Local and systemic immune responses to rectal administration of recombinant cholera toxin B subunit in humans

The induction of immune responses to rectally administered recombinant cholera toxin B subunit (CTB) in humans was studied. Three immunizations induced high levels of CTB-specific antibody-secreting cells, particular of the immunoglobulin A isotype, in both rectum and peripheral blood. Antitoxin antibody responses in rectal secretions and serum were also found.     

Intranasal vaccination of humans with recombinant cholera toxin B subunit induces systemic and local antibody responses in the upper respiratory tract and the vagina.

Forty-five volunteers were vaccinated twice intranasally with 10, 100, or 1,000 microg of cholera toxin B subunit (CTB). Blood and nasal and vaginal secretions were collected before and 1 week after the second vaccination from all volunteers, and the specific and total immunoglobulin A (IgA) and IgG titers were determined by enzyme-linked immunosorbent assay. Samples were also taken 6 months (n = 16) and 1 year (n = 14) after the vaccination. The 10- and 100-microg doses were well tolerated by the volunteers, but the 1,000-microg dose induced increased secretions from the nose and repetitive sneezings for several hours. The CTB-specific serum IgA and IgG increased 21- and 7-fold, respectively, 1 week after vaccination with the medium dose and increased 61- and 37-fold, respectively, after the high dose. In nasal secretions the specific IgA and IgG increased 2- and 6-fold after the medium dose and 2- and 20-fold after the high dose, respectively. In vaginal secretions the specific IgA and IgG increased 3- and 5-fold after the medium dose and 56- and 74-fold after the high dose, respectively. The lowest dose did not induce any significant antibody titer increases in serum or in secretions. The specific IgA and IgG levels in secretions were still elevated after 6 months but were decreasing 1 year after the vaccination. These results show that intranasal vaccination of humans with CTB induces strong systemic and mucosal antibody responses and suggest that CTB may be used as a carrier for antigens that induce protective immunity against systemic as well as respiratory and genital infections.     

Influence of exogenous reproductive hormones on specific antibody production in genital secretions after vaginal vaccination with recombinant cholera toxin B subunit in humans

The objective of this study was to investigate the influence of exogenous reproductive hormones on the local and systemic production of specific immunoglobulin A (IgA) and IgG antibodies after vaginal vaccination with recombinant cholera toxin subunit B (CTB). Three groups of women using either progesterone-containing intrauterine devices (n=9), oral contraceptives (n=8), or no hormonal contraceptive methods (n=9) were vaginally immunized twice, 2 weeks apart. Cervical secretions, vaginal fluids, and serum were collected before and after vaccination. Total and CTB-specific IgA and IgG antibodies in genital secretions and serum were analyzed by enzyme-linked immunosorbent assay. A majority of the women presented strong CTB-specific IgA and IgG antibody responses in cervicovaginal secretions after vaccination, whereas the antitoxin responses in serum were weaker. Exogenously administered steroid hormones did not seem to have any impact on the production of specific antibodies. Both the frequencies and the magnitudes of IgA and IgG antitoxin responses in genital secretions were comparable among the three immunization groups. An association, in particular for IgA, was found between the magnitudes of the CTB-specific antibody responses in cervical secretions and vaginal fluids after vaccination. The sensitivities and positive predictive values of vaginal antibody analyses to reflect responses in cervical secretions were also high, suggesting that vaginal fluids alone might be used for evaluation of genital immune responses in large-scale vaccination studies in the future.     

Induction and distribution of intestinal immune responses after administration of recombinant cholera toxin B subunit in the ileal pouches of colectomized patients

The induction and dissemination of mucosal immune responses to recombinant cholera toxin B subunit (rCTB) administered into the ileal pouches of patients, who had been colectomized because of ulcerative colitis, was analyzed. Biopsies from the duodenum and ileal pouch were collected, along with peripheral blood and ileostomy fluids. Two immunizations induced strong CTB-specific immunoglobulin A (IgA) antibody-secreting cell (ASC) responses in the duodenum in five of five patients, whereas weaker and less-frequent ASC responses were noted in the ileal pouch. Intestine-derived CTB-specific IgA ASCs were found in peripheral blood in three of the five patients. The vaccination also induced significant IgA antitoxin titer rises in ileostomy fluid in all of the patients. Increased production of gamma interferon in cell cultures from the ileal pouch was found in four of five patients after the vaccination. These results clearly indicate that rCTB administered into the distal ileum is capable of inducing B-cell responses in the "entire" small intestine and that homing of immunocompetent cells occurs preferentially to the duodenum.     

