Maria T. Arévalo

The VE-cadherin binding domain of fibrinogen induces endothelial barrier permeability and enhances transendothelial migration of malignant breast epithelial cells.

Fibrin deposition and exudation of plasma fibrinogen (Fg) have long been recognized as hallmarks of inflammation, cardiovascular disease and neoplasia. The Fg‐β15–42 domain binds to the endothelial cell adhesion molecule, VE‐cadherin, promoting endothelial cell proliferation, angiogenesis and leukocyte diapedesis. Furthermore, spontaneous blood‐borne and lymphatic metastasis of some types of tumor emboli requires plasma fibrin(ogen); however, the molecular mechanisms by which this occurs are poorly understood. We sought to determine whether Fg‐β15–42 and VE‐cadherin binding interactions promote endothelial barrier permeability and breast cancer cell transendothelial migration (TEM) using transwell insert culture systems. Synthetic peptides containing/missing residues β15–17 critical for Fg‐β15–42 binding to VE‐cadherin, and antibodies that bind to Fg‐β15–21 (T2G1) and VE‐cadherin (BV9) were used to induce or inhibit Fg‐mediated permeability and TEM. Fg induced dose‐dependent permeability of human umbilical vein and microvascular endothelial but not epithelial cell barriers. Maximal Fg‐induced endothelial permeability required Fg‐β15–42 and VE‐cadherin‐binding interactions involving Fg‐β15–17. Fg‐induced TEM of malignant MDA‐MB‐231 and MCF‐7 breast cancer cells also required Fg‐β15–42 and VE‐cadherin binding; however, such TEM was independent of E‐cadherin or estrogen receptor expression. In contrast, Fg did not induce TEM of nonmalignant MCF‐10A breast epithelial cells. Fg‐induced endothelial permeability was retained in the presence of MDA‐MB‐231 but inhibited in the presence of MCF‐10A cells. It is intriguing to speculate that loss of Fg‐β15–42 binding by premalignant breast epithelial cells serves as a molecular switch to induce a highly aggressive, metastatic breast cancer phenotype. Hence, Fg‐β15–42 represents a potential molecular target for therapeutic intervention of breast cancer metastasis.

Primary human endothelial cells support direct but not antibody-dependent enhancement of dengue viral infection

Microvascular plasma leakage is the hallmark of dengue hemorrhagic fever and dengue shock syndrome. The precise molecular mechanisms leading to microvascular leakage are yet to be determined, but dengue virus (DENV) infection and consequent endothelial cell death has been suggested as its major cause. However, the extent of endothelial cell permissiveness to DENV infection and the magnitude of cell death following DENV infection are controversial. To clarify this issue, we analyzed the kinetics and consequences of DENV infection of human umbilical vein endothelial cells (HUVEC) using a novel molecularly cloned DENV2‐16681 virus. Viral replication was detected as early as 24 hr post‐infection by RT‐PCR and plaque assays. However, merely 2% of HUVEC were DENV antigen‐positive even after 96 hr of infection as measured by the FACS indirect immunofluorescence assays. Unlike monocytes/macrophages, HUVEC did not support antibody dependent enhancement of dengue viral infection due to a lack of FcγRI and FcγRII. Furthermore, DENV infection did not increase HUVEC apoptosis as compared to mock‐infected cells. Because in vitro only a small percentage of endothelial cells were productively infected in vitro with no significant apoptosis occurring in either infected or bystander cells, it would be important to re‐examine whether direct dengue viral infection of endothelium is the major cause of the extensive vascular leakage observed in patients with dengue hemorrhagic fever and dengue shock syndrome. J. Med. Virol. 81:519–528, 2009.

Mucosal vaccination with a multicomponent adenovirus-vectored vaccine protects against Streptococcus pneumoniae infection in the lung

Streptococcus pneumoniae is a major bacterial respiratory pathogen. Current licensed pneumococcal polysaccharide and polysaccharide-protein conjugate vaccines are administered by an intramuscular injection. In order to develop a new-generation vaccine that can be administered in a needle-free mucosal manner, we have constructed early 1 and 3 gene regions (E1/E3) deleted, replication-defective adenoviral vectors encoding pneumococcal surface antigen A (PsaA), the N-fragment of pneumococcal surface protein A (N-PspA), and the detoxified mutant pneumolysin (PdB) from S. pneumoniae strain D39. Intranasal vaccination with the three adenoviral vectors (Ad/PsaA, Ad/N-PspA, and Ad/PdB) in mice resulted in robust antigen-specific serum immunoglobulin G responses, as demonstrated by an enzyme-linked immunosorbent assay. In addition, nasal mucosal vaccination with the combination of the three adenoviral vectors conferred protection against S. pneumoniae strain D39 colonization in mouse lungs. Taken together, these data demonstrate the feasibility of developing a mucosal vaccine against S. pneumoniae using recombinant adenoviruses for antigen delivery.

