Restoration of antitumor immunity through anti-MICA antibodies elicited with a chimeric protein.

BACKGROUND: Natural killer and cytotoxic CD8+ T cells are major players during antitumor immunity. They express NKG2D, an activating receptor that promotes tumor elimination through recognition of the MHC class I chain-related proteins A and B (MICA and MICB). Both molecules are overexpressed on a great variety of tumors from different tissues, making them attractive targets for immunotherapy. However, tumors shed MICA and MICB, and the soluble forms of both (sMICA and sMICB) mediate tumor-immune escape. Some reports indicate that anti-MICA antibodies (Ab) can promote the restoration of antitumor immunity through the induction of direct antitumor effects (antibody-dependent cell-mediated cytotoxicity, ADCC) and scavenging of sMICA. Therefore, we reasoned that an active induction of anti-MICA Ab with an immunogenic protein might represent a novel therapeutic and prophylactic alternative to restore antitumor immunity. METHODS: We generated a highly immunogenic chimeric protein (BLS-MICA) consisting of human MICA fused to the lumazine synthase from Brucella spp (BLS) and used it to generate anti-MICA polyclonal Ab (pAb) and to investigate if these anti-MICA Ab can reinstate antitumor immunity in mice using two different mouse tumors engineered to express MICA. We also explored the underlying mechanisms of this expected therapeutic effect. RESULTS: Immunization with BLS-MICA and administration of anti-MICA pAb elicited by BLS-MICA significantly delayed the growth of MICA-expressing mouse tumors but not of control tumors. The therapeutic effect of immunization with BLS-MICA included scavenging of sMICA and the anti-MICA Ab-mediated ADCC, promoting heightened intratumoral M1/proinflammatory macrophage and antigen-experienced CD8+ T cell recruitment. CONCLUSIONS: Immunization with the chimeric protein BLS-MICA constitutes a useful way to actively induce therapeutic anti-MICA pAb that resulted in a reprogramming of the antitumor immune response towards an antitumoral/proinflammatory phenotype. Hence, the BLS-MICA chimeric protein constitutes a novel antitumor vaccine of potential application in patients with MICA-expressing tumors.

Characterization of structural and immunological properties of a fusion protein between flagellin from Salmonella and lumazine synthase from Brucella.

Aiming to combine the flexibility of Brucella lumazine synthase (BLS) to adapt different protein domains in a decameric structure and the capacity of BLS and flagellin to enhance the immunogenicity of peptides that are linked to their structure, we generated a chimeric protein (BLS-FliC131) by fusing flagellin from Salmonella in the N-termini of BLS. The obtained protein was recognized by anti-flagellin and anti-BLS antibodies, keeping the oligomerization capacity of BLS, without affecting the folding of the monomeric protein components determined by circular dichroism. Furthermore, the thermal stability of each fusion partner is conserved, indicating that the interactions that participate in its folding are not affected by the genetic fusion. Besides, either in vitro or in vivo using TLR5-deficient animals we could determine that BLS-FliC131 retains the capacity of triggering TLR5. The humoral response against BLS elicited by BLS-FliC131 was stronger than the one elicited by equimolar amounts of BLS + FliC. Since BLS scaffold allows the generation of hetero-decameric structures, we expect that flagellin oligomerization on this protein scaffold will generate a new vaccine platform with enhanced capacity to activate immune responses.

Immunization with BLS-Stx2B chimera totally protects dams from early pregnancy loss induced by Shiga toxin type 2 (Stx2) and confers anti-Stx2 immunity to the offspring.

