Most cases of Merkel cell carcinoma (MCC), a rare and highly aggressive type of neuroendocrine skin cancer, are associated with Merkel cell polyomavirus (MCPyV) infection. MCPyV integrates into the host genome, resulting in expression of oncoproteins including a truncated form of the viral large T antigen (LT) in infected cells. These oncoproteins are an attractive target for a therapeutic cancer vaccine. We designed a cancer vaccine that promotes potent, antigen-specific CD4 T cell responses to MCPyV-LT. To activate antigen-specific CD4 T cells in vivo, we utilized our nucleic acid platform, UNITE™ (UNiversal Intracellular Targeted Expression), which fuses a tumor-associated antigen with lysosomal-associated membrane protein 1 (LAMP1). This lysosomal targeting technology results in enhanced antigen presentation and potent antigen-specific T cell responses. LTS220A, encoding a mutated form of MCPyV-LT that diminishes its pro-oncogenic properties, was introduced into the UNITE™ platform. Vaccination with LTS220A-UNITE™ DNA vaccine (ITI-3000) induced antigen-specific CD4 T cell responses and a strong humoral response that were sufficient to delay tumor growth of a B16F10 melanoma line expressing LTS220A. This effect was dependent on the CD4 T cells' ability to produce IFNγ. Moreover, ITI-3000 induced a favorable tumor microenvironment (TME), including Th1-type cytokines and significantly enhanced numbers of CD4 and CD8 T cells as well as NK and NKT cells. Additionally, ITI-3000 synergized with an α-PD-1 immune checkpoint inhibitor to further slow tumor growth and enhance survival. These findings strongly suggest that in pre-clinical studies, DNA vaccination with ITI-3000, using the UNITE™ platform, enhances CD4 T cell responses to MCPyV-LT that result in significant anti-tumor immune responses. These data support the initiation of a first-in-human (FIH) Phase 1 open-label study to evaluate the safety, tolerability, and immunogenicity of ITI-3000 in patients with polyomavirus-positive MCC (NCT05422781).

Abstract The majority of Merkel cell carcinomas (MCC), a rare and highly aggressive type of neuroendocrine skin cancer, are associated with Merkel cell polyomavirus (MCPyV) infection. MCPyV integrates into the host genome, resulting in expression of a truncated form of the viral large T antigen (LT) in infected cells and thus making LT an attractive target for therapeutic cancer vaccines. We designed a cancer vaccine that promotes potent, antigen-specific CD4+ T cell responses to MCPγV-LT. To activate antigen-specific CD4+ T cells in vivo, we utilized our nucleic acid platform, UNITE࣪ (UNiversal Intracellular Targeted Expression), which fuses a tumor-associated antigen with lysosomal-associated membrane protein 1 (LAMP1). This lysosomal targeting technology results in enhanced antigen presentation and a balanced T cell response. LTS220A, encoding a mutated form of MCPγV-LT that diminishes its pro-oncogenic properties, was introduced into the UNITE࣪ platform. In pre-clinical studies, vaccination with LTS220A-UNITE࣪ (ITI-3000) induced antigen-specific CD4+ T cells that were sufficient to delay tumor growth, and this effect was dependent on their ability to produce IFNγ. Moreover, ITI-3000 induced a favorable tumor microenvironment (TME), including significantly enhanced numbers of CD4+ and CD8+ T cells as well as NK and NKT cells. These findings strongly suggest that in pre-clinical studies, DNA vaccination using the UNITE࣪ platform enhances CD4+ T cell responses to MCPγV-LT that result in significant anti-tumor immune responses. We are planning a first-in-human (FIH) Phase 1 open-label study to evaluate the safety, tolerability, and immunogenicity of ITI-3000 in patients with polyomavirus-positive MCC. Patients will receive up to four intramuscular vaccinations of 4mg of ITI-3000 using the PharmaJet Stratis® needle-free injection system. The primary objectives will be safety and tolerability, observing dose-limiting toxicities, serious adverse events, standard clinical assessments, and safety laboratory parameters. Immunogenicity of the vaccine will be measured by peripheral blood assessments of T cell activation using ELISpot and flow cytometry assays. Citation Format: Claire Buchta Rosean, Mohan Karkada, David M. Koelle, Paul Nghiem, Teri Heiland. LAMP1 targeting of the large T antigen of Merkel cell polyomavirus elicits potent CD4+ T cell responses, tumor inhibition, and provides rationale for first-in-human trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2052.

