Immunogenicity of Escherichia coli Outer Membrane Vesicles: Elucidation of Humoral Responses against OMV-Associated Antigens

Outer membrane vesicles (OMVs) produced by Gram-negative bacteria have emerged as a novel and flexible vaccine platform. OMVs can be decorated with foreign antigens and carry potent immunostimulatory components. Therefore, after their purification from the culture supernatant, they are ready to be formulated for vaccine use. It has been extensively demonstrated that immunization with engineered OMVs can elicit excellent antibody responses against the heterologous antigens. However, the definition of the conditions necessary to reach the optimal antibody titers still needs to be investigated. Here, we defined the protein concentrations required to induce antigen-specific antibodies, and the amount of antigen and OMVs necessary and sufficient to elicit saturating levels of antigen-specific antibodies. Since not all antigens can be expressed in OMVs, we also investigated the effectiveness of vaccines in which OMVs and purified antigens are mixed together without using any procedure for their physical association. Our data show that in most of the cases OMV-antigen mixtures are very effective in eliciting antigen-specific antibodies. This is probably due to the capacity of OMVs to "absorb" antigens, establishing sufficiently stable interactions that allow antigen-OMV co-presentation to the same antigen presenting cell. In those cases when antigen-OMV interaction is not sufficiently stable, the addition of alum to the formulation guarantees the elicitation of high titers of antigen-specific antibodies.

Bacterial Outer Membrane Vesicles as a Platform for the Development of a Broadly Protective Human Papillomavirus Vaccine Based on the Minor Capsid Protein L2

Human papillomaviruses (HPVs) are a large family of viruses with a capsid composed of the L1 and L2 proteins, which bind to receptors of the basal epithelial cells and promote virus entry. The majority of sexually active people become exposed to HPV and the virus is the most common cause of cervical cancer. Vaccines are available based on the L1 protein, which self-assembles and forms virus-like particles (VLPs) when expressed in yeast and insect cells. Although very effective, these vaccines are HPV type-restricted and their costs limit broad vaccination campaigns. Recently, vaccine candidates based on the conserved L2 epitope from serotypes 16, 18, 31, 33, 35, 6, 51, and 59 were shown to elicit broadly neutralizing anti-HPV antibodies. In this study, we tested whether E. coli outer membrane vesicles (OMVs) could be successfully decorated with L2 polytopes and whether the engineered OMVs could induce neutralizing antibodies. OMVs represent an attractive vaccine platform owing to their intrinsic adjuvanticity and their low production costs. We show that strings of L2 epitopes could be efficiently expressed on the surface of the OMVs and a polypeptide composed of the L2 epitopes from serotypes 18, 33, 35, and 59 provided a broad cross-protective activity against a large panel of HPV serotypes as determined using pseudovirus neutralization assay. Considering the simplicity of the OMV production process, our work provides a highly effective and inexpensive solution to produce universal anti-HPV vaccines.

Adapting Neutralizing Antibodies to Viral Variants by Structure-Guided Affinity Maturation Using Phage Display Technology

Neutralizing monoclonal antibodies have achieved great efficacy and safety for the treatment of numerous infectious diseases. However, their neutralization potency is often rapidly lost when the target antigen mutates. Instead of isolating new antibodies each time a pathogen variant arises, it can be attractive to adapt existing antibodies, making them active against the new variant. Potential benefits of this approach include reduced development time, cost, and regulatory burden. Here a methodology is described to rapidly evolve neutralizing antibodies of proven activity, improving their function against new pathogen variants without losing efficacy against previous ones. The reported procedure is based on structure-guided affinity maturation using combinatorial mutagenesis and phage display technology. Its use against the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is demonstrated, but it is suitable for any other pathogen. As proof of concept, the method is applied to CoV-X2, a human bispecific antibody that binds with high affinity to the early SARS-CoV-2 variants but lost neutralization potency against Delta. Antibodies emerging from the affinity maturation selection exhibit significantly improved neutralization potency against Delta and no loss of efficacy against the other viral sequences tested. These results illustrate the potential application of structure-guided affinity maturation in facilitating the rapid adaptation of neutralizing antibodies to pathogen variants.

