Friend leukaemia virus-transformed cells, unlike normal stem cells, form spleen colonies in Sl/sld mice.

Neoplastic cells are characterized by partial or total autonomy from the interactions that regulate the behaviour of normal cells in the intact animal. Despite the role of the host cellular environment in governing the proliferation and differentiation of both normal and malignant cells, little is known about these host factors. The characterization of host genes that influence both normal cellular processes, as well as susceptibility to tumour induction, is one approach to identifying such factors. Mice carrying two recessive mutations at the steel (Sl) locus have an environmental defect that affects both normal haematopoietic stem cell function as well as susceptibility to Friend leukaemia virus. In this study, we have used Sl/sld mice to examine whether malignant transformation by this RNA tumour virus results in a population of cells capable of proliferating even in the defective cellular microenvironment of Sl/sld mice. We report here that late after infection, the leukaemic spleens of Friend virus-infected mice contain cells which, unlike normal haematopoietic stem cells, are able to form macroscopic spleen colonies in irradiated mice of genotype Sl/Sld. This observation forms the basis for the first in vivo colony assay for leukaemic cells transformed by Friend virus.