Purification of plant-derived anti-virus mAb through optimized pH conditions for coupling between protein A and epoxy-activated beads

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-FcP) and PAP-FcK (PAP-FcKP). Bio-transmission electron microscopy demonstrated 'Y'-shaped protein particles resembling antibody structures. Moreover, PAP-FcP and PAP-FcKP exhibited a high association rate with human FcγR and FcRn. Vaccination of mice with both PAP-FcP and PAP-FcKP 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.

Effect of an Endoplasmic Reticulum Retention Signal Tagged to Human Anti-Rabies mAb SO57 on Its Expression in Arabidopsis and Plant Growth

Transgenic Arabidopsis thaliana expressing an anti-rabies monoclonal antibody (mAb), SO57, was obtained using Agrobacterium-mediated floral dip transformation. The endoplasmic reticulum (ER) retention signal Lys-Asp-Glu-Leu (KDEL) was tagged to the C-terminus of the anti-rabies mAb heavy chain to localize the mAb to the ER and enhance its accumulation. When the inaccurately folded proteins accumulated in the ER exceed its storage capacity, it results in stress that can affect plant development and growth. We generated T1 transformants and obtained homozygous T3 seeds from transgenic Arabidopsis to investigate the effect of KDEL on plant growth. The germination rate did not significantly differ between plants expressing mAb SO57 without KDEL (SO plant) and mAb SO57 with KDEL (SOK plant). The primary roots of SOK agar media grown plants were slightly shorter than those of SO plants. Transcriptomic analysis showed that expression of all 11 ER stress-related genes were not significantly changed in SOK plants relative to SO plants. SOK plants showed approximately three-fold higher mAb expression levels than those of SO plants. Consequently, the purified mAb amount per unit of SOK plant biomass was approximately three times higher than that of SO plants. A neutralization assay revealed that both plants exhibited efficient rapid fluorescent focus inhibition test values against the rabies virus relative to commercially available human rabies immunoglobulins. KDEL did not upregulate ER stress-related genes; therefore, the enhanced production of the mAb did not affect plant growth. Thus, KDEL fusion is recommended for enhancing mAb production in plant systems.