The enhanced green fluorescent protein (eGFP) is minimally immunogenic in C57BL/6 mice

Bioenergetic shift and proteomic signature induced by lentiviral-transduction of GFP-based biosensors

Fluorescent proteins (FPs) stand as pivotal tools extensively employed across diverse biological research endeavors in various model systems. However, long-standing concerns surround their use due to the numerous side effects associated with their expression. Recent investigations have brought to light the significance of hydrogen peroxide (H2O2) that is associated with the maturation process of green fluorescent protein (GFP) fluorophores. The structural and functional impairments associated with GFP expression are possibly linked to this amount of H2O2. In this study, we assess the impact of the GFP-based HyPer7 biosensor on cellular homeostasis and proteome changes, aiming to identify potential risks related to oxidative stress responses that potentially risks the application of such tools. Cells expressing genome-integrated HyPer7 demonstrated altered mitochondrial membrane potential (MMP), which was alleviated by the addition of antioxidants or culturing cells at physiological normoxia (5 kPa O2). Additionally, HyPer7-expressing cells also exhibited significant impairment in mitochondrial oxidative respiration, suggesting broader mitochondrial dysfunction. Through untargeted proteomics analysis, we identified 26 proteins exhibiting differential expression in HyPer7-expressing cells compared to respective control cells. Functional annotation analysis showed that the list of the delineated proteins is associated with cellular responses to stress and the regulation of antioxidant mechanisms. Our findings underscore the significance of caution and validation in ensuring a thorough comprehension of cellular responses when using fluorescent protein-based tools, thereby enhancing the reliability of the results.

Smooth muscle cells clonally expand in a murine carotid allograft model complicated by immune reactions to reporter transgenes

BACKGROUND AND AIMS

Most experimental studies of allograft vasculopathy (AV) have relied on transplantation between major histocompatibility complex-mismatched inbred mouse strains, but this leads to the complete eradication of donor smooth muscle cells (SMCs) and lesions formed by recipient cells. This is unlike human AV which is thought to form mainly by donor SMCs. Here, we studied sources of neointimal cells in a minor histocompatibility antigen-mismatched AV model by combining male-to-female orthotopic carotid transplantations and lineage tracing by SMC-specific expression of fluorescent proteins.

METHODS

To track SMC-derived cells in allograft vasculopathy, we used male donor mice with SMC-restricted Cre recombination of the mT/mG reporter transgene, which switches expression of membrane-bound red fluorescent protein (RFP) to green fluorescent protein (GFP), or the stochastically recombining Confetti reporter transgene, which yields a mosaic expression of four fluorescent proteins. Donor carotid segments were harvested and orthotopically allografted to female recipients that were wildtype or had non-recombined reporter transgenes. Inhibition of T cell responses by CTLA4Ig was used in some experiments. Sections of lesions harvested after 4 weeks were analyzed by fluorescence microscopy.

RESULTS

Donor-derived SMCs survived and gave rise to part of the neointimal cells in experiments where carotid segments from recombined mT/mG male mice were transplanted into wild-type or non-recombined mT/mG female mice. Sex-mismatched transplants developed significant lesions, increasing the intimal and medial area 4.6-fold (p = 0.038) and 2.0-fold (p = 0.024) compared to sex- and fluorescence-matched controls, respectively. Interestingly, sex-matched fluorescence-positive transplants developed intimal lesions in 50% of fluorescence-naïve recipient controls. To study the clonal structure of the neointimal donor-derived SMC lineage cells, we then transplanted male carotids with heterozygous or homozygous recombined Confetti transgenes into female recipients. These transplants developed lesions with few surviving donor SMCs, indicating that expression of the Confetti reporter increased rejection and donor-specific SMC death. Some of the few remaining donor SMCs underwent clonal expansion. CTLA4Ig administration at the time of surgery did not improve SMC survival in mT/mG or Confetti transplants.

CONCLUSION

Male-to-female transplant models feature donor-derived SMCs, some of which undergo clonal expansion, but immune rejection to fluorescence reporters appears to bias results in lineage tracing models. Overcoming these challenges with alternative reporter transgenes or tolerant recipients is necessary to study the mechanisms by which donor SMCs contribute to allograft vasculopathy.

Identifying Key Drivers of Efficient B Cell Responses: On the Role of T Help, Antigen-Organization, and Toll-like Receptor Stimulation for Generating a Neutralizing Anti-Dengue Virus Response

T help (Th), stimulation of toll-like receptors (pathogen-associated molecular patterns, PAMPs), and antigen organization and repetitiveness (pathogen-associated structural patterns, PASPs) were shown numerous times to be important in driving B-cell and antibody responses. In this study, we dissected the individual contributions of these parameters using newly developed "Immune-tag" technology. As model antigens, we used eGFP and the third domain of the dengue virus 1 envelope protein (DV1 EDIII), the major target of virus-neutralizing antibodies. The respective proteins were expressed alone or genetically fused to the N-terminal fragment of the cucumber mosaic virus (CMV) capsid protein-nCMV, rendering the antigens oligomeric. In a step-by-step manner, RNA was attached as a PAMP, and/or a universal Th-cell epitope was genetically added for additional Th. Finally, a PASP was added to the constructs by displaying the antigens highly organized and repetitively on the surface of CMV-derived virus-like particles (CuMV VLPs). Sera from immunized mice demonstrated that each component contributed stepwise to the immunogenicity of both proteins. All components combined in the CuMV VLP platform induced by far the highest antibody responses. In addition, the DV1 EDIII induced high levels of DENV-1-neutralizing antibodies only if displayed on VLPs. Thus, combining multiple cues typically associated with viruses results in optimal antibody responses.

Clonal tracking in cancer and metastasis

The eradication of many cancers has proven challenging due to the presence of functionally and genetically heterogeneous clones maintained by rare cancer stem cells (CSCs), which contribute to disease progression, treatment refractoriness, and late relapse. The characterization of functional CSC activity has necessitated the development of modern clonal tracking strategies. This review describes viral-based and CRISPR-Cas9-based cellular barcoding, lineage tracing, and imaging-based approaches. DNA-based cellular barcoding technology is emerging as a powerful and robust strategy that has been widely applied to in vitro and in vivo model systems, including patient-derived xenograft models. This review also highlights the potential of these methods for use in the clinical and drug discovery contexts and discusses the important insights gained from such approaches.

GFP Transfection Alters Protein Expression Patterns in Prostate Cancer Cells: A Proteomic Study

PURPOSE

Green Fluorescent Protein is widely used as a cellular marker tool, but its potential influence on cells has been questioned. Although the potential off-target effects of GFP on tumor cells have been studied to some extent, the findings at the molecular level are insufficient to explain the effect of GFP expression on the tumorigenic capacity of cancer cells. Here, we aimed to investigate the effect of GFP expression on the tumorigenicity of PC3 prostate cancer cells.

METHODS

Using GFP-expressing and wild-type PC-3 cells, xenograft models were generated in athymic BALB/C mice. To identify differentially expressed proteins, the change in cells proteome was investigated by label-free quantification with nano-high performance liquid chromatography to tandem mass spectrometry (nHPLC-MS/MS). Proteins that showed significantly altered expression levels were evaluated using the bioinformatics tools.

RESULTS

Unlike the wild-type PC-3 cells, GFP-expressing cells failed to develop tumor. Comparative proteome analysis of GFP-expressing cells with WT PC-3 cells revealed a total of 216 differentially regulated proteins, of which 98 were upregulated and 117 were downregulated.

CONCLUSION

Upon GFP expression, differential changes in several pathways including the immune system, translational machinery, energy metabolism, elements of cytoskeletal and VEGF signaling pathway were observed. Therefore, care should be taken into account to prevent reporting deceitful mechanisms generated from studies utilizing GFP.

