Transplanted interleukin-4--secreting mesenchymal stromal cells show extended survival and increased bone mineral density in the murine femur.

Background: Mesenchymal stromal cell (MSC)-based therapy has great potential to modulate chronic inflammation and enhance tissue regeneration. Crosstalk between MSC-lineage cells and polarized macrophages is critical for bone formation and remodeling in inflammatory bone diseases. However, the translational application of this interaction is limited by the short-term viability of MSCs after cell transplantation.

Methods: Three types of genetically modified (GM) MSCs were created: (1) luciferase-expressing reporter MSCs; (2) MSCs that secrete interleukin (IL)-4 either constitutively; and (3) MSCs that secrete IL-4 as a response to nuclear factor kappa-light-chain-enhancer of activated B cell (NFκB) activation. Cells were injected into the murine distal femoral bone marrow cavity. MSC viability and bone formation were examined in vivo. Cytokine secretion was determined in a femoral explant organ culture model.

Results: The reporter MSCs survived up to 4 weeks post-implantation. No difference in the number of viable cells was found between high (2.5 × 10) and low (0.5 × 10) cell-injected groups. Injection of 2.5 × 10 reporter MSCs increased local bone mineral density at 4 weeks post-implantation. Injection of 0.5 × 10 constitutive IL-4 or NFκB-sensing IL-4-secreting MSCs increased bone mineral density at 2 weeks post-implantation. In the femoral explant organ culture model, LPS treatment induced IL-4 secretion in the NFκB-sensing IL-4-secreting MSC group and IL-10 secretion in all the femur samples. No significant differences in tumor necrosis factor (TNF)α and IL-1β secretion were observed between the MSC-transplanted and control groups in the explant culture.

Discussion: Transplanted GM MSCs demonstrated prolonged cell viability when transplanted to a compatible niche within the bone marrow cavity. GM IL-4-secreting MSCs may have great potential to enhance bone regeneration in disorders associated with chronic inflammation.