Evaluation of immunogen delivery by DNA immunization using non-invasive bioluminescence imaging

The Role of Biological Sex in Pre-Clinical (Mouse) mRNA Vaccine Studies

In this study, we consider the influence of biological sex-specific immune responses on the assessment of mRNA vaccines in pre-clinical murine studies. Recognising the established disparities in immune function attributed to genetic and hormonal differences between individuals of different biological sexes, we compared the mRNA expression and immune responses in mice of both biological sexes after intramuscular injection with mRNA incorporated within lipid nanoparticles. Regarding mRNA expression, no significant difference in protein (luciferase) expression at the injection site was observed between female and male mice following intramuscular administration; however, we found that female BALB/c mice exhibit significantly greater total IgG responses across the concentration range of mRNA lipid nanoparticles (LNPs) in comparison to their male counterparts. This study not only contributes to the scientific understanding of mRNA vaccine evaluation but also emphasizes the importance of considering biological sex in vaccine study designs during pre-clinical evaluation in murine studies.

Advances in Immunocompetent Mouse and Rat Models

Rodent models of breast cancer have played critical roles in our understanding of breast cancer development and progression as well as preclinical testing of cancer prevention and therapeutics. In this article, we first review the values and challenges of conventional genetically engineered mouse (GEM) models and newer iterations of these models, especially those with inducible or conditional regulation of oncogenes and tumor suppressors. Then, we discuss nongermline (somatic) GEM models of breast cancer with temporospatial control, made possible by intraductal injection of viral vectors to deliver oncogenes or to manipulate the genome of mammary epithelial cells. Next, we introduce the latest development in precision editing of endogenous genes using in vivo CRISPR-Cas9 technology. We conclude with the recent development in generating somatic rat models for modeling estrogen receptor-positive breast cancer, something that has been difficult to accomplish in mice.

The use of electroporation to deliver DNA-based vaccines

INTRODUCTION

Nucleic acids represent a promising platform for creating vaccines. One disadvantage of this approach is its relatively low immunogenicity. Electroporation (EP) is an effective way to increase the DNA vaccines immunogenicity. However, due to the different configurations of devices used for EP, EP protocols optimization is required not only to enhance immunogenicity, but also to ensure greater safety and tolerability of the EP procedure.

AREA COVERED

An data analysis for recent years on the DNA vaccines delivery against viral and parasitic infections using EP was carried out. The study of various EP physical characteristics, such as frequency, pulse duration, pulse interval, should be considered along with the immunogenic construct design and the site of delivery of the vaccine, through the study of the immunogenic and protective characteristics of the latter.

EXPERT OPINION

Future research should focus on regulating the humoral and cellular response required for protection against infectious agents by modifying the EP protocol. Significant efforts will be directed to establishing the possibility of redirecting the immune response toward the Th1 or Th2 response by changing the EP physical parameters. It will allow for an individual selective approach during EP, depending on the pathogen type of an infectious disease.

The Expression Kinetics and Immunogenicity of Lipid Nanoparticles Delivering Plasmid DNA and mRNA in Mice

In recent years, lipid nanoparticles (LNPs) have emerged as a revolutionary technology for vaccine delivery. LNPs serve as an integral component of mRNA vaccines by protecting and transporting the mRNA payload into host cells. Despite their prominence in mRNA vaccines, there remains a notable gap in our understanding of the potential application of LNPs for the delivery of DNA vaccines. In this study, we sought to investigate the suitability of leading LNP formulations for the delivery of plasmid DNA (pDNA). In addition, we aimed to explore key differences in the properties of popular LNP formulations when delivering either mRNA or DNA. To address these questions, we compared three leading LNP formulations encapsulating mRNA- or pDNA-encoding firefly luciferase based on potency, expression kinetics, biodistribution, and immunogenicity. Following intramuscular injection in mice, we determined that RNA-LNPs formulated with either SM-102 or ALC-0315 lipids were the most potent (all p-values < 0.01) and immunogenic (all p-values < 0.05), while DNA-LNPs formulated with SM-102 or ALC-0315 demonstrated the longest duration of signal. Additionally, all LNP formulations were found to induce expression in the liver that was proportional to the signal at the injection site (SM102: r = 0.8787, p < 0.0001; ALC0315: r = 0.9012, p < 0.0001; KC2: r = 0.9343, p < 0.0001). Overall, this study provides important insights into the differences between leading LNP formulations and their applicability to DNA- and RNA-based vaccinations.