Novel murine glioblastoma models that reflect the immunotherapy resistance profile of a human disease

BACKGROUND

The lack of murine glioblastoma models that mimic the immunobiology of human disease has impeded basic and translational immunology research. We, therefore, developed murine glioblastoma stem cell lines derived from Nestin-CreERT2QkL/L; Trp53L/L; PtenL/L (QPP) mice driven by clinically relevant genetic mutations common in human glioblastoma. This study aims to determine the immune sensitivities of these QPP lines in immunocompetent hosts and their underlying mechanisms.

METHODS

The differential responsiveness of QPP lines was assessed in the brain and flank in untreated, anti-PD-1, or anti-CTLA-4 treated mice. The impact of genomic landscape on the responsiveness of each tumor was measured through whole exome sequencing. The immune microenvironments of sensitive (QPP7) versus resistant (QPP8) lines were compared in the brain using flow cytometry. Drivers of flank sensitivity versus brain resistance were also measured for QPP8.

RESULTS

QPP lines are syngeneic to C57BL/6J mice and demonstrate varied sensitivities to T cell immune checkpoint blockade ranging from curative responses to complete resistance. Infiltrating tumor immune analysis of QPP8 reveals improved T cell fitness and augmented effector-to-suppressor ratios when implanted subcutaneously (sensitive), which are absent on implantation in the brain (resistant). Upregulation of PD-L1 across the myeloid stroma acts to establish this state of immune privilege in the brain. In contrast, QPP7 responds to checkpoint immunotherapy even in the brain likely resulting from its elevated neoantigen burden.

CONCLUSIONS

These syngeneic QPP models of glioblastoma demonstrate clinically relevant profiles of immunotherapeutic sensitivity and potential utility for both mechanistic discovery and evaluation of immune therapies.

Development of HPV16 mouse and dog models for more accurate prediction of human vaccine efficacy

BACKGROUND

Animal models are essential to understand the physiopathology of human diseases but also to evaluate new therapies. However, for several diseases there is no appropriate animal model, which complicates the development of effective therapies. HPV infections, responsible for carcinoma cancers, are among these. So far, the lack of relevant animal models has hampered the development of therapeutic vaccines. In this study, we used a candidate therapeutic vaccine named C216, similar to the ProCervix candidate therapeutic vaccine, to validate new mouse and dog HPV preclinical models. ProCervix has shown promising results with classical subcutaneous murine TC-1 cell tumor isografts but has failed in a phase II study.

RESULTS

We first generated E7/HPV16 syngeneic transgenic mice in which the expression of the E7 antigen could be switched on through the use of Cre-lox recombination. Non-integrative LentiFlash^® viral particles were used to locally deliver Cre mRNA, resulting in E7/HPV16 expression and GFP reporter fluorescence. The expression of E7/HPV16 was monitored by in vivo fluorescence using Cellvizio imaging and by local mRNA expression quantification. In the experimental conditions used, we observed no differences in E7 expression between C216 vaccinated and control groups. To mimic the MHC diversity of humans, E7/HPV16 transgenes were locally delivered by injection of lentiviral particles in the muscle of dogs. Vaccination with C216, tested with two different adjuvants, induced a strong immune response in dogs. However, we detected no relationship between the level of cellular response against E7/HPV16 and the elimination of E7-expressing cells, either by fluorescence or by RT-ddPCR analysis.

CONCLUSIONS

In this study, we have developed two animal models, with a genetic design that is easily transposable to different antigens, to validate the efficacy of candidate vaccines. Our results indicate that, despite being immunogenic, the C216 candidate vaccine did not induce a sufficiently strong immune response to eliminate infected cells. Our results are in line with the failure of the ProCervix vaccine that was observed at the end of the phase II clinical trial, reinforcing the relevance of appropriate animal models.

Human Adipose Mesenchymal Stromal/Stem Cells Improve Fat Transplantation Performance

The resorption rate of autologous fat transfer (AFT) is 40–60% of the implanted tissue, requiring new surgical strategies for tissue reconstruction. We previously demonstrated in a rabbit model that AFT may be empowered by adipose-derived mesenchymal stromal/stem cells (AD-MSCs), which improve graft persistence by exerting proangiogenic/anti-inflammatory effects. However, their fate after implantation requires more investigation. We report a xenograft model of adipose tissue engineering in which NOD/SCID mice underwent AFT with/without human autologous AD-MSCs and were monitored for 180 days (d). The effect of AD-MSCs on AFT grafting was also monitored by evaluating the expression of CD31 and F4/80 markers. Green fluorescent protein-positive AD-MSCs (AD-MSC-GFP) were detected in fibroblastoid cells 7 days after transplantation and in mature adipocytes at 60 days, indicating both persistence and differentiation of the implanted cells. This evidence also correlated with the persistence of a higher graft weight in AFT-AD-MSC compared to AFT alone treated mice. An observation up to 180 d revealed a lower resorption rate and reduced lipidic cyst formation in the AFT-AD-MSC group, suggesting a long-term action of AD-MSCs in support of AFT performance and an anti-inflammatory/proangiogenic activity. Together, these data indicate the protective role of adipose progenitors in autologous AFT tissue resorption.

Primary tumor associated macrophages activate programs of invasion and dormancy in disseminating tumor cells

Metastases are initiated by disseminated tumor cells (DTCs) that colonize distant organs. Growing evidence suggests that the microenvironment of the primary tumor primes DTCs for dormant or proliferative fates. However, the manner in which this occurs remains poorly understood. Here, using the Window for High-Resolution Intravital Imaging of the Lung (WHRIL), we study the live lung longitudinally and follow the fate of individual DTCs that spontaneously disseminate from orthotopic breast tumors. We find that spontaneously DTCs have increased levels of retention, increased speed of extravasation, and greater survival after extravasation, compared to experimentally metastasized tumor cells. Detailed analysis reveals that a subset of macrophages within the primary tumor induces a pro-dissemination and pro-dormancy DTC phenotype. Our work provides insight into how specific primary tumor microenvironments prime a subpopulation of cells for expression of proteins associated with dissemination and dormancy.

Breaking Entry-and Species Barriers: LentiBOOST® Plus Polybrene Enhances Transduction Efficacy of Dendritic Cells and Monocytes by Adenovirus 5

Due to their ability to trigger strong immune responses, adenoviruses (HAdVs) in general and the serotype5 (HAdV-5) in particular are amongst the most popular viral vectors in research and clinical application. However, efficient transduction using HAdV-5 is predominantly achieved in coxsackie and adenovirus receptor (CAR)-positive cells. In the present study, we used the transduction enhancer LentiBOOST^® comprising the polycationic Polybrene to overcome these limitations. Using LentiBOOST^®/Polybrene, we yielded transduction rates higher than 50% in murine bone marrow-derived dendritic cells (BMDCs), while maintaining their cytokine expression profile and their capability to induce T-cell proliferation. In human dendritic cells (DCs), we increased the transduction rate from 22% in immature (i)DCs or 43% in mature (m)DCs to more than 80%, without inducing cytotoxicity. While expression of specific maturation markers was slightly upregulated using LentiBOOST^®/Polybrene on iDCs, no effect on mDC phenotype or function was observed. Moreover, we achieved efficient HAdV5 transduction also in human monocytes and were able to subsequently differentiate them into proper iDCs and functional mDCs. In summary, we introduce LentiBOOST^® comprising Polybrene as a highly potent adenoviral transduction agent for new in-vitro applications in a set of different immune cells in both mice and humans.

Using a Prime-Boost Vaccination Strategy That Proved Effective for High Resolution Epitope Mapping to Characterize the Elusive Immunogenicity of Survivin

Simple Summary

The generation of tumor-specific T cells remains a pillar of modern cancer immunotherapy. Exogenous vaccines often rely on targeting tumor-associated antigens. The anti-apoptotic protein survivin has been deemed a high priority target due to its overexpression in a wide variety of tumor types. To support the analysis of tumor-associated T cell responses, optimization of epitope mapping would be valuable. A heterologous prime-boost vaccination strategy was designed to target survivin to induce anti-tumor immune responses. However, survivin-specific T cell responses could not be detected in mice. Potential mechanisms to explain this failure were explored. To confirm the robustness of the vaccination platform, enhanced green fluorescent protein (eGFP) was targeted since it has been defined as a protein with relatively low immunogenicity. In this context the vaccination strategy uncovered novel T cell epitopes from eGFP in two strains of mice. This research highlighted the utility of the vaccine platform to triage potential target antigens based on their immunogenicity.