Shiga toxin producing Escherichia coli (STEC) are bacterial pathogens involved in food-borne diseases. Shiga toxin (Stx) is the main virulence factor of STEC and is responsible for systemic complications including Hemolytic Uremic Syndrome (HUS). It has been previously demonstrated that Shiga toxin type 2 (Stx2) induces pregnancy loss in rats in early stage of pregnancy. The main purpose of this study was to determine if an active immunization prevents Stx2 mediated pregnancy loss and confers passive protective immunity to the offspring. For that purpose Sprague Dawley female rats were immunized with the chimera based on the enzyme lumazine synthase from Brucella spp. (BLS) and the B subunit of Shiga toxin 2 (Stx2B) named BLS-Stx2B. After immunization females were mated with males. At day 8 of gestation, dams were challenged intraperitoneally with a sublethal and abortifacient dose of Stx2. The immunization induced high anti-Stx2B-specific antibody titers in sera and most important, prevented pregnancy loss. Pups born and breastfeed by immunized dams had high anti-Stx2B-specific antibody titers in sera. Cross-fostering experiments indicated that passive protective immunity against Stx2 was transmitted through lactation. These results indicate that immunization of adult female rats with BLS-Stx2B prevents Stx2-induced pregnancy loss and confers anti Stx2 protective immunity to the offspring.

Immunization with Fasciola hepatica thioredoxin glutathione reductase failed to confer protection against fasciolosis in cattle.

The liver fluke Fasciola hepatica remains an important agent of food-borne trematode disease producing great economic losses due to its negative effect on productivity of livestock grazing in temperate areas. The prevailing control strategy based on anthelmintic drugs is unsustainable due to widespread resistance hence vaccination appears as an attractive option to pursue. In this study we evaluate the effect of vaccination in calves with a functional recombinant thioredoxin glutathione reductase (rFhTGR) from liver fluke, a critical antioxidant enzyme at the crossroads of the thioredoxin and glutathione metabolism in flatworms. The recombinant enzyme produced in Escherichia coli was tested in two vaccination experiments; in the first trial rFhTGR was administered in combination with Freund́s Incomplete Adjuvant (FIA) in a three-inoculation scheme on weeks 0, 4 and 8; in the second trial rFhTGR was given mixed with Adyuvac 50 or Alum as adjuvants on weeks 0 and 4. In both cases calves were challenged with metacercariae (400 in the first and 500 in the second trial) 2 weeks after the last inoculation. Our results demonstrate that two or three doses of the vaccine induced a non-significant reduction in worm counts of 8.2% (FIA), 3.8% (Adyuvac 50) and 23.0% (Alum) compared to adjuvant controls indicating that rFhTGR failed to induce a protective immunity in challenged calves. All vaccine formulations induced a mixed IgG1/IgG2 response but no booster was observed after challenge. No correlations between antibody titres and worm burdens were found.

Brucella spp. Lumazine Synthase Induces a TLR4-Mediated Protective Response against B16 Melanoma in Mice.

Brucella Lumazine Synthase (BLS) is a highly immunogenic decameric protein which can accept the fusion of foreign proteins at its ten N-termini. These chimeras are very efficient to elicit systemic and oral immunity without adjuvants. BLS signaling via Toll-Like Receptor 4 (TLR4) regulates innate and adaptive immune responses, inducing dendritic cell maturation and CD8(+) T-cell cytotoxicity. In this work we study the effect induced by BLS in TLR4-expressing B16 melanoma. In order to evaluate the effectiveness of BLS as a preventive vaccine, C57BL/6J mice were immunized with BLS or BLS-OVA, and 35 days later were subcutaneously inoculated with B16-OVA melanoma. BLS or BLS-OVA induced a significant inhibition of tumor growth, and 50% of mice immunized with the highest dose of BLS did not develop visible tumors. This effect was not observed in TLR4-deficient mice. For treatment experiments, mice were injected with BLS or BLS-OVA 2 days after the inoculation of B16 cells. Both treatments induced significant and equal tumor growth delay and increased survival. Moreover, BLS and BLS-OVA stimulation were also effective in TLR4-deficient mice. In order to study whether BLS has a direct effect on tumor cells, B16 cells were preincubated with BLS, and after 48h, cells were inoculated. Tumors induced by BLS-stimulated cells had inhibited growth and survival was increased. In the BLS group, 40% of mice did not develop tumors. This effect was abolished by the addition of TLR4/MD2 blocking antibody to cells before BLS stimulation. Our work demonstrates that BLS immunization induces a preventive antitumor response that depends on mice TLR4. We also show that BLS generates a therapeutic effect in mice inoculated with B16 cells. Our results show that BLS acts directly in cultured tumor cells via TLR4, highly suggesting that BLS elicits its therapeutic effects acting on the TLR4 from B16 melanoma cells.