Abstract CD40 ligand (CD40L; CD154) is a transmembrane protein expressed on the surface of activated T cells, particularly on CD4 T cells, that stimulates CD40-dependent activation of antigen-presenting cells, resulting in enhancement of T cell and antibody responses. Soluble multimeric forms of CD40L (sCD40L) act as an effective adjuvant to enhance vaccine immunogenicity. We previously developed a Her2/Neu-LAMP DNA vaccine based on our proprietary UNITE࣪ (UNiversal Intracellular Targeted Expression) platform, which fuses a tumor-associated antigen with lysosomal associated membrane protein 1 (LAMP-1). To increase T cell responses induced by this vaccine, we developed a bicistronic DNA construct in which both the tumor antigen (Her2) fused with LAMP and sCD40L were expressed separately. Secretion of CD40L was confirmed by transient transfection of 293T cells with plasmid DNA followed by ELISA for sCD40L in the cell culture supernatant. Intradermal vaccination of mice with bicistronic Her2-LAMP-sCD40L elicited significantly enhanced Her2-specific T cell and antibody responses compared with mice immunized with Her2-LAMP DNA. Intracellular staining revealed that inclusion of sCD40L in the vaccine induced potent antigen specific T cell IFNγ production, primarily in CD4 T cells. Furthermore, in a murine TSA breast cancer model, Her2-LAMP-sCD40L significantly inhibited tumor growth and prolonged survival in a therapeutic vaccine setting, suggesting that this novel bicistronic vaccine is an effective strategy to promote anti-tumor efficacy in vivo. Ongoing studies are aimed at exploring vaccine-induced changes within the tumor microenvironment, including cytokine profiles, expression of PD-1/PD-L1, and effect on myeloid derived suppressor cells and NK cells. This new approach in bicistronic DNA vaccine design using the UNITE࣪ platform may provide future therapeutic benefit for multiple Her2-expressing cancer types. Citation Format: Wei Shen, Renhuan Xu, Yun-Ting Kao, Mohan Karkada, Teri Heiland. Harnessing soluble CD40L to enhance anti-tumor efficacy of Her2-LAMP DNA vaccine using UNITE࣪ platform [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3553.

Abstract Background: Immune checkpoint blockade (ICB) antibodies have demonstrated that effective induction of T cell responses can elicit tumor regression of different metastatic cancers, although these responses are restricted to certain individuals with specific types of cancer. To enhance these responses, there has been renewed emphasis in developing different types of cancer-specific vaccines to stimulate and direct T cell and B cell immunity to important oncologic targets, such as the oncogene human epidermal growth factor receptor 2 (HER2), which is expressed in ~20% of breast cancers (BC). In our previous work we used a DNA plasmid vaccine targeting HER2, which utilized a lysosome-associated membrane protein 1 (LAMP) domain to traffic HER2 antigen to endolysosomal compartments. We demonstrated that this approach was more effective at eliciting antigen specific CD4+ and CD8+ T cell responses, and provided a significant but limited survival benefit in an endogenous mouse model of HER2+ BC compared to a HER2-wild type vaccine. Methods: In our current study, we explored the use of this modified antigen construct using different vaccine modalities, including DNA plasmid, adenoviral (Ad), modified vaccinia ankara (MVA), and self-replicating RNA vaccines to identify effective vaccine platforms to elicit HER2-specific immunity and anti-tumor immunity. Additionally, we have tested the combination of these modalities in homologous and heterologous vaccine boosting regimens to determine an optimal strategy to elicit anti-tumor immunity in vivo. Results: In our studies, plasmid and MVA vectors elicited suboptimal immune priming responses, in comparison to Ad and self-replicating RNA vectors that elicit significant HER2-specific T and B cell responses upon vaccination. While timing of boosting is critical, our results reflect that certain platforms (e.g., plasmid DNA vectors) are capable of homologous boosting capacity, while others (e.g., Ad vectors) elicit more robust T and B cell responses to capsid epitopes, limiting homologous boosting capacity for HER2-specific immunity. Significantly, using an endogenous model of metastatic HER2+ BC, we have found that heterologous vaccination with different HER2-LAMP targeted vectors can elicit significantly augmented HER2-specific T and B cell responses that translated into more effective anti-tumor immunity. This immunity proved capable of eliciting tumor regression in ~80% of vaccinated mice, compared to 0% using homologous HER2-WT plasmid vaccination, 30% using homologous HER2-LAMP plasmid vaccination, or 50% with HER2-WT heterologous vaccination. Conclusions: These data demonstrate the potential of utilizing heterologous vaccine platforms encoding LAMP-based endolysosomal trafficking vaccines to elicit HER2-specific immunity and effect anti-tumor responses. Citation Format: Robert D. Marek, Alan Chen, Renhuan Xu, Junping Wei, Tao Wang, Xiao Yang, Gangjun Lei, Teri Heiland, Zachary C. Hartman. Vaccination using different platforms encoding HER2-LAMP with heterologous boosting enhances adaptive HER2-specific immunity to enable potent anti-tumor responses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3564.

