DNA/Amphiphilic Block Copolymer Nanospheres Promote Low-dose DNA Vaccination

Intramuscular (i.m.) DNA vaccination induces strong cellular immune responses in the mouse, but only at DNA doses that cannot be achieved in humans. Because antigen expression is weak after naked DNA injection, we screened five nonionic block copolymers of poly(ethyleneoxide)-poly(propyleneoxide) (PEO-PPO) for their ability to enhance DNA vaccination using a β-galactosidase (βGal) encoding plasmid, pCMV-βGal, as immunogen. At a high DNA dose, formulation with the tetrafunctional block copolymers 304 (molecular weight [MW] 1,650) and 704 (MW 5,500) and the triblock copolymer Lutrol (MW 8,600) increased βGal-specific interferon-γ enzyme-linked immunosorbent spot (ELISPOT) responses 2–2.5-fold. More importantly, 704 allowed significant reductions in the dose of antigen-encoding plasmid. A single injection of 2 µg pCMV-βGal with 704 gave humoral and ELISPOT responses equivalent to those obtained with 100 µg naked DNA and conferred protection in tumor vaccination models. However, 704 had no adjuvant properties for βGal protein, and immune responses were only elicited by low doses of pCMV-βGal formulated with 704 if noncoding carrier DNA was added to maintain total DNA dose at 20 µg. Overall, these results show that formulation with 704 and carrier DNA can reduce the dose of antigen-encoding plasmid by at least 50-fold.