Abstract

Survivin is a member of the inhibitor of apoptosis family of proteins and has been reported to be highly expressed in a variety of cancer types, making it a high priority target for cancer vaccination. We previously described a heterologous prime-boost strategy using a replication-deficient adenovirus, followed by an oncolytic rhabdovirus that generates unprecedented antigen-specific T cell responses. We engineered each vector to express a mutated version of full-length murine survivin. We first sought to uncover the complete epitope map for survivin-specific T cell responses in C57BL/6 and BALB/c mice by flow cytometry. However, no T cell responses were detected by intracellular cytokine staining after re-stimulation of T cells. Survivin has been found to be expressed by activated T cells, which could theoretically cause T cell-mediated killing of activated T cells, known as fratricide. We were unable to recapitulate this phenomenon in experiments. Interestingly, the inactivated survivin construct has been previously shown to directly kill tumor cells in vitro. However, there was no evidence in our models of induction of death in antigen-presenting cells due to treatment with a survivin-expressing vector. Using the same recombinant virus-vectored prime-boost strategy targeting the poorly immunogenic enhanced green fluorescent protein proved to be a highly sensitive method for mapping T cell epitopes, particularly in the context of identifying novel epitopes recognized by CD4⁺ T cells. Overall, these results suggested there may be unusually robust tolerance to survivin in commonly used mouse strains that cannot be broken, even when using a particularly potent vaccination platform. However, the vaccination method shows great promise as a strategy for identifying novel and subdominant T cell epitopes.

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.

Direct and Indirect Regulators of Epithelial-Mesenchymal Transition-Mediated Immunosuppression in Breast Carcinomas

The epithelial-to-mesenchymal transition, which conveys epithelial (E) carcinoma cells to quasi-mesenchymal (qM) states, enables them to metastasize and acquire resistance to certain treatments. Murine tumors composed of qM mammary carcinoma cells assemble an immunosuppressive tumor microenvironment (TME) and develop resistance to anti-CTLA4 immune-checkpoint blockade (ICB) therapy, unlike their E counterparts. Importantly, minority populations of qM cells within a tumor can cross-protect their more E neighbors from immune attack. The underlying mechanisms of immunosuppression and cross-protection have been unclear. We demonstrate that abrogation of qM carcinoma cell-derived factors (CD73, CSF1, or SPP1) prevents the assembly of an immunosuppressive TME and sensitizes otherwise refractory qM tumors partially or completely to anti-CTLA4 ICB. Most strikingly, mixed tumors in which minority populations of carcinoma cells no longer express CD73 are now sensitized to anti-CTLA4 ICB. Finally, loss of CD73 also enhances the efficacy of anti-CTLA4 ICB during the process of metastatic colonization. SIGNIFICANCE: Minority populations of qM carcinoma cells, which likely reside in human breast carcinomas, can cross-protect their E neighbors from immune attack. Understanding the mechanisms by which qM carcinoma cells resist antitumor immune attack can help identify signaling channels that can be interrupted to potentiate the efficacy of checkpoint blockade immunotherapies.This article is highlighted in the In This Issue feature, p. 995.

Characterization of the role of Samsn1 loss in multiple myeloma development

The protein SAMSN1 was recently identified as a putative tumor suppressor in multiple myeloma, with re-expression of Samsn1 in the 5TGM1/KaLwRij murine model of myeloma leading to a near complete abrogation of intramedullary tumor growth. Here, we sought to clarify the mechanism underlying this finding. Intratibial administration of 5TGM1 myeloma cells into KaLwRij mice revealed that Samsn1 had no effect on primary tumor growth, but that its expression significantly inhibited the metastasis of these primary tumors. Notably, neither in vitro nor in vivo migration was affected by Samsn1 expression. Both knocking-out SAMSN1 in the RPMI-8226 and JJN3 human myeloma cell lines, and retrovirally expressing SAMSN1 in the LP-1 and OPM2 human myeloma cell lines had no effect on either cell proliferation or migration in vitro. Altering SAMSN1 expression in these human myeloma cells did not affect the capacity of the cells to establish either primary or metastatic intramedullary tumors when administered intratibially into immune deficient NSG mice. Unexpectedly, the tumor suppressive and anti-metastatic activity of Samsn1 in 5TGM1 cells were not evidenced following cell administration either intratibially or intravenously to NSG mice. Crucially, the growth of Samsn1-expressing 5TGM1 cells was limited in C57BL/6/Samsn1-/- mice but not in C57BL/6 Samsn1+/+ mice. We conclude that the reported potent in vivo tumor suppressor activity of Samsn1 can be attributed, in large part, to graft-rejection from Samsn1-/- recipient mice. This has broad implications for the design and interpretation of experiments that utilize cancer cells and knockout mice that are mismatched for expression of specific proteins.

A mouse model that is immunologically tolerant to reporter and modifier proteins

Reporter proteins have become an indispensable tool in biomedical research. However, exogenous introduction of these reporters into mice poses a risk of rejection by the immune system. Here, we describe the generation, validation and application of a multiple reporter protein tolerant ‘Tol' mouse model that constitutively expresses an assembly of shuffled reporter proteins from a single open reading frame. We demonstrate that expression of the Tol transgene results in the deletion of CD8⁺ T cells specific for a model epitope, and substantially improves engraftment of reporter-gene transduced T cells. The Tol strain provides a valuable mouse model for cell transfer and viral-mediated gene transfer studies, and serves as a methodological example for the generation of poly-tolerant mouse strains.

Bresser and Dijkgraaf et al. develop the ‘Tol’ strain, a genetically modified mouse model that expresses a range of shuffled reporter and modifier proteins from a single open reading frame. This strain is immunologically tolerant to these reporter and modifier proteins, providing a valuable model system for cell transfer studies and virus-mediated gene transfer studies.

Immunoresponse to Gene-Modified Hematopoietic Stem Cells

Gene transfer to and correction of hematopoietic stem cells (HSCs) are ideal strategies to cure a number of congenital and acquired disorders. However, transgene products may trigger immunological rejection of modified cells, limiting their therapeutic benefits. Preclinical and clinical data indicate that myeloablative total body irradiation (TBI) allows for efficient engraftment and tolerance to gene-modified HSCs. In contrast, myeloablative chemotherapy using busulfan or similar agents is only sufficient to induce tolerance to gene-modified HSCs producing no or non-immunogenic protein. If cells are modified to produce a protein that is xenogenic or congenitally absent in the patient, additional immunosuppression may be required to prevent an immunological reaction to the transduced cells. New gene editing and in vivo gene therapy techniques could pose additional immune concerns compared to ex vivo gene therapy methods. This review is intended to guide the design of conditioning and immunosuppression therapy in HSC-targeted gene therapy, as well as gene editing.

Lactococcus lactis expressing sand fly PpSP15 salivary protein confers long-term protection against Leishmania major in BALB/c mice

Cutaneous leishmaniasisis a vector-borne disease transmitted by Leishmania infected sand flies. PpSP15 is an immunogenic salivary protein from the sand fly Phlebotomus papatasi. Immunization with PpSP15 was shown to protect against Leishmania major infection. Lactococcus lactis is a safe non-pathogenic delivery system that can be used to express antigens in situ. Here, the codon-optimized Ppsp15-egfp gene was cloned in pNZ8121 vector downstream of the PrtP signal peptide that is responsible for expression and secretion of the protein on the cell wall. Expression of PpSP15-EGFP recombinant protein was monitored by immunofluorescence, flow cytometry and Western blot. Also, expression of protein in cell wall compartment was verified using whole cell ELISA, Western blot and TEM microscopy. BALB/c mice were immunized three times with recombinant L. lactis-PpSP15-EGFPcwa, and the immune responses were followed up, at short-term (ST, 2 weeks) and long-term (LT, 6 months) periods. BALB/c mice were challenged with L. major plus P. papatasi Salivary Gland Homogenate. Evaluation of footpad thickness and parasite burden showed a delay in the development of the disease and significantly decreased parasite numbers in PpSP15 vaccinated animals as compared to control group. In addition, immunized mice showed Th1 type immune responses. Importantly, immunization with L. lactis-PpSP15-EGFPcwa stimulated the long-term memory in mice which lasted for at least 6 months.

