Heterologous saRNA Prime, DNA Dual-Antigen Boost SARS-CoV-2 Vaccination Elicits Robust Cellular Immunogenicity and Cross-Variant Neutralizing Antibodies

We assessed if immune responses are enhanced in CD-1 mice by heterologous vaccination with two different nucleic acid-based COVID-19 vaccines: a next-generation human adenovirus serotype 5 (hAd5)-vectored dual-antigen spike (S) and nucleocapsid (N) vaccine (AdS+N) and a self-amplifying and -adjuvanted S RNA vaccine (AAHI-SC2) delivered by a nanostructured lipid carrier. The AdS+N vaccine encodes S modified with a fusion motif to increase cell-surface expression and an N antigen modified with an Enhanced T-cell Stimulation Domain (N-ETSD) to direct N to the endosomal/lysosomal compartment and increase MHC class I and II stimulation potential. The S sequence in the AAHI-SC2 vaccine comprises the D614G mutation, two prolines to stabilize S in the prefusion conformation, and 3 glutamines in the furin cleavage region to confer protease resistance. CD-1 mice received vaccination by homologous and heterologous prime > boost combinations. Humoral responses to S were the highest with any regimen that included the AAHI-SC2 vaccine, and IgG bound to wild type and Delta (B.1.617.2) variant S1 at similar levels. An AAHI-SC2 prime followed by an AdS+N boost particularly enhanced CD4+ and CD8+ T-cell responses to both wild type and Delta S peptides relative to all other vaccine regimens. Sera from mice receiving AAHI-SC2 homologous or heterologous vaccination were found to be highly neutralizing for all pseudovirus strains tested: Wuhan, Beta, Delta, and Omicron strains. The findings here, taken in consideration with the availability of both vaccines in thermostable formulations, support the testing of heterologous vaccination by an AAHI-SC2 > AdS+N regimen in animal models of SARS-CoV-2 infection to assess its potential to provide increased protection against emerging SARS-CoV-2 variants particularly in regions of the world where the need for cold-chain storage has limited the distribution of other vaccines.

Dual-Antigen COVID-19 Vaccine Subcutaneous Prime Delivery With Oral Boosts Protects NHP Against SARS-CoV-2 Challenge

We have developed a dual-antigen COVID-19 vaccine incorporating genes for a modified SARS-CoV-2 spike protein (S-Fusion) and the viral nucleocapsid (N) protein with an Enhanced T-cell Stimulation Domain (N-ETSD) to increase the potential for MHC class II responses. The vaccine antigens are delivered by a human adenovirus serotype 5 platform, hAd5 [E1-, E2b-, E3-], previously demonstrated to be effective in the presence of Ad immunity. Vaccination of rhesus macaques with the hAd5 S-Fusion + N-ETSD vaccine by subcutaneous prime injection followed by two oral boosts elicited neutralizing anti-S IgG and T helper cell 1-biased T-cell responses to both S and N that protected the upper and lower respiratory tracts from high titer (1 x 106 TCID50) SARS-CoV-2 challenge. Notably, viral replication was inhibited within 24 hours of challenge in both lung and nasal passages, becoming undetectable within 7 days post-challenge.

Intranasal plus subcutaneous prime vaccination with a dual antigen COVID-19 vaccine elicits T-cell and antibody responses in mice

We have developed a COVID-19 vaccine, hAd5 S-Fusion + N-ETSD, that expresses SARS-CoV-2 spike (S) and nucleocapsid (N) proteins with modifications to increase immune responses delivered using a human adenovirus serotype 5 (hAd5) platform. Here, we demonstrate subcutaneous (SC) prime and SC boost vaccination of CD-1 mice with this dual-antigen vaccine elicits T-helper cell 1 (Th1) biased T-cell and humoral responses to both S and N that are greater than those seen with hAd5 S wild type delivering only unmodified S. We then compared SC to intranasal (IN) prime vaccination with SC or IN boosts and show that an IN prime with an IN boost is as effective at generating Th1 biased humoral responses as the other combinations tested, but an SC prime with an IN or SC boost elicits greater T cell responses. Finally, we used a combined SC plus IN (SC + IN) prime with or without a boost and found the SC + IN prime alone to be as effective in generating humoral and T-cell responses as the SC + IN prime with a boost. The finding that SC + IN prime-only delivery has the potential to provide broad immunity-including mucosal immunity-against SARS-CoV-2 supports further testing of this vaccine and delivery approach in animal models of viral challenge.

