A new approach to the classification of human leukaemias: measurement of the relative abundance of a specific RNA sequence by means of molecular hybridisation.

A recombinant plasmid library representing polyadenylated RNAs in the leucocytes of a Ph1-positive chronic granulocytic leukaemia (CGL) has been constructed. One recombinant (designated pCG14) isolated from this library contains a DNA sequence complementary to a small polyadenylated RNA that is abundant in RNA from CGL leucocytes. The relative concentrations of pCG14 RNA in the RNAs from a variety of normal and leukaemic leucocytes and human haemopoietic cell lines have been measured with a molecular hybridisation assay. This has shown that pCG14 RNA is 10 to 50 times more abundant in RNA from CGL leucocytes than in the RNAs from these other cells. The data indicate that the occurrence of pCG14 RNA in high abundance is sufficiently characteristic of a CGL leucocyte population to distinguish it from other populations of leucocytes. They suggest that the measurement of the concentrations of specific RNA species in leucocyte RNA by means of molecular hybridisation with cloned complementary DNAs may provide additional markers for the objective classification of human leukaemias which could be particularly useful since the method exploits a criterion different from any currently in use.