The R0Har RH:33 phenotype results from substitution of exon 5 of the RHCE gene by the corresponding exon of the RHD gene

The crawford variant as a cause of rhd typing discrepancies in blood banks: a case report

We present the case of a 55-year-old Colombian male who showed a discrepancy in the serological typing of the RhD antigen in his first platelet donation. The discrepancy persisted after a serological investigation with multiple Anti-D monoclonal reagents (IgG and IgM) under different conditions (22°C and 37°C, saline, and LISS/Coombs). Furthermore, partial RhD typing was performed, obtaining negative results with a commercially available panel of six Anti-D reagents. Molecular analysis showed a homozygous deletion of RHD and heterozygosity for the Crawford variant (RHCE*ce, RHCE*ceCF), with a predicted phenotype of C-, c+, E-, e+, Vs+, V+. Following the investigation of this case, this man has made 14 platelet donations showing variable reactivity, with agglutinations ranging from - to 2+. Since Crawford red blood cells express some RhD antigen epitopes, they could cause alloimmunization in RhD negative receptors. Likewise, Anti-D alloantibodies have been documented in Crawford variant carriers. Therefore, it is recommended that carriers of this variant be classified as RhD positive if they are blood donors and RhD negative if they are transfusion recipients. Also, in pregnant women carrying a Crawford variant, Anti-D immunoprophylaxis is recommended.

Serological screening and genetic analysis of RhCE variants in the Chinese Southern Han donors

OBJECTIVES

To screen RhCE variants in the Chinese Southern Han donors for molecular genetic analysis.

BACKGROUND

More than hundreds of RhCE variant alleles have been described to resulting in weak and/or partial expression of RhCE antigens, generation of low-prevalence antigens and/or absence of a high-prevalence antigen of Rh system, which mainly reported in the people of African origin. In this study, the serological screening and molecular genetic analysis of RhCE variants were performed in the Chinese Southern Han donors.

METHODS

The blood samples of E(+) donors were preliminarily collected. Then, RhCE antigens of the E(+) samples were further typed by using two sets of monoclonal anti-C, anti-c, anti-e and another anti-E. When weak expression of RhCE antigens was found, direct sequencing for 10 exons of RHCE gene, RH genotyping analysis by using multiplex ligation-dependent probe amplification, flow cytometric analysis and even cDNA sequencing were performed.

RESULTS

A total of 4487 E(+) samples were collected and four samples with weak expression of antigens were detected. RHCE*Ce375G and RHCE*Ce667T variant alleles were identified in two samples with weak expression of e antigen, respectively. But no variant alleles were found in another two samples with weak expression of C antigen.

CONCLUSION

The variant RHCE*Ce375G validated by mRNA sequencing and the deduced RHCE*Ce667T alleles were firstly identified in the Chinese population. The DCE haplotype might account for the weak expression of C antigen in two donors.

Application of a Multivariant, Caucasian-Specific, Genotyped Donor Panel for Performance Validation of MDmulticard®, ID-System®, and Scangel® RhD/ABO Serotyping

BACKGROUND: Validations of routinely used serological typing methods require intense performance evaluations typically including large numbers of samples before routine application. However, such evaluations could be improved considering information about the frequency of standard blood groups and their variants. METHODS: Using RHD and ABO population genetic data, a Caucasian-specific donor panel was compiled for a performance comparison of the three RhD and ABO serological typing methods MDmulticard (Medion Diagnostics), ID-System (DiaMed) and ScanGel (Bio-Rad). The final test panel included standard and variant RHD and ABO genotypes, e.g. RhD categories, partial and weak RhDs, RhD DELs, and ABO samples, mainly to interpret weak serological reactivity for blood group A specificity. All samples were from individuals recorded in our local DNA blood group typing database. RESULTS: For 'standard' blood groups, results of performance were clearly interpretable for all three serological methods compared. However, when focusing on specific variant phenotypes, pronounced differences in reaction strengths and specificities were observed between them. CONCLUSIONS: A genetically and ethnically predefined donor test panel consisting of 93 individual samples only, delivered highly significant results for serological performance comparisons. Such small panels offer impressive representative powers, higher as such based on statistical chances and large numbers only.

RHCE alleles detected after weak and/or discrepant results in automated Rh blood grouping of blood donors in Northern Germany

BACKGROUND

More than 170 weak or partial RHD alleles are currently known. A similar heterogeneity of RHCE alleles may be anticipated, but a large-scale systematic analysis of the molecular bases of altered C, c, E, and e antigenicity in European blood donors was lacking.

STUDY DESIGN AND METHODS

Between November 2004 and October 2006, samples collected from 567,105 blood donors in the northwest of Germany were surveyed for weakened and/or discrepant serologic reaction patterns of the C, c, E, or e antigens in automated testing. Samples from 187 donors with systematic typing problems were further investigated by manual typing and in 122 donors by DNA typing. The polymorphisms determining C, c, E, and e, as well as three repeatedly found substitutions, M167K, G96S, and L115R, were tested by PCR-SSP. Further analysis consisted of sequencing of the exons of RHCE. In addition, 13 referred samples were analyzed.