Efficient cancer modeling through CRISPR-Cas9/HDR-based somatic precision gene editing in mice

CRISPR-Cas9 has been used successfully to introduce indels in somatic cells of rodents; however, precise editing of single nucleotides has been hampered by limitations of flexibility and efficiency. Here, we report technological modifications to the CRISPR-Cas9 vector system that now allows homology-directed repair-mediated precise editing of any proto-oncogene in murine somatic tissues to generate tumor models with high flexibility and efficiency. Somatic editing of either Kras or Pik3ca in both normal and hyperplastic mammary glands led to swift tumorigenesis. The resulting tumors shared some histological, transcriptome, and proteome features with tumors induced by lentivirus-mediated expression of the respective oncogenes, but they also exhibited some distinct characteristics, particularly showing less intertumor variation, thus potentially offering more consistent models for cancer studies and therapeutic development. Therefore, this technological advance fills a critical gap between the power of CRISPR technology and high-fidelity mouse models for studying human tumor evolution and preclinical drug testing.

Optimization of In Vivo Electroporation Conditions and Delivery of DNA Vaccine Encoding SARS-CoV-2 RBD Using the Determined Protocol

Vaccination against SARS-CoV-2 and other viral infections requires safe, effective, and inexpensive vaccines that can be rapidly developed. DNA vaccines are candidates that meet these criteria, but one of their drawbacks is their relatively weak immunogenicity. Electroporation (EP) is an effective way to enhance the immunogenicity of DNA vaccines, but because of the different configurations of the devices that are used for EP, it is necessary to carefully select the conditions of the procedure, including characteristics such as voltage, current strength, number of pulses, etc. In this study, we determined the optimal parameters for delivery DNA vaccine by electroporation using the BEX CO device. BALB/c mice were used as a model. Plasmid DNA phMGFP was intramuscular (I/M) injected into the quadriceps muscle of the left hind leg of animals using insulin syringes, followed by EP. As a result of the experiments, the following EP parameters were determined: direct and reverse polarity rectangular DC current in three pulses, 12 V voltage for 30 ms and 950 ms intervals, with a current limit of 45 mA. The selected protocol induced a low level of injury and provided a high level of GFP expression. The chosen protocol was used to evaluate the immunogenicity of the DNA vaccine encoding the receptor-binding domain (RBD) of the SARS-CoV-2 protein (pVAXrbd) injected by EP. It was shown that the delivery of pVAXrbd via EP significantly enhanced both specific humoral and cellular immune responses compared to the intramuscular injection of the DNA vaccine.

Different protective efficacies of a novel antigen-specific DNA vaccine encoding chicken type Ⅱ collagen via intramuscular, subcutaneous, and intravenous vaccination against experimental rheumatoid arthritis