Electrotransfer of CpG free plasmids enhances gene expression in skin

Skin is a very suitable target for gene therapy and DNA vaccination due to its accessibility, its surface and its ability to produce transgenes. Gene electrotransfer (GET) to the skin is under development for clinical applications for DNA vaccine or local treatment such as wound healing. Local treatments are effective if the expression of the plasmid affects only the local environment (skin) by inducing an efficient concentration over a prolonged period. In this study, we evaluate the control of expression in the skin of a plasmid coding a fluorescent protein by its CpG (cytosine-phosphate-guanine motif) content. Two fluorescent reporter genes are evaluated: tdTomato and GFP. The expression is followed on the long term by in vivo fluorescence imaging. Our results show that GET mediated expression in the skin can be controlled by the CpG content of the plasmid. Long term expression (>120 days) can be obtained at high level with CpG-free constructs associated with a proper design of the electrodes where the field distribution mediating the gene electrotransfer is present deep in the skin.

GFP transgenic animals in biomedical research: a review of potential disadvantages

Green Fluorescent protein (GFP) transgenic animals are accepted tools for studying various physiological processes, including organ development and cell migration. However, several in vivo studies claimed that GFP may impair transgenic animals' health. Glomerulosclerosis was observed in transgenic mice and rabbits with ubiquitous reporter protein expression. Heart-specific GFP expression evoked dilated cardiomyopathy and altered cardiac function in transgenic mouse and zebrafish lines, respectively. Moreover, growth retardation and increased axon swelling were observed in GFP and yellow fluorescent protein (YFP) transgenic mice, respectively. This review will focus on the potential drawbacks of the applications of GFP transgenic animals in biomedical research.

Preparation and Testing of Cells Expressing Fluorescent Proteins for Intravital Imaging of Tumor Microenvironment

Intravital microscopy is widely used for in vivo studies of the mechanisms of carcinogenesis and response to antitumor therapy. For visualization of tumor cells in vivo, cell lines expressing fluorescent proteins are needed. Expression of exogenous proteins can affect cell growth rate and their tumorigenic potential. Therefore, comprehensive analysis of the morphofunctional properties of transduced cells is required for creating appropriate models of tumor microenvironment. In the present study, six lines of mouse tumor cells expressing green and red fluorescent proteins were derived. Analysis of cells morphology, growth kinetics, and response to chemotherapy in vitro revealed no significant differences between wild-type and transduced cell lines. Introduction of fluorescent proteins into the genome of 4T1 (murine breast cancer) and B16-F10 (murine melanoma) cells did not affect tumor growth rate after subcutaneous implantation to mice, while both CT26-GFP and CT26-RFP cells (murine colon cancer) were rejected starting from day 8 after implantation. Elucidation of the mechanisms underlying CT26-GFP/RFP rejection is required to modify transduction technique for creating the models of tumor microenvironment accessible for in vivo visualization. Transduced 4T1 and B16-F10 cell lines can be used for intravital microscopic imaging of tumor cells, neoplastic vasculature, and leukocyte subpopulations.

Bone marrow chimeras-a vital tool in basic and translational research

Bone marrow chimeras are used routinely in immunology research as well as in other fields of biology. Here, we provide a concise state-of-the-art review about the types of chimerisms that can be achieved and the type of information that each model generates. We include separate sections for caveats and future developments. We provide examples from the literature in which different types of chimerism were employed to answer specific questions. While simple bone marrow chimeras allow to dissect the role of genes in distinct cell populations such as the hematopoietic cells versus non-hematopoietic cells, mixed bone marrow chimeras can provide detailed information about hematopoietic cell types and the intrinsic and extrinsic roles of individual genes. The advantages and caveats of bone marrow chimerism for the study of microglia are addressed, as well as alternatives to irradiation that minimize blood-brain-barrier disruption. Elementary principles are introduced and their potential is exemplified through summarizing recent studies.

The Effect of Tissue Preparation and Donor Age on Striatal Graft Morphology in the Mouse

Huntington's disease (HD) is a progressive neurodegenerative disease in which striatal medium spiny neurons (MSNs) are lost. Neuronal replacement therapies aim to replace MSNs through striatal transplantation of donor MSN progenitors, which successfully improve HD-like deficits in rat HD models and have provided functional improvement in patients. Transplants in mouse models of HD are more variable and have lower cell survival than equivalent rat grafts, yet mice constitute the majority of transgenic HD models. Improving the quality and consistency of mouse transplants would open up access to this wider range of rodent models and facilitate research to increase understanding of graft mechanisms, which is essential to progress transplantation as a therapy for HD. Here we determined how donor age, cell preparation, and donor/host strain choice influenced the quality of primary embryonic grafts in quinolinic acid lesion mouse models of HD. Both a within-strain (W-S) and a between-strain (B-S) donor/host paradigm were used to compare transplants of donor tissues derived from mice at embryonic day E12 and E14 prepared either as dissociated suspensions or as minimally manipulated tissue pieces (TP). Good graft survival was observed, although graft volume and cellular composition were highly variable. The effect of cell preparation on grafts differed significantly depending on donor age, with E14 cell suspensions yielding larger grafts compared to TP. Conversely, TP were more effective when derived from E12 donor tissue. A W-S model produced larger grafts with greater MSN content, and while high levels of activated microglia were observed across all groups, a greater number was found in B-S transplants. In summary, we show that the effect of tissue preparation on graft morphology is contingent on the age of donor tissue used. The presence of microglial activation in all groups highlights the host immune response as an important consideration in mouse transplantation.

Non-viral, Tumor-free Induction of Transient Cell Reprogramming in Mouse Skeletal Muscle to Enhance Tissue Regeneration

Overexpression of Oct3/4, Klf4, Sox2, and c-Myc (OKSM) transcription factors can de-differentiate adult cells in vivo. While sustained OKSM expression triggers tumorigenesis through uncontrolled proliferation of toti- and pluripotent cells, transient reprogramming induces pluripotency-like features and proliferation only temporarily, without teratomas. We sought to transiently reprogram cells within mouse skeletal muscle with a localized injection of plasmid DNA encoding OKSM (pOKSM), and we hypothesized that the generation of proliferative intermediates would enhance tissue regeneration after injury. Intramuscular pOKSM administration rapidly upregulated pluripotency (Nanog, Ecat1, and Rex1) and early myogenesis genes (Pax3) in the healthy gastrocnemius of various strains. Mononucleated cells expressing such markers appeared in clusters among myofibers, proliferated only transiently, and did not lead to dysplasia or tumorigenesis for at least 120 days. Nanog was also upregulated in the gastrocnemius when pOKSM was administered 7 days after surgically sectioning its medial head. Enhanced tissue regeneration after reprogramming was manifested by the accelerated appearance of centronucleated myofibers and reduced fibrosis. These results suggest that transient in vivo reprogramming could develop into a novel strategy toward the acceleration of tissue regeneration after injury, based on the induction of transiently proliferative, pluripotent-like cells in situ. Further research to achieve clinically meaningful functional regeneration is warranted.

