HLA class I and beta-2-microglobulin (beta 2m) expression in a moderately differentiated laryngeal squamous cell carcinoma appeared to be downregulated when analyzed by immunohistochemical procedures using the monomorphic anti-HLA class I monoclonal antibody (mAb; W6/32), locus-specific (HCA2 and HC10) and allele-specific (LT129.11 and KRE501) mAbs and anti-beta 2m mAbs. To reveal the molecular basis of downregulated HLA class I expression, HLA-A typing was performed on DNA derived from peripheral blood lymphocytes (PBL) and the tumor. Sequencing-based typing (SBT) revealed HLA-A*02011, 31012. In addition to HLA-A*02011, 31012 alleles, the tumor contained an HLA-A*31012 allele, which lacked all introns when sequenced from the initiation codon through exon eight. The 3' UTR region was intact up to at least 200 bp downstream. The mutant HLA-A*31012 is restricted to laryngeal tumor tissue since it was not amplified in flanking tumor-free laryngeal tissue. The mutant HLA-A*31012 shares structural characteristics with processed pseudogenes, i.e., absence of introns and an intact 3' UTR. This indicates that the mutant HLA-A*31012 allele resulted from a retroposition (reverse transcription and integration) from the processed transcript of the wild-type HLA-A*31012 allele within a clonal tumor cell. Genes Chromosomes Cancer 27:26-34, 2000. (C) 2000 Wiley-Liss, Inc.

Down-regulated human leukocyte antigen (HLA) class I expression is frequently correlated with allelic loss at 6p21.3, which is the location of the HLA coding sequence, in head and neck squamous cell carcinomas (HNSCCs). Previously, we have demonstrated loss of heterozygosity (LOH) at 6p21.3 for at least one locus in 49% of the HNSCCs using 5 microsatellite markers spanning the 4 megabase HLA region. In the present study, the detection threshold (25%) to assign LOH was addressed by laser-assisted microdissection of tumor cells from tumors containing marginal loss. In addition, we describe high density microsatellite analysis of chromosome 6p21.3 in HNSCC with down-regulated HLA class I expression. The purpose of this study was to refine the identification of genetic alterations at 6p21.3 and to pinpoint allelic loss to individual HLA class I genes, using additional markers closely located to the HLA-A, -B, and -C loci and the transporter associated with antigen processing (TAP) genes. LOH analysis by amplification of microsatellite markers and subsequent fluorescent detection is a rapid and sensitive technique to predict HLA class I loss phenotypes in tumors. LOH can be identified at 25% relative signal reduction. Analysis of heterogeneous tumor samples and samples containing a small amount of tumor cells is facilitated by laser-assisted microdissection of tumor cells. In addition, we showed that accurate HLA LOH analysis requires application of microsatellite markers in close proximity to HLA class I and TAP genes.

Short tandem repeat (STR) markers are currently used to define loss of heterozygosity (LOH) of genes and chromosomes in tumors. Chromosome 6 and chromosome 15 STR markers are applied to define loss of HLA and related genes (e.g. TAP and beta(2)m) The number of STR identified in the HLA region is still increasing. In this study, seven representative STR markers covering the 6p/6q arms of chromosome 6 including the HLA region and two for chromosome 15 flanking the beta(2)m gene, were selected as minimally required for reliable LOH studies. A multiplex polymerase chain reaction (PCR) strategy is proposed when small number of cells are available in microdissected tumor samples.

Loss at the chromosomal region 6p21.3 is a frequent event in head and neck squamous cell carcinomas (HNSCC). Since the human leukocyte antigen (HLA) complex is located at 6p21.3, loss of heterozygosity (LOH) of this region may provide tumour cells with an immune-escape tumour phenotype. In the present study, we have studied the correlation of HLA class I, TAP1 and TAP2 expression and LOH at 6p21.3. HLA class I and TAP1 and TAP2 protein expression was analysed by immunohistochemical procedures. A panel of 41 HNSCC with downregulated HLA class I expression was selected for LOH studies using 5 microsatellite markers located at 6p21.3 (D6S105, D6S265, D6S276, D6S273, D6S291) and 2 markers located at the chromosome 6 centromere (D6S473) and the 6p telomere (D6S277). In addition, LOH of the beta-2-nmicroglobulin (beta2m) gene was studied using 2 microsatellite markers flanking the beta2m gene (D15S126 and D15S153) and was correlated with beta2m and HLA class I expression. In 20/41 (49%) of the HNSCC, allelic loss for at least one locus at 6p21.3 was found. Loss at 15q was found in 4/10 (40%) HNSCC with downregulated beta2m expression and in 12/41 (29%) HNSCC with downregulated HLA class I expression. Our data show that downregulation of HLA class I expression is correlated with loss of chromosomal regions at 6p21.3 in HNSCC. In addition, LOH at 6p21.3 and 15q in 10 paired samples of DNA derived from the primary HNSCC, the lymph node metastases and from peripheral blood lymphocytes (PBLs) was studied. Five (5/10) primary tumours contained the same deletion as the corresponding lymph node metastases. The other cases contained deletions either in the primary tumour (3 cases) or in the lymph node metastases (1 case) or no deletions at all (1 case).

In cryostat sections of 84 head and neck squamous cell carcinomas (HNSCC) HLA class I and β2m expression was analysed using monomorphic and locus specific monoclonal antibodies. Loss of expression was heterogeneous and none of the tumours tested showed a total loss of HLA class I and/or β2m when analysed with W6/32, which recognises HLA class I determinants and anti-β2m MoAbs. Weak HLA class I and β2m expression was found in 9 tumours (11%) and heterogeneous expression was found in 2 tumours (2%). When analysed with locus-specific antibodies (HCA2 and HC10, anti-HLA-A and anti-HLA-B/C, respectively) 37 tumours (44%) showed a loss, weak or heterogeneous expression of one or both loci. Tumours showing a down-regulated HLA class I expression were analysed for mutations in either allele of the β2m gene by sequencing based mutation analysis (SBMA). Exon 1 and exons 2 and 3 were amplified separately by PCR using M13-tailed intron-specific primers. PCR products were sequenced in two directions. In none of the tumours mutations in the β2m gene were detected. In 59% of the tumours with down-regulated HLA class I expression, lost or down-regulated TAP 1 expression was found when analysed with anti-TAP 1 antibodies. This indicates an important role for TAP in down-regulation of HLA class I expression in HNSCC.