Tolerizing DNA vaccines encoding key autoantigens are one of emerging strategies for the treatment of rheumatoid arthritis (RA). Among these vaccines, the most representative is pcDNA-CCOL2A1, an antigen-specific DNA vaccine encoding chicken type Ⅱ collagen (CCⅡ) with significant therapeutic and prophylactic efficacy in collagen-induced arthritis (CIA) rat models. We compared the in situ expression levels of CCOL2A1-mRNA and CCⅡ protein and the protective efficacies against CIA after a single dose (300 μg/kg) of this vaccine via intramuscular (IM), subcutaneous (SC) and intravenous (IV) vaccinations. The IM vaccination routes resulted in good protective efficacies in terms of decreasing CIA incidence and severity and significantly improved radiographic and histopathologic findings and scores of joints. Furthermore, IM, SC, and IV vaccinations markedly decreased serum levels of anti-type Ⅱ collagen (CⅡ) IgG antibodies, but only IM vaccination significantly reduced serum levels of rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibody. The vaccine exhibited a continuous CCOL2A1-mRNA expression in the tail and abdominal subcutaneous tissue injection sites, but no CCOL2A1-mRNA signal was observed in muscle. Strikingly, CCⅡ protein expression levels at the three injection sites were comparable with minimal variation. IM administration may be considered the preferred route for RA treatment in clinical practice.

Mesenchymal Stem Cells Can Both Enhance and Inhibit the Cellular Response to DNA Immunization by Genes of Nonstructural Proteins of the Hepatitis C Virus

Despite extensive research, there is still no vaccine against the hepatitis C virus (HCV). The aim of this study was to investigate whether MSCs can exhibit adjuvant properties during DNA vaccination against hepatitis C. We used the pcNS3-NS5B plasmid encoding five nonstructural HCV proteins and MSCs derived from mice bone marrow. Five groups of DBA mice were immunized with the plasmid and/or MSCs in a different order. Group 1 was injected with the plasmid twice at intervals of 3 weeks; Group 2 with the plasmid, and after 24 h with MSCs; Group 3 with MSCs followed by the plasmid the next day; Group 4 with only MSCs; and Group 5 with saline. When the MSCs were injected prior to DNA immunization, the cell immune response to HCV proteins assessed by the level of IFN-γ synthesis was markedly increased compared to DNA alone. In contrast, MSCs injected after DNA suppressed the immune response. Apparently, the high level of proinflammatory cytokines detected after DNA injection promotes the conversion of MSCs introduced later into the immunosuppressive MSC2. The low level of cytokines in mice before MSC administration promotes the high immunostimulatory activity of MSC1 in response to a DNA vaccine. Thus, when administered before DNA, MSCs are capable of exhibiting promising adjuvant properties.

Mesenchymal Stem Cells Can Both Enhance and Inhibit the Cellular Response to DNA Immunization by Genes of Nonstructural Proteins of the Hepatitis C Virus

Despite extensive research, there is still no vaccine against the hepatitis C virus (HCV). The aim of this study was to investigate whether MSCs can exhibit adjuvant properties during DNA vaccination against hepatitis C. We used the pcNS3-NS5B plasmid encoding five nonstructural HCV proteins and MSCs derived from mice bone marrow. Five groups of DBA mice were immunized with the plasmid and/or MSCs in a different order. Group 1 was injected with the plasmid twice at intervals of 3 weeks; Group 2 with the plasmid, and after 24 h with MSCs; Group 3 with MSCs followed by the plasmid the next day; Group 4 with only MSCs; and Group 5 with saline. When the MSCs were injected prior to DNA immunization, the cell immune response to HCV proteins assessed by the level of IFN-γ synthesis was markedly increased compared to DNA alone. In contrast, MSCs injected after DNA suppressed the immune response. Apparently, the high level of proinflammatory cytokines detected after DNA injection promotes the conversion of MSCs introduced later into the immunosuppressive MSC2. The low level of cytokines in mice before MSC administration promotes the high immunostimulatory activity of MSC1 in response to a DNA vaccine. Thus, when administered before DNA, MSCs are capable of exhibiting promising adjuvant properties.