RESULTS

RHcE(M167K) known as E variant I was the most frequent allele, found in 70 of 122 analyzed donors. Among 13 referred samples, C typing problems predominated. Overall, 34 different underlying alleles were detected, 23 of which were new. Molecular causes included single-amino-acid substitutions, gene conversions, multiple dispersed amino acid substitutions, protein extensions, and in-frame amino acid deletions.

CONCLUSION

In addition to RHcE(M167K), a large number of different alleles are underlying CcEe typing problems. Molecular mechanisms parallel those found in RHD. Elucidation of the molecular bases of variant antigens is important to improve serologic and molecular typing methods.

RhCE protein variants in Southwestern Germany detected by serologic routine testing

BACKGROUND

Variant RHCE alleles with diminished expression of C, c, E, and e antigens have been described and indicate the genetic diversity of this gene locus in several populations. In this study the molecular background of variant RhCE antigens identified by standard serologic routine testing in German blood donors and patients was determined.

STUDY DESIGN AND METHODS

Samples from blood donors and patients were routinely analyzed for RhCE phenotype using the PK7200 analyzer with two sets of monoclonal anti-C, -c, -E, and -e reagents. Samples with confirmed variant RhCE antigens were analyzed by nucleotide sequencing of the 10 RHCE exons. A multiplex polymerase chain reaction with sequence-specific priming (PCR-SSP) method was established for rapid typing of the rare RHCE alleles.

RESULTS

We identified 43 samples with serologic RhCE variants. Molecular analysis revealed variant RHCE alleles in 34 samples. Altogether 22 RHCE alleles were detected; 10 have not been published before. Twenty alleles harbored distinct single-nucleotide substitutions, 18 of which encoded amino acid changes and 2 of which occurred in noncoding regions. Two samples represented RHCE-D-CE hybrid alleles involving different segments of the RHCE Exon 5. A multiplex PCR-SSP screening for 17 RHCE alleles was negative in 1344 samples of the DNA bank GerBS. The cumulative phenotype frequency was estimated between 1 in 488 (0.20%) and 1 in 8449 (0.012%).

CONCLUSION

Single-amino-acid substitutions were the molecular basis for variant RhCE antigen expression in most samples. Nucleotide substitutions in RHCE exons were excluded as possible mechanism of diminished RhCE antigen expression in one-fifth of the serologically identified samples.

Weak D phenotypes and transfusion safety: where do we stand in daily practice?

BACKGROUND

Weak D Types 1, 2, and 3 recipients cannot be immunized when exposed to D antigen. Molecular biology is very efficient to type weak D variants but rarely implemented in daily practice. The serologic typing practice of weak D in a Caucasian patient population was analyzed and a transfusion strategy is proposed.

STUDY DESIGN AND METHODS

Samples typed either ddCcee or ddccEe in routine laboratories were tested with the indirect antiglobulin test (D(u) test). D(u)-positive samples were screened for weak D alleles Types 1, 2, and 3 and further tested with immunoglobulin M (IgM) anti-D reagents, used in a fully automated device.

RESULTS

A total of 468 of 55,162 samples were found to be ddCcee or ddccEe. Ninety-three expressed weak D after the D(u) test leading to D+ assignment for transfusion. Seventy-three percent of D(u)-positive samples were weak D alleles Type 1, 2, or 3. Almost all weak D Types 1, 2, and 3 were positive with IgM reagents in gel matrix with an automated device. Other variants that could be potentially associated with anti-D alloimmunization, however, were also positive.

CONCLUSION

Serology is very sensitive to detect weak D Types 1, 2, and 3, but there is no cutoff to distinguish variants of clinical significance. When molecular analysis is not available, it is proposed that a D+ status for blood recipients found to be weak D with a sensitive method be assigned, except for women of childbearing age or younger, because of the remaining possibility to be partial D or other rare weak D who can be immunized.

How I manage donors and patients with a weak D phenotype

PURPOSE OF REVIEW

Since the adoption of molecular blood-group typing, the considerable heterogeneity of the serologic entities weak D and DEL at the molecular level has come to light. I offer an approach to the management of donors and patients expressing D antigen weakly and carrying any of the various molecular types of weak D and DEL.

RECENT FINDINGS

More than 50 distinct weak D alleles have been described. An internet-based survey of anti-D immunizations occurring in D-positive transfusion recipients reveals that no allo-anti-D has been observed in patients carrying prevalent weak D types. Allo-immunizations are documented for weak D types 4.2 (also known as DAR), 11 and 15. Anti-D immunizations have been reported in D-negative persons transfused with weak D and DEL red blood cells.

SUMMARY

Patients carrying any of the prevalent weak D types 1, 2, 3 or 4.1 are not prone to allo-anti-D immunization and may safely be transfused with D-positive red blood cells. Pregnant women with these weak D types need not receive RhIg. We should pay attention to weak D- or DEL-positive blood units that are labelled D-negative. The clinical benefit of removing DEL blood units from our supply of D-negative red blood cell units should be determined.

The RHCE allele ceCF: the molecular basis of Crawford (RH43)

BACKGROUND

The Crawford antigen (RH43) was described in 1980. It occurred in African American people, as a low-prevalence Rhesus antigen, who were also VS+.

STUDY DESIGN AND METHODS

Twelve blood samples were analyzed because of inquiries into discrepant reactions in routine anti-D typing. The RHCE alleles were determined by nucleotide sequencing from genomic DNA. The D epitope profile was determined with 60 monoclonal anti-D. The population frequency was estimated in four major US regional blood centers.

