Suppression of an Already Established Tumor Growing through Activated Mucosal CTLs Induced by Oral Administration of Tumor Antigen with Cholera Toxin

Abstract

Priming of CTLs at mucosal sites, where various tumors are originated, seems critical for controlling tumors. In the present study, the effect of the oral administration of OVA plus adjuvant cholera toxin (CT) on the induction of Ag-specific mucosal CTLs as well as their effect on tumor regression was investigated. Although OVA-specific TCRs expressing lymphocytes requiring in vitro restimulation to gain specific cytotoxicity could be detected by OVA peptide-bearing tetramers in both freshly isolated intraepithelial lymphocytes and spleen cells when OVA was orally administered CT, those showing direct cytotoxic activity without requiring in vitro restimulation were dominantly observed in intraepithelial lymphocytes. The magnitude of such direct cytotoxicity at mucosal sites was drastically enhanced after the second oral administration of OVA with intact whole CT but not with its subcomponent, an A subunit (CTA) or a B subunit (CTB). When OVA plus CT were orally administrated to C57BL/6 mice bearing OVA-expressing syngeneic tumor cells, E.G7-OVA, in either gastric tissue or the dermis, tumor growth was significantly suppressed after the second oral treatment; however, s.c. or i.p. injection of OVA plus CT did not show any remarkable suppression. Those mucosal OVA-specific CTLs having direct cytotoxicity expressed CD8αβ but not CD8αα, suggesting that they originated from thymus-educated cells. Moreover, the infiltration of such OVA-specific CD8+ CTLs was observed in suppressed tumor tissues. These results indicate that the growth of ongoing tumor cells can be suppressed by activated CD8αβ CTLs with tumor-specific cytotoxicity via an orally administered tumor Ag with a suitable mucosal adjuvant.

Inactivation of tumor‐specific CD8+ CTLs by tumor‐infiltrating tolerogenic dendritic cells

“…22 Moreover, as we demonstrated recently, the selective activation of a specific subset of DCs, such as DEC-205 + DCs, by depleting 33D1 + DCs seems to activate both CD8 + CTLs and NK effectors without additional tumor-antigen stimulation in vivo . 3, 29 It was also found that suppression of previously established tumor growth by activated mucosal CD8 + CTLs could be elicited by oral administration of tumor antigen with CT. 13 The upregulated expression of costimulatory molecules on TIDCs within regressed tumors mediated via oral administration of tumor antigen with CT has also been confirmed (Wakabayashi and Takahashi, manuscript in preparation). These findings suggest that tolerogenic DCs within tumors can be converted to functional DCs through the activation of DEC-205 + DCs.…”

“…To estimate the volume of the growing tumor mass, diameters of both the length ( a ) and the width ( b ) of the mass were measured every other day through day 15, after which the tumor volume ( V ) was calculated according to the formula V = ab 2 /2, as described previously. 13 When the longer axis of each tumor was >20 mm in diameter, all of the mice were anesthetized and killed according to the National Institutes of Health guidelines.…”

“…11, 12 Indeed, we have previously demonstrated that tumor-specific CD8 + CTLs can be induced by OVA-expressing EL4 thymoma (E.G7) cells through oral immunization with OVA and cholera toxin (CT). 13 Furthermore, it has recently been reported that a vaccine containing the known adjuvant immunostimulating complex elicited a high frequency of antigen-specific CD8 + CTLs capable of tumor cell killing in different tumor models. 14, 15 …”

Co-operation of Innate and Acquired Immunity for Controlling Tumor Cells

“…As indicated in Fig 5, it has turned out that the most suitable CTL epitope peptides within externally captured antigenic proteins are selected to present in association with class I MHC in DEC-205-positive DCs via cross-presentation (Moriya et al, 2010). We have shown that such cross-presentation, the shift of the antigen-presentation pathway from the class II MHC to class I MHC processing route for externally captured antigenic proteins, can be achieved by a bark-derived saponin-associated adjuvant, such as ISCOMs (Takahashi et al, 1990), cholera toxin (CT) (Wakabayashi et al, 2008), and BCG (Higuchi et al, 2009). We have also demonstrated (Fujimoto et al, 2004) that TLR3-signaling of DCs, previously loaded antigenic proteins, by double-stranded RNA, polyriboinosinic polyribocytidylic acid (poly(I:C)), which reflects a natural genetic product from a variety of viruses, can generate the cross-presentation.…”

Mucosal vaccines

“…The oral administration of antigen combined with cholera toxin generated CD8 + T cell responses capable of controlling the growth of gastric tumors expressing ovalbumin, whereas the same vaccine formulation did not reproduce the anti-tumor effect when administered subcutaneously. 165 The adoptive transfer of anti-tumor CD8 + T cells induced by s.c. immunization could protect against the development of subcutaneous tumors but not gastric tumors. 166 Similarly, the immunization of mice with DCs by the s.c. route allowed the control of subcutaneous tumors, but not lung metastases.…”