Glioblastoma multiforme (GBM) is an aggressive form of brain cancer with a median survival of 15 months that has remained unchanged despite advances in the standard of care. GBM cells express human cytomegalovirus (HCMV) proteins, providing a unique opportunity for targeted therapy. We utilized our UNITE (UNiversal Intracellular Targeted Expression) platform to develop a multi-antigen DNA vaccine (ITI-1001) that codes for the HCMV proteins pp65, gB, and IE-1. The UNITE platform involves lysosomal targeting technology, fusing lysosome-associated membrane protein 1 (LAMP1) with target ntigens. We demonstrate evidence of increased antigen presentation by both MHC-I and -II, delivering a robust antigen-specific CD4 and CD8 T-cell response in addition to a strong humoral response. Using a syngeneic orthotopic GBM mouse model, therapeutic treatment with the ITI-1001 vaccine resulted in ~56% survival of tumor-bearing mice. Investigation of the tumor microenvironment showed significant CD4 infiltration as well as enhanced Th1 and cytotoxic CD8 T activation. Regulatory T cells were also upregulated after ITI-1001 vaccination. In addition, tumor burden negatively correlated with activated interferon (IFN)γ+ CD4 T cells, reiterating the importance of CD4 activation in ITI-1001 efficacy and in identifying treatment responders and non-responders. Further characterization of these two groups showed high infiltration of CD3+, CD4+, and CD8+ T cells in responders compared to non-responders. Thus, we show that vaccination with HCMV antigens using the ITI-1001-UNITE platform generates strong cellular and humoral immune responses, triggering significant antitumor activity, leading to enhanced survival in a mouse model of GBM.

β-Defensins are a family of conserved small cationic antimicrobial peptides with different significant biological functions.The majority of mammalian β-defensins are expressed in epididymis, and many of them are predicted to have post-translational modifications. However, only a few of its members have been well studied due to the limitations of expressing and purifying bioactive proteins with correct post-translational modifications efficiently.Here we developed a novel Fc tagged lentiviral system and Fc tagged prokaryotic expression systems provided new options for β-defensins expression and purification.The novel lentiviral system contains a secretive signal peptide, an N-terminal IgG Fc tag, a green fluorescent protein (GFP), and a puromycin selection marker to facilitate efficient expression and fast purification of β-defensins by protein A magnetic or agarose beads.It also enables stable and large-scale expression of β-defensins with regular biological activities and post-translational modification.Purified β-defensins such as Bin1b and a novel human β-defensin hBD129 showed antimicrobial activity, immuno-regulatory activity, and expected post-translational phosphorylation, which were not found in Escherichia coli (E. coli) in expressed form.Furthermore, we successfully applied the novel system to identify mBin1b interacting proteins, explaining Bin1b in a better way. These results suggest that the novel lentiviral system is a powerful approach to produce correct post-translational processed β-defensins with bioactivities and is useful to identify their interacting proteins. This study has laid the foundation for future studies to characterize function and mechanism of novel β-defensins.

