Pierre-Yves Le Pennec

Proof of principle for transfusion of in vitro–generated red blood cells

In vitro RBC production from stem cells could represent an alternative to classic transfusion products. Until now the clinical feasibility of this concept has not been demonstrated. We addressed the question of the capacity of cultured RBCs (cRBCs) to survive in humans. By using a culture protocol permitting erythroid differentiation from peripheral CD34(+) HSC, we generated a homogeneous population of cRBC functional in terms of their deformability, enzyme content, capacity of their hemoglobin to fix/release oxygen, and expression of blood group antigens. We then demonstrated in the nonobese diabetes/severe combined immunodeficiency mouse that cRBC encountered in vivo the conditions necessary for their complete maturation. These data provided the rationale for injecting into one human a homogeneous sample of 10(10) cRBCs generated under good manufacturing practice conditions and labeled with (51)Cr. The level of these cells in the circulation 26 days after injection was between 41% and 63%, which compares favorably with the reported half-life of 28 ± 2 days for native RBCs. Their survival in vivo testifies globally to their quality and functionality. These data establish the proof of principle for transfusion of in vitro-generated RBCs and path the way toward new developments in transfusion medicine. This study is registered at http://www.clinicaltrials.gov as NCT0929266.

Characterization of the Gene Encoding the Human Kidd Blood Group/Urea Transporter Protein EVIDENCE FOR SPLICE SITE MUTATIONS IN JknullINDIVIDUALS

The Kidd (JK) blood group is carried by an integral membrane glycoprotein which transports urea through the red cell membrane and is also present on endothelial cells of the vasa recta in the kidney. The exon-intron structure of the human blood group Kidd/urea transporter gene has been determined. It is organized into 11 exons distributed over 30 kilobase pairs. The mature protein is encoded by exons 4–11. The transcription initiation site was identified by 5′-rapid amplification of cDNA ends-polymerase chain reaction at 335 base pairs upstream of the translation start point located in exon 4. The 5′-flanking region, from nucleotide −837 to −336, contains TATA and inverted CAAT boxes as well as GATA-1/SP1 erythroid-specificcis-acting regulatory elements. Analysis of the 3′-untranslated region reveals that the two equally abundant erythroid transcripts of 4.4 and 2.0 kilobase pairs arise from usage of different alternative polyadenylation signals. No obvious abnormality of the Kidd/urea transporter gene, including the 5′- and 3′-untranslated regions, has been detected by Southern blot analysis of the blood of two unrelated Jknull individuals (B.S. and L.P.), which lacks all Jk antigens and Jk proteins on red cells, but was genotyped as homozygous for a “silent”Jk b allele. Further analysis indicated that different splice site mutations occurred in each variant. The first mutation affected the invariant G residue of the 3′-acceptor splice site of intron 5 (variant B.S.), while the second mutation affected the invariant G residue of the 5′-donor splice site of intron 7 (variant L.P.). These mutations caused the skipping of exon 6 and 7, respectively, as seen by sequence analysis of the Jk transcripts present in reticulocytes. Expression studies in Xenopusoocytes demonstrated that the truncated proteins encoded by the spliced transcripts did not mediate a facilitated urea transport compared with the wild type Kidd/urea transporter protein and were not expressed on the oocyte’s plasma membrane. These findings provide a rational explanation for the lack of Kidd/urea transporter protein and defect in urea transport of Jknull cells.

ABCB6 is dispensable for erythropoiesis and specifies the new blood group system Langereis.

The human ATP-binding cassette (ABC) transporter ABCB6 has been described as a mitochondrial porphyrin transporter essential for heme biosynthesis, but it is also suspected to contribute to anticancer drug resistance, as do other ABC transporters located at the plasma membrane. We identified ABCB6 as the genetic basis of the Lan blood group antigen expressed on red blood cells but also at the plasma membrane of hepatocellular carcinoma (HCC) cells, and we established that ABCB6 encodes a new blood group system (Langereis, Lan). Targeted sequencing of ABCB6 in 12 unrelated individuals of the Lan(−) blood type identified 10 different ABCB6 null mutations. This is the first report of deficient alleles of this human ABC transporter gene. Of note, Lan(−) (ABCB6−/−) individuals do not suffer any clinical consequences, although their deficiency in ABCB6 may place them at risk when determining drug dosage.

