Notably, the recombinant IL-7 gene encapsulated in CS-PEG-PEI provoked the best increases of immunoglobulins, CD4+ and CD8+ T cells, TLRs, and cytokines in the blood of the mice, implying that chitosan-PEG-PEI can become a promising carrier for in vivo IL-7 gene expression to enhance the innate and adaptive immunity for the prevention of animal diseases. The gene discussed is CD4; the disease is non-human animal disease.