Arg substitution at codon 61 of NRAS (N-RAS/61plus;), were also examined. Melanoma cells and clones were used as targets of allogeneic LAK in a 4-h51Crrelease assay. LAK showed a higher lysis on melanoma lines and clones harbouring a mutated RAS compared with counterparts bearing no RAS mutations. In addition, LAK-mediated lysis drastically decreased on Me665/2 sublines progressively selected by exposure to LAK. This loss was paralleled by a reduction or even disappearance of N-RAS/61plus;mRNA signal in Me665/2 sublines. To evaluate whether N-RAS could directly modulate LAK susceptibility to lysis, N-RAS/61plus;gene was transfected in two N-RAS wild type (N-RAS/61-) 665/2 melanoma clones by a cosmid vector. In contrast to the high lysability of melanoma cells constitutively expressing the mutationally active N-RAS oncogene, N-RAS/61plus;transfectants did not show a consistent high lysability by LAK, compared with some control pSV2neo transfectants. Taken together, these results indicate that expression of a mutated RAS gene can be considered as a factor, although not the only one, that characterizes human melanoma cells with high susceptibility to lysis and may thus affect their response to therapeutic lymphocytes.
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