T-cell stimulating vaccines empower CD3 bispecific antibody therapy in solid tumors

CD3 bispecific antibody (CD3 bsAb) therapy is clinically approved for refractory hematological malignancies, but responses in solid tumors have been limited so far. One of the main hurdles in solid tumors is the lack of sufficient T-cell infiltrate. Here, we show that pre-treatment vaccination, even when composed of tumor-unrelated antigens, induces CXCR3-mediated T-cell influx in immunologically 'cold' tumor models in male mice. In the absence of CD3 bsAb, the infiltrate is confined to the tumor invasive margin, whereas subsequent CD3 bsAb administration induces infiltration of activated effector CD8 T cells into the tumor cell nests. This combination therapy installs a broadly inflamed Th1-type tumor microenvironment, resulting in effective tumor eradication. Multiple vaccination formulations, including synthetic long peptides and viruses, empower CD3 bsAb therapy. Our results imply that eliciting tumor infiltration with vaccine-induced tumor-(un)related T cells can greatly improve the efficacy of CD3 bsAbs in solid tumors.

Pyroptosis-inducing active caspase-1 as a genetic adjuvant in anti-cancer DNA vaccination

Pyroptosis is a recently discovered form of inflammatory programmed necrosis characterized by caspase-1-mediated and gasdermin D-dependent cell death leading to the release of pro-inflammatory cytokines such as Interleukin-1 beta (IL-1β). Here, we evaluated whether pyroptosis could be exploited in DNA vaccination by incorporating a constitutively active variant of caspase-1 to the antigen-expressing DNA. In vitro, transfection with constitutively active caspase-1 DNA induced pro-IL-1β maturation and IL-1β release as well as gasdermin D-dependent cell death. To test active caspase-1 as a genetic adjuvant for the induction of antigen-specific T cell responses, mice were vaccinated intradermally with a DNA vaccine consisting of the active caspase-1 plasmid together with a plasmid encoding an ovalbumin-derived CD8 T cell epitope. Active caspase-1 accelerated and amplified antigen-specific CD8 T cell responses when administered simultaneously with the DNA vaccine at an equimolar dose. Moreover, upon challenge with melanoma cells expressing ovalbumin, mice vaccinated with the antigen vaccine adjuvanted with active caspase-1 showed significantly better survival compared to the non-adjuvanted group. In conclusion, we have developed a novel genetic adjuvant that for the first time employs the pyroptosis pathway to improve DNA vaccination against cancer.

770 Personalized synthetic polyepitope DNA cancer vaccines encoding a novel pyroptotic adjuvant to generate effective anti-tumor T cell immunity

Background

As every tumor carries its unique set of neoantigens distinguishing it from healthy tissue, cancer vaccines need to be produced quickly and on an individual basis to swiftly induce a broad immune response targeting multiple antigens. DNA provides an ideal platform to achieve this, as a single polyepitope vaccine can encode multiple (>20) antigens. However, standard plasmid DNA vaccines take months to produce and tend to be poorly immunogenic in humans.

Methods

To address the first issue, a GMP-compatible method (AmpliVax) was developed that allows the simultaneous production of milligram amounts of multiple DNA vaccines in single vessel reactions within two days. This method relies on a primer-free, isothermal, rolling-circle amplification using high fidelity DNA polymerase and RNA polymerase to amplify circular DNA templates into linear double-stranded concatemers. Concatemers are digested into single linear expression cassettes which are subsequently protected by nuclease-resistant caps. To improve DNA vaccine immunogenicity, two avenues were explored. First, neoantigen DNA vaccines were tested in a therapeutic setting together with a checkpoint inhibitor drug. Second, DNA vaccines were combined with a novel caspase-1-based genetic adjuvant (PyroVant) that induces pyroptosis by exploiting the inflammasome pathway.

Results

Upon intradermal injection in mice, synthetic AmpliVax DNA vaccines matched plasmid DNA vaccines in terms of in vivo expression, immunogenicity and tumor protection. While treatment of mice carrying an MC38 colorectal tumor with either a polyepitope neoantigen DNA vaccine or anti-PD-1 did not significantly delay tumor outgrowth compared to untreated mice (0% survival), the combination of the neoantigen vaccine and anti-PD1 resulted in up to 70% tumor-free survival. PyroVant DNA accelerated and amplified antigen-specific CD8 T cell responses when administered simultaneously with a polyepitope DNA vaccine. What's more, subsequent challenge with melanoma cells revealed that PyroVant also significantly improved tumor-free survival.

