Expression of human Flt3 ligand in Pichia pastoris and its biological characteristics

Flt3 ligand (FL) is a cytokine that stimulates the proliferation and differentiation of hematopoietic stem cells/progenitors. In order to obtain high level of recombinant human soluble FL (rhFL) production, an artificial gene for rhFL was synthesized by using favored genetic codons of the yeast Pichia pastoris. Then the gene was cloned into the vector pPICz alpha A and the resulting construct was introduced into Pichia pastoris for expression. It was found that it was possible to obtain biologically active rhFL with a yield of over 30 mg/L of yeast culture. The rhFL stimulated colony formation from cord blood. rhFL, SCF, GM-CSF and IL-3 are the most promising combination for the in vitro expansion of stem/progenitor cells. It was also showed that rhFL increased the induction of dendritic cells from cord blood in combination with GM-CSF, TNF alpha and IL-4. Interestingly, rhFL stimulated the growth of an endothelial cell line; this effect has not been reported before.