THROMBOPOIETIC POTENTIAL AND SERIAL REPOPULATING ABILITY OF MURINE HEMATOPOIETIC STEM-CELLS CONSTITUTIVELY EXPRESSING INTERLEUKIN-11

Based on transplantation studies with bone marrow cultured under vario us conditions, a role of interleukin 11 (IL-11) in the self-renewal an d/or the differentiation commitment of hematopoietic stem cells has be en indicated. To better evaluate the in vivo effects of IL-11 on stem/ progenitor cell biology, lethally irradiated mice were serially transp lanted with bone marrow cells transduced with a defective retrovirus, termed MSCV-mIL-11, carrying the murine IL-11 (mIL-11) cDNA and the ba cterial neomycin phosphotransferase Inco) gene. High serum levels (i.e ., >1 ng/ml) of mIL-11 in all (20/20) primary and 86% (12/14) of secon dary long-term 'reconstituted mice, as well as 86% (12/14) of tertiary recipients examined at 6 weeks posttransplant, demonstrated persisten ce of vector expression subsequent to transduction of bone marrow prec ursors functionally definable as totipotent hematopoietic stem cells, In agreement with results obtained with human IL-11 in other myeloabla tion models, ectopic mIL-11 expression accelerated recovery of platele ts, neutrophils, and, to some extent, total leukocytes while preferent ially increasing peripheral platelet counts in fully reconstituted mic e. When analyzed 5 months posttransplant, tertiary MSCV-mIL-11 recipie nts had a significantly greater percentage of G418-resistant colony-fo rming cells in their bone marrow compared with control MSCV animals. C ollectively, these data show that persistent stimulation of platelet p roduction by IL-11 is not detrimental to stem cell repopulating abilit y; rather, they suggest that IL-11 expression in vivo may have resulte d in enhanced maintenance of the most primitive hematopoietic stem cel l compartment. The prolonged expression achieved by the MSCV retrovira l vector, despite the presence of a selectable marker, contrasts with the frequent transcriptional extinction observed with other retroviral vectors carrying two genes. These findings have potentially important implications for clinical bone marrow transplantation and gene therap y of the hematopoietic system.