Two Alleles with RHCE*nt818C>T Change Encode the Low Prevalence Rh Antigen STEM.

Abstract

3159 Poster Board III-96 Background According to the original (and only) report, the low prevalence Rh antigen, STEM, is associated with an altered e phenotype. Approximately 65% of hrS– and 30% of hrB– RBCs from South African donors are STEM+. STEM has a variable expression, which is an inherited characteristic. Anti-STEM has induced mild HDFN (Marais, et al., Transf Med 1993;3:35-41). The purpose of this study was to determine the molecular basis associated with STEM expression. Material and Methods Blood samples and reagents were from our collections. Hemagglutination and DNA extraction were performed by standard methods. Molecular testing included direct sequencing and cloning of cDNA, AS-PCR, PCR-FRLP, and sequencing specific exons of gDNA. Results Three STEM+ samples (including the original index case) had RHCE*ceBI [ce 48C (16C), 712G (238V), 818T (273V), 1132G (378V)] (Noizat-Pirenne, et al., Blood 2002;100:4223-31) and 6 had a new allele, which we name RHCE*ceSM (ce 48C, 712G, 818T). In contrast, 8 STEM– samples (which included hrS– and hrB– samples) did not have the RHCE*818C>T change. RBCs with the ceBI phenotype expressed STEM more strongly than those with the ceSM phenotype. Conclusions The previously reported allele RHCE*ceBI and a new allele, RHCE*ceSM, encode the STEM antigen. This study also revealed other new findings: (i) ceSM encodes a weaker expression of STEM than does ceBI, which explains the previously reported variable expression, (ii) provides an explanation for why not all hrS– and hrB– RBCs express STEM. RBCs with ceAR, ceMO, and ceEK, phenotypes are hrS– STEM–, and RBCs with ceS phenotypes type hrB–, STEM–, (iii) ceBI and ceSM do not express hrS but do express hrB. It is likely that anti-hrS made by hrS– STEM– people (ceAR, ceMO, ceEK) will be incompatible with hrS– STEM+ RBCs, and vice versa. Our findings provide a means to positively identify the STEM+ phenotypes, which, by hemagglutination, is virtually impossible due to the dearth of anti-STEM. Further, it provides a tool to provide suitable antigen-negative RBC products to a patient who has made an ‘e-like’ antibody. Disclosures No relevant conflicts of interest to declare.

The low‐prevalence Rh antigen STEM (RH49) is encoded by two different RHCE*ce818T alleles that are often in cis to RHD*DOL

“…We report here an expansion of our initial findings 7‐9 that two alleles with a RHCE * ce818C>T change encode the e+/− hr S − STEM+ phenotype. These alleles are 1) the previously reported RHCE * ceBI 10 (IBST provisional name RHCE * 01.08 or RHCE * ce.08 ), which was previously not known to encode a novel low‐prevalence antigen, and 2) the novel allele, RHCE * ceSM (ISBT provisional name RHCE * 01.09 or RHCE * ce.09 ).…”

RHD*DOL1 and RHD*DOL2 encode a partial D antigen and are in cis with the rare RHCE*ceBI allele in people of African descent

“… 13 The AR , EK, and BI suffixes were given after the two first letters of the name of the index patients. A fourth allele, RHCE * ceSM , was also recently described 31 . RHCE * ceAR is the most frequent of those alleles, followed by RHCE * ceEK and RHCE * ceBI 13,32 .…”

“…The low‐prevalence Rh antigen STEM (RH49) 37 was recently described to be encoded by both RHCE * ceBI and RHCE * ceSM. 31,34 STEM was reported to correspond to the c.818C>T change in RHCE 31 . The molecular basis of RHCE * ceAR , RHCE * ceEK , RHCE * ceBI, and RHCE * ceSM are detailed in Fig.…”

“…The molecular basis of RHCE * ceAR , RHCE * ceEK , RHCE * ceBI, and RHCE * ceSM are detailed in Fig. 2 13,31 …”

Red cells from the original JAL+ proband are also DAK+ and STEM+

“…We conclude that the second RHCE*ce allele in J. Allen is RHce*ceBI ( RHCE*01.08 or RHCE*ce.08 ), which is reported to encode STEM. [14] RHCE*ceBI is often in cis to RHD*DOL, and direct sequencing of RHD exons 4, and 5, revealed, respectively, RHD*509T/C (Met170Thr), and 667T/G (Phe223Val). This is consistent with the presence of an RHD*DOL allele [15].…”