Immunogenicity and Pre-Clinical Efficacy of an OMV-Based SARS-CoV-2 Vaccine

The vaccination campaign against SARS-CoV-2 relies on the world-wide availability of effective vaccines, with a potential need of 20 billion vaccine doses to fully vaccinate the world population. To reach this goal, the manufacturing and logistic processes should be affordable to all countries, irrespective of economical and climatic conditions. Outer membrane vesicles (OMVs) are bacterial-derived vesicles that can be engineered to incorporate heterologous antigens. Given the inherent adjuvanticity, such modified OMVs can be used as vaccines to induce potent immune responses against the associated proteins. Here, we show that OMVs engineered to incorporate peptides derived from the receptor binding motif (RBM) of the spike protein from SARS-CoV-2 elicit an effective immune response in vaccinated mice, resulting in the production of neutralizing antibodies (nAbs) with a titre higher than 1:300. The immunity induced by the vaccine is sufficient to protect the animals from intranasal challenge with SARS-CoV-2, preventing both virus replication in the lungs and the pathology associated with virus infection. Furthermore, we show that OMVs can be effectively decorated with the RBM of the Omicron BA.1 variant and that such engineered OMVs induce nAbs against Omicron BA.1 and BA.5, as measured using the pseudovirus neutralization infectivity assay. Importantly, we show that the RBM438-509 ancestral-OMVs elicited antibodies which efficiently neutralize in vitro both the homologous ancestral strain, the Omicron BA.1 and BA.5 variants with a neutralization titre ranging from 1:100 to 1:1500, suggesting its potential use as a vaccine targeting diverse SARS-CoV-2 variants. Altogether, given the convenience associated with the ease of engineering, production and distribution, our results demonstrate that OMV-based SARS-CoV-2 vaccines can be a crucial addition to the vaccines currently available.

Anti-Tumor Efficacy of In Situ Vaccination Using Bacterial Outer Membrane Vesicles

In situ vaccination (ISV) is a promising cancer immunotherapy strategy that consists of the intratumoral administration of immunostimulatory molecules (adjuvants). The rationale is that tumor antigens are abundant at the tumor site, and therefore, to elicit an effective anti-tumor immune response, all that is needed is an adjuvant, which can turn the immunosuppressive environment into an immunologically active one. Bacterial outer membrane vesicles (OMVs) are potent adjuvants since they contain several microbe-associated molecular patterns (MAMPs) naturally present in the outer membrane and in the periplasmic space of Gram-negative bacteria. Therefore, they appear particularly indicted for ISV. In this work, we first show that the OMVs from E. coli BL21(DE3)Δ60 strain promote a strong anti-tumor activity when intratumorally injected into the tumors of three different mouse models. Tumor inhibition correlates with a rapid infiltration of DCs and NK cells. We also show that the addition of neo-epitopes to OMVs synergizes with the vesicle adjuvanticity, as judged by a two-tumor mouse model. Overall, our data support the use of the OMVs in ISV and indicate that ISV efficacy can benefit from the addition of properly selected tumor-specific neo-antigens.