Abstract B62: A novel combination HER2, brachyury, and MUC1 adenovirus based vaccines for a multitargeted immunotherapy approach to treat breast cancer

Many studies have shown that most breast cancers express a diverse array of tumor associated antigens (TAA), and the ability to simultaneously target multiple TAA as opposed to targeting a single TAA by immunotherapy could be of clinical benefit, especially in terms of breaking tolerance, impacting tumor growth and increasing overall survival. We report here the development and testing of two new recombinant TAA vaccines containing MUC1 and Brachyury that will be combined with our Ad5 [E1-, E2b-]-HER2/neu vaccine as a multi-target immunotherapeutic. MUC1 is a TAA that is over expressed in 70% of breast cancers and has been recognized as a priority TAA target for tumor immunotherapy. One of the major barriers to immunotherapy is the inability to target antigens that are involved in the progression of primary tumors to a metastatic state. Brachyury represents a new and attractive target as it plays an essential role in epithelial mesenchymal transition and targets cancer stem cells. A recently published study showed that Brachyury is over-expressed in breast cancer and is associated with poor prognosis. Our vaccines are based on an Ad5 [E1-, E2b-]- gene delivery platform that has an E1 gene deletion and additional early 2b (E2b) gene region deletions by removing the DNA polymerase (pol) and pre-terminal protein (pTP) genes. Potent T cell and antibody responses can be induced against vector-expressed antigens even in the presence of hyper Ad5 immunity. Using a truncated non-oncogenic HER2/neu gene in our delivery platform, we reported that this product candidate induces HER2/neu directed humoral and T cell directed immune responses. In addition, the Ad5 [E1-, E2b-]-HER2/neu significantly inhibits tumor growth of HER2/neu expressing tumors in a mouse model. This product candidate has been manufactured under cGMP and will initiate Phase I/2 clinical trials to evaluate immunotherapy treatment of patients with HER2+ breast cancer. To characterize our two new vaccines, Ad5 [E1-, E2b-]-MUC1 and Ad5 [E1-, E2b-]-Brachyury, immunogenicity studies were performed in mice. In collaboration with Dr. Jeffrey Schlom at the NCI we have generated an Ad5 [E1-, E2b-]-MUC1c vaccine that is modified with agonist peptides that results in increased immunogenic activity. In our studies, cell mediated immune (CMI) responses were determined by ELISpot assays and intracellular cytokine staining. Robust T cell responses and TNF-α/IFN-γ expressing polyfunctional CD4+ and CD8+ cells were detected in mice immunized with Ad5 [E1-, E2b-]-MUC1c but not control mice. In immunotherapy protocols, significant anti-tumor activity and increased survival was observed in mice bearing MUC1 expressing tumors and treated with Ad5 [E1-, E2b-]-MUC1c. These results indicate that our Ad5 [E1-, E2b-]-MUC1c can induce anti MUC1 directed anti-tumor responses. We have also generated an Ad5 [E1-, E2b-]-Brachyury modified to contain a HLA-A2 binding epitope that increases immunogenicity. After mice were immunized with this vaccine, splenocytes from immunized mice when stimulated with Brachyury peptide pools gave significant T cell responses compared to controls. As seen with our MUC1 vaccine, Ad5 [E1-, E2b-]-Brachyury also induced polyfunctional TNF-α/IFN-γ expressing CD4+ and CD8+ T cells. These results indicate that Ad5 [E1-, E2b-]-Brachyury can induce an immune response in vivo. This study lays the foundation to test whether a multi-targeted immunotherapy employing HER2/neu, MUC1 and Brachyury vaccines can result in greater anti-tumor activity against established tumors as well as prevent the development of metastatic disease in breast cancer patients.

Citation Format: Yvette Latchman, Adrian Rice, Joseph Balint, Elizabeth Gabitzsch, Jeffrey Schlom, Frank Jones. A novel combination HER2, brachyury, and MUC1 adenovirus based vaccines for a multitargeted immunotherapy approach to treat breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr B62.

Effect of the vaccine Ad5 [E1-, E2b-]-CEA(6D) on CEA-directed CMI responses in patients with advanced CEA-expressing malignancies in a phase I/II clinical trial