RESULTS

The novel RHce(W16C, Q233E, L245V) allele, dubbed ceCF, was found to be occurring in the cde haplotype as cause of the reactivity with the immunoglobulin M anti-D GAMA401. The ceCF phenotype expressed few D epitopes resembling but not matching the reaction patterns observed with other RhCE variants, like R0 (Har), ceRT, and ceSL. The frequency of the ceCF phenotype was 0.056 percent among African American persons and 0.007 percent in the general US population.

CONCLUSION

The novel RHce(W16C, Q233E, L245V) allele, which is a variant of the known ce(s) allele, RHce(W16C, L245V), occurs in a haplotype with the RHD deletion and represents the molecular basis of the Crawford antigen.

The RHCE allele ceSL: the second example for D antigen expression without D-specific amino acids

BACKGROUND

The example of ceRT proved that the expression of some D epitopes does not require D-specific amino acids. This allele denoted as RHce(R154T) caused the "false-positive" reactions that were observed in ccddee blood donors who typed positive for the D antigen with some monoclonal anti-D. No other example exposing a similar molecular mechanism was known.

STUDY DESIGN AND METHODS

Eleven donor and 1 patient ccddee samples were collected in Switzerland that typed "false-positive" with some monoclonal anti-D in bromelain technique. Their RHCE alleles were determined by nucleotide sequencing from genomic DNA and by a polymerase chain reaction with sequence-specific priming. The D epitope profile was compared to ceRT. The population frequencies were estimated in Switzerland and Germany by serology or at the molecular level, respectively.

RESULTS

The "false-positive" reactions were caused by the RHCE allele RHce(S122L) occurring in the cde haplotype. Its ceSL phenotype expressed few D epitopes that belonged to the D epitope 6 group. The frequency of ceSL among D- donors was about 1:675 in the region of Bern, Switzerland. No ceSL donors were found elsewhere in Switzerland or in southwestern Germany.

CONCLUSION

ceSL represented the second molecular mechanism for D antigen expression without any D-specific amino acids. ceSL and ceRT were useful to delineate the molecular mechanisms of D expression by RhCE proteins carrying amino acids not representative for the RhD proteins. The ceSL population frequencies differed significantly among three Swiss and German populations.

Serological studies of monoclonal RH antibodies with RH1 (D), RH2 (C), RH3 (E) and RH5 (e) variant RBCs

One hundred and forty five Mabs against RH antigens were tested. In this paper, we chose to detail reactivity of MoAbs directed against variant RBCs of the CNRGS collection for which we studied the molecular background. Because we developed procedures to identify variants of the RhD, RhC, RhE and Rhe antigens, we were especially interested in finding new monoclonal antibodies that could help us to characterize more accurately these variants. Therefore, we drew parallels between our procedures and results obtained with the 2001 workshop antibodies.

The RHCE allele ceRT: D epitope 6 expression does not require D-specific amino acids

BACKGROUND

False-positive D typing in patients may lead to anti-D immunization caused by D+ transfusions or by omission of anti-D prophylaxis. Known causes of such errors are RhCE variants carrying RhD-specific amino acids and cold agglutinin activity of some frequently used monoclonal anti-D.

STUDY DESIGN AND METHODS

The molecular basis of eight samples referred because of "false-positive" reactions with some commercial monoclonal anti-D was investigated by PCR and nucleotide sequencing from genomic DNA. PCR with sequence-specific priming was developed to specifically detect the underlying aberrant RHCE allele. The D epitope profile of the allele was determined by serology.

RESULTS

The aberrant reactivity of the samples was caused by the RHCE allele RHCE(R154T) that occurred in a cde haplotype. The phenotype dubbed ceRT expressed the important D epitope 6, which is the target epitope of most monoclonal anti-D used in routine typing.

DISCUSSION

The characterization of ceRT demonstrated a previously unknown mechanism of antigen D expression that does not require any D-specific amino acid. At least for some D epitopes, D-like structures may be mimicked by RhCE proteins carrying amino acid substitutions not representative for RhD.

A Dc- phenotype encoded by an RHCE-D(5-7/8)-CE hybrid allele

BACKGROUND AND OBJECTIVES

The Rh system is genetically controlled by the homologous RHD and RHCE genes that encode the RhD and RhCcEe polypeptides, respectively. Deletions, point mutations and rearrangements between both genes are responsible for the great polymorphism of this system. The aim of this work was to analyse the genetic basis of a Dc- phenotype.

MATERIALS AND METHODS

DNA samples from the Dc- propositus and family members were obtained from peripheral blood. RHCE intron 4-exon 5 and RH exons 4, 5, 6 and 7 were analysed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Exon 9 was studied by PCR-sequence-specific primers (SSP). The RH locus was further analysed by using a PCR designed for a hybrid allele.

RESULTS

No RHCE-specific fragments were found when analysing exons 5, 6 and 7 of the RH locus from the propositus' DNA, while exons 4 and 9 of both RH genes were present.

CONCLUSIONS

The results obtained indicated that the Dc- phenotype is encoded by a novel RHCE-D(5-7/8)-CE hybrid allele.

