The present disclosure relates to polynucleotides encoding tethered interleukin-12 (IL-12) polypeptides comprising an IL-12 polypeptide and a membrane domain. The present disclosure also relates to vectors comprising the polynucleotides; host cells comprising the polynucleotides or vectors, polypeptides encoded by the polynucleotides; compositions comprising the polynucleotides, vectors, host cells, or polypeptides and a delivery agent; and uses thereof, including treatment of cancer.