The early cellular and humoral immune response to primary and booster oral immunization with cholera toxin B subunit

The immune response to cholera toxin B subunit given orally was studied in 13 human volunteers. A serum IgG and IgA antitoxin response was observed, which was boosted by a second immunization. Using an immunospot assay, cells spontaneously secreting anti-toxin IgG and IgA, but not IgM appeared transiently in the blood after immunization. There were 105 IgG- and 87 IgA-secreting cells per 2 x 10(6) mononuclear cells 7 days after the first immunization, and 282 IgG- and 413 IgA-secreting cells 5 days after the second immunization. A polyclonal increase in total IgM-secreting cells was observed. Few anti-toxin-secreting cells were observed in the bone marrow at the peak of the circulating cell response, which could be accounted for by contamination of the sample with peripheral blood, suggesting that the bone marrow is not a significant site of anti-toxin-secreting cells after oral immunization.     

Mucosal immune responses and protection against tetanus toxin after intranasal immunization with recombinant Lactobacillus plantarum

The use of live microorganisms as an antigen delivery system is an effective means to elicit local immune responses and thus represents a promising strategy for mucosal vaccination. In this respect, lactic acid bacteria represent an original and attractive approach, as they are safe organisms that are used as food starters and probiotics. To determine whether an immune response could be elicited by intranasal delivery of recombinant lactobacilli, a Lactobacillus plantarum strain of human origin (NCIMB8826) was selected as the expression host. Cytoplasmic production of the 47-kDa fragment C of tetanus toxin (TTFC) was achieved at different levels depending on the plasmid construct. All recombinant strains proved to be immunogenic by the intranasal route in mice and able to elicit very high systemic immunoglobulin G (IgG1, IgG2b, and IgG2a) responses which correlated to the antigen dose. No significant differences in enzyme-linked immunosorbent assay IgG titers were observed when mice were immunized with live or mitomycin C-treated recombinant lactobacilli. Nevertheless, protection against the lethal effect of tetanus toxin was obtained only with the strains producing the highest dose of antigen and was greater following immunization with live bacteria. Significant TTFC-specific mucosal IgA responses were measured in bronchoalveolar lavage fluids, and antigen-specific T-cell responses were detected in cervical lymph nodes, both responses being higher in mice receiving a double dose of bacteria (at a 24-h interval) at each administration. These results demonstrate that recombinant lactobacilli can induce specific humoral (protective) and mucosal antibodies and cellular immune response against protective antigens upon nasal administration.     

Intranasal administration of recombinant Neisseria gonorrhoeae transferrin binding proteins A and B conjugated to the cholera toxin B subunit induces systemic and vaginal antibodies in mice

The transferrin binding proteins (TbpA and TbpB) comprise the gonococcal transferrin receptor and are considered potential antigens for inclusion in a vaccine against Neisseria gonorrhoeae. Intranasal (IN) immunization has shown promise in development of immunity against sexually transmitted disease pathogens, in part due to the induction of antigen-specific genital tract immunoglobulin A (IgA) and IgG. Conjugation of antigens to the highly immunogenic cholera toxin B subunit (Ctb) enhances antibody responses in the serum and mucosal secretions following IN vaccination. In the current study, we characterized the anti-Tbp immune responses following immunization of mice IN with recombinant transferrin binding proteins (rTbpA and rTbpB) conjugated to rCtb. We found that both rTbpA-Ctb and rTbpB-Ctb conjugates administered IN induced antibody responses in the serum and genital tract. IN immunization resulted in both IgA and IgG in the genital tract; however, subcutaneous immunization mainly generated IgG. Surprisingly, rTbpA alone was immunogenic and induced serum and mucosal antibody responses similar to those elicited against the rTbpA-Ctb conjugate. Overall, rTbpB was much more immunogenic than rTbpA, generating serum IgG levels that were greater than those elicited against rTbpA. Bactericidal assays conducted with sera collected from mice immunized IN with TbpA and/or TbpB indicated that both antigens generated antibodies with bactericidal activity. Anti-TbpA antibodies were cross-bactericidal against heterologous gonococcal strains, whereas TbpB-specific antibodies were less cross-reactive. By contrast, antibodies elicited via subcutaneous immunization were not cross-bactericidal against heterologous strains, indicating that IN vaccination could be the preferred route for elicitation of biologically functional antibodies.     

Manipulation of intestinal immune responses against ovalbumin by cholera toxin and its B subunit in mice.