Mesenchymal Stem Cells Can Both Enhance and Inhibit the Cellular Response to DNA Immunization by Genes of Nonstructural Proteins of the Hepatitis C Virus

Despite extensive research, there is still no vaccine against the hepatitis C virus (HCV). The aim of this study was to investigate whether MSCs can exhibit adjuvant properties during DNA vaccination against hepatitis C. We used the pcNS3-NS5B plasmid encoding five nonstructural HCV proteins and MSCs derived from mice bone marrow. Five groups of DBA mice were immunized with the plasmid and/or MSCs in a different order. Group 1 was injected with the plasmid twice at intervals of 3 weeks; Group 2 with the plasmid, and after 24 h with MSCs; Group 3 with MSCs followed by the plasmid the next day; Group 4 with only MSCs; and Group 5 with saline. When the MSCs were injected prior to DNA immunization, the cell immune response to HCV proteins assessed by the level of IFN-γ synthesis was markedly increased compared to DNA alone. In contrast, MSCs injected after DNA suppressed the immune response. Apparently, the high level of proinflammatory cytokines detected after DNA injection promotes the conversion of MSCs introduced later into the immunosuppressive MSC2. The low level of cytokines in mice before MSC administration promotes the high immunostimulatory activity of MSC1 in response to a DNA vaccine. Thus, when administered before DNA, MSCs are capable of exhibiting promising adjuvant properties.

Design of SARS-CoV-2 hFc-Conjugated Receptor-Binding Domain mRNA Vaccine Delivered via Lipid Nanoparticles

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been identified as the causal agent of COVID-19 and stands at the center of the current global human pandemic, with death toll exceeding one million. The urgent need for a vaccine has led to the development of various immunization approaches. mRNA vaccines represent a cell-free, simple, and rapid platform for immunization, and therefore have been employed in recent studies toward the development of a SARS-CoV-2 vaccine. Herein, we present the design of an mRNA vaccine, based on lipid nanoparticles (LNPs)-encapsulated SARS-CoV-2 human Fc-conjugated receptor-binding domain (RBD-hFc). Several ionizable lipids have been evaluated in vivo in a luciferase (luc) mRNA reporter assay, and two leading LNPs formulations have been chosen for the subsequent RBD-hFc mRNA vaccine strategy. Intramuscular administration of LNP RBD-hFc mRNA elicited robust humoral response, a high level of neutralizing antibodies and a Th1-biased cellular response in BALB/c mice. The data in the current study demonstrate the potential of these lipids as promising candidates for LNP-based mRNA vaccines in general and for a COVID19 vaccine in particular.

Lentiviral vector induces high-quality memory T cells via dendritic cells transduction

We report a lentiviral vector harboring the human β2-microglobulin promoter, with predominant expression in immune cells and minimal proximal enhancers to improve vector safety. This lentiviral vector efficiently transduces major dendritic cell subsets in vivo. With a mycobacterial immunogen, we observed distinct functional signatures and memory phenotype in lentiviral vector- or Adenovirus type 5 (Ad5)-immunized mice, despite comparable antigen-specific CD8⁺ T cell magnitudes. Compared to Ad5, lentiviral vector immunization resulted in higher multifunctional and IL-2-producing CD8⁺ T cells. Furthermore, lentiviral vector immunization primed CD8⁺ T cells towards central memory phenotype, while Ad5 immunization favored effector memory phenotype. Studies using HIV antigens in outbred rats demonstrated additional clear-cut evidence for an immunogenic advantage of lentiviral vector over Ad5. Additionally, lentiviral vector provided enhance therapeutic anti-tumor protection than Ad5. In conclusion, coupling lentiviral vector with β2-microglobulin promoter represents a promising approach to produce long-lasting, high-quality cellular immunity for vaccinal purposes.

