Abstract
The replication-competent Friend leukemia virus (F-MuLV) induces leukemias involving three hematopoietic lineages after a latent period of several months. In an attempt to elucidate the early events of the leukemogenic process, we looked for a method allowing the isolation and the long term in vitro maintenance of preleukemic cells. When established as long-term cultures according to the technique described by Dexter et al, bone marrow cells obtained from 7/7 apparently healthy F-MuLV-infected preleukemic mice led to the accumulation of immature myeloblastic cells, and to the generation of permanent myeloblastic cell lines, which in most cases further became tumorigenic in preirradiated recipient animals. The delays required to obtain cell lines were shorter when the duration of the in vivo infection was longer, suggesting that these cells were committed into the leukemogenic pathway before their transfer into culture flasks. The myelomonocytic preleukemic cells exhibited normal sensitivity to purified preparations of CSFs, but acquired the capacity to grow in the absence of exogenous CSF stimulation. Examination of integrated provirus copies demonstrated that the preleukemic cell proliferation involved a single or a few clones which may progress in vitro from a preleukemic to a fully malignant stage without major modifications of the integrated provirus copies.
