Nanoparticle-based vaccines, compositions, kits and methods are used for the effective delivery of one or more antigens in vivo for vaccination and antibody (e.g., monoclonal antibody) production, and for the effective delivery of peptides, proteins, siRNA, RNA or DNA to PAPCs or MHC class II positive cells (e.g. tumor cells). Antigens may be, for example, DNA that results in expression of the gene of interest and induction of a robust and specific immune response to the expressed protein in a subject (e.g., mammal). Antigens may also be immunogenic peptides or polypeptides that are processed and presented. In one embodiment, a nanoparticle-based method to deliver antigens in vivo as described herein includes injection of a vaccine composed of a DNA encoding at least one antigen, or at least one antigenic peptide or polypeptide conjugated to a charged dendrimer (e.g., PADRE-derivatized dendrimer) that is also conjugated to a T helper epitope (e.g., PADRE). Negatively-charged plasmids bind naturally to a positively-charged PADRE-dendrimer, while peptide or polypeptide antigens can be chemically linked to the PADRE-dendrimer if they are not negatively-charged. Alternatively, negatively-charged dendrimers may be used. The compositions, kits, vaccines and methods described herein have both prophylactic and treatment applications, i.e., can be used as a prophylactic to prevent onset of a disease or condition in a subject, as well as to treat a subject having a disease or condition. A vaccine as described herein can be used to mount an immune response against any infectious pathogen or cancer.