In vivo delivery of pPERDBY to BALB/c mice by LacVax® DNA-I and comparison of elicited immune response with conventional immunization methods

The non-invasive food grade Lactococcus lactis (L. lactis) represents a safe and attractive alternative to invasive pathogens for the delivery of plasmid DNA at mucosal sites. We have earlier shown the DNA delivery potential of r-L. lactis harboring DNA vaccine reporter plasmid; pPERDBY in vitro. In the present work, we examined in vivo delivery potential of food grade non-invasive r-L. lactis::pPERDBY (LacVax^® DNA-I) in BALB/c mice. Moreover, using EGFP as a model antigen, we also characterized and compared the immune response elicited by LacVax^® DNA-I with other conventional vaccination approaches using protein and naked DNA immunization. The presence of antigen-specific serum IgG and fecal secretory IgA (sIgA) antibodies demonstrated in vivo DNA delivery and immune elicitation potential of the developed LacVax^® DNA-I. As compared with intramuscular injection, oral delivery of pPERDBY via L. lactis resulted in a significantly rapid increase in IgG and higher sIgA titers, indicating the immunogenic and immunostimulatory properties of the LacVax^® DNA-I. The needle-free immunization with LacVax^® DNA-I led to increased production of IL-4, an indicator of Th2 screwed response. To the best of our knowledge, this report for the first time outlines comparison of orally administered LacVax^® DNA-I with other conventional vaccination approaches.

Cellular GFP Toxicity and Immunogenicity: Potential Confounders in in Vivo Cell Tracking Experiments

Green Fluorescent protein (GFP), used as a cellular tag, provides researchers with a valuable method of measuring gene expression and cell tracking. However, there is evidence to suggest that the immunogenicity and cytotoxicity of GFP potentially confounds the interpretation of in vivo experimental data. Studies have shown that GFP expression can deteriorate over time as GFP tagged cells are prone to death. Therefore, the cells that were originally marked with GFP do not survive and cannot be accurately traced over time. This review will present current evidence for the immunogenicity and cytotoxicity of GFP in in vivo studies by characterizing these responses.

The power of bioluminescence imaging in understanding host-pathogen interactions

Infectious diseases are one of the leading causes of death worldwide. Modelling and understanding human infection is imperative to developing treatments to reduce the global burden of infectious disease. Bioluminescence imaging is a highly sensitive, non-invasive technique based on the detection of light, produced by luciferase-catalysed reactions. In the study of infectious disease, bioluminescence imaging is a well-established technique; it can be used to detect, localize and quantify specific immune cells, pathogens or immunological processes. This enables longitudinal studies in which the spectrum of the disease process and its response to therapies can be monitored. Light producing transgenic rodents are emerging as key tools in the study of host response to infection. Here, we review the strategies for identifying biological processes in vivo, including the technology of bioluminescence imaging and illustrate how this technique is shedding light on the host-pathogen relationship.

Portal branch ligation does not counteract the inhibiting effect of temsirolimus on extrahepatic colorectal metastatic growth

The mTor-inhibitor temsirolimus (TEM) has potent anti-tumor activities on extrahepatic colorectal metastases. Treatment of patients with advanced disease may require portal branch ligation (PBL). While PBL can induce intrahepatic tumor growth, the effect of PBL on extrahepatic metastases under TEM treatment is unknown. Therefore, we analyzed the effects of TEM treatment on extrahepatic metastases during PBL-associated liver regeneration. GFP-transfected CT26.WT colorectal cancer cells were implanted into the dorsal skinfold chamber of BALB/c-mice. Mice were randomized to four groups (n = 8). One was treated daily with TEM (1.5 mg/kg), PBS-treated animals served as controls. Another group underwent PBL of the left liver lobe and received daily TEM treatment. Animals with PBL and PBS treatment served as controls. Tumor vascularization and growth as well as tumor cell migration, proliferation and apoptosis were studied over 14 days. In non-PBL animals TEM treatment inhibited tumor cell proliferation as well as vascularization and growth of the extrahepatic metastases. PBL did not influence tumor cell engraftment, vascularization and metastatic growth. Of interest, TEM treatment significantly reduced tumor cell engraftment, neovascularization and metastatic groth also after PBL. PBL does not counteract the inhibiting effect of TEM on extrahepatic colorectal metastatic growth.

Long-term intravital imaging of the multicolor-coded tumor microenvironment during combination immunotherapy

The combined-immunotherapy of adoptive cell therapy (ACT) and cyclophosphamide (CTX) is one of the most efficient treatments for melanoma patients. However, no synergistic effects of CTX and ACT on the spatio-temporal dynamics of immunocytes in vivo have been described. Here, we visualized key cell events in immunotherapy-elicited immunoreactions in a multicolor-coded tumor microenvironment, and then established an optimal strategy of metronomic combined-immunotherapy to enhance anti-tumor efficacy. Intravital imaging data indicated that regulatory T cells formed an 'immunosuppressive ring' around a solid tumor. The CTX-ACT combined-treatment elicited synergistic immunoreactions in tumor areas, which included relieving the immune suppression, triggering the transient activation of endogenous tumor-infiltrating immunocytes, increasing the accumulation of adoptive cytotoxic T lymphocytes, and accelerating the infiltration of dendritic cells. These insights into the spatio-temporal dynamics of immunocytes are beneficial for optimizing immunotherapy and provide new approaches for elucidating the mechanisms underlying the involvement of immunocytes in cancer immunotherapy.

DOI:http://dx.doi.org/10.7554/eLife.14756.001

Melanoma is a form of skin cancer that is particularly difficult to treat. A new approach that has shown a lot of promise in treating many different cancers, including melanoma, is called “immunotherapy”. This technique harnesses the immune system – the body’s natural defences that help to protect against infections and disease – to combat cancer.

One powerful type of immunotherapy involves injecting patients with cells called lymphocytes, which form part of the immune system. This is known as adoptive cell therapy and can activate the immune system to fight cancer, helping to shrink tumors. This treatment can be made even more powerful by combining it with a drug called cyclophosphamide and this combination, known as CTX-ACT, is currently one of the most efficient treatments for melanoma. Yet, little information is available to indicate why this treatment is so effective.

Using mice implanted with melanoma cells, Qi, Li et al. sought to understand how CTX-ACT treatment works, with the goal of optimising it to increase its success. The results showed that a protective barrier of immune cells that suppresses the anti-tumor immune response – called an “immunosuppressive ring” – surrounds untreated tumors. CTX-ACT treatment can breakdown these rings, helping to reactivate the anti-tumor immune reaction in the tumors. This allows both the injected and mouse’s own immune cells to move into the tumor and destroy cancer cells.

Qi, Li et al. used their findings to optimise treatment and succeeded in controlling tumor growth in the mice for several weeks. These new insights could be used to improve current immunotherapies, and offer new approaches for investigating the involvement of immune cells in the treatment of a wide range of different cancers.

DOI:http://dx.doi.org/10.7554/eLife.14756.002

Liver-specific knockout of arginase-1 leads to a profound phenotype similar to inducible whole body arginase-1 deficiency

Arginase-1 (Arg1) converts arginine to urea and ornithine in the distal step of the urea cycle in liver. We previously generated a tamoxifen-inducible Arg1 deficient mouse model (Arg1-Cre) that disrupts Arg1 expression throughout the whole body and leads to lethality ≈ 2 weeks after gene disruption. Here, we evaluate if liver-selective Arg1 loss is sufficient to recapitulate the phenotype observed in global Arg1 knockout mice, as well as to gauge the effectiveness of gene delivery or hepatocyte transplantation to rescue the phenotype. Liver-selective Arg1 deletion was induced by using an adeno-associated viral (AAV)-thyroxine binding globulin (TBG) promoter-Cre recombinase vector administered to Arg1 “floxed” mice; Arg1^fl/fl). An AAV vector expressing an Arg1-enhanced green fluorescent protein (Arg1-eGFP) transgene was used for gene delivery, while intrasplenic injection of wild-type (WT) C57BL/6 hepatocytes after partial hepatectomy was used for cell delivery to “rescue” tamoxifen-treated Arg1-Cre mice. The results indicate that liver-selective loss of Arg1 (> 90% deficient) leads to a phenotype resembling the whole body knockout of Arg1 with lethality ≈ 3 weeks after Cre-induced gene disruption. Delivery of Arg1-eGFP AAV rescues more than half of Arg1 global knockout male mice (survival > 4 months) but a significant proportion still succumb to the enzyme deficiency even though liver expression and enzyme activity of the fusion protein reach levels observed in WT animals. Significant Arg1 enzyme activity from engrafted WT hepatocytes into knockout livers can be achieved but not sufficient for rescuing the lethal phenotype. This raises a conundrum relating to liver-specific expression of Arg1. On the one hand, loss of expression in this organ appears to be both necessary and sufficient to explain the lethal phenotype of the genetic disorder in mice. On the other hand, gene and cell-directed therapies suggest that rescue of extra-hepatic Arg1 expression may also be necessary for disease correction. Further studies are needed in order to illuminate the detailed mechanisms for pathogenesis of Arg1-deficiency.

