Compositions and methods for therapeutic delivery

A recombinant retroviral vector comprising a nucleic acid construct comprising a first polynucleotide sequence encoding P40 subunit of Interleukin-12 (IL-12), a second polynucleotide sequence encoding P35 subunit of Interleukin-12, and a third polynucleotide sequence between the first and second polynucleotide sequences, wherein the third polynucleotide sequence encodes a cleavage site that facilitates cleavage between P40 subunit and P35 subunit.