Delivery of 4-1BB ligand (4-1BBL) and interleukin 12 (IL-12) via poly(β-amino ester) (PBAE) nanoparticles (NPs) enables reprogramming of tumor cells into tumor-associated antigen-presenting cells (tAPCs), stimulating anti-tumor immune responses. The gene discussed is TNFSF9; the disease is neoplasm.