Cationic micelles formed from poly(ethylene glycol)-bl-poly(propylene sulfide)-bl-poly(ethylene imine) (PEG-b-PPS-b-PEI) and from mixtures of poly(ethylene glycol)-bl-poly(propylene sulfide) (PEG-b-PPS) with PEG-b-PPS-b-PEI were explored as non-viral vectors for plasmid DNA (pDNA) transfection in a tumor immunotoxicity model. Complexes with pDNA were found to be templated exclusively by the size of the pDNA-free micelles and ranged from 240 nm (for PEG-b-PPS-b-PEI) to 30 nm (for mixed micelles of PEG-b-PPS/PEG-b-PPS-b-PEI). Both formulations transfected melanoma cells well in vitro. As a model with a functional read-out of tumor cell death, one with likely only small bystander effects, tumors were transfected with an antigen transgene, using an antigen to which the recipient animals had been previously vaccinated with a Th1-biasing adjuvant. Reduction in tumor growth, increase in intratumoral infiltration of cytotoxic T lymphocytes and accumulation of Th1-biasing cytokines indicated that both micelle formulations transfected efficiently compared with naked pDNA and with low cytotoxicity. (C) 2011 Elsevier Ltd. All rights reserved.