We studied the effect of mucosal presentation of ovalbumin (OVA) conjugated to cholera toxin (CT) or cholera toxin B subunit (CTB) on the intestinal immune responses against OVA. Mice were primed intraperitoneally (i.p.) with OVA in a water-in-oil emulsion and boosted intraduodenally (i.d.) with OVA conjugated to CT or CTB in various molar ratios. Responses were evaluated by testing intestinal secretions for OVA-specific antibodies and by quantifying the OVA-specific antibody secreting cells (ASC) in the lamina propria of the small intestine. OVA-CT conjugates were tested in a molar ratio ranging from 1.8:1 to 4500:1. OVA-CTB conjugates were tested in a molar ratio ranging from 0.25:1 to 500:1. The optimum intestinal immune response was reached at a molar ratio of 1.8:1 for OVA-CT and 5:1 for OVA-CTB. The binding capacity of OVA-CTB, but not of OVA-CT, to GM1 ganglioside corresponded with the capacity to enhance the intestinal immune response. The effect of conjugating CTB or CT to OVA on the immune response against OVA was more striking when mice were not only boosted i.d., but also primed i.d. Both OVA-CT and OVA-CTB induced detectable immune responses, whereas free OVA did not. Therefore, the carrier effect of CT or CTB is essential to trigger a mucosal immune response against OVA when presented mucosally only. We conclude that enhancing antigen uptake greatly facilitates mucosal immune responses.     

Systemic and mucosal immune responses in mice after mucosal immunization with group B streptococcus type III capsular polysaccharide-cholera toxin B subunit conjugate vaccine

Group B streptococci (GBS) colonize the female genital and rectal tracts and can cause invasive infection in susceptible newborns. An optimally effective GBS vaccine should induce mucosal and systemic immunity. In this study, we investigate the local and systemic immune responses to GBS type III capsular polysaccharide (CPS) after mucosal vaccination of mice via intranasal, peroral, rectal, and vaginal routes, with GBS type III CPS conjugated with recombinant cholera toxin B subunit (GBS III CPS-rCTB). Cholera toxin (CT) was added as an adjuvant. Immunoglobulin G (IgG) and IgA antibodies to the CPS were tested in serum, lungs, and intestinal, rectal, and vaginal extracts by enzyme-linked immunosorbent assay. The conjugated CPS administered by intranasal, peroral, rectal, and vaginal routes was much more effective at inducing both mucosal and systemic antibody responses to GBS III CPS than was unconjugated CPS. The CPS-specific immune responses in various organs were dependent on the route of immunization. Generally, the highest levels of IgA and IgG were generated in the regions or sites of the conjugate exposure. Thus, intranasal vaccination elicited the highest anti-CPS IgA and IgG antibody levels in the lungs, whereas peroral administration in the intestinal site and vaginal vaccination elicited the highest antibody levels in the vagina. Rectal vaccination was superior to the other routes in inducing high antibody levels in the rectum. The four routes of mucosal vaccination also induced distant antibody responses to CPS. Rectal vaccination induced high specific IgA levels in the vagina and intestine, and oral administration induced high specific IgA levels in the lungs and rectum. All four routes of vaccination with the conjugate elicited similarly high levels of anti-CPS IgG in serum. Intranasal vaccination with different doses of the conjugate (10, 30, and 80 microg of CPS) did not have a significant influence on the anti-CPS specific antibody responses. Intranasal immunization induced better antibody responses when one dose of the conjugate was divided and given on three consecutive days compared to administration of the full dose on one occasion. In conclusion, rectal and vaginal vaccination may be the best way of stimulating anti-CPS immune responses in the rectal and vaginal tracts, while high levels of anti-CPS antibodies in the lungs can be achieved after intranasal administration. The vaccination regimen thus might influence the mucosal immune response to CPS. This conjugate may serve as an effective mucosal vaccine for preventing mucosal colonization and invasive infection caused by GBS.     