Relative immunogenicity of Fya and K antigens in a Caucasian population, based on HLA class II restriction analysis.

BACKGROUND: It has long been known that relative immunogenicity is a characteristic of protein red blood cell (RBC) antigens, but the mechanisms remain unclear. The aim of this work was to elucidate the mechanisms underlying this relative immunogenicity.

Null alleles of ABCG2 encoding the breast cancer resistance protein define the new blood group system Junior.

The breast cancer resistance protein, also known as ABCG2, is one of the most highly studied ATP-binding cassette (ABC) transporters because of its ability to confer multidrug resistance. The lack of information on the physiological role of ABCG2 in humans severely limits cancer chemotherapeutic approaches targeting this transporter. We report here that ABCG2 comprises the molecular basis of a new blood group system (Junior, Jr) and that individuals of the Jr(a−) blood type have inherited two null alleles of ABCG2. We identified five frameshift and three nonsense mutations in ABCG2. We also show that the prevalence of the Jr(a−) blood type in the Japanese and European Gypsy populations is related to the p.Gln126* and p.Arg236* protein alterations, respectively. The identification of ABCG2−/− (Jr(a−)) individuals who appear phenotypically normal is an essential step toward targeting ABCG2 in cancer and also in understanding the physiological and pharmacological roles of this promiscuous transporter in humans.

RhD variants in Caucasians: consequences for checking clinically relevant alleles

BACKGROUND:  Weak D type carriers cannot be immunized against D except when antigen density is below 400 antigens per RBC, whereas partial D carriers can produce anti‐D.

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.

Heterogeneity of blood group RhE variants revealed by serological analysis and molecular alteration of the RHCE gene and transcript

After testing red cells from 12 RhE variants with a panel of anti‐E monoclonal antibodies (MoAbs), four patterns of reactivity were detected indicating that the MoAbs may recognize four distinct E epitopes designated epE1, epE2, epE3 and epE4. The variants were classified into four categories (cat EI to EIV) which carried epE1 and epE2, epE1 and epE4, epE1, epE3 and epE4, and all four epitopes, respectively. Molecular analysis of the transcripts and genomic DNA of the variants from cat EI, EII and EIII displayed three distinct genetic alterations. Cat EI variants exhibited a point mutation (T500A) in exon 4 of the RHCE gene that resulted in a Met167Lys substitution in the third extracellular loop of the RhcE protein. Cat EII variant carried a hybrid gene structure characterized by replacement of exons 1–3 (or 2–3) of the RHCE gene by their specific counterparts in the RHD gene. This latter variant was also associated with a weak expression of the RhC antigen. In cat EIII variants there was a partial DNA exchange of exon 5 sequences (nt 697 and 712) between the RHCE and the RHD genes, generating a hybrid Rh cE‐D‐cE protein carrying the Glu233 and Val238 substitutions.

Heterogeneous molecular background of the weak C, VS+, hrB-, HrB-phenotype in black persons

BACKGROUND: The rare HrB– phenotype is encoded by the (C)ces haplotype when present at the homozygous state. This haplotype contains two altered genes: a hybrid RHD‐CE‐Ds gene segregated with a ces allele of RHCE (733C>G and 1006G>T substitutions in Exon 5 and Exon 7 respectively). The aim of this study was to further investigate the molecular background of the (C)ces haplotype.

Analysis of RhCE variants among 806 individuals in France: considerations for transfusion safety, with emphasis on patients with sickle cell disease

BACKGROUND: DNA testing has enabled the documenting of numerous variants of RHCE alleles, especially in individuals of African origin. The risk for production of clinically significant alloantibodies to Rh antigens of patients carrying variant RHCE alleles has led us to analyze the different RhCE variants investigated by molecular biology. Alloimmunization was analyzed regarding the RHCE genetic profile.