Bernadette Ferraro

Clinical Applications of DNA Vaccines: Current Progress

It was discovered almost 20 years ago that plasmid DNA, when injected into the skin or muscle of mice, could induce immune responses to encoded antigens. Since that time, there has since been much progress in understanding the basic biology behind this deceptively simple vaccine platform and much technological advancement to enhance immune potency. Among these advancements are improved formulations and improved physical methods of delivery, which increase the uptake of vaccine plasmids by cells; optimization of vaccine vectors and encoded antigens; and the development of novel formulations and adjuvants to augment and direct the host immune response. The ability of the current, or second-generation, DNA vaccines to induce more-potent cellular and humoral responses opens up this platform to be examined in both preventative and therapeutic arenas. This review focuses on these advances and discusses both preventive and immunotherapeutic clinical applications.

A DNA Vaccine against Chikungunya Virus Is Protective in Mice and Induces Neutralizing Antibodies in Mice and Nonhuman Primates

Chikungunya virus (CHIKV) is an emerging mosquito-borne alphavirus indigenous to tropical Africa and Asia. Acute illness is characterized by fever, arthralgias, conjunctivitis, rash, and sometimes arthritis. Relatively little is known about the antigenic targets for immunity, and no licensed vaccines or therapeutics are currently available for the pathogen. While the Aedes aegypti mosquito is its primary vector, recent evidence suggests that other carriers can transmit CHIKV thus raising concerns about its spread outside of natural endemic areas to new countries including the U.S. and Europe. Considering the potential for pandemic spread, understanding the development of immunity is paramount to the development of effective counter measures against CHIKV. In this study, we isolated a new CHIKV virus from an acutely infected human patient and developed a defined viral challenge stock in mice that allowed us to study viral pathogenesis and develop a viral neutralization assay. We then constructed a synthetic DNA vaccine delivered by in vivo electroporation (EP) that expresses a component of the CHIKV envelope glycoprotein and used this model to evaluate its efficacy. Vaccination induced robust antigen-specific cellular and humoral immune responses, which individually were capable of providing protection against CHIKV challenge in mice. Furthermore, vaccine studies in rhesus macaques demonstrated induction of nAb responses, which mimicked those induced in convalescent human patient sera. These data suggest a protective role for nAb against CHIKV disease and support further study of envelope-based CHIKV DNA vaccines.

Co-delivery of PSA and PSMA DNA vaccines with electroporation induces potent immune responses

Prostate cancer (PCa) remains a significant public health problem. Current treatment modalities for PCa can be useful, but may be accompanied by deleterious side effects and often do not confer long-term control. Accordingly, additional modalities, such as immunotherapy, may represent an important approach for PCa treatment. The identification of tissue-specific antigens engenders PCa an attractive target for immunotherapeutic approaches. Delivery of DNA vaccines with electroporation has shown promising results for prophylactic and therapeutic targets in a variety of species including humans. Application of this technology for PCa immunotherapy strategies has been limited to single antigen and epitope targets. We sought to test the hypothesis that a broader collection of antigens would improve the breadth and effectiveness of a PCa immune therapy approach. We therefore developed highly optimized DNA vaccines encoding prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA) as a dual antigen approach to immune therapy of PCa. PSA-and PSMA-specific cellular immunogenicity was evaluated in a mouse model for co-delivery and single antigen vaccination. Mice received 2 immunizations spaced 2 weeks apart and immunogenicity was evaluated 1 week after the second vaccination. Both the PSA and PSMA vaccines induced robust antigen-specific IFNγ responses by ELISpot. Further characterization of cellular immunogenicity by flow cytometry indicated strong antigen-specific TNFα production by CD4+ T cells and IFNγ and IL-2 secretion by both CD4+ and CD8+ T cells. There was also a strong humoral response as determined by PSA-specific seroconversion. These data support further study of this novel approach to immune therapy of PCa.

