<scp>KHOZ</scp> (<scp>KEL41</scp>): A novel low‐prevalence antigen in the Kell blood group system antithetical to <scp>KHIZ</scp> (<scp>KEL40</scp>)

The Kell blood group system (ISBT 006) comprises many antigens that are carried on a single-pass transmembrane glycoprotein.1, 2 The Kell glycoprotein is encoded by the KEL gene, which is highly polymorphic.3 KEL*01 and KEL*02 encode major antigens K and k, respectively.3 The most recent antigen added into the KEL system, numbered KEL40, was identified through a female patient in France, of Turkish heritage, who presented with an antibody to a high-prevalence antigen.4 Her plasma reacted (3+) with all untreated, papain-treated, and trypsin-treated red blood cells (RBCs) but failed to react with KEL null RBCs, K0 (Ku–).4 The patient's antibody reactivity was completely inhibited by soluble recombinant KEL protein. Genomic sequencing showed the patient was homozygous for KEL*02 c.1538G>A (rs143144958), predicting an amino acid change p.Arg513Gln. In gnomAD v4.1.0, the rs143144958 (chr7:142,943,837) has an allele frequency of 2.1 × 10−5 in Europeans (non-Finnish), 8.8 × 10−5 in South Asians, 4.5 × 10−5 in East Asians and 1.3 × 10−5.5 The patient's antibody recognized a novel high-prevalence antigen, arising from the p.Arg513 amino acid. This was recognized by the International Society of Blood Transfusion (ISBT) Working Party (WP) on Red Cell Immunogenetics and Blood Group Terminology (RCI and BGT) as KEL40, named KHIZ after the proband's name, with the patient lacking the KHIZ antigen (KHIZ–).3 Concurrently, a female Australian patient presenting with multiple myeloma and with a history of transfusions experienced a hemolytic transfusion reaction (HTR) after receiving a unit of RBCs issued by electronic crossmatch. Prior to this HTR event, the antibody screen was repeatedly negative and therefore an electronic crossmatch was deemed appropriate. Following this HTR, laboratory investigations showed her plasma failed to react with any reagent RBC screening cell panels (saline room temperature and PEG-indirect antiglobulin test [IAT]) but reacted (3+) with the transfused donor RBCs by Column Agglutination Technology-IAT. This report shows that the donor's RBCs express a low-prevalence KEL antigen antithetical to KHIZ. Blood samples from the Australian blood donor of Italian heritage, who donates regularly, and the patient (pre-transfusion) were investigated. Antibody identification tests were performed using standard immunohematology methods with untreated, papain-treated, trypsin-treated, chymotrypsin-treated, and 0.2 M Dithiothreitol (DTT)-treated reagent RBCs as well as RBCs with the following KEL phenotypes: Js(a+), KEL:17, VONG+, and KHIZ−. Genotyping was determined by Immucor HEA BeadChip and Massively Parallel Sequencing (MPS).6 The Australian blood donor RBCs were group O, D+C+E−c−e+, K−k+, Kp(a−b+) and the patient (pre-transfusion sample) was group O, D+, K−k+. The Australian patient's plasma reacted with papain-treated, trypsin-treated, and chymotrypsin-treated donor RBCs (IAT) but was negative with 0.2 M DTT-treated donor RBCs (IAT). This reactivity profile narrowed down the probable specificity to blood group systems including KEL. Plasma from the patient failed to react with the following respective RBC phenotypes: Js(a+), KEL:17, VONG+ RBCs but reacted (3+) with KHIZ− RBCs. Plasma from the French patient, who formed anti-KHIZ, reacted (3+) with the Australian donor RBCs. BeadChip and MPS genotyping predicted K−k+, Kp(a−b+), and Js(a−b+) for the patient and the blood donor. In addition, MPS showed that the blood donor was KEL c.1538G/A (NM_000420.3:c.1538G/A heterozygous), predicting p.Arg513 and p.Gln513, Figure 1. DNA sequence was assigned accession number GenBank MG818162 (https://www.ncbi.nlm.nih.gov/nuccore/MG818162). No other variants were detected on either the KEL or XK genes for the blood donor and patient. The Australian blood donor expresses both the high-prevalence KHIZ antigen and a novel low-prevalence KEL antigen defined by the antibody in the plasma from the Australian patient. The ISBT WP on RCI and BGT assigned KEL41 for this low-prevalence antigen named KHOZ: K (KEL system), H (first letter of patient's surname), and OZ (the colloquial name for Australia). The presence of a low-prevalence KEL antigen does not impact the blood donor's eligibility to donate blood. Therefore, this blood donor continues with regular blood donation, and there have been no other reports of incompatibility following the transfusion of red blood cells from this donor. The Australian patient had formed an antibody recognizing the low-prevalence antigen, KHOZ, expressed on the RBCs of the blood donor (KHIZ+, KHOZ+), and on the patient from France shown to be KHIZ−, KHOZ+. High-prevalence KHIZ (KEL40), encoded by KEL c.1538G (p.Arg513), and low-prevalence KHOZ (KEL41), encoded by KEL c.1538A (p.Gln513) are antithetical antigens. Anti-KHOZ was clinically significant in our patient, who developed an HTR. Australian Governments fund Australian Red Cross Lifeblood for the provision of blood, blood products, and services to the Australian community. This study has approval from the Australian Red Cross Lifeblood Human Research Ethics Committee Application Number 2019#04. We thank Dr. Lydia Singaraveloo for her contributions to this study. Open access publishing facilitated by University of the Sunshine Coast, as part of the Wiley - University of the Sunshine Coast agreement via the Council of Australian University Librarians. The authors have disclosed no conflicts of interest.