Genetic modification of ex-vivo expanded stem cells for clinical application

Abstract

Stem cell therapy is currently considered as an important regime for repairing, replacing or enhancing the biological functions of the damaged tissues. Among adult stem cells, hematopoietic stem cells (HSCs) are commonly used for cure of hematological disorders. However, the number of HSCs obtained from sources like bone marrow, peripheral or umbilical cord blood is not sufficient for routine clinical application. Thus, ex-vivo expansion of HSCs becomes critically important. Ex-vivo culture and expansion of stem cells are challenging, as stem cells differentiate in culture rather than self-renew. Lack of clarity about the factors responsible for quiescence and differentiation of HSCs, investigators struggled to optimize conditions for ex vivo expansion. As we understand better, various strategies can be incorporated to mimic in vivo conditions for successful expansion of stem cells. However, characterization and biological functionality should also be tested for expanded stem cells prior to clinical application. To treat ischemia by enhancing therapeutic angiogenesis and neo-vascularization, the role of genetic modification of HSCs with pro-angiogenic factors is the focus of this review.

Figure 1.

HSC regulation within bone marrow. Factors responsible for maintenance of stem cell self-renewal versus differentiation are indicated with arrowheads.

Figure 2.

Stem cell expansion, modification and therapy for ischemia. Purified HSCs were seeded on the nanofiber-coated plate supplemented with serum-free media and growth factors for expansion. Expanded HSCs were genetically modified with pro-angiogenic factors and injected into the circulation via left ventricle of a murine hind limb ischemic model. Doppler images were taken for monitoring revascularization in the limbs.

Figure 3.

Schematic of revascularization process after genetically modified stem cell therapy in ischemic tissue. A. Ischemia generates high level of HIF-1α thus causing upregulation and production of angiogenic factors such as VEGF, PDGF, HGF, FGF-2 and others. B. SDF-1 and VEGF causes migration of EPCs from bone marrow to ischemic region and stabilizes endothelial cells near the ischemic region. C. Migration of injected genetically modified stem cells to the ischemic region via CXCR4-SDF-1 interaction. D. VEGF mediates vascular endothelial permeability and as a result migration of stem cells occur. E. Angiogenic factor causes proliferation of smooth muscle cells. F. Various angiogenic factors in presence of stem cell (both transplanted and host) along with proliferated smooth muscle and endothelial cells and other supporting cells mediate neo-vascularization and angiogenesis to ischemic tissues from pre-existing blood vessels.