Unique Th1/Th2 Phenotypes Induced during Priming and Memory Phases by Use of Interleukin-12 (IL-12) or IL-28B Vaccine Adjuvants in Rhesus Macaques

ABSTRACT Adjuvant compounds are usually included in vaccinations in order to bolster total vaccine-specific responses or to tailor an immune response toward a desired endpoint, such as the production of gamma interferon or an increase in antibody titers. While most adjuvants are studied in regard to their impact on vaccine-specific responses during and just after the vaccination period, a detailed analysis of how adjuvants skew the Th1/Th2 axis at more distant time points is not often undertaken. In the current study, we present data that suggests that adjuvants differ in their relative abilities to bolster and skew immune responses in the short term compared with more distant time points. To that end, we have employed interleukin-12 (IL-12) and IL-28B as adjuvants for DNA vaccination of rhesus macaques. While both adjuvants were able to bolster Th1-biased responses, our analysis shows that this skewing was achieved through different mechanisms. Moreover, analysis 3 months after the final immunization revealed the activity of the IL-12 adjuvant to be short lived, while the IL-28B adjuvant continued to exert its influence on the immune system. Taken together, these data suggest that the scientific and medical communities would benefit from a more detailed analysis of adjuvant function, including the determination of long-term influences of administered adjuvants.

Inducing Humoral and Cellular Responses to Multiple Sporozoite and Liver-Stage Malaria Antigens Using Exogenous Plasmid DNA

ABSTRACT A vaccine candidate that elicits humoral and cellular responses to multiple sporozoite and liver-stage antigens may be able to confer protection against Plasmodium falciparum malaria; however, a technology for formulating and delivering such a vaccine has remained elusive. Here, we report the preclinical assessment of an optimized DNA vaccine approach that targets four P. falciparum antigens: circumsporozoite protein (CSP), liver stage antigen 1 (LSA1), thrombospondin-related anonymous protein (TRAP), and cell-traversal protein for ookinetes and sporozoites (CelTOS). Synthetic DNA sequences were designed for each antigen with modifications to improve expression and were delivered using in vivo electroporation (EP). Immunogenicity was evaluated in mice and nonhuman primates (NHPs) and assessed by enzyme-linked immunosorbent assay (ELISA), gamma interferon (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) assay, and flow cytometry. In mice, DNA with EP delivery induced antigen-specific IFN-γ production, as measured by ELISpot assay and IgG seroconversion against all antigens. Sustained production of IFN-γ, interleukin-2, and tumor necrosis factor alpha was elicited in both the CD4+ and CD8+ T cell compartments. Furthermore, hepatic CD8+ lymphocytes produced LSA1-specific IFN-γ. The immune responses conferred to mice by this approach translated to the NHP model, which showed cellular responses by ELISpot assay and intracellular cytokine staining. Notably, antigen-specific CD8+ granzyme B+ T cells were observed in NHPs. Collectively, the data demonstrate that delivery of gene sequences by DNA/EP encoding malaria parasite antigens is immunogenic in animal models and can harness both the humoral and cellular arms of the immune system.

Intradermal DNA vaccination enhanced by low-current electroporation improves antigen expression and induces robust cellular and humoral immune responses.

DNA represents an ideal vaccine platform for HIV and many infectious diseases because of its safety, stability, and ease of manufacture. However, the immunogenicity of DNA vaccines has traditionally been low compared with viral vectors, recombinant protein, and live attenuated vaccines. The immunogenicity of DNA vaccines has been significantly enhanced by delivery with in vivo electroporation. Further improvements now allow electroporation to be performed in the dermis, which could potentially improve patient tolerability and may further enhance immunogenicity. In this study we examined how the current of intradermal vaccination impacts antigen expression, inflammation, and the induction of both humoral and cellular immunity in guinea pigs and nonhuman primates. We observed that a lower (0.1 A) current reduced inflammation and improved antigen expression compared with a 0.2 A current. The improved antigen expression resulted in a trend toward higher cellular immune responses but no impact on HIV- and influenza-specific binding titers. This study highlights the need for optimization of electroporation conditions in vivo in order to balance enhanced plasmid transfection with a loss of expression due to tissue inflammation and necrosis. These results suggest that a lower, 0.1-A current may not only improve patient tolerability but also improve immunogenicity.

