This invention is directed to a soluble complex of ligands that binds to surface molecules of hemopoietic cells and result in their activation or expansion. The complex may be used in the activation and/or expansion of hemopoietic cells, optionally in combination with their transduction. The complex of ligands bind at least two cell surface molecules, such as one that plays a role in cell-cell adhesion and one that may or may not activate or stimulate the cell to promote growth and/or proliferation after binding to a ligand. A complex of ligands that bind two hemopoietic cell stimulatory molecules is also provided. The invention further provides for the use of the complex to target vectors to hemopoietic cells.