[Immunohematologic characteristics in the Afro-caribbean population. Consequences for transfusion safety]

Polymorphism encountered within the immunogenic blood group antigens is responsible for allo-immunization after transfusion or pregnancy. Antigen frequency differs depending on the ethnic background. This is the case for the Afro-caribbean population. Three levels of differences can be identified: common antigens in the RH, FY, JK and MNS blood groups, high frequency antigens in the RH, KEL, FY and MNS blood groups and low frequency antigens in the RH and KEL blood groups. When donors are primarily European caucasian in ancestry, the ethnic polymorphism may affect donor service in term of supply and demand. The effects of differences in antigen frequency are especially important when long term transfusion support is needed such as in sickle cell disease. When a Black patient is immunized against an association of common antigens for the Caucasian population (ex: anti-RH2, anti-FY1, anti-JK2, anti-MNS3) or against a high frequency antigen always present in the Caucasian population (anti-MNS5), only rare blood from the same ethnic population kept frozen at the rare blood bank can be transfused to avoid immuno-haemolytic accidents.

Rare RHCE phenotypes in black individuals of Afro-Caribbean origin: identification and transfusion safety

The molecular backgrounds of variants encountered in Afro-Caribbean black individuals and associated with the production of clinically significant antibodies against high-incidence antigens (anti-RH18, anti-RH34) and against Rhe epitopes were determined. We showed that RH:-18 phenotypes are produced by 3 distinct RHCE alleles: ceEK carrying 48G>C (exon 1), 712A>G, 787A>G, 800T>A (exon 5); ceBI carrying 48G>C (exon 1), 712A>G (exon 5), 818C>T (exon 6), 1132C>G (exon 8); and the already known ceAR allele carrying 48G>C (exon 1), 712A>G, 733C>G, 787A>G, 800T>A (exon 5), and 916A>G (exon 6). The RH:-34 phenotype is produced by the (C)ce(s) haplotype described previously and composed of a hybrid D-CE(3-8)-D gene with 4 extra mutations next to a ce(s) allele (733C>G; exon 5) with an extra mutation in exon 7 (1006G>T). Partial Rhe with risk of immunization against lacking epitopes can be produced by the new ce(s) allele carrying an extra mutation in exon 3 (340C>T) and by the ceMO allele described previously. A population of sickle cell disease patients was screened to estimate the incidence of these rare alleles, with the conclusion that a procedure is required to detect the associated phenotypes in black donors to ensure transfusion safety for patients. We also described a new variant [ce(s)(748)] and variants carrying different altered alleles in nonimmunized patients and for whom the risk of immunization is discussed.

RHCE-D-CE hybrid genes can cause false-negative DNA typing of the Rh e antigen

BACKGROUND AND OBJECTIVES

DNA typing of the human Rh blood groups generally shows good agreement with serologically defined phenotypes. However, in the present report we describe four individuals who were declared Rh e negative by genotyping although they express the Rh e antigen.

MATERIALS AND METHODS

Serotyping was performed using mono- and polyclonal Rh antisera. Fluorescent multiplex sequence-specific polymerase chain reactions (PCR-SSPs) identified RHD exons and the polymorphisms usually associated with the Rh E/e or Rh C/c/C(W) antigens. Additional PCR amplification reactions, which were carried out to reveal RHCE-D-CE hybrid genes, analysed exon 5 of the RH genes, the location of the polymorphism (676C-->G) coding for the Rh E and Rh e antigens.

RESULTS

Four individuals were identified who expressed Rh e antigens but were negative by PCR-SSP typing for common Rhe-coding sequences. In one family analysed in detail, an RHCE-D5-CE hybrid gene associated with Rh e antigen expression was identified. A concomitant RHcE allele accounted for a seemingly regular typing pattern by conventional RH PCR.

CONCLUSIONS

The presence of RHCE-D5-CE hybrid alleles may cause false-negative DNA-typing results for the Rh e antigen that are easily overlooked unless appropriate RH hybrid PCR-SSPs are incorporated into conventional DNA-typing protocols. These and previous data strongly caution against an uncritical interpretation of RH DNA-typing results.

Molecular background of D(C)(e) haplotypes within the white population

BACKGROUND

D(C)(e) and D(C)e haplotypes may be encountered in the white population. Few data are available on the molecular backgrounds responsible for depressed expression of C and e.

STUDY DESIGN AND METHODS

Individuals of white origin carrying a D(C)(e) genotype resulting in depressed expression of C or both C and e were subdivided into two categories based on the RBC reactivity with the human sera Mol and Hor, which contain antibodies against low-frequency antigens of the Rh (RH) system and other non-Rh low-frequency antigens. Neither Hor+, Mol+ nor Hor+, Mol- RBCs expressed the V (RH10), VS (RH20), and/or Rh32 (RH32) low-frequency antigens. These results suggested that Hor+, Mol+ variants expressed Rh33 (RH33 or Har) and FPTT (RH50), whereas Hor+, Mol- variants might express an undefined low-frequency antigen. Further serologic and molecular analyses were performed.

