Soluble RANKL expression in Lactococcus lactis and investigation of its potential as an oral vaccine adjuvant

Abstract

BackgroundTo initiate mucosal immune responses, antigens in the intestinal lumen must be transported into gut-associated lymphoid tissue through M cells. Recently, it has been increasingly recognized that receptor activator of NF-kB ligand (RANKL) controls M cell differentiation by interacting with RANK expressed on the sub-epithelium of Peyer’s patches. In this study, we increased the number of M cells using soluble RANKL (sRANKL) as a potent mucosal adjuvant.ResultsFor efficient oral delivery of sRANKL, we constructed recombinant Lactococcus lactis (L. lactis) IL1403 secreting sRANKL (sRANKL-LAB). The biological activity of recombinant sRANKL was confirmed by observing RANK-RANKL signaling in vitro. M cell development in response to oral administration of recombinant L. lactis was determined by 1.51-fold higher immunohistochemical expression of M cell marker GP-2, compared to that of non-treatment group. In addition, an adjuvant effect of sRANKL was examined by immunization of mice with M-BmpB as a model antigen after treatment with sRANKL-LAB. Compared with the wild-type L. lactis group, the sRANKL-LAB group showed significantly increased systemic and mucosal immune responses specific to M-BmpB.ConclusionsOur results show that the M cell development by sRANKL-LAB can increase the antigen transcytotic capability of follicle-associated epithelium, and thereby enhance the mucosal immune response, which implies that oral administration of sRANKL is a promising adjuvant strategy for efficient oral vaccination.Electronic supplementary materialThe online version of this article (doi:10.1186/s12865-015-0132-x) contains supplementary material, which is available to authorized users.

A review on Lactococcus lactis: from food to factory

“…To date, L. lactis has been used to co-produce or secrete a wide range of other adjuvants and growth factors. Successful examples include murine IL-12 [81], transforming growth factor beta 1 (TGF-β1) [82], insulin-like growth factor I [83], receptor activator of nuclear factor kappa-B ligand (RANKL) [84] and others as detailed in Table 2.…”

Efficacy of orally administered porcine epidemic diarrhea vaccine-loaded hydroxypropyl methylcellulose phthalate microspheres and RANKL-secreting L. lactis

“…Natural infection or oral immunization with live virus can generate sufficient mucosal or lactogenic immunity, whereas intramuscular administration induces a systemic immune response that provides little lactogenic immunity (Song et al, 2016;Chattha et al, 2015). In general, subunit oral vaccines show poor immunogenicity, and although some toxin adjuvants such as cholera toxin and E. coli heat-labile toxin can act as mucosal vaccine adjuvants, obvious safety concerns prevent their use in a clinical setting (Kim et al, 2015). Notably, a recent study demonstrated the importance of the receptor activator of NF-kB ligand (RANKL) for controlling M cell differentiation in Peyer's patches (Knoop et al, 2009).…”

“…The RANKL/RANK system plays an important role in development and regulation of the immune system; for example, it is involved in lymph-node organogenesis, lymphocyte differentiation, dendritic cell survival, and T-cell activation, and it promotes the functions of antigenpresenting cells (Maharjan et al, 2016). Therefore, increasing the number of microfold cells (M cells) by delivering RANKL may be a promising biomimetic strategy to increase the efficacy of oral vaccination (Kim et al, 2015). Oral vaccination of pregnant sows to induce lactogenic immunity is a fundamental strategy used to protect suckling pigs from infection with PEDV (Langel et al, 2016).…”

Adjuvant Strategies for Lactic Acid Bacterial Mucosal Vaccines

“…There were three LAB adjuvant studies that did not fit into the above categories: Japanese herbal medicines (Juzen-taiho-to (JTT) and Hochi-ekki-to (HEY)), receptor activator of nuclear factor kappa-B ligand (RANKL), and thymosin α-1 [116][117][118]. They are briefly reviewed in Table 5 and their mechanisms of action described here.…”

“…A study by Kim et al aimed to increase the immune response to an oral L. lactis vaccine against the bacterium Brachyspira hyodysenteriae through the secretion of the M cell-inducing protein RANKL [117]. M cells are important for pathogen uptake from the intestinal lumen and transport into the Peyer's patches [121].…”