Immunogenicity and pre-clinical efficacy of an OMV-based SARS-CoV-2 vaccine

The vaccination campaign against SARS-CoV-2 relies on the world-wide availability of effective vaccines, with a potential need of 20 billion vaccine doses to fully vaccinate the world population. To reach this goal, the manufacturing and logistic processes should be affordable to all countries, irrespectively of economical and climatic conditions. Outer membrane vesicles (OMV) are bacterial-derived vesicles that can be engineered to incorporate heterologous antigens. Given the inherent adjuvanticity, such modified OMV can be used as vaccine to induce potent immune responses against the associated protein. Here we show that OMVs engineered to incorporate peptides derived from the receptor binding motif (RBM) of the spike protein from SARS-CoV-2 elicit an effective immune response in vaccinated mice, resulting in the production of neutralizing antibodies (nAbs). The immunity induced by the vaccine is sufficient to protect the animals from intranasal challenge with SARS-CoV-2, preventing both virus replication in the lungs and the pathology associated with virus infection. Furthermore, we show that OMVs can be effectively decorated with the RBM of the Omicron BA.1 variant and that such engineered OMVs induced nAbs against Omicron BA.1 and BA.5, as judged by pseudovirus infectivity assay. Importantly, we show that the RBM438-509 ancestral-OMVs elicited antibodies which efficiently neutralized in vitro both the homologous ancestral strain, the Omicron BA.1 and BA.5 variants, suggesting its potential use as a pan SARS-CoV-2 vaccine. Altogether, given the convenience associated with ease of engineering, production and distribution, our results demonstrate that OMV-based SARS-CoV-2 vaccines can be a crucial addition to the vaccines currently available.

Generation and in vivo validation of an IL-12 fusion protein based on a novel anti-human FAP monoclonal antibody

BACKGROUND

In this study, we describe the generation of a fully human monoclonal antibody (named '7NP2') targeting human fibroblast activation protein (FAP), an antigen expressed in the microenvironment of different types of solid neoplasms.

METHODS

7NP2 was isolated from a synthetic antibody phage display library and was improved by one round of mutagenesis-based affinity maturation. The tumor recognition properties of the antibody were validated by immunofluorescence procedures performed on cancer biopsies from human patients. A fusion protein consisting of the 7NP2 antibody linked to interleukin (IL)-12 was generated and the anticancer activity of the murine surrogate product (named mIL12-7NP2) was evaluated in mouse models. Furthermore, the safety of the fully human product (named IL12-7NP2) was evaluated in Cynomolgus monkeys.

RESULTS

Biodistribution analysis in tumor-bearing mice confirmed the ability of the product to selectively localize to solid tumors while sparing healthy organs. Encouraged by these results, therapy studies were conducted in vivo, showing a potent antitumor activity in immunocompetent and immunodeficient mouse models of cancer, both as single agent and in combination with immune checkpoint inhibitors. The fully human product was tolerated when administered to non-human primates.

CONCLUSIONS

The results obtained in this work provided a rationale for future clinical translation activities using IL12-7NP2.

A Novel Antibody-IL15 Fusion Protein Selectively Localizes to Tumors, Synergizes with TNF-based Immunocytokine, and Inhibits Metastasis

IL15 is an immunostimulatory cytokine that holds promises for cancer therapy, but its performance (alone or as partner for fusion proteins) has often been limited by suboptimal accumulation in the tumor and very rapid clearance from circulation. Most recently, the Sushi Domain (SD, the shortest region of IL15 receptor α, capable of binding to IL15) has been fused to IL15-based anticancer products to increase its biological activity. Here, we describe two novel antibody fusion proteins (termed F8-F8-IL15 and F8-F8-SD-IL15), specific to the alternatively spliced EDA domain of fibronectin (a marker of tumor neoangiogenisis, expressed in the majority of solid and hematologic tumors, but absent in normal healthy tissues) and featuring the F8 antibody in single-chain diabody format (with a short linker between VH and VL, thus allowing the domains to pair with the complementary ones of another chain). Unlike previously described fusions of the F8 antibody with human IL15, F8-F8-IL15 and F8-F8-SD-IL15 exhibited a preferential uptake in solid tumors, as evidenced by quantitative biodistribution analysis with radioiodinated protein preparations. Both products were potently active in vivo against mouse metastatic colon carcinomas and in sarcoma lesion in combination with targeted TNF. The results may be of clinical significance, as F8-F8-IL15 and F8-F8-SD-IL15 are fully human proteins, which recognize the cognate tumor-associated antigen with identical affinity in mouse and man.