Protection of mice against Shiga toxin 2 (Stx2)-associated damage by maternal immunization with a Brucella lumazine synthase-Stx2 B subunit chimera.

Hemolytic-uremic syndrome (HUS) is defined as the triad of anemia, thrombocytopenia, and acute kidney injury. Enterohemorrhagic Shiga toxin (Stx)-producing Escherichia coli (EHEC), which causes a prodromal hemorrhagic enteritis, remains the most common etiology of the typical or epidemic form of HUS. Because no licensed vaccine or effective therapy is presently available for human use, we recently developed a novel immunogen based on the B subunit of Shiga toxin 2 (Stx2B) and the enzyme lumazine synthase from Brucella spp. (BLS) (BLS-Stx2B). The aim of this study was to analyze maternal immunization with BLS-Stx2B as a possible approach for transferring anti-Stx2 protection to the offspring. BALB/c female mice were immunized with BLS-Stx2B before mating. Both dams and pups presented comparable titers of anti-Stx2B antibodies in sera and fecal extracts. Moreover, pups were totally protected against a lethal dose of systemic Stx2 injection up to 2 to 3 months postpartum. In addition, pups were resistant to an oral challenge with an Stx2-producing EHEC strain at weaning and did not develop any symptomatology associated with Stx2 toxicity. Fostering experiments demonstrated that anti-Stx2B neutralizing IgG antibodies were transmitted through breast-feeding. Pups that survived the EHEC infection due to maternally transferred immunity prolonged an active and specific immune response that protected them against a subsequent challenge with intravenous Stx2. Our study shows that maternal immunization with BLS-Stx2B was very effective at promoting the transfer of specific antibodies, and suggests that preexposure of adult females to this immunogen could protect their offspring during the early phase of life.

Immunization with a chimera consisting of the B subunit of Shiga toxin type 2 and brucella lumazine synthase confers total protection against Shiga toxins in mice.

The striking feature of enterohemorrhagic Escherichia coli (EHEC) infections is the production of Shiga toxins (Stx) implicated in the development of the life-threatening hemolytic uremic syndrome. Despite the magnitude of the social impact of EHEC infections, no licensed vaccine or effective therapy is available for human use. One of the biggest challenges is to develop an effective and safe immunogen to ensure nontoxicity, as well as a strong input to the immune system to induce long-lasting, high-affinity Abs with anti-Stx-neutralizing capacity. The enzyme lumazine synthase from Brucella spp. (BLS) is a highly stable dimer of pentamers and a scaffold with enormous plasticity on which to display foreign Ags. Taking into account the advantages of BLS and the potential capacity of the B subunit of Stx2 to induce Abs that prevent Stx2 toxicity by blocking its entrance into the host cells, we engineered a new immunogen by inserting the B subunit of Stx2 at the amino termini of BLS. The resulting chimera demonstrated a strong capacity to induce a long-lasting humoral immune response in mice. The chimera induced Abs with high neutralizing capacity for Stx2 and its variants. Moreover, immunized mice were completely protected against i.v. Stx2 challenge, and weaned mice receiving an oral challenge with EHEC were completely protected by the transference of immune sera. We conclude that this novel immunogen represents a promising candidate for vaccine or Ab development with preventive or therapeutic ends, for use in hemolytic uremic syndrome-endemic areas or during future outbreaks caused by pathogenic strains of Stx-producing E. coli.

