Delivery agent

1. A method for delivering a peptide or protein into a target cell, the method comprising contacting the peptide or protein with a polycationic agent and a polyanionic agent to form a complex, and contacting the complex with the target cell to deliver the peptide or protein thereto, wherein

(1) the polyanionic agent comprises an inorganic polyphosphate or a polyoxometalate; and/or

(2) the polycationic agent comprises a polyalkyleneimine.

2. The method of claim 1 , wherein the polyanionic agent comprises a polyoxometalate.

3. The method of claim 2 , wherein the polyoxometalate comprises a molybdenum or tungsten polyoxometalate and optionally carries a heteroatom.

4. The method of claim 1 , wherein the polyanionic agent comprises a polyphosphate.

5. The method of claim 4 , wherein the polyphosphate comprises a nucleic acid or a synthetic analogue thereof.

6. The method of claim 1 , wherein the polycationic agent comprises a polyalkyleneimine.

7. The method of claim 1 , wherein the polycationic agent comprises a polyhydroxyalkyleneimine.

8. The method of claim 7 , wherein the polyhydroxyalkyleneimine is polyhydroxypropyleneimine.

9. The method of claim 6 , wherein the polyalkyleneimine comprises a polyethyleneimine.

10. The method of claim 1 , wherein the peptide or protein is contacted with the polyanionic agent prior to contacting the polycationic agent.

11. The method of claim 1 , wherein the peptide or protein comprises an enzyme, an antibody or a non-enzymatic, non-antibody protein.

12. The method of claim 1 , wherein the target cell is a suspension cell, an adherent cell, a primary cell or cultured cell.

13. A product comprising a peptide or protein, a polycationic agent, and a polyanionic agent as a combined preparation, wherein;

(1) the polyanionic agent comprises an inorganic polyphosphate or a polyoxometalate; and

(2) the polycationic agent comprises a polyalkyleneimine or a polyhydroxyalkyleneimine.