Comparison of serum humoral responses induced by oral immunization with the hepatitis B virus core antigen and the cholera toxin B subunit

The hepatitis B virus core (HBc) virus-like particle (VLP) is known as one of the most immunogenic antigens and carrier vehicles in different immunization strategies. Recent findings are suggesting the potential of the HBc VLPs as an oral immunogen. Here, we focus on the induction of serum humoral responses by oral administration of HBc VLPs in preparations substantially free of lipopolysaccharide and immunomodulating encapsidated RNA. The full-length HBc antigen was used, because the C-terminal arginine-rich tail may contribute to the immunogenicity of the antigen as the region is involved in cell surface heparan sulfate binding and internalization of the protein. Serum antibody levels and isotypes were determined following oral administration of the HBc VLPs with the perspective of using the HBc VLP as an immunostimulatory and carrier molecule for epitopes of blood-borne diseases in oral immunization vaccination strategies. Following oral administration of the HBc VLP preparations to mice, a strong serum humoral response was induced with mainly immunoglobulin G2a (IgG2a) antibodies, pointing toward a Th1 response which is essential in the control of intracellular pathogens. Intraperitoneal immunization with the HBc VLP induced a stronger, mixed Th1/Th2 response. Finally, a comparison was made with the induced serum humoral response following oral administration of the recombinant cholera toxin B pentamer, a commonly used oral immunogen. These immunizations, in contrast, induced predominantly antibodies of the IgG1 isotype, indicative of a Th2 response. These data suggest that the HBc VLP can be an interesting carrier molecule in oral vaccine development.     

Immune response of the female rat genital tract after oral and local immunization with keyhole limpet hemocyanin conjugated to the cholera toxin B subunit.

The immune response of the female rat genital tract was evaluated with Lewis rats given primary and secondary immunizations with keyhole limpet hemocyanin (KLH) alone or coupled to the cholera toxin (CT) B subunit (CTB) by the oral or intravaginal-uterine route or a combination of routes. CT (2 to 5 micrograms) was administered as an adjuvant with the KLH-CTB conjugate. While a significant mucosal immunoglobulin A (IgA) response was induced by KLH, there were no significant differences among the immunized groups in the levels of IgA antibodies in salivary gland, gut, vaginal, and uterine secretions, with the exception that rats immunized only orally with the KLH-CTB conjugate lacked a detectable vaginal response. Levels of IgA antibodies to CT, however, were significantly increased in genital tract secretions of rats immunized locally versus orally with the KLH-CTB conjugate. Antibody activity of the IgG isotype against both KLH and CT was significantly elevated in genital tract secretions of rats immunized with KLH-CTB by the oral or intravaginal-uterine route and given genital tract boosters, in comparison with the results for the other groups. IgM antibody titers were generally negligible in the different secretions. An enzyme-linked spot-forming assay revealed IgA and IgG antibody-secreting cells in salivary gland and uterine tissues. A highly significant correlation between the numbers of antibody-secreting cells and antibody titers existed for uterine IgG but not IgA responses to KLH among the different groups of rats. In conclusion, a vigorous local immune response was induced after immunization of the female rat reproductive tract alone or in combination with peroral challenge with the KLH-CTB conjugate.     

Expression and mutagenesis of recombinant cholera toxin A subunit

ADP-ribosylating protein exotoxins from Vibrio cholerae (CT) and Escherichia coli (LT-I) share two short regions of sequence similarity with Bordetella pertussis toxin (PT). Previous studies have indicated that substitution of arginine for lysine 7 within the first region of CT drastically decreases ADP ribosyltransferase activity. We have more closely defined the role of other amino acids in this region by generating modified proteins in which arginine 7 was replaced with lysine (R7K), aspartate 9 was replaced with arginine (D9R), glycine was substituted for proline 12 (P12G), amino acids 6 to 13 were deleted (Δ613) or the C-terminal KDEL sequence was changed to NEDL. The modified proteins R7K, D9R and Δ613 exhibited undetectable ADP ribosyltransferase activity. Comparison of the tryptic digest of R7K with native CT suggested that changes in protein conformation may be responsible for the loss of ADP-ribosylation activity.     

Protective efficacy in humans of killed whole-vibrio oral cholera vaccine with and without the B subunit of cholera toxin.

Natural protection from cholera is associated with local intestinal antibacterial and antitoxic antibodies, which appear to act synergistically. Although current parenteral cholera vaccines offer insufficient protection, new vaccines administered orally have more promise. Killed Vibrio cholerae, alone or given with the B subunit of cholera toxin, was evaluated in adult volunteers. Vaccinees, who received three doses of either vaccine, and unvaccinated controls ingested 10(6) V. cholerae organisms to determine the protective efficacy of the vaccines. The combination vaccine provided 64% protection, and the whole vibrio vaccine given alone provided 56% protection. In addition, illnesses in vaccines were milder than those in controls, and both vaccines gave complete protection against more severe disease. This substantial level of protection against a dose of V. cholerae that caused cholera in nearly 90% of controls suggests that these vaccines might provide at least as high a level of protection if given to the population of an endemic area. Indeed, a field efficacy trial is underway in Bangladesh, and preliminary data indicate a protective efficacy of 85% for a killed whole vibrio plus B subunit vaccine similar to that tested in volunteers and an efficacy of 58% for the killed whole vibrio vaccine alone. Thus, the studies in human volunteers were successful in predicting the substantial protection afforded by the vaccines in a cholera endemic area.     