Proteome-minimized outer membrane vesicles from Escherichia coli as a generalized vaccine platform

Because of their potent adjuvanticity, ease of manipulation and simplicity of production Gram‐negative Outer Membrane Vesicles OMVs have the potential to become a highly effective vaccine platform. However, some optimization is required, including the reduction of the number of endogenous proteins, the increase of the loading capacity with respect to heterologous antigens, the enhancement of productivity in terms of number of vesicles per culture volume. In this work we describe the use of Synthetic Biology to create Escherichia coli BL21(DE3)Δ60, a strain releasing OMVs (OMVs_Δ60) deprived of 59 endogenous proteins. The strain produces large quantities of vesicles (> 40 mg/L under laboratory conditions), which can accommodate recombinant proteins to a level ranging from 5% to 30% of total OMV proteins. Moreover, also thanks to the absence of immune responses toward the inactivated endogenous proteins, OMVs_Δ60 decorated with heterologous antigens/epitopes elicit elevated antigens/epitopes‐specific antibody titers and high frequencies of epitope‐specific IFN‐γ‐producing CD8⁺ T cells. Altogether, we believe that E. coli BL21(DE3)Δ60 have the potential to become a workhorse factory for novel OMV‐based vaccines.

Novel human monoclonal antibodies specific to the alternatively spliced domain D of Tenascin C efficiently target tumors in vivo

Antibody-based delivery of bioactive molecules represents a promising strategy for the improvement of cancer immunotherapy. Here, we describe the generation and characterization of R6N, a novel fully human antibody specific to the alternatively spliced domain D of Tenascin C, which is highly expressed in the stroma of primary tumors and metastasis. The R6N antibody recognized its cognate tumor-associated antigen with identical specificity in mouse and human specimens. Moreover, the antibody was able to selectively localize to solid tumors in vivo as evidenced by immunofluorescence-based biodistribution analysis. Encouraged by these results, we developed a novel fusion protein (termed mIL12-R6N) consisting of the murine interleukin 12 fused to the R6N antibody in homodimeric tandem single-chain variable fragment arrangement. mIL12-R6N exhibited potent antitumor activity in immunodeficient mice bearing SKRC52 renal cell carcinoma, as well as in immunocompetent mice bearing SMA-497 glioma. The experiments presented in this work provide a rationale for possible future applications for the R6N antibody for the treatment of cancer patients.

Vaccination With a FAT1-Derived B Cell Epitope Combined With Tumor-Specific B and T Cell Epitopes Elicits Additive Protection in Cancer Mouse Models

Human FAT1 is overexpressed on the surface of most colorectal cancers (CRCs) and in particular a 25 amino acid sequence (D8) present in one of the 34 cadherin extracellular repeats carries the epitope recognized by mAb198.3, a monoclonal antibody which partially protects mice from the challenge with human CRC cell lines in xenograft mouse models. Here we present data in immune competent mice demonstrating the potential of the D8-FAT1 epitope as CRC cancer vaccine. We first demonstrated that the mouse homolog of D8-FAT1 (mD8-FAT1) is also expressed on the surface of CT26 and B16F10 murine cell lines. We then engineered bacterial outer membranes vesicles (OMVs) with mD8-FAT1 and we showed that immunization of BALB/c and C57bl6 mice with engineered OMVs elicited anti-mD8-FAT1 antibodies and partially protected mice from the challenge against CT26 and EGFRvIII-B16F10 cell lines, respectively. We also show that when combined with OMVs decorated with the EGFRvIII B cell epitope or with OMVs carrying five tumor-specific CD4+ T cells neoepitopes, mD8-FAT1 OMVs conferred robust protection against tumor challenge in C57bl6 and BALB/c mice, respectively. Considering that FAT1 is overexpressed in both KRAS⁺ and KRAS⁻ CRCs, these data support the development of anti-CRC cancer vaccines in which the D8-FAT1 epitope is used in combination with other CRC-specific antigens, including mutation-derived neoepitopes.