Engineered cytokine secretion from human mesenchymal stem cells influences in vivo hematopoiesis

In the current studies, we examined the duration and effects of cytokine cDNA introduction and protein secretion from human mesenchymal stem cells (HuMSC), in beige/nude/xid (bnx) mice. HuMSC were engineered to secrete human Erythropoietin, Interleukin (IL-)3, or IL-7, using MoMuLV-based retroviral vectors. Engineered MSC were introduced via neo-organoid implantation, biochamber implantation, or intravenous injection. The latter route resulted in the highest sustained levels of human cytokines in the murine serum. Sequentially measured systemic levels of huEpo were 1.1±0.4 U/ml serum at 1 month post-transplantation and 0.6±0.1 U/ml at 2 months (N=8). HuIL-7 levels were 281±29 pg/ml at 1 month and 45.7±6 at 6 months (N=7). HuIL-3 levels were 209.4±15.5 pg/ml at 1 month and 35.5±5 at 6 months (N=7). To determine whether the decrease was due to cell loss or to reduction in expression, we are now implanting the engineered MSC in a dissolvable polymer, to allow precise recovery of the vascularized cell mass. There were significant influences from the MSC on the development of co-transplanted human hematopoietic stem cells (HSC). HuIL-3 allowed huHSC survival in bnx mice, with none in control animals. HuEpo significantly increased the hematocrit and production of BFU-E and mature RBC. Human RBC were blocked at the BFU-E stage in mice that did not receive huEpo. HuIL-7 significantly increased the levels of human CD3+CD4+ T cells that developed from purified HSC in the murine marrow. Retroviral-mediated engineering of human MSC is an effective model to study the impact of sustained, supraphysiological levels of specific cytokines on co-transplanted human hematopoietic stem cells.