Heteropentameric cholera toxin B subunit chimeric molecules genetically fused to a vaccine antigen induce systemic and mucosal immune responses: a potential new strategy to target recombinant vaccine antigens to mucosal immune systems

Noninvasive mucosal vaccines are attractive alternatives to parenteral vaccines. Although the conjugation of vaccine antigens with the B subunit of cholera toxin (CTB) is one of the most promising strategies for vaccine delivery to mucosal immune systems, the molecule cannot tolerate large-protein fusion, as it severely impairs pentamerization and loses affinity for GM1-ganglioside. Here we report a new strategy, in which steric hindrance between CTB-antigen fusion subunits is significantly reduced through the integration of unfused CTB "molecular buffers" into the pentamer unit, making them more efficiently self-assemble into biologically active pentamers. In addition, the chimeric protein took a compact configuration, becoming small enough to be secreted, and one-step affinity-purified proteins, when administered through a mucosal route, induced specific immune responses in mice. Since our results are not dependent on the use of a particular expression system or vaccine antigen, this strategy could be broadly applicable to bacterial enterotoxin-based vaccine design.     

Oral immunization of mice with a live recombinant Yersinia enterocolitica O:9 strain that produces the cholera toxin B subunit.

The 70-kilobase pYV plasmid of Yersinia enterocolitica encodes a set of proteins called Yops that are produced during infection. To use Y. enterocolitica as a live carrier to present the cholera toxin B (CT-B) subunit to the immune system, we constructed an operon fusion between ctxB and the yop51 gene. This operon fusion was either cloned on an RSF1010-derived plasmid or integrated into the pYV plasmid itself. In Y. enterocolitica, both constructions directed the synthesis of free CT-B only under conditions of Yops production, i.e., at 37 degrees C in a medium deprived of Ca2+. Bacteria containing both types of recombinant plasmids were given orally to mice. A serum antibody response against CT-B was detected in both cases. A secretory immunoglobulin A activity specific to CT-B was also observed in the intestinal secretions. According to immunoblot analysis, the serum antibody response was only directed against the polymeric form of the B subunit. The ctxB gene was also inserted in frame within yop51, giving a chimeric Yop51-CT-B protein that was secreted into the surrounding medium. In this case, however, no antibody response was observed after oral inoculation of mice. This lack of response probably results from the inability of the hybrid protein to assemble into the polymeric form of the B subunit.     

Intestinal and systemic immune responses to an oral cholera toxoid B subunit whole-cell vaccine administered during zinc supplementation

Zinc plays a critical role in the normal functioning of the immune system. We investigated whether zinc sulfate administered orally to adult zinc-replete volunteers modulates systemic and intestinal immune responses to an oral killed cholera toxoid B subunit (CTB) whole-cell cholera vaccine. The 30 participants were immunized twice, with a 17-day interval. The vaccinees in the intervention group ingested 45 mg of elemental zinc thrice daily for 9 days starting 2 days before each vaccine dose. The median serum anti-CTB immunoglobulin A (IgA) and IgG responses from day 0 to day 30, i.e. after two vaccine doses, were 13-fold lower (P value for identical distribution, <0.005) in the zinc-supplemented compared to the nonsupplemented vaccinees. The median serum vibriocidal responses from baseline to after one (day 0 to day 17) and two (day 0 to day 30) vaccine doses were at least sixfold (P = 0.033) and fourfold (P = 0.091) higher, while the median fecal anti-CTB IgA response after two doses was estimated to be fourfold higher (P = 0.084) in the zinc-supplemented vaccinees. These observations show that zinc reduces the antitoxin and may enhance the antibacterial responses in serum. Zinc may also improve the intestinal antitoxin immune response. Oral zinc administration has the potential to modify critical immune responses to antigens applied to mucosal surfaces.     

Strain-specific local and systemic cell-mediated immune responses to cytomegalovirus in humans.

