Plant-Derived Recombinant Macromolecular PAP-IgG Fc as A Novel Prostate Cancer Vaccine Candidate Eliciting Robust Immune Responses

Prostatic acid phosphatase (PAP) is a specific protein that is highly expressed in prostate cancer. In this study, we constructed two recombinant PAP fusion genes: PAP fused to the immunoglobulin G (IgG) Fc fragment (designated PAP-Fc) and PAP-Fc fused to the endoplasmic reticulum retention sequence KDEL (designated PAP-FcK). Transgenic Nicotiana tabacum plants expressing these recombinant macromolecular proteins (MPs) were generated using Agrobacterium-mediated transformation, and the presence of both genes was confirmed through genomic PCR. Western blot analysis validated the expression of PAP-Fc and PAP-FcK MPs, which were successfully purified via protein A affinity chromatography. Size-exclusion high-performance liquid chromatography revealed dimeric peaks for PAP-Fc (PAP-Fc^P) and PAP-FcK (PAP-FcK^P). Bio-transmission electron microscopy demonstrated 'Y'-shaped protein particles resembling antibody structures. Moreover, PAP-Fc^P and PAP-FcK^P exhibited a high association rate with human FcγR and FcRn. Vaccination of mice with both PAP-Fc^P and PAP-FcK^P resulted in increased total IgG against PAP and enhanced activation of CD4⁺ T cells, comparable to mice immunized with PAP, which served as a positive control. These findings indicate that both plant-derived MPs can effectively induce adaptive immunity, positioning them as promising candidates for prostate cancer vaccines. Overall, plants expressing PAP-Fc and PAP-FcK represent a viable production system for antigenic macromolecule-based prostate cancer vaccines.