An optimized SIV DNA vaccine can serve as a boost for Ad5 and provide partial protection from a high-dose SIVmac251 challenge.

One limitation in the development of an improved cellular response needed for an effective HIV-vaccine is the inability to induce robust effector T-cells capable of suppressing a heterologous challenge. To improve cellular immune responses, we examined the ability of an optimized DNA vaccine to boost the cellular immune responses induced by a highly immunogenic Ad5 prime. Five Chinese rhesus macaques received pVax encoding consensus (con) gag/pol/env intramuscularly (IM) with electroporation followed by the Merck Ad5 gag/pol/nef vaccine. A second group of five animals were vaccinated with Merck Ad5 gag/pol/nef followed by pVax gag/pol/env. One year following vaccination, Ad5-prime DNA-boosted monkeys and four unvaccinated controls received an intrarectal challenge with 1000 ID50 SIV(mac)251. The quality and magnitude of the T-cell response was analyzed by ELISpot and polyfunctional flow cytometry. We observed that an Ad5-prime DNA-boost resulted in significantly elevated SIV-specific T-cell responses even compared with animals receiving a DNA-prime Ad5-boost. Ad5 prime DNA boosted animals were capable of suppressing a pathogenic SIV(mac)251 challenge. Peak control correlated with the expansion of HLA-DR(+) CD8(+) T-cells two weeks post-infection. These data illustrate that high optimization of a DNA vaccine can drive of immune responses primed by a robust vector system. This previously unachievable feature of these newly optimized DNAs warrants future studies of this strategy that may circumvent issues of serology associated with viral vector prime-boost systems.

Ki-67 staining for determination of rhesus macaque T cell proliferative responses ex vivo.

The capacity for robust proliferation upon re‐infection is a hallmark of adaptive immunity and the basis of vaccination. A widely used animal model for the study of human disease is the rhesus macaque (RM), where capacity for proliferation can be assessed ex vivo using carboxyfluorescein succinimidyl ester (CFSE)‐based dilution assays. However, we show over the course of the standard ex vivo proliferation assay that CFSE‐labeling at commonly used dye concentrations induces significant cell death, but that this phenomenon is dose‐dependent. Here, we describe an alternative semiquantitative method for estimating T cell proliferative responses that avoids the putative biases associated with chemical modification. RM peripheral blood mononuclear cells were stimulated ex vivo with cognate peptides for 5 days, immunostained for intracellular Ki‐67, and then analyzed by flow cytometry. We describe a gating strategy using Ki‐67 and side light scatter, also a marker of blastogenesis, which correlates strongly with data from CFSE dilution. We show that this method is a valid tool for measuring RM antigen‐specific cellular proliferation ex vivo and can be used as an alternative to CFSE dilution assays.

Abstract LB-253: Control of tumor growth in vivo by a synthetic multi-antigen DNA immune therapy for prostate cancer

