MOLECULAR ANALYSIS OF AN HLA-DP MUTANT-CELL LINE SELECTED FOR ITS RESISTANCE TO KILLING BY HLA-DPW2-SPECIFIC T-CELL CLONES

A collection of HLA-DP mutants was generated, using ICR 191 as the mut agenic agent and resistance to lysis mediated by HLA-DPw2 allospecific cytotoxic T lymphocytes (CTLs) as the selection criterion. These muta nts were derived from the HLA haploid lymphoblastoid cell line 45.1. L oss of HLA-DPw2 surface expression accounted for the lack of HLA-DPw2 CTL recognition in all the mutants. However, one of them, 45.EM19, bin ds to DPw2-specific monoclonal antibodies (mAb) after cell permeabiliz ation. HLA-DPA1 and DPB1 mRNA expression studies permitted the classif ication of the mutants in four categories: 1) DPA1-negative, DPB1-posi tive; 2) DPA1-positive, DPB1-negative; 3) DPA1- and DPB1-negative, and 4) DPA1- and DPB1-positive mutants. Mutant 45.EM19 is included in the last group. The cloning and sequencing of the full-length DPA1 (DPA1 0103) and DPB1 (DPB102012) cDNAs from this mutant showed no changes i n the DPA1 sequence compared to the wild-type sequence. However, a fra me-shift mutation in the DPB1 gene exon coding for the transmembrane r egion was detected. The insertion of a guanine nucleotide provokes an extension of the open reading frame, increasing the length of the C-te rminal domain and changing the hydropathicity pattern of the transmemb rane domain. This change should be responsible for the phenotype of th e 45.EM19 mutant.