Mutation in the beta 2m gene is not a frequent event in head and neck squamous cell carcinomas

In cryostat sections of 84 head and neck squamous cell carcinomas (HNSCC) HLA class I and beta 2m 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 beta 2m when analysed with W6/32, which recognises HLA class I determinants and anti-beta 2m MoAbs. Weak HLA class I and beta 2m 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 beta 2m 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 beta 2m 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.