A polymeric protein induces specific cytotoxicity in a TLR4 dependent manner in the absence of adjuvants.

Lumazine synthase from Brucella spp. (BLS) is a highly immunogenic decameric protein. It is possible to insert foreign peptides or proteins at its ten-amino acid termini. These chimeras elicit systemic and oral immunity without adjuvants, which are commonly needed in the formulation of subunit-based vaccines. Here, we show that BLS induces the cross presentation of a covalently attached peptide OVA(257-264) and a specific cytotoxic response to this peptide in the absence of adjuvants. Unlike other subunit-based vaccines, this chimera induces rapid activation of CTLs and a specific cytotoxic response, making this polymeric protein an ideal antigen carrier for vaccine development. Adoptive transfer of transgenic OT-I T cells revealed efficient cross presentation of BLS-OVA(257-264)in vivo. BLS-OVA(257-264) immunization induced the proliferation of OVA(257-264)-specific CD8+ lymphocytes and also increased the percentage of OVA(257-264)-specific CD8+ cells expressing the early activation marker CD69; after 5 days, the percentage of OVA(257-264)-specific CD8+ cells expressing high levels of CD44 increased. This cell subpopulation showed decreased expression of IL-7Rα, indicating that BLS-OVA(257-264) induced the generation of CD8+ effector cells. BLS-OVA(257-264) was cross presented in vitro independently of the presence of a functional TLR4 in the DCs. Finally, we show that immunization of wild type mice with the chimera BLS-OVA(257-264) without adjuvants induced a strong OVA(257-264)-specific effector cytotoxic response. This cytotoxicity is dependent on TLR4 as is not induced in mice lacking a functional receptor. These data show that TLR4 signaling is necessary for the induction of a cytotoxic response but not for antigen cross presentation.

Knockout of the dhfr-ts gene in Trypanosoma cruzi generates attenuated parasites able to confer protection against a virulent challenge.

BACKGROUND: Trypanosoma cruzi is a protozoan parasite that causes severe disease in millions of habitants of developing countries. Currently there is no vaccine to prevent this disease and the available drugs have the consequences of side effects. Live vaccines are likely to be more effective in inducing protection than recombinant proteins or DNA vaccines; however, safety problems associated to their use have been pointed out. In recent years, increasing knowledge on the molecular genetics of Trypanosomes has allowed the identification and elimination of genes that may be necessary for parasite infectivity and survival. In this sense, targeted deletion or disruption of specific genes in the parasite genome may protect against such reversion to virulent genotypes. METHODS AND FINDINGS: By targeted gene disruption we generated monoallelic mutant parasites for the dhfr-ts gene in a T. cruzi strain that has been shown to be naturally attenuated. In comparison to T. cruzi wild type epimastigotes, impairment in growth of dhfr-ts(+/-) mutant parasites was observed and mutant clones displayed decreased virulence in mice. Also, a lower number of T. cruzi-specific CD8(+) T cells, in comparison to those induced by wild type parasites, was detected in mice infected with mutant parasites. However, no remarkable differences in the protective effect of TCC wild type versus TCC mutant parasites were observed. Mice challenged with virulent parasites a year after the original infection with the mutant parasites still displayed a significant control over the secondary infection. CONCLUSION: This study indicates that it is possible to generate genetically attenuated T. cruzi parasites able to confer protection against further T. cruzi infections.

The polymeric antigen BLSOmp31 confers protection against Brucella ovis infection in rams.