Employing the techniques of complement fixation, immunofluorescence, and in vitro lymphocyte transformation assay, the antibody and cell-mediated immunity to cytomegalovirus (CMV) were studied in the serum, peripheral blood lymphocytes, tonsillar lymphocytes, and cord blood lymphocytes. The study population consisted of 32 children undergoing tonsillectomy and adenoidectomy. In the lymphocyte transformation assay, three strains of CMV (AD-169, ADH-1-41, and Davis), herpes simplex type 1, and phytohemagglutinin were employed as antigens. Sixty-five percent of the subjects were found to have CMV-specific antibody activity. The lymphocyte transformation response to phytohemagglutinin was similar in all subjects. No CMV-specific lymphocyte transformation activity was detected in cultures of cord blood lymphocytes. Significant cell-mediated immunity was observed in the tonsillar lymphocytes of 30% (3/10) of the seronegative individuals and in the peripheral blood lymphocytes obtained from one such subject. Over 75% (16/21) of the seropositive subjects demonstrated cell-mediated immunity against one or more strains of CMV in the peripheral blood lymphocytes and tonsillar lymphocytes. In the lymphocyte transformation assay, no cross-reactivity was apparent between CMV and herpes simplex type 1. These studies demonstrate the presence of strain-specific systemic and mucosal cell-mediated immune response to CMV in humans. The frequency and distribution of lymphocyte transformation responses to the three CMV strains suggest antigenic heterogeneity of CMV.     

Intranasal immunization of mice with group B streptococcal protein rib and cholera toxin B subunit confers protection against lethal infection

Intranasal immunization of mice with Rib, a cell surface protein of group B streptococcus (GBS), conjugated to or simply coadministered with the recombinant cholera toxin B subunit, induces systemic immunoglobulin G (IgG) and local IgA antibody responses and confers protection against lethal GBS infection. These findings have implications for the development of a human GBS vaccine.     

Adjuvant effects of cholera toxin b subunit on immune response to recombinant thyrotropin receptor in mice

We had previously shown that BALB/c mice immunized with the extracellular domain of human thyrotropin receptor (ETSHR) developed moderate hyperthyroxinemia. The antibody responses in these mice were predominantly of the IgG1 subclass. Since cholera toxin B subunit (CT-B) has direct effects on the thyroid, and is known to activate B lymphocytes and cause enhanced IgG1 production, we tested the ability of CT-B to modulate the antibody response to ETSHR. CT-B is unique in that it not only elicits a strong immune response to itself, but more importantly, when given with other antigens acts as a potent adjuvant. In the present study, BALB/c mice given ETSHR with CFA or CT-B via ip route showed higher titers of antibodies to ETSHR when compared to mice similarly immunized with ETSHR alone, or with IFA. Antibodies in ETSHR+CT-B immunized mice were mostly of the IgG1 subclass and reacted predominantly with ETSHR peptides 1 (aa 22-41), 21 (aa 322-341), and 23 (352-371). In contrast, animals immunized with ETSHR+CFA showed IgG1, IgG2a and IgG2b responses and reacted with peptides 1 and 21. Furthermore, mice immunized with ETSHR along with CT-B showed significantly higher levels of thyrotropin (TSH) binding inhibitory immunoglobulins (TBII) compared to those that did not receive CT-B. None of the mice immunized with a control antigen showed antibody response to ETSHR. These results suggested that CT-B could enhance and modulate immune response to ETSHR.     

Oral administration of a recombinant cholera toxin B subunit promotes mucosal healing in the colon

Cholera toxin B subunit (CTB) is a component of a licensed oral cholera vaccine. However, CTB has pleiotropic immunomodulatory effects whose impacts on the gut are not fully understood. Here, we found that oral administration in mice of a plant-made recombinant CTB (CTBp) significantly increased several immune cell populations in the colon lamina propria. Global gene expression analysis revealed that CTBp had more pronounced impacts on the colon than the small intestine, with significant activation of TGFβ-mediated pathways in the colon epithelium. The clinical relevance of CTBp-induced impacts on colonic mucosa was examined. In a human colon epithelial model using Caco2 cells, CTBp, but not the non-GM1-binding mutant G33D-CTBp, induced TGFβ-mediated wound healing. In a dextran sodium sulfate (DSS) acute colitis mouse model, oral administration of CTBp protected against colon mucosal damage as manifested by mitigated body weight loss, decreased histopathological scores, and blunted escalation of inflammatory cytokine levels while inducing wound healing-related genes. Furthermore, biweekly oral administration of CTBp significantly reduced disease severity and tumorigenesis in the azoxymethane/DSS model of ulcerative colitis and colon cancer. Altogether, these results demonstrate CTBp's ability to enhance mucosal healing in the colon, highlighting its potential application in ulcerative colitis therapy besides cholera vaccination.