Technological approaches to streamline vaccination schedules, progressing towards single-dose vaccines

Vaccines represent the most successful medical intervention in history, with billions of lives saved. Although multiple doses of the same vaccine are typically required to reach an adequate level of protection, it would be advantageous to develop vaccines that induce protective immunity with fewer doses, ideally just one. Single-dose vaccines would be ideal to maximize vaccination coverage, help stakeholders to greatly reduce the costs associated with vaccination, and improve patient convenience. Here we describe past attempts to develop potent single dose vaccines and explore the reasons they failed. Then, we review key immunological mechanisms of the vaccine-specific immune responses, and how innovative technologies and approaches are guiding the preclinical and clinical development of potent single-dose vaccines. By modulating the spatio-temporal delivery of the vaccine components, by providing the appropriate stimuli to the innate immunity, and by designing better antigens, the new technologies and approaches leverage our current knowledge of the immune system and may synergize to enable the rational design of next-generation vaccination strategies. This review provides a rational perspective on the possible development of future single-dose vaccines.

Translational Nanomedicine Boosts Anti-PD1 Therapy to Eradicate Orthotopic PTEN-Negative Glioblastoma

Glioblastoma (GBM) is resistant to immune checkpoint inhibition due to its low mutation rate, phosphatase and tensin homologue (PTEN)-deficient immunosuppressive microenvironment, and high fraction of cancer stem-like cells (CSCs). Nanomedicines fostering immunoactivating intratumoral signals could reverse GBM resistance to immune checkpoint inhibitors (ICIs) for promoting curative responses. Here, we applied pH-sensitive epirubicin-loaded micellar nanomedicines, which are under clinical evaluation, to synergize the efficacy of anti-PD1antibodies (aPD1) against PTEN-positive and PTEN-negative orthotopic GBM, the latter with a large subpopulation of CSCs. The combination of epirubicin-loaded micelles (Epi/m) with aPD1 overcame GBM resistance to ICIs by transforming cold GBM into hot tumors with high infiltration of antitumor immune cells through the induction of immunogenic cell death (ICD), elimination of immunosuppressive myeloid-derived suppressor cells (MSDCs), and reduction of PD-L1 expression on tumor cells. Thus, Epi/m plus aPD1 eradicated both PTEN-positive and PTEN-negative orthotopic GBM and provided long-term immune memory effects. Our results indicate the high translatable potential of Epi/m plus aPD1 for the treatment of GBM.

Comparative Profiling of Metastatic 4T1- vs. Non-metastatic Py230-Based Mammary Tumors in an Intraductal Model for Triple-Negative Breast Cancer

The transition of ductal carcinoma in situ (DCIS) to invasive carcinoma (IC) in breast cancer can be faithfully reproduced by the intraductal mouse model. Envisaging to use this model for therapeutic testing, we aimed to in-depth characterize the tumor immunity associated with the differential progression of two types of intraductal tumors. More specifically, we focused on triple-negative breast cancer (TNBC) and intraductally inoculated luciferase-expressing metastatic 4T1 and locally invasive Py230 cells in lactating mammary glands of syngeneic BALB/c and C57BL/6 female mice, respectively. Although the aggressive 4T1 cells rapidly formed solid tumors, Py230 tumors eventually grew to a similar size through enhanced proliferation. Yet, ductal tumor cell breakthrough and metastasis occurred earlier in the 4T1- compared to the Py230-based intraductal model and was associated with high expression of matrix metalloproteinase (MMP)-9, vascular endothelial growth factor (VEGF), chitinase 3-like 1 (CHI3L1) and lipocalin 2 (LCN2) as well as an increased influx of immune cells (mainly macrophages, neutrophils and T-cells). Moreover, activated cytotoxic T-cells, B-cells and programmed death-1 (PD-1)-positive cells were more prominent in the 4T1-based intraductal model in line with enhanced pro-inflammatory cytokine and gene expression profiles. Py230-based tumors showed a more immunosuppressed anti-inflammatory profile with a high amount of regulatory T-cells, which may account for the decreased T-cell activation but increased proliferation compared to the 4T1-based tumors. Taken together, our results highlight the differential immunological aspects of aggressive metastatic and non-aggressive intraductal progression of 4T1- vs. Py230-based tumors, providing a base for future studies to explore therapy using these intraductal TNBC models.