Engineering influenza viral vectors

The influenza virus is a respiratory pathogen with a negative-sense, segmented RNA genome. Construction of recombinant influenza viruses in the laboratory was reported starting in the 1980s. Within a short period of time, pioneer researchers had devised methods that made it possible to construct influenza viral vectors from cDNA plasmid systems. Herein, we discuss the evolution of influenza virus reverse genetics, from helper virus-dependent systems, to helper virus-independent 17-plasmid systems, and all the way to 3- and 1- plasmid systems. Successes in the modification of different gene segments for various applications, including vaccine and gene therapies are highlighted.

A new complementing cell line for replication-incompetent E1–deleted adenovirus propagation

Recombinant adenoviruses (Ad) are being explored as promising delivery systems for gene therapy and vaccination. However, there is a concern about the possibility of generating replication-competent adenoviruses (RCA) using the human embryonic kidney 293 cell line. We have constructed a new cell line named the UR cell line which can be used to produce Ad vectors free of RCA. This cell line is based on the human embryonic lung HEL 299 cell. We first constructed a shuttle plasmid which encodes the E1A/E1B sequence that is necessary for adenovirus replication. The shuttle plasmid was then transfected into HEL 299 cells. The presence of the E1A/E1B sequence and protein expression in the stably transformed UR cells was confirmed. Viruses produced in UR cells were still RCA-free after ten test passages, while adenovirus produced in 293 cells had generated RCA during the fourth passage. We conclude that the UR cell line is sufficiently stable, can effectively produce a virus yield comparable with 293 cells, and does not generate RCA formation during Ad propagation.

Protective immunity against tularemia provided by an adenovirus-vectored vaccine expressing Tul4 of Francisella tularensis.

ABSTRACT Francisella tularensis, a category A bioterrorism agent, is a highly infectious organism that is passed on via skin contact and inhalation routes. A live attenuated vaccine strain (LVS) has been developed, but it has not been licensed for public use by the FDA due to safety concerns. Thus, there exists a need for a safer and improved vaccine. In this study, we have constructed a replication-incompetent adenovirus, Ad/opt-Tul4, carrying a codon-optimized gene for expression of a membrane protein, Tul4, of F. tularensis LVS. Its ability to protect against lethal challenge and its immunogenicity were evaluated in a murine model. An intramuscular injection of a single dose (1 × 107 PFU) of Ad/opt-Tul4 elicited a robust Tul4-specific antibody response. Assays suggest a Th1-driven response. A single dose elicited 20% protection against challenge with 100 × 50% lethal dose (LD50) F. tularensis LVS; two additional booster shots resulted in 60% protection. In comparison, three doses of 5 μg recombinant Tul4 protein did not elicit significant protection against challenge. Therefore, the Ad/opt-Tul4 vaccine was more effective than the protein vaccine, and protection was dose dependent. Compared to LVS, the protection rate is lower, but an adenovirus-vectored vaccine may be more attractive due to its enhanced safety profile and mucosal route of delivery. Furthermore, simple genetic modification of the vaccine may potentially produce antibodies protective against a fully virulent strain of F. tularensis. Our data support the development and further research of an adenovirus-vectored vaccine against Tul4 of F. tularensis LVS.