We have engineered the polymeric vaccine BLSOmp31 by decorating the highly immunogenic and decameric Brucella lumazine synthase with an exposed loop of the Brucella outer membrane protein Omp31. In the present study, we have immunized different groups of rams with the recombinant chimera rBLSOmp31 in two different adjuvants (Incomplete Freund Adjuvant-IFA and QUIL A) and with the plasmid pCIBLSOmp31 administered either by i.m. injection alone or by using electroporation. In addition, we have used a heterologous prime-boost strategy consisting of repeated pCIBLSOmp31 electroporation priming followed by a single protein boost. Both, chimera rBLSOmp31 in IFA and the prime-boost strategy induced the highest IgG specific antibodies with bacteriolytic activity. While electroporation-enhanced humoral immune responses as compared to pCIBLSOmp31 injection alone, the highest levels of specific IFN-gamma and protection against bacterial challenge were achieved with prime-boost (76%) and chimera rBLSOmp31 in IFA (63%). Taken together these results strongly support the usefulness of the chimera BLSOmp31 as a vaccine against Brucella ovis in ovine brucellosis.

Multiple display of a protein domain on a bacterial polymeric scaffold.

The multiple display of protein domains on polymeric scaffolds is an emerging technology for many applications. BLS is a highly immunogenic protein that has an oligomeric structure formed by a 17.2 kDa subunit arranged as a dimer of pentamers. Here we describe the production as well as the structural, functional, and immunological properties of a 9 kDa double-stranded RNA-binding domain (RBD3) fused to the structure of BLS. We demonstrate that the BLS and RBD3 modules are stably and independently folded in the structure of the chimera and form a decameric structure of 255 kDa as the native BLS oligomers. The polymeric display of RBD3 in the structure of BLS increases the dsRNA binding strength of this domain both in vitro and in vivo, and also enhances its immunogenicity to the point that it breaks the tolerance of mice to the RBD3 self-antigen. Our results underscore the BLS display strategy as a powerful tool for biotechnological and therapeutic applications.

Brucella lumazine synthase elicits a mixed Th1-Th2 immune response and reduces infection in mice challenged with Brucella abortus 544 independently of the adjuvant formulation used.

The immunogenicity and protective efficacy of recombinant lumazine synthase from Brucella spp. (rBLS) administered with different adjuvants was evaluated in mice. Mice were immunized with rBLS in the absence or the presence of aluminum hydroxide gel (BLS-Al), monophosphoryl lipid A (BLS-MPA), or incomplete Freund's adjuvant (BLS-IFA). rBLS per se induced a vigorous immunoglobulin G (IgG) response, with high titers of IgG1 as well as IgG2. All the adjuvants increased this response; the BLS-IFA formulation was the most effective at inducing BLS-specific IgG antibodies. In addition, after in vitro stimulation with rBLS, spleen cells from BLS-IFA-, BLS-Al-, or BLS-MPA-immunized mice proliferated and produced interleukin-2 (IL-2), gamma interferon (IFN-gamma), IL-10, and IL-4, suggesting the induction of a mixed Th1-Th2 response. Immunization with rBLS protected mice against challenge with B. abortus 544. The levels of protection in the spleen were similar for all adjuvants, but only BLS-Al and BLS-IFA were effective in the liver. Our results indicate that BLS might be a useful candidate for the development of subunit vaccines against brucellosis, since it elicits antigen-specific cellular responses, with production of IFN-gamma and protection, independently of the adjuvant formulation used.

Diminished production of T helper 1 cytokines correlates with T cell unresponsiveness to Brucella cytoplasmic proteins in chronic human brucellosis.

This study evaluated the cellular immune response against Brucella species cytoplasmic protein (CP) in peripheral blood mononuclear cells (PBMC) of 25 patients with brucellosis. In vitro proliferation and cytokine gene expression and production were investigated. PBMC from 14 patients proliferated in response to CP (responder patients [RPs]) and cells from 11 patients did not (nonresponder patients [NRPs]). CP-specific interleukin (IL)-2 and interferon-gamma were significantly induced in PBMC from RPs, compared with cells from NRPs. No significant differences were found in the production of IL-10 between the 2 groups. CP did not induce IL-4 production. A close relationship was observed between the clinical status of the patients and the T cell response against CP. Patient with acute infections responded to CP and induced production of T helper 1 (Th1) cytokines, whereas chronically infected patients did not. Diminished production of Th1 cytokines may contribute to T cell unresponsiveness in chronic human brucellosis.

