Deletions in the MAL gene result in loss of Mal protein, defining the rare inherited AnWj-negative blood group phenotype.

The genetic background of the high prevalence red blood cell antigen AnWj has remained unresolved since its identification in 1972, despite reported associations with both CD44 and Smyd1 histone methyltransferase. Development of anti-AnWj, which may be clinically significant, is usually due to transient suppression of antigen expression, but a small number of individuals with persistent, autosomally-recessive inherited AnWj-negative phenotype have been reported. Whole exome sequencing of individuals with the rare inherited AnWj-negative phenotype revealed no shared mutations in CD44H or SMYD1, but instead we discovered homozygosity for the same large exonic deletion in MAL, which was confirmed in additional unrelated AnWj-negative individuals. MAL encodes an integral multi-pass membrane proteolipid, Myelin and Lymphocyte protein (Mal), which has been reported to have essential roles in cell transport and membrane stability. AnWj-positive individuals were shown to express full-length Mal on their red cell membranes, which was not present on the membranes of AnWj-negative individuals, whether of an inherited or suppression background. Furthermore, binding of anti-AnWj was able to inhibit binding of anti-Mal to AnWj-positive red cells, demonstrating the antibodies bind to the same molecule. Over-expression of Mal in an erythroid cell-line resulted in expression of AnWj antigen, regardless of the presence or absence of CD44, demonstrating that Mal is both necessary and sufficient for AnWj expression. Our data resolve the genetic background of the inherited AnWj-negative phenotype, forming the basis of a new blood group system, further reducing the number of remaining unsolved blood group antigens.

Missense mutations in PIEZO1, which encodes the Piezo1 mechanosensor protein, define Er red blood cell antigens.

Despite the identification of the high-incidence red cell antigen Era nearly 40 years ago, the molecular background of this antigen, together with the other 2 members of the Er blood group collection, has yet to be elucidated. Whole exome and Sanger sequencing of individuals with serologically defined Er alloantibodies identified several missense mutations within the PIEZO1 gene, encoding amino acid substitutions within the extracellular domain of the Piezo1 mechanosensor ion channel. Confirmation of Piezo1 as the carrier molecule for the Er blood group antigens was demonstrated using immunoprecipitation, CRISPR/Cas9-mediated gene knockout, and expression studies in an erythroblast cell line. We report the molecular bases of 5 Er blood group antigens: the recognized Era, Erb, and Er3 antigens and 2 novel high-incidence Er antigens, described here as Er4 and Er5, establishing a new blood group system. Anti-Er4 and anti-Er5 are implicated in severe hemolytic disease of the fetus and newborn. Demonstration of Piezo1, present at just a few hundred copies on the surface of the red blood cell, as the site of a new blood group system highlights the potential antigenicity of even low-abundance membrane proteins and contributes to our understanding of the in vivo characteristics of this important and widely studied protein in transfusion biology and beyond.

Patient interleukin-18 GCG haplotype associates with improved survival and decreased transplant-related mortality after unrelated-donor bone marrow transplantation.

Interleukin-18 (IL-18), a proinflammatory cytokine, is elevated in patients with acute graft-versus-host disease (aGVHD). IL-18 induces Th1 differentiation and cytotoxic T-lymphocyte function, both of which have been implicated in the pathogenesis of aGVHD. However, recent studies have shown that neutralization of IL-18 by antibodies leads to an increased risk of aGVHD-related mortality while administration of IL-18 significantly improved survival. We have genotyped a cohort of 157 patient/donor pairs undergoing unrelated donor bone marrow transplantation (BMT) for three polymorphisms recently identified in the promoter of the IL-18 gene: G-137C, C-607A and G-656T. Using phase software, three main haplotypes were reconstructed: GCG, CAT and GAT. We found no association between the occurrence of aGVHD and patient/donor haplotypes. The presence of the GCG haplotype in patients was associated with significantly decreased risk of transplant-related mortality at 100 d (23% in patients with GCG vs. 48% in patients without GCG, P < 0.01) and at 1 year (36% vs. 65%, P < 0.01). The presence of the GCG haplotype in patients was also associated with improved survival (57% vs. 32%, P < 0.01). Cox regression analysis showed that the presence of the GCG haplotype was associated with a twofold increased probability of survival. These data suggest that the IL-18 promoter GCG haplotype may influence survival after unrelated donor BMT without altering the risk of aGVHD.