Provided herein are nanoparticles comprising a polyplex core comprising one or more pH-responsive polymers and one or more anionic immune adjuvants, wherein each pH-responsive polymer comprises ionizable amine groups; and a shell of bacterial cell membrane components at least partially coating the polyplex core, wherein the bacterial cell membrane components comprise TLR 2 and/or TLR 4 agonists. Also provided are methods of stimulating an immune response in a mammal using the nanoparticle.