Identification of B*9550, a novel B*15 allele, in a Mexican bone marrow donor from Veracruz State C. Alaez 1 , A. Munguía 1 , A. H. Flores 1 , K. Gomez 2 & C. Gorodezky 1 1 Department of Immunology and Immunogenetics, Instituto de Diagno ´stico y Referencia Epidemiolo ´gicos, Secretary of Health, Mexico City, Mexico 2 Servicio de Oncologı ´a Pediatrica, Hospital Regional de Rio Blanco, Veracruz, Mexico Key words: human leukocyte antigen-B*9550; new allele; Mexican Mestizo Human leukocyte antigen-B*9550 is a novel allele identified in a Mexican Mestizo bone marrow donor from Veracruz. The human leukocyte antigen (HLA)-B locus is the most polymorphic locus of the entire human genome. As of July 2008, 1077 alleles were described encoding for 911 proteins. HLA-B*15 has the highest variability (157 alleles) of all the HLA-B groups (1). Here we describe B*9550, a novel B*15 allele, identified during typing of newly recruited donors for the Mexican Bone Marrow Donor Registry (DONORMO). The donor is a Mexican Mestizo male born in Veracruz. His HLA phenotype is A*31, A*68 B*3905, B*9550, Cw*03, Cw*07, DRB1*0407, DRB1*0802, DQB1*0302, DQB1*0402. The donor’s B locus showed an unusual hybridization pattern using the HLA-B updated reverse dot-blot typing kit (Innogenetics, Inc., Gent, Belgium). This pattern could not be completely assigned to a pair of B alleles. Therefore, HLA- B exons 2, 3 and 4 were sequenced in both directions using the AlleleSEQR HLA-B kit (Atria Genetics, San Francisco, CA) and an ABI Prism 310 Genetic Analyzer (Applied Biosys- tems, Foster City, CA). The ASSIGN 3.51 software was used for analysis (Conexio Genomics, Applecross, Western Australia, Australia). No exact match was found: the B*1530, B*3905 allele pair had two mismatches in exon 3 at positions 463 and 477. The sequence for exon 4 for B*1530 was not available in the library, but considering exon 4 of the sample, the best assignment was B*3905, B*1563, with three mismatches in the following positions: 412 (sample consensus A expected R), 463 (sample consensus M expected A) and 477 (sample consensus S expected G). To further confirm the allele assignment, B*15 and B*39 were amplified separately using two group-specific primers: S4B4 (specific for B*15, *45, *46, *49 and *50) and S4B8 (specific for B*14, *38, *39 and *6701) (Protrans, Ketsch, Germany). Both polymerase chain reaction products were sequenced for exons 2–4. The results showed an exact match for B*3905. However, for B*9550, there were three mismatches with B*1563 at nucleotides 412 (codon 114), 463 (codon 131) and 477 (codon 135) (Figure 1). At position 412, G/A (codon 114 GAC/AAC) resulted in a coding change of 114D to N. At position 463, A/C (codon 131 AGC/CGC) resulted in a coding change 131S to R. In addition, G/C was found at position 477 (codon 135 GCG/GCC). The substitution at codon 135 is synonymous and 135A is present in both alleles. This new allele was reconfirmed with the donor’s father typing and is part of haplotype A*68-B*9550-Cw*03- DRB1*0802-DQB1*0402. B*9550 was submitted to the GenBank; the accession number is FJ360529. The name B*9550 has been officially assigned by the World Health Organization (WHO) Nomenclature Committee in July 2008. This follows the agreed policy that, subject to the condition stated in the most recent Nomenclature report (2), names will be assigned to new sequences as they are identified. A list of such new names will be published in the following WHO Nomenclature report. Because B*9550 has only two differences with B*1530 (positions 463 and 477), we sequenced the exon 4 of two B*1530 bone marrow donors (Figure 1). The sequence of B*1530-exon 4 is identical to that of B*9550 and was also submitted to the GenBank; the accession number is FJ609980. The IMGT/HLA submission number is HWS10005932. The frequency of B*1530 in Mexicans is by far much higher than that seen for B*1563 (B*1530, allele frequency ¼ 1% at the DONORMO). It may be suggested that B*9550 was generated by a gene conversion event in which B*1530 acts as a recipient of a segment spanning 614 ª 2009 John Wiley & Sons A/S  Tissue Antigens 73, 604–628