Interleukin-21 enhances the antibody avidity elicited by DNA prime and MVA boost vaccine

Enhancement of the magnitude or affinity of protective antibodies (Abs) induced by vaccine adjuvant is highly desirable to prevent challenging pathogens such as HIV-1. IL-21 plays a crucial role in germinal center reactions during humoral immune responses. However, the effect of IL-21 as a vaccine adjuvant on the quantity and quality of antigen-specific Abs elicited by DNA prime and MVA boost vaccine, a commonly used vaccine strategy, remains unknown. To close this knowledge gap, female adult B6N mice were primed with DNA vaccine twice (days 0, 14, 100 µg, I.M.) and boosted with MVA vaccine (day 28, 2 × 10⁷ pfu, I.M.) with or without an IL-21 DNA adjuvant (days 3, 17, 31, 40 µg, I.M.), in which HIV-1 gag was expressed as a model antigen. With the addition of an IL-21 adjuvant, we found significantly increased avidity of antigen-specific Abs at multiple time points in a longitudinal follow up. Collectively, our results suggest that an IL-21 immune adjuvant can significantly increase Ab quality induced by heterologous DNA-MVA prime-boost vaccine strategy.

The Immunogenicity in Mice of HCV Core Delivered as DNA Is Modulated by Its Capacity to Induce Oxidative Stress and Oxidative Stress Response

HCV core is an attractive HCV vaccine target, however, clinical or preclinical trials of core-based vaccines showed little success. We aimed to delineate what restricts its immunogenicity and improve immunogenic performance in mice. We designed plasmids encoding full-length HCV 1b core and its variants truncated after amino acids (aa) 60, 98, 152, 173, or up to aa 36 using virus-derived or synthetic polynucleotides (core191/60/98/152/173/36_191v or core152s DNA, respectively). We assessed their level of expression, route of degradation, ability to trigger the production of reactive oxygen species/ROS, and to activate the components of the Nrf2/ARE antioxidant defense pathway heme oxygenase 1/HO-1 and NAD(P)H: quinone oxidoreductase/Nqo-1. All core variants with the intact N-terminus induced production of ROS, and up-regulated expression of HO-1 and Nqo-1. The capacity of core variants to induce ROS and up-regulate HO-1 and Nqo-1 expression predetermined their immunogenicity in DNA-immunized BALB/c and C57BL/6 mice. The most immunogenic was core 152s, expressed at a modest level and inducing moderate oxidative stress and oxidative stress response. Thus, immunogenicity of HCV core is shaped by its ability to induce ROS and oxidative stress response. These considerations are important in understanding the mechanisms of viral suppression of cellular immune response and in HCV vaccine design.

DNA immunization site determines the level of gene expression and the magnitude, but not the type of the induced immune response

Optimization of DNA vaccine delivery improves the potency of the immune response and is crucial to clinical success. Here, we inquired how such optimization impacts the magnitude of the response, its specificity and type. BALB/c mice were DNA-immunized with two model immunogens, HIV-1 protease and reverse transcriptase by intramuscular or intradermal injections with electroporation. DNA immunogens were co-delivered with DNA encoding luciferase. Delivery and expression were monitored by in vivo bioluminescence imaging (BLI). The endpoint immune responses were assessed by IFN-γ/IL-2 FluoroSpot, multiparametric flow cytometry and antibody ELISA. Expression and immunogenicity were compared in relation to the delivery route. Regardless of the route, protease generated mainly IFN-γ, and reverse transcriptase, IL-2 and antibody response. BLI of mice immunized with protease- or reverse transcriptase/reporter plasmid mixtures, demonstrated significant loss of luminescence over time. The rate of decline of luminescence strongly correlated with the magnitude of immunogen-specific response, and depended on the immunogenicity profile and the immunization route. In vitro and in vivo BLI-based assays demonstrated that intradermal delivery strongly improved the immunogenicity of protease, and to a lesser extent, of reverse transcriptase. Immune response polarization and epitope hierarchy were not affected. Thus, by changing delivery/immunogen expression sites, it is possible to modulate the magnitude, but not the type or fine specificity of the induced immune response.

