A single-step immunization by sustained antigen release.

An inert polymer pellet less than 1 mm in diameter, implanted subcutaneously in mice, releases free antigen continuously and enhances antibody formation for over 6 months. The immune response stimulated by sustained antigen delivery is comparable to the secondary response induced by the same total dose of antigen emulsified in complete Freund's adjuvant. The sustained release polymer implants, using antigens over a wide molecular weight range, proved effective in eliciting prolonged antibody formation. The antigens tested included bovine serum albumin, gamma-globulin, and ribonuclease. Superior biocompatibility and release characteristics make the ethylene-vinyl acetate copolymer a promising method for the single-step induction of immunity.