HLA class I expression and chromosomal deletions at 6p and 15q in head andneck squamous cell carcinomas

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) c omplex is located at 6p21.3, loss of heterozygosity (LOH) of this region ma y provide tumour cells with an immune-escape tumour phenotype, In the prese nt study, we have studied the correlation of HLA class I, TAP1 and TAP2 exp ression and LOH at 6p21.3. HLA class I and TAP1 and TAPE protein expression was analysed by immunohistochemical procedures, A panel of 41 HNSCC with d ownregulated HLA class I expression was selected for LOH studies using 5 mi crosatellite markers located at 6p21.3 (D6S105, D6S265, D6S276, D6S273, D6S 291) and 2 markers located at the chromosome 6 centromere (D6S473) and the 6p telomere (D6S277). In addition, LOH of the beta-2-microglobulin (beta(2) m) gene was studied using 2 microsatellite markers flanking the beta(2)m ge ne (D15S126 and D15S153) and was correlated with beta(2)m and HLA class I e xpression. 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 downre gulated beta(2)m expression and in 12/41 (29%) HNSCC with downregulated HLA class I expression. Our data show that downregulation of HLA class I expre ssion 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 lymp hocytes (PBLs) was studied. Five (5/10) primary tumours contained the same deletion as the corresponding lymph node metastases. The other cases contai ned deletions either in the primary tumour (3 cases) or in the lymph node m etastases (1 case) or no deletions at all (1 case).