyticus genomic DNA. The gene contains a single open reading frame coding for a protein of 422 amino acid residues with a putative N-terminal signal peptide. Its authenticity was confirmed by colinearity of deduced amino acid sequences with the peptide sequences, and synthesis of enzyme in E. coli.