Enzymatic removal of blood group ABO antigens to develop universal red blood cells (RBCs) was a pioneering vision originally proposed more than 25 years ago. Although the feasibility of this approach was demonstrated in clinical trials for group B RBCs, a major obstacle in translating this technology to clinical practice has been the lack of efficient glycosidase enzymes. Here we report two bacterial glycosidase gene families that provide enzymes capable of efficient removal of A and B antigens at neutral pH with low consumption of recombinant enzymes. The crystal structure of a member of the alpha-N-acetylgalactosaminidase family reveals an unusual catalytic mechanism involving NAD+. The enzymatic conversion processes we describe hold promise for achieving the goal of producing universal RBCs, which would improve the blood supply while enhancing the safety of clinical transfusions.

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In search of ␣-galactosidases with improved kinetic properties for removal of the immunodominant ␣1,3-linked galactose residues of blood group B antigens, we recently identified a novel prokaryotic family of ␣-galactosidases (CAZy GH110) with highly restricted substrate specificity and neutral pH optimum (Liu, Q. P., Sulzenbacher, G., Yuan, H., Bennett, E. P., Pietz, G., Saunders, K., Spence, J., Nudelman, E., Levery, S. B., White, T., Neveu, J. M., Lane, W. S., Bourne, Y., Olsson, M. L., Henrissat, B., and Clausen, H. (2007) Nat. Biotechnol. 25, 454 -464). One member of this family from Bacteroides fragilis had exquisite substrate specificity for the branched blood group B structure Gal␣1-3(Fuc␣1-2)Gal, whereas linear oligosaccharides terminated by ␣1,3-linked galactose such as the immunodominant xenotransplantation epitope Gal␣1-3Gal␤1-4GlcNAc did not serve as substrates. Here we demonstrate the existence of two distinct subfamilies of GH110 in B. fragilis and thetaiotaomicron strains. Members of one subfamily have exclusive specificity for the branched blood group B structures, whereas members of a newly identified subfamily represent linkage specific ␣1,3-galactosidases that act equally well on both branched blood group B and linear ␣1,3Gal structures. We determined by one-dimensional 1 H NMR spectroscopy that GH110 enzymes function with an inverting mechanism, which is in striking contrast to all other known ␣-galactosidases that use a retaining mechanism. The novel GH110 subfamily offers enzymes with highly improved performance in enzymatic removal of the immunodominant ␣3Gal xenotransplantation epitope.

Recent developments in the use of pattern recognition receptors (PRRs) aim to harness the innate power of the immune system for cancer therapy. Understanding how to recruit PRRs, such as RIG-I, in a tumor-selective manner is critical for its adoption in the clinic. We describe the use of a tumor-selective template-based agonist of RIG-I to induce type-I IFN signaling and tumor cell apoptosis. The agonist, termed ss-ppp-miRNA-21, comprises a single stranded RNA oligonucleotide modified with a 5-triphosphate and complementary to an endogenous miRNA enriched in tumor cells. We demonstrate the efficacy of the template-directed approach and detail mechanistic studies validating the hypothesis of a template-directed RIG-I agonist assembly using miRNA-21 as a target. The template-directed strategy described here moves us closer to making RIG-I a clinically relevant target in oncology because it achieves targeted activation of innate immunity in the tumor microenvironment in the context of systemic agonist injection.