e14565 Background: Glioblastoma (GBM) is an aggressive form of brain cancer with a median survival of 15 months which has remained unchanged despite technological advances in the standard of care. GBM cells specifically express human cytomegalovirus (HCMV) proteins providing a unique opportunity for targeted therapy. Methods: We utilized our UNITE (UNiversal Intracellular Targeted Expression) platform to develop a multi-antigen DNA vaccine (ITI-1001) that codes for the HCMV proteins- pp65, gB and IE-1. The UNITE platform involves lysosomal targeting technology, fusing lysosome-associated protein 1 (LAMP1) with target antigens resulting in increased antigen presentation by MHC-I and II. ELISpot, flow cytometry and ELISA techniques were used to evaluate the vaccine immunogenicity and a syngeneic, orthotopic GBM mouse model that expresses HCMV proteins was used for efficacy studies. The tumor microenvironment studies were done using flow cytometry and MSD assay. Results: ITI-1001 vaccination showed a robust antigen-specific CD4 and CD8 T cell response in addition to a strong humoral response. Using GBM mouse model, therapeutic treatment of ITI-1001 vaccine resulted in ̃56% survival with subsequent long-term immunity. Investigating the tumor microenvironment showed significant CD4 T cell infiltration as well as enhanced Th1 and CD8 T cell activation. Regulatory T cells were also upregulated upon ITI-1001 vaccination and would be an attractive target to further improve this therapy. In addition, tumor burden negatively correlated with number of activated CD4 T cells (CD4 IFNγ+) reiterating the importance of CD4 activation in ITI-1001 efficacy and potentially identifying treatment responders and non-responders. Further characterization of these two groups showed high infiltration of CD3+, CD4+ and CD8+ T cells in responders compared with non- responders along with higher CD8 T cell activation. Conclusions: Thus, we show that vaccination with HCMV antigens using the ITI-1001-UNITE platform generates strong cellular and humoral immune responses, triggering significant anti-tumor activity that leads to enhanced survival in mice with GBM.

BackgroundThe majority of Merkel cell carcinomas (MCC), a rare and highly-aggressive type of neuroendocrine skin cancer, are associated with Merkel cell polyomavirus (MCPyV) infection. MCPyV integrates into the host genome, resulting in expression of a truncated form of the viral large T antigen (LT) in infected cells, and making LT an attractive target for therapeutic cancer vaccines. While induction of tumor-reactive CD8+ T cells is a major goal of cancer therapy, CD4+ T cells provide essential support to CD8+ T cells by promoting their expression of cytotoxic effector molecules and increasing their migratory capacity. Cytokines secreted by CD4+ T cells, such as IFNγ, can also exert desirable effects on the tumor microenvironment. Therefore, we set out to design a cancer vaccine that promotes potent, antigen-specific CD4+ T cell responses to MCPyV-LT.MethodsTo activate antigen-specific CD4+ T cells in vivo, we utilized our nucleic acid platform, UNITE (UNiversal Intracellular Targeted Expression), which fuses a tumor-associated antigen with lysosomal-associated membrane protein 1 (LAMP1). This lysosomal targeting technology results in enhanced antigen presentation and a balanced T cell response. LTS220A, encoding a mutated form of MCPyV-LT that abrogates its pro-oncogenic properties, was introduced into the UNITE platform. LTS220A-UNITE, known as ITI-3000, was administered to female C57BL/6 mice intradermally in the ear with electroporation.ResultsITI-3000 promoted a potent, antigen-specific CD4+ T cell response to MCPyV-LT. Vaccination with ITI-3000 significantly delayed and slowed growth of B16F10 tumors expressing LTS220A in prophylactic and therapeutic settings, respectively. ITI-3000 induced a favorable tumor microenvironment (TME), including significantly enhanced numbers of CD4+ T cells, CD8+ T cells, NK cells, and NKT cells. Tumor-infiltrating myeloid cells were reduced in frequency in vaccinated mice and polarized towards an anti-tumor phenotype. Cytokine analysis of the TME showed significantly enhanced levels of cytokines associated with anti-tumor immune responses in ITI-3000-vaccinated mice, including IFNγ, TNFα, IL-2, and IL-1β. Additionally, ITI-3000 synergized with PD-1 blockade, further reducing tumor burden and enhancing survival in mice receiving combination therapy.ConclusionsWe find that DNA vaccination with ITI-3000 using the UNITE platform enhances CD4+ T cell responses to MCPyV-LT and results in anti-tumor immune responses in a mouse model of Merkel cell carcinoma.Ethics ApprovalThis study was approved by Immunomic Therapeutics’ Institutional Animal Care and Use Committee, protocol number 16-11-002.

