A Novel Adjuvant System for High‐Efficiency Subunit Vaccines Against Porcine Deltacoronavirus

Summary The immunopotentiation efficacy of polydimethyl diallyl ammonium chloride (pDMDAAC) nanoparticles (NPs) as an adjuvant for the spike (S) protein subunit vaccine of porcine deltacoronavirus (PDCoV) was investigated, with particular emphasis on the combination of the NPs with the STING agonist cGAMP. Following dorsal subcutaneous immunization in mice, ELISA and virus neutralization assays revealed that the combination of pDMDAAC NPs and cGAMP (S‐pDMDAAC–cGAMP) significantly enhanced PDCoV‐specific IgG antibody titers and neutralizing antibody (nAb) potency in serum compared with the S protein alone. Further analysis via CCK‐8 assay indicated there was markedly augmented splenic lymphocyte proliferation capacity in the S‐pDMDAAC–cGAMP group, indicating robust cellular immune activation. Cytokine profiling showed elevated secretion levels of IFN‐γ, IL‐4, and TNF‐α in splenocytes, while flow cytometric analysis revealed increased proportions of CD3 + CD4 + and CD3 + CD8 + T lymphocytes, accompanied by elevated B‐cell populations in inguinal lymph nodes and spleen. These results collectively indicated that pDMDAAC NPs substantially potentiate both humoral and cellular immunity toward the PDCOVID‐19S protein and cGAMP amplified this adjuvant effect.