Lymphoma cell contamination of PBSC: a murine model

In P-388 bearing BDF 1 mice stem cell mobilisation was tested on the survival of lethally irradiated isologous recipients. Contamination of the graft with lymphoma cells was evaluated by the number of clonogenic lymphoma cells (CFU-L) and the ability of the graft to induce lymphoma in non-irradiated recipients. A mobilisation protocol (200 mg/kg cyclophosphamide (CY) i.p. or 200 mg/kg CY followed by 125 μg/kg G-CSF administered every 12 h for 3 consecutive days, starting 14 days after lymphoma initiation) that resulted in a substantial stem cell mobilisation in normal mice, mobilised too few CFU-L to induce lymphoma in the recipients: 50 μl of blood obtained after mobilisation protected lethally irradiated mice but did not induce lymphoma in normal recipients. A minimum graft of bone marrow (2 × 10 5 cells, with 5580 CFU-L) from untreated P-388 bearing donors killed irradiated recipients presumably by lymphoma and not bone marrow failure. The mobilisation protocol reduced CFU-L so much that no lymphoma-associated death occurred even after the transplantation of 10 × 10 5 bone marrow cells. These data suggest that, although the PBSC mobilisation protocol may also mobilise some clonogenic lymphoma cells, with the minimum graft size no lymphoma transfer can be observed.