RESULTS

Molecular analysis of Hor+, Mol+ variants revealed a hybrid gene structure RHCe-D(5)-Ce, in which exon 5 of RHCE (RHCe allele) was replaced by exon 5 of RHD (the so-called RHCeVA allele). The presence of exon 5RHD resulted in several amino acid alterations predicted in the external loop 4 of the CeVA polypeptide. Molecular analysis of Hor+, Mol- variants revealed the presence of a new RHCe allele characterized by a single point mutation C340T within exon 3 (the so-called RHCeMA allele), resulting in a R114W substitution predicted on the external loop 2 of the CeMA polypeptide. A serologic study showed a different pattern of reactivity with C and e MoAbs.

CONCLUSION

Two types of mutations resulted in amino acid substitutions predicted in external loops 4 and 2, respectively, which altered both the C and e reactivity, and indicated conformation changes or defective interaction between nonadjacent loops of the Ce polypeptide. Serologic analysis showed that together with Hor and Mol sera testing, the use of different C and e MoAbs could help to identify these variants within the white population.

Two new alleles of the RHCE gene in Black individuals: the RHce allele ceMO and the RHcE allele cEMI

Six unrelated individuals of Afro-Caribbean origin, whose red cells have a marked reduction of the Rhe antigen expression, have been identified. All exhibited the same serological profile with anti-e monoclonal antibodies and lacked expression of the high frequency e-related antigen hrS. Transcripts and genomic analysis showed that these phenotypes resulted from the presence of two new RHCE alleles, ceMO and cEMI. The ceMO allele corresponded to a RHce gene carrying a G667T mutation (exon 5) and was detected at the homozygous state in sample 1 and at the heterozygous state in samples 2-6. The G667T mutation resulted in a Val223Phe substitution on the Rhce polypeptide, in close proximity to Ala226 (e-antigen polymorphism), which might account for the altered expression of e. The ceMO allele is also associated with the lack of expression of the hrS antigen. The absence of the hrS antigen expression may have implications in transfusion as hrS-negative individuals may develop clinically significant antibodies. The cEMI allele corresponded to a silent RHE allele carrying a nine nucleotide deletion within exon 3 and was detected at the heterozygous state in sample 2. This deletion resulted in a shortened polypeptide of 414 residues (instead of 417) that was absent (or severely reduced) at the red cell surface, as the E antigen was undetectable using serology and Western blot analysis with anti-E reagents. In DNA-based polymerase chain reaction genotyping for RHE determination, the cEMI allele provided a false positive result as the cells carrying this allele are serologically phenotyped as E-negative. The incidence of this allele in the Black population is unknown but, as shown already for D genotyping, one must exercise caution when genotyping is performed to detect the e/E polymorphism.

Prenatal genotyping for the RhD blood group antigen: considerations in developing an accurate test

Experience performing prenatal genotyping for RHD has shown that consideration must be given to developing a molecular test capable of detecting recombination/gene conversion events involving the RHD and RHCE genes that can lead to erroneous results. Out of 50 prenatal RHD tests performed over the past 5 years, four samples were encountered that gave false-positive results. In only one of the tests, incorrect results were issued to the physician. In the other three instances, the erroneous nature of the test results was revealed through the analysis of multiple regions of the RHD gene and, more importantly, because the mother, and sometimes the father, were tested in parallel with the fetus. In an extension of the observations obtained from the prenatal testing program, a large panel of RhD-negative blood donors were subjected to molecular analysis of the RHD gene. Of 1,183 donors screened, 187 were found to phenotype as RhD negative. Of the 187 donors confirmed RhD negative serologically, 22 (11.8%) were found to retain remnants of the RHD gene that, depending upon the characteristics of the molecular assay performed, could lead to a false-positive result in a genotyping assay. On the basis of the experience presented here, it is recommended that any molecular RHD assay include an analysis of multiple areas of the RHD gene so as to allow for the detection of recombination/gene conversion events between the RHD and RHCE genes. Moreover, it is strongly recommended that the mother (at a minimum) and father be subjected to molecular analysis simultaneously with the fetus to confirm that the known phenotypes of the parent(s) are consistent with their respective genotypes.

CHO expression of a novel human recombinant IgG1 anti-RhD antibody isolated by phage display

Replacement of the hyperimmune anti-Rhesus (Rh) D immunoglobulin, currently used to prevent haemolytic disease of the newborn, by fully recombinant human anti-RhD antibodies would solve the current logistic problems associated with supply and demand. The combination of phage display repertoire cloning with precise selection procedures enables isolation of specific genes that can then be inserted into mammalian expression systems allowing production of large quantities of recombinant human proteins. With the aim of selecting high-affinity anti-RhD antibodies, two human Fab libraries were constructed from a hyperimmune donor. Use of a new phage panning procedure involving bromelin-treated red blood cells enabled the isolation of two high-affinity Fab-expressing phage clones. LD-6-3 and LD-6-33, specific for RhD. These showed a novel reaction pattern by recognizing the D variants D(III), D(IVa), D(IVb), D(Va), D(VI) types I and II. D(VII), Rh33 and DFR. Full-length immunoglobulin molecules were constructed by cloning the variable regions into expression vectors containing genomic DNA encoding the immunoglobulin constant regions. We describe the first, stable, suspension growth-adapted Chinese hamster ovary (CHO) cell line producing a high affinity recombinant human IgG1 anti-RhD antibody adapted to pilot-scale production. Evaluation of the Fc region of this recombinant antibody by either chemiluminescence or antibody-dependent cell cytotoxicity (ADCC) assays demonstrated macrophage activation and lysis of red blood cells by human lymphocytes. A consistent source of recombinant human anti-RhD immunoglobulin produced by CHO cells is expected to meet the stringent safety and regulatory requirements for prophylactic application.