In Vivo Visualization of Tumor Antigen-containing Microparticles Generated in Fluorescent-protein-elicited Immunity

In vivo optical spatio-temporal imaging of the tumor microenvironment is useful to explain how tumor immunotherapies work. However, the lack of fluorescent antigens with strong immunogenicity makes it difficult to study the dynamics of how tumors are eliminated by any given immune response. Here, we develop an effective fluorescent model antigen based on the tetrameric far-red fluorescent protein KatushkaS158A (tfRFP), which elicits both humoral and cellular immunity. We use this fluorescent antigen to visualize the dynamic behavior of immunocytes as they attack and selectively eliminate tfRFP-expressing tumors in vivo; swarms of immunocytes rush toward tumors with high motility, clusters of immunocytes form quickly, and numerous antigen-antibody complexes in the form of tfRFP(+) microparticles are generated in the tumor areas and ingested by macrophages in the tumor microenvironment. Therefore, tfRFP, as both a model antigen and fluorescent reporter, is a useful tool to visualize specific immune responses in vivo.

EGFP reporter protein: its immunogenicity in Leishmania-infected BALB/c mice

Optical reporter genes such as green fluorescent protein (GFP) and luciferase are efficiently and widely used in monitoring and studying the protective/therapeutic potential of candidate agents in leishmaniasis. But several observations and controversial reports have generated a main concern, whether enhanced GFP (EGFP) affects immune response. To address this issue, we studied the immunogenicity of EGFP in vivo by two lines of stably transfected parasites (Leishmania major (EGFP) or L. major (EGFP-LUC)) in BALB/c model and/or as a recombinant protein (rEGFP) produced in vitro by bacteria in parallel. Disease progression was followed by footpad swelling measurements and parasite burden in draining lymph nodes using microtitration assay and real-time PCR, and immune responses were also evaluated in spleen. EGFP-expressing parasites generated larger swellings in comparison with wild-type (L. major) while mice immunized with rEGFP and challenged with wild-type parasite were quite comparable in footpad swelling with control group without significant difference. However, both conventional and molecular approaches revealed no significant difference in parasite load between different groups. More importantly, no significant inflammatory responses were detected in groups with higher swelling size measured by interferon-γ (IFN-γ), interleukin (IL)-10, IL-5, and nitric oxide against frozen and thawed lysate of parasite as stimulator. Altogether, these results clearly revealed that EGFP protein expressed in prokaryotic and eukaryotic hosts is not an immunological reactive molecule and acts as a neutral protein without any side effects in mice. So, EGFP expressing Leishmania could be a safe and reliable substitution for wild-types that simplifies in situ follow-up and eliminates the animal scarification wherever needed during the study.

mRNA-based vaccines synergize with radiation therapy to eradicate established tumors

BACKGROUND

The eradication of large, established tumors by active immunotherapy is a major challenge because of the numerous cancer evasion mechanisms that exist. This study aimed to establish a novel combination therapy consisting of messenger RNA (mRNA)-based cancer vaccines and radiation, which would facilitate the effective treatment of established tumors with aggressive growth kinetics.

METHODS

The combination of a tumor-specific mRNA-based vaccination with radiation was tested in two syngeneic tumor models, a highly immunogenic E.G7-OVA and a low immunogenic Lewis lung cancer (LLC). The molecular mechanism induced by the combination therapy was evaluated via gene expression arrays as well as flow cytometry analyses of tumor infiltrating cells.

RESULTS

In both tumor models we demonstrated that a combination of mRNA-based immunotherapy with radiation results in a strong synergistic anti-tumor effect. This was manifested as either complete tumor eradication or delay in tumor growth. Gene expression analysis of mouse tumors revealed a variety of substantial changes at the tumor site following radiation. Genes associated with antigen presentation, infiltration of immune cells, adhesion, and activation of the innate immune system were upregulated. A combination of radiation and immunotherapy induced significant downregulation of tumor associated factors and upregulation of tumor suppressors. Moreover, combination therapy significantly increased CD4+, CD8+ and NKT cell infiltration of mouse tumors.

CONCLUSION

Our data provide a scientific rationale for combining immunotherapy with radiation and provide a basis for the development of more potent anti-cancer therapies.

Large T Antigen-Specific Cytotoxic T Cells Protect Against Dendritic Cell Tumors through Perforin-Mediated Mechanisms Independent of CD4 T Cell Help

Our newly generated murine tumor dendritic cell (MuTuDC) lines, generated from tumors developing in transgenic mice expressing the simian virus 40 large T antigen (SV40LgT) and GFP under the DC specific promoter CD11c, reproduce the phenotypic and functional properties of splenic wild type CD8α⁺ conventional DCs. They have an immature phenotype with low co-stimulation molecule expression (CD40, CD70, CD80, and CD86) that is upregulated after activation with toll-like receptor ligands. We observed that after transfer into syngeneic C57BL/6 mice, MuTuDC lines were quickly rejected. Tumors grew efficiently in large T transgene-tolerant mice. To investigate the immune response toward the large T antigen that leads to rejection of the MuTuDC lines, they were genetically engineered by lentiviral transduction to express luciferase and tested for the induction of DC tumors after adoptive transfer in various gene deficient recipient mice. Here, we document that the MuTuDC line was rejected in C57BL/6 mice by a CD4 T cell help-independent, perforin-mediated CD8 T cell response to the SV40LgT without pre-activation or co-injection of adjuvants. Using depleting anti-CD8β antibodies, we were able to induce efficient tumor growth in C57BL/6 mice. These results are important for researchers who want to use the MuTuDC lines for in vivo studies.

Options for tracking GFP-Labeled transplanted myoblasts using in vivo fluorescence imaging: implications for tracking stem cell fate

BACKGROUND

Green fluorescent protein (GFP) is a useful biomarker, widely used in biomedical research to track stem cells after transplantation and/or to assess therapeutic transgene expression. However, both GFP and therapeutic gene products themselves may be immunogenic to the recipient. The main aim of this study was to use animal models to evaluate potential impact of GFP on the cell engraftment and to optimize tracking strategies prior to transplantation.

RESULTS

By using a fluorescent imaging (FLI) system, we investigated the dynamic cell behavior of GFP-transduced myoblasts in tibialis anterior (TA) muscles of immunocompetent mdx mice and immuno-compromised nude mice over a period of three months. The results suggested an apparent underlying host immunorejection in the mdx mice. Dystrophin immunostaining showed that the engraftment of wild type myoblasts was much more effective than that of the GFP-labeled counterparts in the mdx mice, further confirming an antigen role of GFP in this process. We tracked the GFP-transduced myoblasts in C57BL/6 mice and found GFP to be minimally immunogenic in these animals, as indicated by the GFP signal maintaining a much stronger level than that found in mdx and BALB/c mice at parallel time points. We also compared the in vivo cell behavior differences between myoblasts from virally GFP-transduced and GFP transgenic mice. The latter displayed much better engraftment, as determined both biomaging and histological observations.

CONCLUSIONS

Our results not only demonstrated the immunogenicity of GFP in immunocompetent mice, but determined the optimized conditions for GFP-based in vivo stem cells tracking, that can potentially be extrapolated to human biomedical research.

Human papillomavirus (HPV) type 16 E7 protein bodies cause tumour regression in mice

BACKGROUND

Human papillomaviruses (HPV) are the causative agents of cervical cancer in women, which results in over 250 000 deaths per year. Presently there are two prophylactic vaccines on the market, protecting against the two most common high-risk HPV types 16 and 18. These vaccines remain very expensive and are not generally affordable in developing countries where they are needed most. Additionally, there remains a need to treat women that are already infected with HPV, and who have high-grade lesions or cervical cancer.