Codon optimization and improved delivery/immunization regimen enhance the immune response against wild-type and drug-resistant HIV-1 reverse transcriptase, preserving its Th2-polarity

DNA vaccines require a considerable enhancement of immunogenicity. Here, we optimized a prototype DNA vaccine against drug-resistant HIV-1 based on a weak Th2-immunogen, HIV-1 reverse transcriptase (RT). We designed expression-optimized genes encoding inactivated wild-type and drug-resistant RTs (RT-DNAs) and introduced them into mice by intradermal injections followed by electroporation. RT-DNAs were administered as single or double primes with or without cyclic-di-GMP, or as a prime followed by boost with RT-DNA mixed with a luciferase-encoding plasmid (“surrogate challenge”). Repeated primes improved cellular responses and broadened epitope specificity. Addition of cyclic-di-GMP induced a transient increase in IFN-γ production. The strongest anti-RT immune response was achieved in a prime-boost protocol with electroporation by short 100V pulses done using penetrating electrodes. The RT-specific response, dominated by CD4+ T-cells, targeted epitopes at aa 199–220 and aa 528–543. Drug-resistance mutations disrupted the epitope at aa 205–220, while the CTL epitope at aa 202–210 was not affected. Overall, multiparametric optimization of RT strengthened its Th2- performance. A rapid loss of RT/luciferase-expressing cells in the surrogate challenge experiment revealed a lytic potential of anti-RT response. Such lytic CD4+ response would be beneficial for an HIV vaccine due to its comparative insensitivity to immune escape.

Luciferase Expression Allows Bioluminescence Imaging But Imposes Limitations on the Orthotopic Mouse (4T1) Model of Breast Cancer

Implantation of reporter-labeled tumor cells in an immunocompetent host involves a risk of their immune elimination. We have studied this effect in a mouse model of breast cancer after the orthotopic implantation of mammary gland adenocarcinoma 4T1 cells genetically labelled with luciferase (Luc). Mice were implanted with 4T1 cells and two derivative Luc-expressing clones 4T1luc2 and 4T1luc2D6 exhibiting equal in vitro growth rates. In vivo, the daughter 4T1luc2 clone exhibited nearly the same, and 4T1luc2D6, a lower growth rate than the parental cells. The metastatic potential of 4T1 variants was assessed by magnetic resonance, bioluminescent imaging, micro-computed tomography, and densitometry which detected 100-μm metastases in multiple organs and bones at the early stage of their development. After 3-4 weeks, 4T1 generated 11.4 ± 2.1, 4T1luc2D6, 4.5 ± 0.6; and 4T1luc2, <1 metastases per mouse, locations restricted to lungs and regional lymph nodes. Mice bearing Luc-expressing tumors developed IFN-γ response to the dominant CTL epitope of Luc. Induced by intradermal DNA-immunization, such response protected mice from the establishment of 4T1luc2-tumors. Our data show that natural or induced cellular response against the reporter restricts growth and metastatic activity of the reporter-labelled tumor cells. Such cells represent a powerful instrument for improving immunization technique for cancer vaccine applications.

Preservation of tumor-host immune interactions with luciferase-tagged imaging in a murine model of ovarian cancer

BACKGROUND

Ovarian cancer is immunogenic and residual tumor volume after surgery is known to be prognostic. Ovarian cancer often follows a recurring-remitting course and microscopic disease states may present ideal opportunities for immune therapies. We sought to establish the immune profile of a murine model of ovarian cancer that allows in vivo tumor imaging and the quantitation of microscopic disease.