Abstract The majority of Merkel cell carcinomas (MCC), a rare and highly-aggressive type of neuroendocrine skin cancer, are associated with Merkel cell polyomavirus (MCPyV) infection. MCPyV integrates into the host genome, resulting in expression of a truncated form of the viral large T antigen (LT) in infected cells and making LT an attractive target for therapeutic cancer vaccines. While induction of tumor-reactive CD8+ T cells is a major goal of cancer therapy, CD4+ T cells provide essential support to CD8+ T cells by promoting their expression of cytotoxic effector molecules and increasing their migratory capacity. Cytokines secreted by CD4+ T cells, such as IFNγ, can also exert desirable effects on the tumor microenvironment. Therefore, we set out to design a cancer vaccine that promotes potent, antigen-specific CD4+ T cell responses to MCPyV-LT. To activate antigen-specific CD4+ T cells in vivo, we utilized our nucleic acid platform, UNITE (UNiversal Intracellular Targeted Expression), which fuses a tumor-associated antigen with lysosomal-associated membrane protein 1 (LAMP1). This lysosomal targeting technology results in enhanced antigen presentation and a balanced T cell response. LTS220A, encoding a mutated form of MCPyV-LT that abrogates its pro-oncogenic properties, was introduced into the UNITE platform. Intradermal vaccination with LTS220A-UNITE promoted a potent, antigen-specific CD4+ T cell response to MCPyV-LT. Additionally, prophylactic vaccination with LTS220A-UNITE prevented growth of B16F10 tumors expressing LTS220A in 100% of mice. Therefore, we find that DNA vaccination using the UNITE platform enhances CD4+ T cell responses to MCPyV-LT and prevents tumor growth when given prophylactically. Future studies will test the efficacy of LTS220A-UNITE for use as a therapeutic cancer vaccine. Citation Format: Claire Buchta Rosean, Pratima Sinha, David M. Koelle, Paul Nghiem, Teri Heiland. LAMP1 targeting of the large T antigen of Merkel cell polyomavirus elicits potent CD4+ T cell responses and prevents tumor growth [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4585.

Adjuvant-pulsed peptide vaccines hold great promise for the prevention and treatment of different diseases including cancer. However, it has been difficult to maximize vaccine efficacy due to numerous obstacles including the unfavorable tolerability profile of adjuvants, instability of peptide antigens, limited cellular uptake, and fast diffusion from the injection site, as well as systemic adverse effects. Here we describe a robust lipidation approach for effective nanoparticle co-delivery of low-molecular weight immunomodulators (TLR7/8 agonists) and peptides (SIINFEKL) with a potent in vivo prophylactic effect. The lipidation approaches (C16-R848 and C16-SIINFEKL) increased their hydrophobicity that is intended not only to improve drug encapsulation efficiency but also to facilitate the membrane association, intracellular trafficking, and subcellular localization. The polymer–lipid hybrid nanoparticles (PLNs) are designed to sustain antigen/adjuvant levels with less systemic exposure. Our results demonstrated that a lipidated nanovaccine can induce effective immunity by enhancing the expansion and activation of antigen-specific CD8+ T cells. This adaptive immune response led to substantial tumor suppression with improved overall survival in a prophylactic setting. Our new methodology enhances the potential of nanovaccines for anti-tumor therapy.