A DNA vaccine encoding lumazine synthase from Brucella abortus induces protective immunity in BALB/c mice.

This study was conducted to evaluate the immunogenicity of the Brucella abortus lumazine synthase (BLS) gene cloned into the pcDNA3 plasmid, which is driven by the cytomegalovirus promoter. Injection of plasmid DNA carrying the BLS gene (pcDNA-BLS) into BALB/c mice elicited both humoral and cellular immune responses. Antibodies to the encoded BLS included immunoglobulin G1 (IgG1) IgG2a, IgG2b, IgG3, and IgM isotypes. Animals injected with pcDNA-BLS exhibited a dominance of IgG2a over IgG1. In addition, spleen cells from vaccinated animals produced interleukin-2 and gamma interferon but not IL-10 or IL-4 after in vitro stimulation with recombinant BLS (rBLS), suggesting the induction of a Th1 response. Protection was evaluated by comparing the levels of infection in the spleens of vaccinated mice challenged with B. abortus 544. Immunization with pcDNA-BLS- reduced the bacterial burden relative to those in the control groups. Mice immunized with rBLS produced a significant humoral response but did not show a specific cellular response or any protection from challenge. Altogether, these data suggest that pcDNA-BLS is a good immunogen for the production of humoral and cell-mediated responses in mice and is a candidate for use in future studies of vaccination against brucellosis.

The 18-kDa cytoplasmic protein of Brucella species --an antigen useful for diagnosis--is a lumazine synthase.

Previous studies have shown that the detection of antibodies to an 18-kDa cytoplasmic protein of Brucella spp. is useful for the diagnosis of human and animal brucellosis. This protein has now been expressed in recombinant form in Escherichia coli. The recombinant protein is soluble only under reducing conditions, but alkylation with iodoacetamide renders it soluble in non-reducing media. As shown by gel exclusion chromatography, this soluble form arranges in pentamers of 90 kDa. The reactivity of human and animal sera against the recombinant protein was similar to that found with the native protein present in brucella cytoplasmic fraction, suggesting that the recombinant protein is correctly folded. The protein has low but significant homology (30%) with lumazine synthases involved in bacterial riboflavin biosynthesis, which also arrange as pentamers. Biological tests on the crude extract of the recombinant bacteria and on the purified recombinant protein showed that the biological activity of the Brucella spp. 18-kDa protein is that of lumazine synthase. Preliminary crystallographic analysis showed that the Brucella spp. lumazine synthase arranges in icosahedric capsids similar to those formed by the lumazine synthases of other bacteria. The high immunogenicity of this protein, potentially useful for the design of acellular vaccines, could be explained by this polymeric arrangement.

A dhfr-ts- Leishmania major knockout mutant cross-protects against Leishmania amazonensis.

E10-5A3 is a dhfr-ts- Leishmania major double knockout auxotrophic shown previously to induce substantial protection against virulent L. major infection in both genetically susceptible and resistant mice. We investigated the capacity of dhfr-ts- to protect against heterologous infection by L. amazonensis. The degree of protection was evaluated by immunization of BALB/c or C57BL/6 mice with E10-5A3, followed by L. amazonensis challenge. Whether immunized by subcutaneous (SC) or intravenous (IV) inoculation, susceptible and resistant mice displayed a partial degree of protection against challenge with virulent L. amazonensis. SC-immunized BALB/c mice developed lesions 40 to 65% smaller than non immunized mice, while IV immunization led to protection ranging from 40 to 75% in four out of six experiments compared to non immunized animals. The resistant C57BL/6 mice displayed comparable degrees of protection, 57% by SC and 49% by IV immunization. Results are encouraging as it has been previously difficult to obtain protection by SC vaccination against Leishmania, the preferred route for human immunization.