Competition among leukemic cells

We investigated competition among leukemic cells induced by Moloney murine leukemia virus (MoLV) in order to understand the mechanisms involved in the generation of leukemia. We used six leukemic cells lines from Balb/C mice infected with MoLV. Each line had a unique genetic marker which enabled us to trace it in mixtures of cells either in vivo or in vitro. The markers were a unique rearrangement of T-cell receptors, the integration sites of the retrovirus and rearrangements in the Pim-1 oncogene. A mixture of two cell lines (1:1) injected into intact Balb/C mice usually produced a monoclonal tumor originating from one cell line. In most cases, the cell lines that were aggressive in vivo were also dominant in mixing experiments in vitro. In some lines, we could correlate the aggressiveness of the tumor to its superior growth rate and lower requirement for serum factors in vitro. In others, this correlation did not hold, and we assumed that host factors like the immune system contribute to the malignant potential of the leukemic cell.