Hybrid cell lines, derived from fusion of rodent cells with peripheral leukocytes from patients with chronic myeloid leukaemia (CML) and from normal donors, were assayed for the present of CML-associated changes in the carbohydrate moieties of membrane glycoproteins. Expression of this characteristic phenotype did occur in several hybrid clones derived from fusions both with leukaemic and normal human leukocytes. But, expression was only observed when tumourigenic rodent cells were used as fusion partners, and was not observed after fusion with non-tumourigenic rodent cells. Chromosome analysis of the hybrid cells did not reveal a single human chromosome- or chromosomal aberration (e.g. the Philadelphia chromosome)-bearing factor(s) responsible for this expression. The phenotypic expression observed could be due to dissociation of certain human genes from their regulator(s), as a result of chromosome loss in interspecific cell hybrids.

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