Cytogenetic analysis of the spontaneous murine B-cell leukemia (BCL1

Cytogenetic studies were carried out on the spontaneous transplantable murine B cell leukemia (BCL₁) of BALB/c mice, a recently discovered model of chronic lympholytic leukemia. BCL₁ tumor cells appear as medium to large size mature lymphocytes located predominantly in the blood (up to 500,000/mm³) and in the x50 enlarged spleen. BCL₁ cells obtained from the spleen show a certain degree of spontaneous proliferation unlike peripheral blood lymphocytes (PBL), but both show a good in vitro response to the B-cell mitogen lipopolysaccharide (LPS). Out of 213 spontaneously dividing spleen cells and LPS stimulated PBL studied, the majority (75.5%) showed a rather stable and complex female karyotype consisting of 36 chromosomes. No normal representative of chromosome Nos. 6, 8, 12 and 15 was present and only one normal representative was found for chromosome Nos. 4, 5, 9, 14 and X. Two deleted chromosomes and seven characteristic marker chromosomes, originating from complex chromosomal rearrangements could be identified in each cell. Of special interest was the t(12:15) translocation, which had been found in several murine plasmacytomas. No direct correlation between the chromosomal changes and the phenotypic characteristics of BCL₁ tumor cells could be made. However, the highly specific karyotype may serve as a useful marker in identifying single BCL₁ tumor cells.