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Background: Adenovirus (Ad) vectors are promising platforms for use as cancer vaccines because of their substantial immunogenicity; however, Ad-specific neutralizing antibodies, present due to natural infection, limit their use. We created a new vector containing additional deletions of the E2b gene and observed that this Ad5 [E1-, E2b-] vector, engineered to express carcinoembryonic antigen (CEA(6D)), could induce antitumor immune responses in mice despite pre-existing Ad5 immunity. The purpose of the current translational study was to evaluate the immunologic effect of increasing doses of Ad5 [E1-, E2b-]-CEA(6D) in mice and then to extended these pre-clinical observations into a phase I/II study. Methods: Ad5 naïve female C57Bl/6 mice, 4-6 weeks old, were immunized subcutaneously 3 times at 2 week intervals with doses of 1.4X107 viral particles (vp) up to1.4X109 vp of Ad5 [E1-, E2b-]-CEA(6D). Two weeks after the last immunization, splenocytes were harvested for immune determinations. Cohorts of patients (n=25 total) with advanced colorectal cancer, refractory to prior therapies, received escalating doses of Ad5 [E1-, E2B-]-CEA(6D) (109 to 1011 vp) subcutaneously every 3 weeks for 3 immunizations.CEA-specific cell mediated immunity was measured by ELISPOT. Results: Increasing doses of Ad5 [E1-, E2b-]-CEA(6D) in mice induced increasing CEA-specifc CMI responses. Similarly, patients who received the highest dose of Ad5 [E1-, E2b-]-CEA(6D) exhibited the highest levels of CEA-specific CMI responses. The induction of CEA-specific CMI responses increased over the course of the 3 injections despite the presence of pre-existing Ad5 immunity in the majority (75%) of patients. There were no drug related grade 3/4 toxicities.Two patients with stable disease remained so during the study. All other patients experienced progressive disease; however, 1-year survival was 54%. Conclusions: Multiple homologous doses of Ad5 [E1-, E2b-]-CEA(6D) could break tolerance and generate CEA-specific CMI responses in the setting of Ad specific immunity in colorectal cancer patients.

A sustained-release formulation of doxycycline hyclate (Atridox) prevents simultaneous infection of Anaplasma phagocytophilum and Borrelia burgdorferi transmitted by tick bite

Current prophylaxis for infected tick bites consists of personal protective measures directed towards ticks. This study compared the efficacy of a single oral dose of doxycycline with that of a single injection of sustained-release doxycycline in a model of Lyme borreliosis and Anaplasma phagocytophilum infection. Dosages of doxycycline were equilibrated based on previously determined peak plasma levels in mice [oral, 2.4 microg (ml plasma)(-1); sustained release, 1.9 microg (ml plasma)(-1)] determined 8 h after inoculation. In challenge experiments where five Borrelia burgdorferi-infected and five A. phagocytophilum-infected nymphs were used per mouse, only 20 and 30 % of mice were protected from B. burgdorferi and A. phagocytophilum infection, respectively, using oral doxycycline. In contrast, 100 % of mice receiving sustained-release doxycycline were protected from A. phagocytophilum infection, as indicated by real-time PCR of blood samples, quantitative PCR and culture isolation of spleen samples, and protected against B. burgdorferi infection as demonstrated by culture of ear, heart and bladder. Although 15-40 copies of A. phagocytophilum could be amplified from the spleens of mice treated with sustained-release doxycycline, no viable A. phagocytophilum from these spleens could be cultured in HL-60 cells. In contrast, 7/10 mice receiving oral doxycycline were PCR- and culture-positive for A. phagocytophilum, with copy numbers ranging from 800 to 10 000 within the spleen, as determined by quantitative PCR. Other correlates with A. phagocytophilum infection included a significant difference in spleen mass (mean of 110 mg for sustained-release treatment versus a mean of 230 mg for oral treatment) and the number of splenic lymphoid nodules (mean of 8 for sustained-release treatment versus mean of 12.5 for oral doxycycline) as determined by histopathology. These studies indicate that a single injection of a sustained-release formulation antibiotic may offer a viable prophylactic treatment option for multiple infectious agents in patients presenting with tick bites.

A doxycycline hyclate rodent bait formulation for prophylaxis and treatment of tick-transmitted Borrelia burgdorferi

The prophylactic and curative potential of doxycycline hyclate formulated in a rodent bait at concentrations of 250 and 500 mg/Kg was evaluated in a murine model of Lyme borreliosis. Both bait formulations prevented tick-transmitted Borrelia burgdorferi infection in 100% of C3H/HeJ mice (N = 16), as well as cured acute, established infection in mice (N = 8) exposed to bait for 14 days. Spirochete infection was cleared in 88.9% to 100% of infected nymphs feeding on mice fed 250 and 500 mg/Kg antibiotic bait formulations, respectively. These data provide evidence for exploring alternative techniques to prevent transmission of Lyme disease spirochetes.

Prophylactic use of sustained-release doxycycline blocks tick-transmitted infection by Anaplasma phagocytophilum in a murine model

A sustained-release formulation of doxycycline hyclate was tested for its ability to block Anaplasma phagocytophilum infection in mice. Mice treated with sustained-release doxycycline showed no splenomegaly and their blood samples were negative by PCR on days 7, 14, and 21. Control mice treated with either oral doxycycline or water had significant splenomegaly and were PCR positive at multiple time points. The sustained-release doxycycline formulation was shown to be efficacious for preventing tick-transmitted A. phagocytophilum infection in a mouse model.