METHODS

In this paper, we characterize the immunogenicity of a therapeutic vaccine that targets the E7 protein of the most prevalent high-risk HPV - type 16 - the gene which has previously been shown to be effective in DNA vaccine trials in mice. The synthetic shuffled HPV-16 E7 (16E7SH) has lost its transforming properties but retains all naturally-occurring CTL epitopes. This was genetically fused to Zera®, a self-assembly domain of the maize γ-zein able to induce the accumulation of recombinant proteins into protein bodies (PBs), within the endoplasmic reticulum in a number of expression systems.

RESULTS

High-level expression of the HPV 16E7SH protein fused to Zera® in plants was achieved, and the protein bodies could be easily and cost-effectively purified. Immune responses comparable to the 16E7SH DNA vaccine were demonstrated in the murine model, with the protein vaccine successfully inducing a specific humoral as well as cell mediated immune response, and mediating tumour regression.

CONCLUSIONS

The fusion of 16E7SH to the Zera® peptide was found to enhance the immune responses, presumably by means of a more efficient antigen presentation via the protein bodies. Interestingly, simply mixing the free PBs and 16E7SH also enhanced immune responses, indicating an adjuvant activity for the Zera® PBs.

Differentiated neuroprogenitor cells incubated with human or canine adenovirus, or lentiviral vectors have distinct transcriptome profiles

Several studies have demonstrated the potential for vector-mediated gene transfer to the brain. Helper-dependent (HD) human (HAd) and canine (CAV-2) adenovirus, and VSV-G-pseudotyped self-inactivating HIV-1 vectors (LV) effectively transduce human brain cells and their toxicity has been partly analysed. However, their effect on the brain homeostasis is far from fully defined, especially because of the complexity of the central nervous system (CNS). With the goal of dissecting the toxicogenomic signatures of the three vectors for human neurons, we transduced a bona fide human neuronal system with HD-HAd, HD-CAV-2 and LV. We analysed the transcriptional response of more than 47,000 transcripts using gene chips. Chip data showed that HD-CAV-2 and LV vectors activated the innate arm of the immune response, including Toll-like receptors and hyaluronan circuits. LV vector also induced an IFN response. Moreover, HD-CAV-2 and LV vectors affected DNA damage pathways--but in opposite directions--suggesting a differential response of the p53 and ATM pathways to the vector genomes. As a general response to the vectors, human neurons activated pro-survival genes and neuron morphogenesis, presumably with the goal of re-establishing homeostasis. These data are complementary to in vivo studies on brain vector toxicity and allow a better understanding of the impact of viral vectors on human neurons, and mechanistic approaches to improve the therapeutic impact of brain-directed gene transfer.

Enhanced green fluorescent protein transgenic expression in vivo is not biologically inert

Enhanced green fluorescent protein (EGFP) is a widely used biological reporter. However, the effects of EGFP expression in vivo are still unclear. To investigate the effects of EGFP transgenic expression in vivo, we employed an NMR-based metabonomics method to analyze the metabonome of EGFP transgenic mice. The results show that the metabonomes of urine, liver, and kidney of the EGFP transgenic mice are different from their wild-type counterparts. The EGFP mice expressed high levels of urinary 3-ureidopropionate, which is due to the down-regulated transcriptional level of β-ureidopropionase. The expression of EGFP in vivo also affects other metabolic pathways, including nucleic acid metabolism, energy utilization, and amino acids catabolism. These findings indicate that EGFP transgenic expression is not as inert as has been considered. Our investigation provides a holistic view on the effect of EGFP expression in vivo, which is useful when EGFP is employed as a functional biological indicator. Our work also highlights the potential of a metabonomics strategy in studying the association between molecular phenotypes and gene function.

Systemic and local infection routes govern different cellular dissemination pathways during gammaherpesvirus infection in vivo

Human gammaherpesviruses cause morbidity and mortality associated with infection and transformation of lymphoid and endothelial cells. Knowledge of cell types involved in virus dissemination from primary virus entry to virus latency is fundamental for the understanding of gammaherpesvirus pathogenesis. However, the inability to directly trace cell types with respect to virus dissemination pathways has prevented definitive conclusions regarding the relative contribution of individual cell types. Here, we describe that the route of infection affects gammaherpesvirus dissemination pathways. We constructed a recombinant murine gammaherpesvirus 68 (MHV-68) variant harboring a cassette which switches fluorescent markers in a Cre-dependent manner. Since the recombinant virus which was constructed on the wild-type background was attenuated, in this study we used an M1-deleted version, which infected mice with normal kinetics. Infection of Cre-transgenic mice with this convertible virus was used to estimate the quantitative contribution of defined cell types to virus productivity and dissemination during the acute phase of MHV-68 infection. In systemic infection, we found splenic vascular endothelial cells (EC) among the first and main cells to produce virus. After local infection, the contribution of EC to splenic virus production did not represent such early kinetics. However, at later time points, B cell-derived viruses dominated splenic productivity independently of systemic or local infection. Systemic versus local infection also governed the cell types involved in loading peritoneal exudate cells, leading to latency in F4/80- and CD11b-positive target cells. Systemic infection supported EC-driven dissemination, whereas local infection supported B cell-driven dissemination.

Nonmyeloablative conditioning regimen to increase engraftment of gene-modified hematopoietic stem cells in young rhesus monkeys

Immune responses to transgene products may lead to rejection of transduced cells, limiting successful gene therapy for genetic diseases. While moderate dosages of chemotherapeutic agents such as busulfan may increase hematopoietic stem cells (HSC) engraftment, they are not immune suppressive and do not abrogate immune responses to transgene products. Studies focused on nonmyeloablative conditioning with busulfan ± fludarabine in a clinically relevant monkey model to induce immune suppression to allow cells expressing a foreign transgene product to persist. Bone marrow CD34(+) HSC were transduced in two equal fractions using simian immunodeficiency virus (SIV)-based lentiviral vectors carrying a nonexpressed DNA sequence tag (NoN) and the green fluorescent protein (GFP) reporter gene. Post-transplant there was no evidence of elimination of cells containing the potentially immunogenic GFP gene; several recipients had stable persistence of cells, and no differences were detected with fludarabine, which was rapidly cleared. Antibodies and cellular immune responses to GFP developed in recipients with the highest levels of GFP-marked cells, although these cells were not eliminated. These studies establish a clinically relevant pediatric primate model to assess the effects of conditioning regimens on the engraftment of transduced HSC and the immune responses to cells expressing a foreign gene product.

Early protective effect of bone marrow mononuclear cells against ischemic white matter damage through augmentation of cerebral blood flow

BACKGROUND AND PURPOSE

To investigate the efficacy of bone marrow mononuclear cell (BMMNC) treatment against ischemic white matter (WM) damage in a hypoperfused brain.

METHODS

Mice were administered intravenous treatment of vehicle, spleen-derived marrow mononuclear cells (MNCs), or BMMNCs (5 × 10⁶ cells) obtained from enhanced green fluorescent protein transgenic mice 24 hours after bilateral common carotid artery stenosis (BCAS), and then euthanized at either 1 day or 30 days after treatment.

RESULTS

Laser speckle perfusion imaging analyses revealed marked recovery of cerebral blood flow (CBF) in the early phase after BMMNC treatment (6 hours after administration), before histological evidence of angiogenesis was assessed by fluorescein-isothiocyanate-dextran perfusion assay. BMMNC treatment induced an increase in vascular endothelial growth factor and Ser1177 phosphorylated endothelial nitric oxide synthase levels in the BCAS-induced mouse brains at 1 day after the treatment. BCAS-induced ischemic WM lesions were significantly improved 30 days after BMMNC treatment despite any evidence of direct structural incorporation of donor BMMNCs into endothelial cells and oligodendrocytes. Instead, enhanced green fluorescent protein-positive donor cells with morphological features of pericytes were observed in the vessel walls. Post-BMMNC administration of an NOS inhibitor abolished early CBF recovery and produced protective effects against ischemic WM damage.