Molecular biology and genetics of the Rh blood group system

The Rh (Rhesus) blood group system is the most complex of the known human blood group polymorphisms. The expression of its antigens is controlled by a two-component genetic system consisting of RH and RHAG loci, which encode Rh30 polypeptides and Rh50 glycoprotein, respectively. Over the past decade, there has been a rapid advance in knowledge of the biochemistry, molecular biology, and genetics of the Rh genes and proteins. The primary structures of D and CcEe antigens have become well understood and the molecular genetic basis of a vast array of phenotype polymorphisms has been delineated. The identification of various molecular defects associated with Rh deficiency syndrome clarifies the nature of the amorph, suppressor, and modifier genes. The observed mutation spectrum defines a basic set of components essential for Rh complex assembly in the erythrocyte membrane. The resulting molecular information, combined with new experimental tools, is helping to dissect the fine structure of Rh antigens in terms of epitope mapping. The discovery of novel Rh homologs in primitive organisms and in nonerythroid tissues opens new avenues of research beyond the scope of erythrocytes and Rh antigens. This review provides an update on the Rh family in antigen expression, phenotype diversity, and disease association.

The Rh blood group system: a review

The Rh blood group system is one of the most polymorphic and immunogenic systems known in humans. In the past decade, intense investigation has yielded considerable knowledge of the molecular background of this system. The genes encoding 2 distinct Rh proteins that carry C or c together with either E or e antigens, and the D antigen, have been cloned, and the molecular bases of many of the antigens and of the phenotypes have been determined. A related protein, the Rh glycoprotein is essential for assembly of the Rh protein complex in the erythrocyte membrane and for expression of Rh antigens. The purpose of this review is to provide an overview of several aspects of the Rh blood group system, including the confusing terminology, progress in molecular understanding, and how this developing knowledge can be used in the clinical setting. Extensive documentation is provided to enable the interested reader to obtain further information.

Molecular Configuration of Rh D Epitopes as Defined by Site-Directed Mutagenesis and Expression of Mutant Rh Constructs in K562 Erythroleukemia Cells

The Rh D antigen is the most clinically important protein blood group antigen of the erythrocyte. It is expressed as a collection of at least 37 different epitopes. The external domains of the Rh D protein involved in epitope presentation have been predicted based on the analysis of variant Rh D protein structures inferred from their cDNA sequences and their D epitope expression. This analysis can never be absolute because (1) most partial D phenotypes involve multiple amino acid changes in the Rh D protein and (2) deficiency for 1 or more epitopes may be due to gross structural alteration in the variant Rh D protein structure. We report here the amino acid requirements for the majority of D epitopes. They have been defined by generating a series of novel Rh mutant constructs by mutagenesis using an Rh cE cDNA as template and mutagenic oligonucleotide primers. When transfected into K562 cells, the D epitope expression of the derived mutant clones was then assessed by flow cytometry. The introduction of 9 externally predicted Rh D-specific amino acids on the Rh cE protein was sufficient to express 80% of all tested D epitopes, whereas other clones expressed none. We concluded from our data that the D epitope expression is consistent with at least 6 different epitope clusters localized on external regions of the Rh D protein, most involving overlapping regions within external loops 3, 4, and 6.

Molecular Configuration of Rh D Epitopes as Defined by Site-Directed Mutagenesis and Expression of Mutant Rh Constructs in K562 Erythroleukemia Cells

The Rh D antigen is the most clinically important protein blood group antigen of the erythrocyte. It is expressed as a collection of at least 37 different epitopes. The external domains of the Rh D protein involved in epitope presentation have been predicted based on the analysis of variant Rh D protein structures inferred from their cDNA sequences and their D epitope expression. This analysis can never be absolute because (1) most partial D phenotypes involve multiple amino acid changes in the Rh D protein and (2) deficiency for 1 or more epitopes may be due to gross structural alteration in the variant Rh D protein structure. We report here the amino acid requirements for the majority of D epitopes. They have been defined by generating a series of novel Rh mutant constructs by mutagenesis using an Rh cE cDNA as template and mutagenic oligonucleotide primers. When transfected into K562 cells, the D epitope expression of the derived mutant clones was then assessed by flow cytometry. The introduction of 9 externally predicted Rh D-specific amino acids on the Rh cE protein was sufficient to express 80% of all tested D epitopes, whereas other clones expressed none. We concluded from our data that the D epitope expression is consistent with at least 6 different epitope clusters localized on external regions of the Rh D protein, most involving overlapping regions within external loops 3, 4, and 6.

