Immune Responses to Plant-Derived Recombinant Colorectal Cancer Glycoprotein EpCAM-FcK Fusion Protein in Mice

Epidermal cell adhesion molecule (EpCAM) is a tumor-associated antigen (TAA), which has been considered as a cancer vaccine candidate. The EpCAM protein fused to the fragment crystallizable region of immunoglobulin G (IgG) tagged with KDEL endoplasmic reticulum (ER) retention signal (EpCAM-FcK) has been successfully expressed in transgenic tobacco (Nicotiana tabacum cv. Xanthi) and purified from the plant leaf. In this study, we investigated the ability of the plant-derived EpCAM-FcK (EpCAM-FcK(P)) to elicit an immune response in vivo. The animal group injected with the EpCAM-FcK(P) showed a higher differentiated germinal center (GC) B cell population (~9%) compared with the animal group injected with the recombinant rhEpCAM-Fc chimera (EpCAM-Fc(M)). The animal group injected with EpCAM-FcK(P) (~42%) had more differentiated T follicular helper cells (Tfh) than the animal group injected with EpCAM-Fc(M) (~7%). This study demonstrated that the plant-derived EpCAM-FcK fusion antigenic protein induced a humoral immune response in mice.