High Frequency of HLA-B44 Allelic Losses in Human Solid Tumors Teresa Cabrera, Isabel Maleno, Miguel Angel Lopez-Nevot, Maximino Redondo, Maria Angustias Fernandez, Antonia Collado, and Federico Garrido ABSTRACT: Human leukocyte antigen (HLA) class I downregulation, a frequent phenomenon observed in a variety of human tumors, favors tumor immune escape from T-lymphocyte recognition. However, it is not known whether a particular HLA class I allele is lost more frequently than others. To address this question we ana- lyzed HLA class I expression in tumor tissues derived from 300 patients diagnosed as having breast, colorectal, or laryngeal carcinomas. Cryostatic tumor sections and a broad panel of anti-HLA class I monoclonal antibodies were used. We found that the HLA-B44 allele was lost more frequently than other HLA class I alleles, and that the difference was not related with changes in HLA-B44 allele frequencies between patients and controls. In addi- tion, we observed that 35% of the HLA-B44 negative tumors presented HLA haplotype loss associated with loss of heterozygosity. These tests were performed on DNA samples obtained from microdissected tumor tissues. The results seem to indicate that HLA class I allelic losses are not randomly distributed during tumor development but that some HLA class I alleles, and HLA-B44 in particular, are more frequently downregulated and may play an im- portant role in immune escape mechanisms. Human Im- munology 64, 941–950 (2003). © American Society for Histocompatibility and Immunogenetics, 2003. Pub- lished by Elsevier Inc. KEYWORDS: HLA; expression; tumor; LOH; HLA- B44 ABBREVIATIONS HLA human leukocyte antigen PBL peripheral blood lymphocyte LOH loss of heterozygosity MIN microsatellite instability LMP low-molecular-weigh protein HPV human papilloma virus STRs short tandem repeats SSO sequence-specific oligonucleotide mAb monoclonal antibody TAP transporter-associated antigen processing CTL cytotoxic T lymphocyte IFN interferon INTRODUCTION Human tumors derived from human leukocyte antigen (HLA) class I positive epithelia totally or partially lose HLA class I antigens during tumor development [1–3]. This finding has been interpreted as a consequence of immune selection of HLA class I deficient tumor cell clones by a highly selective antitumor immune response mediated by cytotoxic T lymphocytes and directed against tumor-specific antigens [4 – 6]. These variant clones can escape specific T-cell responses and acquire new properties that allow them to invade and metasta- size. Evidence obtained recently in experimental tumor systems supports this hypothesis [7]. Altered HLA class I tumor phenotypes can be classi- fied into several major groups depending on the mech- anism and the number of alleles lost: HLA total loss (phenotype I), HLA haplotype loss (phenotype II), HLA-A or -B locus loss (phenotype III), HLA allelic losses (phenotype IV), compound phenotype (phenotype From the Departamento de Ana ´slisis Clı´nicos (T.C., I.M., M.A.L.-N., M.A.F., F.G.), and Unidad de Investigacio ´n (A.C.), Hospital Universi- tario Virgen de las Nieves, Universidad de Granada, Granada, Spain; and the Departamento de Ana ´lisis Clı´nicos (M.R.), Hospital Costa del Sol, Marbella, Spain. Address reprint requests to: Dr. Federico Garrido, Servicio de Ana ´lisis Clı´nicos, Hospital Virgen de las Nieves, Avda. Fuerzas Armadas n.2, 18014 Granada, Spain; Tel: +34 (958) 283147; Fax: +34 (958) 283147; E-mail: federico.garrido.sspa@juntadeandalucia.es. Received February 20, 2003; revised June 6, 2003; accepted June 16, 2003. Human Immunology 64, 941–950 (2003) © American Society for Histocompatibility and Immunogenetics, 2003 0198-8859/03/$–see front matter Published by Elsevier Inc. doi:10.1016/S0198-8859(03)00164-2