Conclusions

In conclusion, we have created a novel synthetic DNA vaccine platform suitable for the production of effective personalized cancer vaccines. Current efforts are aimed at testing combinations of therapeutic synthetic DNA vaccines, PyroVant and checkpoint inhibitors in multiple pre-clinical tumor models.

Targeting HIF-1 alpha transcriptional activity drives cytotoxic immune effector cells into melanoma and improves combination immunotherapy

Hypoxia is a key factor responsible for the failure of therapeutic response in most solid tumors and promotes the acquisition of tumor resistance to various antitumor immune effectors. Reshaping the hypoxic immune suppressive tumor microenvironment to improve cancer immunotherapy is still a relevant challenge. We investigated the impact of inhibiting HIF-1α transcriptional activity on cytotoxic immune cell infiltration into B16-F10 melanoma. We showed that tumors expressing a deleted form of HIF-1α displayed increased levels of NK and CD8⁺ effector T cells in the tumor microenvironment, which was associated with high levels of CCL2 and CCL5 chemokines. We showed that combining acriflavine, reported as a pharmacological agent preventing HIF-1α/HIF-1β dimerization, dramatically improved the benefit of cancer immunotherapy based on TRP-2 peptide vaccination and anti-PD-1 blocking antibody. In melanoma patients, we revealed that tumors exhibiting high CCL5 are less hypoxic, and displayed high NK, CD3⁺, CD4⁺ and CD8⁺ T cell markers than those having low CCL5. In addition, melanoma patients with high CCL5 in their tumors survive better than those having low CCL5. This study provides the pre-clinical proof of concept for a novel triple combination strategy including blocking HIF-1α transcription activity along vaccination and PD-1 blocking immunotherapy.

A poly-neoantigen DNA vaccine synergizes with PD-1 blockade to induce T cell-mediated tumor control

The combination of immune-stimulating strategies has the potency to improve immunotherapy of cancer. Vaccination against neoepitopes derived from patient tumor material can generate tumor-specific T cell immunity, which could reinforce the efficacy of checkpoint inhibitor therapies such as anti-PD-1 treatment. DNA vaccination is a versatile platform that allows the inclusion of multiple neoantigen-coding sequences in a single formulation and therefore represents an ideal platform for neoantigen vaccination. We developed an anti-tumor vaccine based on a synthetic DNA vector designed to contain multiple cancer-specific epitopes in tandem. The DNA vector encoded a fusion gene consisting of three neoepitopes derived from the mouse colorectal tumor MC38 and their natural flanking sequences as 40 amino acid stretches. In addition, we incorporated as reporter epitopes the helper and CTL epitope sequences of ovalbumin. The poly-neoantigen DNA vaccine elicited T cell responses to all three neoantigens and induced functional CD8 and CD4 T cell responses to the reporter antigen ovalbumin after intradermal injection in mice. The DNA vaccine was effective in preventing outgrowth of B16 melanoma expressing ovalbumin in a prophylactic setting. Moreover, the combination of therapeutic DNA vaccination and anti-PD-1 treatment was synergistic in controlling MC38 tumor growth whereas individual treatments did not succeed. These data demonstrate the potential of DNA vaccination to target multiple neoepitopes in a single formulation and highlight the cooperation between vaccine-based and checkpoint blockade immunotherapies for the successful eradication of established tumors.

Dielectric constant of liquid alkanes and hydrocarbon mixtures

The complex dielectric constants of n-alkanes with two to seven carbon atoms have been measured. The measurements were conducted using a slotted-line technique at 1.2 GHz and at atmospheric pressure. The temperature was varied from the melting point to the boiling point of the respective alkanes. The real part of the dielectric constant was found to decrease with increasing temperature and correlate with the change in the molar volume. An upper limit to all the loss tangents was established at 0.001. The complex dielectric constants of a few mixtures of liquid alkanes were also measured at room temperature. For a pentane-octane mixture the real part of the dielectric constant could be explained by the Clausius-Mosotti theory. For the mixtures of n-hexane-ethylacetate and n-hexane-acetone the real part of the dielectric constants could be explained by the Onsager theory extended to mixtures. The dielectric constant of the n-hexane-acetone mixture displayed deviations from the Onsager theory at the highest fractions of acetone. The dipole moments of ethylacetate and acetone were determined for dilute mixtures using the Onsager theory and were found to be in agreement with their accepted gas-phase values. The loss tangents of the mixtures exhibited a linear relationship with the volume fraction for low concentrations of the polar liquids.