Prostate cancer (PCa) is one of the leading causes of cancer deaths among men with limited treatment options. Accordingly, new approaches, such as immunotherapy, may represent important approaches for PCa treatment. Electroporation (EP) delivered DNA vaccines has recently shown promising results for therapeutic immunotherapy strategies has been limited to single antigen and epitope targets with limited success. We hypothesized that a broader collection of antigens adjuvanted by plasmid encoded IL-12 would bypass immune tolerance and improve the breadth and effectiveness of a PCa immunotherapy approach. We tested this hypothesis in NHP for immune tolerance effects as well as in the highly relevant TRAMP-C2 challenge model. We developed highly optimized DNA vectors encoding consensus antigens for important PCa targets prostate-specific antigen (SynCon PSA), prostate-specific membrane antigen (SynCon PSMA), and human six-transmembrane epithelial antigen of the prostate (STEAP). In mice the vaccines demonstrated potent IFNγ production by ELISpot (2740 SFU) and robust immune responses in the CD4+ (0.53%) and CD8+ (3.0%) T cell compartments. Further, sera from immunized mice reacted in ELISA with relevant targets and specifically stained LNCaP cells, a human PCa cell line, as well as human PCa tumor sections, supporting that the vaccine antigens induced relevant antibody responses. Vaccination of Rhesus Macaques, which share greater than 98% identity with humans, showed robust anti-PSA, PSMA and STEAP IFNγ production (612 SFU), potential for cytotoxic T cell function, and antigen specific seroconversion supporting the ability of these constructs to break tolerance. The therapeutic potential of PSMA, STEAP, and the combination of PSMA and STEAP, alone or with the molecular adjuvant IL-12, was evaluated in mice in the TRAMP-C2 tumor model. Alone, PSMA, STEAP or PSMA+STEAP demonstrated prolonged survival and a modest impact on tumor growth. However, the combination of synthetic vaccine antigens with IL-12 resulted in 100% efficacy in treatment and clearance of tumors resulting in 100% survival. These data support further study of this novel immune therapy of PCa. Citation Format: Bernadette Ferraro, Jewell N. Walters, Emma L. Reuschel, Amritha Balakrishnan, Matthew P. Morrow, Amir S. Khan, Niranjan Y. Sardesai, Laurent M. Humeau, David B. Weiner. Control of tumor growth in vivo by a synthetic multi-antigen DNA immune therapy for prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-253.

210. Complete Control of Tumor Growth In Vivo By a Synthetic Consensus Multi-Antigen DNA Immune Therapy for Prostate Cancer

Prostate cancer (PCa) is one of the leading causes of cancer deaths among men with limited treatment options. Accordingly, new approaches, such as immunotherapy, may represent important approaches for PCa treatment. Electroporation (EP) delivered DNA vaccines has recently shown promising results for therapeutic treatment of HPV early disease in humans. Application of this technology for PCa immunotherapy strategies has been limited to single antigen and epitope targets with limited success. We hypothesized that a broader collection of antigens adjuvanted by plasmid encoded IL-12 would bypass immune tolerance and improve the breadth and effectiveness of a PCa immunotherapy approach. We tested this hypothesis in NHP for immune tolerance effects as well as in the highly relevant TRAMP-C2 challenge model. We developed highly optimized DNA vectors encoding consensus antigens for important PCa targets prostate-specific antigen (SynCon PSA), prostate-specific membrane antigen (SynCon PSMA), and human six-transmembrane epithelial antigen of the prostate (STEAP). In mice the vaccines demonstrated potent IFNγ production by ELISpot (2740 SFU) and robust immune responses in the CD4+ (0.53%) and CD8+ (3.0%) T cell compartments. Further, sera from immunized mice reacted in ELISA with relevant targets and specifically stained LNCaP cells, a human PCa cell line, as well as human PCa tumor sections, supporting that the vaccine antigens induced relevant antibody responses. Vaccination of Rhesus Macaques, which share greater than 98% identity with humans, showed robust anti-PSA, PSMA and STEAP IFNγ production (612 SFU), potential for cytotoxic T cell function, and antigen specific seroconversion supporting the ability of these constructs to break tolerance. The therapeutic potential of PSMA, STEAP, and the combination of PSMA and STEAP, alone or with the molecular adjuvant IL-12, was evaluated in mice in the TRAMP-C2 tumor model. Alone, PSMA, STEAP or PSMA+STEAP demonstrated prolonged survival and a modest impact on tumor growth. However, the combination of synthetic vaccine antigens with IL-12 resulted in 100% efficacy in treatment and clearance of tumors resulting in 100% survival. These data support further study of this novel immune therapy of PCa.