Rh phenotype prediction by DNA typing and its application to practice

The complexity of the RHD and RHCE genes, which is the greatest of all blood group systems, confounds analysis at the molecular level. RH DNA typing was introduced in 1993 and has been applied to prenatal testing. PCR-SSP analysis covering multiple polymorphisms was recently introduced for the screening and initial characterization of partial D. Our objective is to summarize the accrued knowledge relevant to the approaches to Rh phenotype prediction by DNA typing, their possible applications beyond research laboratories and their limitations. The procedures, results and problems encountered are highly detailed. It is recommended that DNA typing comprises an analysis of more than one polymorphism. We discuss future directions and propose a piecemeal approach to improve reliability and cost-efficiency of blood group genotyping that may eventually replace the prevalent serology-based techniques even for many routine tasks. Transfusion medicine is in the unique position of being able to utilize the most extensive phenotype databases available to check and develop genotyping strategies.

Antenatal genotyping of the blood groups of the fetus

Antenatal genotyping of the fetus is now in widespread use as an aid to the clinical management in cases where there is the potential of haemolytic disease of the newborn occurring. The rapid diagnosis of an antigen-negative fetus will preclude the requirement for further, potentially risky invasive procedures being performed, whilst the determination of an antigen-positive fetus allows the potential of intensifying obstetric care for this pregnancy. Molecular genotyping is a major clinical application which has led from the determination of the molecular bases of blood group antigens expressed, most of which have been defined at the level of the gene. All assays used are dependent on the Polymerase Chain Reaction amplification of fetal DNA derived from either amniotic fluid or chorionic villi. Recent work has explored the potential of utilising fetal cells found to be present in maternal peripheral blood as a source of nucleic acid for prenatal diagnosis. Using non-invasive methods will preclude exposing mother and fetus to the potential hazards of invasive methods (amniocentesis, chorionic villus sampling and cordocentesis) which include miscarriage, fetal malformations and further maternal alloimmunisation.

Three Molecular Structures Cause Rhesus D Category VI Phenotypes With Distinct Immunohematologic Features

Rhesus D category VI (DVI) is the clinically most important partial D. DVI red blood cells were assumed to possess very low RhD antigen density and to be caused by twoRHD-CE-D hybrid alleles. Because there was no population-based work-up, we screened three populations in central Europe for DVI. Twenty-six DVI samples were detected and examined by exon-specific RHD polymerase chain reaction with sequence-specific primers (PCR-SSP). A new genotype, hereby designated D category VI type III, was characterized as a RHD-Ce(3-6)-D hybrid allele by sequencing of the cDNA, parts of intron 1, and by PCR-restriction fragment length polymorphism (PCR-RFLP) of intron 2. Rhesus introns 5 and 6 were sequenced and the 3′ breakpoints of all knownDVItypes shown to be distinct. We differentiated the 5′ breakpoints of DVItypeI andDVItype II by a newly devised RHD-PCR. Thus, the DVI phenotype originated in at least three independent molecular events. Each DVI type showed distinct immunohematologic features in flow cytometry. The number of RhD proteins accessible on the red blood cells' surface ofDVItype III was normal (about 12,000 antigens/cell; DVItypeI, 500;DVItype II, 2,400) based on the determination of an RhD epitope density profile. DVItype II and DVItype III occurred as CDe haplotypes, and DVItype I as a cDE haplotype.The distribution of the DVItypes varied significantly in three German-speaking populations. Genotyping strategies should take account of allelic variations in partial RhD. The reconsideration of previous serologic and clinical data for partial D in view of the underlying molecular structures may be worthwhile.

Three Molecular Structures Cause Rhesus D Category VI Phenotypes With Distinct Immunohematologic Features

Rhesus D category VI (DVI) is the clinically most important partial D. DVI red blood cells were assumed to possess very low RhD antigen density and to be caused by twoRHD-CE-D hybrid alleles. Because there was no population-based work-up, we screened three populations in central Europe for DVI. Twenty-six DVI samples were detected and examined by exon-specific RHD polymerase chain reaction with sequence-specific primers (PCR-SSP). A new genotype, hereby designated D category VI type III, was characterized as a RHD-Ce(3-6)-D hybrid allele by sequencing of the cDNA, parts of intron 1, and by PCR-restriction fragment length polymorphism (PCR-RFLP) of intron 2. Rhesus introns 5 and 6 were sequenced and the 3′ breakpoints of all knownDVItypes shown to be distinct. We differentiated the 5′ breakpoints of DVItypeI andDVItype II by a newly devised RHD-PCR. Thus, the DVI phenotype originated in at least three independent molecular events. Each DVI type showed distinct immunohematologic features in flow cytometry. The number of RhD proteins accessible on the red blood cells' surface ofDVItype III was normal (about 12,000 antigens/cell; DVItypeI, 500;DVItype II, 2,400) based on the determination of an RhD epitope density profile. DVItype II and DVItype III occurred as CDe haplotypes, and DVItype I as a cDE haplotype.The distribution of the DVItypes varied significantly in three German-speaking populations. Genotyping strategies should take account of allelic variations in partial RhD. The reconsideration of previous serologic and clinical data for partial D in view of the underlying molecular structures may be worthwhile.

