Analysis of Human Lymphocyte Antigen Class I Expression in Gastric Cancer by Reverse Transcriptase–Polymerase Chain Reaction Nirmal Dutta, Durjoy Majumder, Arnab Gupta, Debendra Nath Guha Mazumder, and Subrata Banerjee ABSTRACT: Malignant cells have been reported to escape immune surveillance by modulation of human lymphocyte antigen (HLA) class Ia molecule and/or other accessory molecules like TAP (transporter associated with antigen processing) and 2-M expression. Most of these reports, however, are based on immunohistochemistry techniques with polymorphic- or isotype-specific antibodies. In the present study, we have instead used a locus-specific reverse transcriptase–polymerase chain reaction– based approach to detect the transcriptional expression of HLA class Ia as well as accessory molecules in gastric cancer. Our results indicate that HLA class Ia transcript is totally absent in only 9% of cancer cases. Locus-specific expression of HLA-A and -B could, however, be detected in 54% cases, whereas HLA-C was expressed in most of the cancer tissues. Inter- estingly, in some cases where HLA class Ia expression was observed, TAP1 expression could not be detected. Further- more, we also investigated the frequency of nonclassical or HLA class Ib expression for molecules such as HLA-E and -G. HLA-G transcript was absent in gastric tissues both in cancerous and autologous normal region, whereas HLA-E was observed in a number of gastric cancers. Altogether these selective locus-specific losses of HLA class I along with impaired expression of accessory molecules may ex- plain the complex phenomena by which gastric tumors escape both cytotoxic T-lymphocyte– as well as natural killer cell–mediated immune defense. Human Immunology 66, 164 –169 (2005). © American Society for Histocom- patibility and Immunogenetics, 2004. Published by Elsevier Inc. KEYWORDS: gastric cancer; HLA class Ia; HLA class Ib; transcription ABBREVIATIONS 2m 2-microglobulin GC gastric cancer HLA human lymphocyte antigen IHC immunohistochemistry mAb monoclonal antibody NK natural killer PBS phosphate buffered solution RT-PCR reverse transcriptase–polymerase chain reaction TAP transporter associated with antigen processing INTRODUCTION In humans, major histocompatibility complex class I antigens are highly polymorphic molecules encoded by three closely linked loci designated human lymphocyte antigen (HLA)-A, -B, and -C. Major histocompatibility complex class I heavy chain noncovalently associate with a nonpolymorphic light chain 2-microglobulin (2m) and are ubiquitously expressed in all nucleated cells. They present intracellular peptides to cytotoxic T-lym- phocytes, enabling the process of immune recognition [1, 2]. Downregulation or complete loss of HLA class Ia antigen expression has been reported in a variety of human tumors and was proposed to be a mechanism to evade immune surveillance and tumor progression [3–5]. From the Biophysics Division (N.D., D.M., S.B.), Saha Institute of Nuclear Physics, Kolkata, and Gastrointestinal Oncology Department (A.G., D.N.G.M.), Cancer Centre Welfare Home and Research Institute, Thakurpukur, Kolkata, India. Address reprint requests to: Dr. Subrata Banerjee, Biophysics Division, Saha Institute of Nuclear Physics, Sector I Block AF, Bidhannagar, Kolkata 700 064, India; Tel: (91) 33-2337 0379; Fax: (91) 33-2337-4637; E-mail: subrata@biop.saha.ernet.in. Human Immunology 66, 164 –169 (2005) © American Society for Histocompatibility and Immunogenetics, 2004 0198-8859/05/$–see front matter Published by Elsevier Inc. doi:10.1016/j.humimm.2004.10.010