Targeted Silencing of Anthrax Toxin Receptors Protects against Anthrax Toxins

Background: Existing anthrax postexposure antibiotic treatments are inadequate because they do not clear the high levels of secreted anthrax toxins. Results: Susceptible cells treated with anthrax toxin receptor-targeted siRNAs became resistant to anthrax toxin-mediated cytotoxicity. Conclusion: RNAi-targeted silencing of anthrax toxin receptors prevents toxins from entering target cells and inducing pathogenesis. Significance: Toxin receptor-targeted RNAi can be developed as a postexposure treatment against anthrax. Anthrax spores can be aerosolized and dispersed as a bioweapon. Current postexposure treatments are inadequate at later stages of infection, when high levels of anthrax toxins are present. Anthrax toxins enter cells via two identified anthrax toxin receptors: tumor endothelial marker 8 (TEM8) and capillary morphogenesis protein 2 (CMG2). We hypothesized that host cells would be protected from anthrax toxins if anthrax toxin receptor expression was effectively silenced using RNA interference (RNAi) technology. Thus, anthrax toxin receptors in mouse and human macrophages were silenced using targeted siRNAs or blocked with specific antibody prior to challenge with anthrax lethal toxin. Viability assays were used to assess protection in macrophages treated with specific siRNA or antibody as compared with untreated cells. Silencing CMG2 using targeted siRNAs provided almost complete protection against anthrax lethal toxin-induced cytotoxicity and death in murine and human macrophages. The same results were obtained by prebinding cells with specific antibody prior to treatment with anthrax lethal toxin. In addition, TEM8-targeted siRNAs also offered significant protection against lethal toxin in human macrophage-like cells. Furthermore, silencing CMG2, TEM8, or both receptors in combination was also protective against MEK2 cleavage by lethal toxin or adenylyl cyclase activity by edema toxin in human kidney cells. Thus, anthrax toxin receptor-targeted RNAi has the potential to be developed as a life-saving, postexposure therapy against anthrax.

Intranasal immunization with influenza antigens conjugated with cholera toxin subunit B stimulates broad spectrum immunity against influenza viruses

Frequent mutation of influenza viruses keep vaccinated and non-vaccinated populations vulnerable to new infections, causing serious burdens to public health and the economy. Vaccination with universal influenza vaccines would be the best way to effectively protect people from infection caused by mismatched or unforeseen influenza viruses. Presently, there is no FDA approved universal influenza vaccine. In this study, we expressed and purified a fusion protein comprising of influenza matrix 2 protein ectodomain peptides, a centralized influenza hemagglutinin stem region, and cholera toxin subunit B. Vaccination of BALB/c mice with this novel artificial antigen resulted in potent humoral immune responses, including induction of specific IgA and IgG, and broad protection against infection by multiple influenza viruses. Furthermore, our results demonstrated that when used as a mucosal antigen, cholera toxin subunit B improved antigen-stimulated T cell and memory B cell responses.

A dual purpose universal influenza vaccine candidate confers protective immunity against anthrax

Preventive influenza vaccines must be reformulated annually because of antigen shift and drift of circulating influenza viral strains. However, seasonal vaccines do not always match the circulating strains, and there is the ever‐present threat that avian influenza viruses may adapt to humans. Hence, a universal influenza vaccine is needed to provide protective immunity against a broad range of influenza viruses. We designed an influenza antigen consisting of three tandem M2e repeats plus HA2, in combination with a detoxified anthrax oedema toxin delivery system (EFn plus PA) to enhance immune responses. The EFn‐3×M2e‐HA2 plus PA vaccine formulation elicited robust, antigen‐specific, IgG responses; and was protective against heterologous influenza viral challenge when intranasally delivered to mice three times. Moreover, use of the detoxified anthrax toxin system as an adjuvant had the additional benefit of generating protective immunity against anthrax. Hence, this novel vaccine strategy could potentially address two major emerging public health and biodefence threats.

Addition of poly (propylene glycol) to multiblock copolymer to optimize siRNA delivery.

Previous studies have examined different strategies for siRNA delivery with varying degrees of success. These include use of viral vectors, cationic liposomes, and polymers. Several copolymers were designed and synthesized based on blocks of poly(ethylene glycol) PEG, poly(propylene glycol) PPG, and poly(l-lysine). These were designated as P1, P2, and P3. We studied the copolymer self-assembly, siRNA binding, particle size, surface potential, architecture of the complexes, and siRNA delivery. Silencing of GFP using copolymer P3 to deliver GFP-specific siRNA to Neuro-2a cells expressing GFP was almost as effective as using Lipofectamine 2000, with minimal cytotoxicity. Thus, we have provided a new copolymer platform for siRNA delivery that we can continue to modify for improved delivery of siRNA in vitro and eventually in vivo.