Human D(IIIa) erythrocytes: RhD protein is associated with multiple dispersed amino acid variations

As a partial D antigen of the Rh blood group system, the D category IIIa phenotype occurs mainly in Blacks, but its molecular basis has not been defined. Here we describe studies of the D category D(IIIa) and VS+ red blood cells (RBC) from two unrelated probands by Southern blot, cDNA PCR, and nucleotide sequencing. Rh haplotyping by Sph I restriction fragment length polymorphisms indicated that the two probands carried Dce/dCe and Dce/DcE genotypes, respectively. Sequence analysis of Rh cDNAs showed that their erythroid cells expressed both D and CE transcripts. Nevertheless, the D transcripts were found to contain four nucleotide changes scattered in three exons: nt455 A-to-C (exon 3), nt602 C-to-G (exon 4), nt 654 C-to-G (exon 5), and nt667 T-to-G (exon 5). These variations resulted in the following amino acid substitutions characteristic of RhCE polypeptides: 152 Asn-to-Thr, 201 Thr-to-Arg, 218 Ile-to-Met, and 223 Phe-to-Val. The 152Thr and 223Val residues were predicted to reside in proximity to the third and fourth extracellular loops, respectively. Together, these results establish a correlation of the four amino acid changes in the RhD protein with the expression of D(IIIa) as a partial D antigen on the RBC membrane. Since the varied nucleotides identified in D(IIIa) all pre-exist in CE, they are likely to have originated from CE by templated micro-conversion event(s). The identification of a specific nt736 C-to-G transversion in CE in the two probands suggests that 245Val may involve the expression of VS antigen.

Evidence of Genetic Diversity Underlying Rh D−, Weak D (Du), and Partial D Phenotypes as Determined by Multiplex Polymerase Chain Reaction Analysis of the RHD Gene

The human blood group Rh antigens are expressed by proteins encoded by a pair of highly homologous genes located at chromosome 1p34-36. One of the genes (RHCE ) encodes Rh CcEe antigens, while the other (RHD) the D antigen. Point mutations in the RHCE gene generate the C/c and E/e polymorphisms, while it has been shown that an RHD gene deletion can generate the D-negative phenotype. We have analyzed intron 4 of the RHCE and RHD genes and have defined the site of an RHD-specific deletion located in this intron. Using a multiplex RHD typing assay, which combines a reverse polymerase chain reaction (PCR) primer, which straddles this RHD-specific sequence, and a pair of primers located in exon 10 of the RHD gene, we have analyzed 357 different genomic DNA samples derived from individuals expressing D+, D−, weak D, and partial D phenotypes. Of these, we have noted a significant discordance with our multiplex PCR assay in the D− phenotypes dCcee and dccEe (which have been previously described) and weak D phenotypes. Our results suggest that in five serologically D− individuals we have identified an apparently intact RHD gene. Sequence analysis of transcripts obtained from one of these individuals (of phenotype dCCee) illustrates the presence of full-length RHD transcripts, which have a point mutation at nucleotide 121 (C → T), which generates an in-frame stop codon (Gln41Stop). Thus, we describe a different molecular basis for generating the D− phenotype to the complete RHD gene deletion described previously. We also show that there are discordances with serotype and the multiplex assay in weak D and partial D phenotypes, indicating that the underlying molecular basis can be heterogeneous. Existing Rh D PCR assays assume the complete absence of the RHD gene in D− phenotypes. We describe a different molecular basis for generating the D− phenotype to the complete RHD gene deletion described previously.

Tentative model for the mapping of D epitopes on the RhD polypeptide

The partial D phenotypes correspond to D-positive individuals that may develop anti-D antibodies following immunization by transfusion or pregnancy, since they lack some of the D epitopes that compose the D antigen. When these red cells are tested with a panel of human monoclonal anti-D, different patterns of reactivity are observed and at least nine distinct epitopes termed epD1 to epD9 can be identified. Molecular analysis of partial D variants have shown that the loss of some D epitopes is associated either with intergenic recombination events between the D and CE genes generating hybrid gene structures D-CE-D or CE-D-CE, or with point mutations of the D gene. Based on these findings, a tentative model that correlates critical amino acid positions and D epitope expression on the D protein was proposed. Although recent studies suggest that the D antigen may be composed of as many as 30 epitopes, the relatively simple model presented here may be useful to serologists as a preliminary approach to understanding the basis of D antigenic variation in terms of structure-activity relationship.

Rh DNA--coordinator's report

Four laboratories contributed to molecular analysis of 66 Rh variant samples originating from 12 countries. Most studies were carried out on genomic DNA using allele-specific-PCR, PCR-RFLP or nucleotide exon sequencing. In some cases, the molecular basis of some new phenotypes was established by DNA sequence analysis and the basis for the DVIE haplotypes was revisited.

Molecular biology of partial D phenotypes

We have examined all DVI variant phenotypes submitted to the workshop by a combination of RT-PCR, multiplex RHD PCR and immunoblotting with Rh antipeptide sera. Our findings suggest that all DVI phenotypes arise through hybrid RHD-RHCE-RHD genes. Genomic DNA derived from all DVI samples were shown to be RHD intron 4 negative when analysed with an RHD intron 4/exon 10 multiplex assay. We assume therefore that all DVI phenotypes involve gene conversion events involving at least exons 4 and 5 of the RHD gene. Analysis of a novel D and E variant phenotype individual (ISBT49) by RT-PCR has allowed the identification of a hybrid Rh gene composed of exons 1-4 RHD: 5 RHCE/D and 6-10 RHD. We propose that the partial D & E phenotype observed arises through D & E expression on the hybrid RHD-RHCE-RHD protein: as no transcripts encoding Rh E could be found.