In certain embodiments, this disclosure relates to conjugates comprising a polypeptide of GM-CSF and a polypeptide IL-4. Typically, the GM-CSF and IL-4 are connected by a linker, e.g., polypeptide. In certain embodiments, the disclosure relates to isolated nucleic acids encoding these polypeptide conjugates, vectors comprising nucleic acid encoding polypeptide conjugates, and protein expression systems comprising these vectors such as infectious viral particles and host cells comprising such nucleic acids.