CONCLUSIONS

BMMNC treatment provides marked protection against ischemic WM damage, enhancing CBF in the early phase and in subsequent angiogenesis, both of which involve nitric oxide synthase activation. These findings suggest promise for the application of BMMNCs for subcortical ischemic vascular dementia.

A novel Cre recombinase imaging system for tracking lymphotropic virus infection in vivo

Background

Detection, isolation, and identification of individual virus infected cells during long term infection are critical to advance our understanding of mechanisms of pathogenesis for latent/persistent viruses. However, current approaches to study these viruses in vivo have been hampered by low sensitivity and effects of cell-type on expression of viral encoded reporter genes. We have designed a novel Cre recombinase (Cre)-based murine system to overcome these problems, and thereby enable tracking and isolation of individual in vivo infected cells.

Methodology/Principal findings

Murine gammaherpesvirus 68 (MHV-68) was used as a prototypic persistent model virus. A Cre expressing recombinant virus was constructed and characterised. The virus is attenuated both in lytic virus replication, producing ten-fold lower lung virus titres than wild type virus, and in the establishment of latency. However, despite this limitation, when the sEGFP7 mouse line containing a Cre-activated enhanced green fluorescent protein (EGFP) was infected with the Cre expressing virus, sites of latent and persistent virus infection could be identified within B cells and macrophages of the lymphoid system on the basis of EGFP expression. Importantly, the use of the sEGFP7 mouse line which expresses high levels of EGFP allowed individual virus positive cells to be purified by FACSorting. Virus gene expression could be detected in these cells. Low numbers of EGFP positive cells could also be detected in the bone marrow.

Conclusions/Significance

The use of this novel Cre-based virus/mouse system allowed identification of individual latently infected cells in vivo and may be useful for the study and long-term monitoring of other latent/persistent virus infections.

Adeno-associated virus capsid structure drives CD4-dependent CD8+ T cell response to vector encoded proteins

The immunological sequelae of adeno-associated virus (AAV)-mediated gene transfer in vivo is quite complex. In murine models, most AAV capsids are associated with minimal or dysfunctional T cell responses to antigenic transgene products. In this study we compared T cell activation against AAV2/8 and AAV2/rh32.33 vectors expressing nuclear-targeted LacZ (nLacZ), GFP, or firefly luciferase in murine skeletal muscle. We show that, unlike AAV8, AAVrh32.33 yields qualitatively and quantitatively robust T cell responses to both the capsid and transgene product. AAV2/rh32.33.CB.nLacZ, but not AAV2/8, drives a high degree of cellular infiltration and a loss of detectable transgene expression in C57BL/6 mice. However, cellular immunity to AAVrh32.33 is ablated in the absence of CD4, CD40L, or CD28, permitting stable beta-galactosidase expression. Treatment of CD40L(-/-) mice with the CD40 agonist, FGK45, failed to restore the CD8 response to AAV2/rh32.33.nLacZ, suggesting that additional factors are involved. Our results suggest that specific domains within the AAVrh32.33 capsid augment the adaptive response to both capsid and transgene Ags in a CD4-dependent pathway involving CD40L signaling and CD28 costimulation. Structural comparison of the AAV8 and rh32.33 capsids has identified key differences that may drive differential immunity by affecting tropism, Ag presentation or the activation of innate immunity. This murine model of AAV-mediated cytotoxicity allows us to delineate the mechanism of viral immune activation, which is relevant to the translation of AAV technology in higher order species.

Gender-dependent survival of allogeneic trophoblast stem cells in liver

In view of the well-known phenomenon of trophoblast immune privilege, trophoblast stem cells (TSCs) might be expected to be immune privileged, which could be of interest for cell or gene therapies. Yet in the ectopic sites tested so far, TSC transplants fail to show noticeable immune privilege and seem to lack physiological support. However, we show here that after portal venous injection, green fluorescent protein (GFP)-labeled TSCs survive for several months in the livers of allogeneic female but not male mice. Gonadectomy experiments revealed that this survival does not require the presence of ovarian hormones but does require the absence of testicular factors. By contrast, GFP-labeled allogeneic embryonic stem cells (ESCs) are reliably rejected; however, these same ESCs survive when mixed with unlabeled TSCs. The protective effect does not require immunological compatibility between ESCs and TSCs. Tumors were not observed in animals with either successfully engrafted TSCs or coinjected ESCs. We conclude that in a suitable hormonal context and location, ectopic TSCs can exhibit and confer immune privilege. These findings suggest applications in cell and gene therapy as well as a new model for studying trophoblast immunology and physiology.

ICP0 inhibits the decrease of HSV amplicon-mediated transgene expression

The herpes simplex virus (HSV) amplicon vector produces an initial host response that limits transgene expression. In this study, we hypothesized that restoration of the HSV gene infected cell protein (ICP0) into the amplicon could circumvent this host response and thus overcome silencing of encoded transgenes. To test this, we constructed an amplicon vector that encodes the ICP0 under control of its native promoter (ICP0+ amplicon). Expression of ICP0 was transient and, at a multiplicity of infection (MOI) of 1, did not significantly alter interferon (IFN)-based responses against the vector or cell kinetics/apoptosis of infected cells. Chromatin immunoprecipitation (ChIP) PCR analysis revealed that conventional amplicon DNA became associated with histone deacetylase 1 (HDAC1) immediately after infection, whereas ICP0+ amplicon DNA remained relatively unbound by HDAC1 for at least 72 hours after infection. Mice administered systemic ICP0+ amplicon exhibited significantly greater and more sustained transgene expression in their livers than did those receiving conventional amplicon, likely due to increased transcriptional or post-transcriptional activity rather than increased copy numbers of vector DNA. These findings indicate that restoration of ICP0 expression may be employed within HSV amplicon constructs to decrease transgene silencing in vitro and in vivo.

The major virus-producing cell type during murine cytomegalovirus infection, the hepatocyte, is not the source of virus dissemination in the host

The course of systemic viral infections is determined by the virus productivity of infected cell types and the efficiency of virus dissemination throughout the host. Here, we used a cell-type-specific virus labeling system to quantitatively track virus progeny during murine cytomegalovirus infection. We infected mice that expressed Cre recombinase selectively in vascular endothelial cells or hepatocytes with a murine cytomegalovirus for which Cre-mediated recombination would generate a fluorescently labeled virus. We showed that endothelial cells and hepatocytes produced virus after direct infection. However, in the liver, the main contributor to viral load in the mouse, most viruses were produced by directly infected hepatocytes. Remarkably, although virus produced in hepatocytes spread to hepatic endothelial cells (and vice versa), there was no significant spread from the liver to other organs. Thus, the cell type producing the most viruses was not necessarily the one responsible for virus dissemination within the host.

Resistance of mature T cells to oncogene transformation

Leukemia caused by retroviral insertional mutagenesis after stem cell gene transfer has been reported in several experimental animals and in patients treated for X-linked severe combined immunodeficiency. Here, we analyzed whether gene transfer into mature T cells bears the same genotoxic risk. To address this issue in an experimental "worst case scenario," we transduced mature T cells and hematopoietic progenitor cells from C57BL/6 (Ly5.1) donor mice with high copy numbers of gamma retroviral vectors encoding the potent T-cell oncogenes LMO2, TCL1, or DeltaTrkA, a constitutively active mutant of TrkA. After transplantation into RAG-1-deficient recipients (Ly5.2), animals that received stem cell transplants developed T-cell lymphoma/leukemia for all investigated oncogenes with a characteristic phenotype and after characteristic latency periods. Ligation-mediated polymerase chain reaction analysis revealed monoclonality or oligoclonality of the malignancies. In striking contrast, none of the mice that received T-cell transplants transduced with the same vectors developed leukemia/lymphoma despite persistence of gene-modified cells. Thus, our data provide direct evidence that mature T cells are less prone to transformation than hematopoietic progenitor cells.