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Distribution of HLA class I altered phenotypes in colorectal carcinomas: high frequency of HLA haplotype loss associated with loss of heterozygosity in chromosome region 6p21
Authors:Isabel?Maleno  Carmen?Maria?Cabrera  Teresa?Cabrera  Laura?Paco  Miguel?Angel?López-Nevot  Antonia?Collado  Antonio?Ferrón  Email author" target="_blank">Federico?GarridoEmail author
Institution:(1) Servicio de Análisis Clínicos, Hospital Universitario Virgen de las Nieves, Avd. Fuerzas Armadas 2, 18014 Granada, Spain;(2) Unidad Experimental, Hospital Universitario Virgen de las Nieves, 18014 Granada, Spain;(3) Servicio de Cirugía, Hospital Universitario Virgen de las Nieves, 18014 Granada, Spain
Abstract:HLA class I loss or down-regulation is a widespread mechanism used by tumor cells to avoid tumor recognition by cytotoxic T lymphocytes, and thus favor tumor immune escape. Multiple mechanisms are responsible for these HLA class I alterations. In different epithelial tumors, loss of heterozygosity (LOH) at chromosome region 6p21.3, leading to HLA haplotype loss, occurs in 6–50% of all cases depending on the tumor entity. In this paper we report the frequency of LOH at 6p21 in 95 colorectal carcinomas (CRC) previously analyzed for altered HLA class I expression with immunohistological techniques. We used PCR microsatellite amplification of selected STR markers located on Chromosome 6 to identify LOH with DNA from microdissected tumor tissues and the surrounding stroma. Sequence-specific oligonucleotide analysis was performed in microdissected stroma and tumor cells for HLA typing, and to detect HLA haplotype loss. A high frequency (40%) of HLA haplotype loss was found in CRC. Eight tumors showed microsatellite instability. We sometimes observed two or more mechanisms responsible for HLA alteration within the same HLA-altered phenotype, such as LOH and HLA class I total loss. In 25 tumors (26%) no HLA class I alteration could be identified. These data are potentially relevant for CRC patients undergoing T-cell-based immunotherapy.
Keywords:HLA  Loss of heterozygosity  Haplotype loss  Escape  Colorectal carcinomas
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