Pigeon circovirus(PiCV)is globally widespread and is considered a potential cause of young pigeon sickness syndrome(YPDS),which leads to severe immunosuppression and high mortality.Due to the inability of PiCV to be cultured in cells,the development of traditional vac-cines is severely limited,and no effective vaccines is currently available.To develop a novel PiCV DNA candidate vaccine,we cloned the △Cap gene lacking a nuclear localization signal(NLS),and fused it at its C-terminus with the transmembrane and cytoplasmic regions of the Newcastle dis-ease virus(NDV)F protein(△Cap-TMCT).Two DNA vaccine candidates were constructed:pCAGG-△Cap,targeting intracellular expression,and pCAGG-△Capt,for cell surface expression,respectively.The results of indirect immunofluorescence and Western blot analyses confirmed suc-cessful expression of both recombinant plasmids in DF1 cells.Immunization studies in mice re-vealed that pCAGG-△Capt induced significantly higher levels of specific IgG antibodies,T-cell re-sponses,and cytokine secretion compared to pCAGG-△Cap,as assessed by ELISA,flow cytome-try,and ELISpot assays.These findings suggest that targeting △Cap-TMCT fusion protein to the cell surface can effectively enhance its immunogenicity,highlighting its potential as a PiCV DNA vaccine candidate.This study provides new strategies and theoretical foundations for the design and development of PiCV DNA vaccines.

Pigeon circovirus(PiCV)is globally widespread and is considered a potential cause of young pigeon sickness syndrome(YPDS),which leads to severe immunosuppression and high mortality.Due to the inability of PiCV to be cultured in cells,the development of traditional vac-cines is severely limited,and no effective vaccines is currently available.To develop a novel PiCV DNA candidate vaccine,we cloned the △Cap gene lacking a nuclear localization signal(NLS),and fused it at its C-terminus with the transmembrane and cytoplasmic regions of the Newcastle dis-ease virus(NDV)F protein(△Cap-TMCT).Two DNA vaccine candidates were constructed:pCAGG-△Cap,targeting intracellular expression,and pCAGG-△Capt,for cell surface expression,respectively.The results of indirect immunofluorescence and Western blot analyses confirmed suc-cessful expression of both recombinant plasmids in DF1 cells.Immunization studies in mice re-vealed that pCAGG-△Capt induced significantly higher levels of specific IgG antibodies,T-cell re-sponses,and cytokine secretion compared to pCAGG-△Cap,as assessed by ELISA,flow cytome-try,and ELISpot assays.These findings suggest that targeting △Cap-TMCT fusion protein to the cell surface can effectively enhance its immunogenicity,highlighting its potential as a PiCV DNA vaccine candidate.This study provides new strategies and theoretical foundations for the design and development of PiCV DNA vaccines.