RESULTS AND DISCUSSION

Baseline imaging and weight measurements were taken within 1 and 2 weeks after intraperitoneal tumor injection, respectively. Significantly higher photons per second from baseline imaging were first observed 5 weeks after tumor cell injection (p < 0.05) and continued to be significant through 8 weeks after injection (p < 0.01), whereas a significant increase in weight above baseline was not observed until day 56 (p < 0.0001). Expression of luc2 in ID8 cells did not alter the cellular immune microenvironment of the tumor. FOXP3+ T cells were more likely to be detected in the intraepithelial compartment and CD4+ T cells in the stroma as compared to CD3+ T cells, which were found equally in stroma and intraepithelial compartments.

CONCLUSIONS

Use of an intraperitoneal tumor expressing a codon-optimized firefly luciferase in an immunocompetent mouse model allows tumor quantitation in vivo and detection of microscopic tumor burdens. Expression of this foreign protein does not significantly effect tumor engraftment or the immune microenvironment of the ID8 cells in vivo and may allow novel immunotherapies to be assessed in a murine model for their translational potential to ovarian cancers in remission or minimal disease after primary cytoreductive surgery or chemotherapy.

METHODS

Mouse ovarian surface epithelial cells from C57BL6 mice transformed after serial passage in vitro were transduced with a lentiviral vector expressing a codon optimized firefly luciferase (luc2). Cell lines were selected and luc2 expression functionally confirmed in vitro. Cell lines were intraperitoneally (IP) implanted in albino C57BL/6/BrdCrHsd-Tyrc mice and albino B6(Cg)-Tyrc-2 J/J mice for serial imaging. D-luciferin substrate was injected IP and tumors were serially imaged in vivo using a Xenogen IVIS. Tumor take, weights, and luminescent intensities were measured. Immunohistochemistry was performed on tumors and assessed for immune infiltrates in stromal and intraepithelial compartments.

The site of administration influences both the type and the magnitude of the immune response induced by DNA vaccine electroporation

We investigated the influence of the site of administration of DNA vaccine on the induced immune response. DNA vaccines were administered by electroporation at three different sites: tibial cranial muscle, abdominal skin and ear pinna. Aiming to draw general conclusions about DNA vaccine delivery, we successively used several plasmids encoding either luciferase and ovalbumin as models or gp160 and P1A as vaccines against HIV and P815 mastocytoma, respectively. Low levels and duration of luciferase transgene expression were observed after electroporation of the abdominal skin, partly explaining its lower immunogenic performance as compared to the other sites of administration. Analyses of OT-I CD8+ and OT-II CD4+ T cell responses highlighted the differential impact of the delivery site on the elicited immune response. Muscle electroporation induced the strongest humoral immune response and both muscle and ear pinna sites induced cellular immunity against gp160. Ear pinna delivery generated the highest level of CTL responses against P1A but electroporation of muscle and ear pinna were equally efficient in delaying P815 growth and improving mice survival. The present study demonstrated that the site of administration is a key factor to be tested in the development of DNA vaccine.

DNA vaccination strategy targets epidermal dendritic cells, initiating their migration and induction of a host immune response

The immunocompetence and clinical accessibility of dermal tissue offers an appropriate and attractive target for vaccination. We previously demonstrated that pDNA injection into the skin in combination with surface electroporation (SEP), results in rapid and robust expression of the encoded antigen in the epidermis. Here, we demonstrate that intradermally EP-enhanced pDNA vaccination results in the rapid induction of a host humoral immune response. In the dermally relevant guinea pig model, we used high-resolution laser scanning confocal microscopy to observe direct dendritic cell (DC) transfections in the epidermis, to determine the migration kinetics of these cells from the epidermal layer into the dermis, and to follow them sequentially to the immediate draining lymph nodes. Furthermore, we delineate the relationship between the migration of directly transfected epidermal DCs and the generation of the host immune response. In summary, these data indicate that direct presentation of antigen to the immune system by DCs through SEP-based in vivo transfection in the epidermis, is related to the generation of a humoral immune response.