Preliminary validation of varicella zoster virus thymidine kinase as a novel reporter gene for PET

PET reporter systems for the brain

Positron emission tomography (PET) can be used as a noninvasive method to longitudinally monitor and quantify the expression of proteins in the brain in vivo. It can be used to monitor changes in biomarkers of mental health disorders, and to assess therapeutic interventions such as stem cell and molecular genetic therapies. The utility of PET monitoring depends on the availability of a radiotracer with good central nervous system (CNS) penetration and high selectivity for the target protein. This review evaluates existing methods for the visualization of reporter proteins and/or protein function using PET imaging, focusing on engineered systems, and discusses possible approaches for future success in the development of high-sensitivity and high-specificity PET reporter systems for the brain.

Alpha-Herpesvirus Thymidine Kinase Genes Mediate Viral Virulence and Are Potential Therapeutic Targets

Alpha-herpesvirus thymidine kinase (TK) genes are virulence-related genes and are nonessential for viral replication; they are often preferred target genes for the construction of gene-deleted attenuated vaccines and genetically engineered vectors for inserting and expressing foreign genes. The enzymes encoded by TK genes are key kinases in the nucleoside salvage pathway and have significant substrate diversity, especially the herpes simplex virus 1 (HSV-1) TK enzyme, which phosphorylates four nucleosides and various nucleoside analogues. Hence, the HSV-1 TK gene is exploited for the treatment of viral infections, as a suicide gene in antitumor therapy, and even for the regulation of stem cell transplantation and treatment of parasitic infection. This review introduces the effects of α-herpesvirus TK genes on viral virulence and infection in the host and classifies and summarizes the current main application domains and potential uses of these genes. In particular, mechanisms of action, clinical limitations, and antiviral and antitumor therapy development strategies are discussed.

Biosafety and bioefficacy assessment of human mesenchymal stem cells: what do we know so far?

An outstanding amount of resources has been used in research on manipulation of human stem cells, especially mesenchymal stem cells (MSCs), for various clinical applications. However, human MSCs have not been fully utilized in clinical applications due to restrictions with regard to their certain biosafety and bioefficacy concerns, for example, genetic abnormality, tumor formation, induction of host immune response and failure of homing and engraftment. This review summarizes the biosafety and bioefficacy assessment of human MSCs in terms of genetic stability, tumorigenicity, immunogenicity, homing and engraftment. The strategies used to reduce the biosafety concerns and improve the bioefficacy of human MSCs are highlighted. In addition, the approaches that can be implemented to improve their biosafety and bioefficacy assessment are briefly discussed.

Stem Cells Application in Thoracic Surgery: Current Perspective and Future Directions

Two main fields of clinical applications of stem cells in thoracic surgery have been explored: (a) regenerative medicine, that is a branch of translational research in tissue engineering and molecular biology dealing with the replacement, engineering or regeneration of cells, tissues and organs to restore normal function; (b) drug loading and delivery, that is an emerging field proposing stem cells as vectors to deliver anti-cancer agents for targeted therapies.Bronchopleural fistula is a pathological connection between the bronchus and the pleural cavity that may develop after lung resection, thus causing pleural empyema due to colonization by resident airway bacteria; stem cells and regenerative medicine approach can effectively contribute to impaired bronchial healing, thus preventive a septic and ventilator catastrophe.In the field of thoracic oncology, MSC are probably one of the best choice for anticancer drug delivery, emerging as potential experimental approach to malignant mesothelioma treatment.The goal of this review is to focus on clinical applications of stem cell technologies in thoracic surgery, emphasizing regenerative medicine aspects as well as drug loading and delivery in thoracic oncology.

Applications of in vivo imaging in the evaluation of the pathophysiology of viral and bacterial infections and in development of countermeasures to BSL3/4 pathogens

While preclinical and clinical imaging have been applied to drug discovery/development and characterization of disease pathology, few examples exist where imaging has been used to evaluate infectious agents or countermeasures to biosafety level (BSL)3/4 threat agents. Viruses engineered with reporter constructs, i.e., enzymes and receptors, which are amenable to detection by positron emission tomography (PET), single photon emission tomography (SPECT), or magnetic resonance imaging (MRI) have been used to evaluate the biodistribution of viruses containing specific therapeutic or gene transfer payloads. Bioluminescence and nuclear approaches involving engineered reporters, direct labeling of bacteria with radiotracers, or tracking bacteria through their constitutively expressed thymidine kinase have been utilized to characterize viral and bacterial pathogens post-infection. Most PET, SPECT, CT, or MRI approaches have focused on evaluating host responses to the pathogens such as inflammation, brain neurochemistry, and structural changes and on assessing the biodistribution of radiolabeled drugs. Imaging has the potential when applied preclinically to the development of countermeasures against BSL3/4 threat agents to address the following: (1) presence, biodistribution, and time course of infection in the presence or absence of drug; (2) binding of the therapeutic to the target; and (3) expression of a pharmacologic effect either related to drug mechanism, efficacy, or safety. Preclinical imaging could potentially provide real-time dynamic tools to characterize the pathogen and animal model and for developing countermeasures under the U.S. FDA Animal Rule provision with high confidence of success and clinical benefit.

Current Perspectives in Mesenchymal Stromal Cell Therapies for Airway Tissue Defects

Lung cancer is the leading cause of cancer death and respiratory diseases are the third cause of death in industrialized countries; for this reason the airways and cardiopulmonary system have been the focus of extensive investigation, in particular of the new emerging branch of regenerative medicine. Mesenchymal stromal cells (MSCs) are a population of undifferentiated multipotent adult cells that naturally reside within the human body, which can differentiate into osteogenic, chondrogenic, and adipogenic lineages when cultured in specific inducing media. MSCs have the ability to migrate and engraft at sites of inflammation and injury in response to cytokines, chemokines, and growth factors at a wound site and they can exert local reparative effects through transdifferentiation and differentiation into specific cell types or via the paracrine secretion of soluble factors with anti-inflammatory and wound-healing activities. Experimental and clinical evidence exists regarding MSCs efficacy in airway defects restoration; although clinical MSCs use, in the daily practice, is not yet completely reached for airway diseases, we can argue that MSCs do not represent any more merely an experimental approach to airway tissue defects restoration but they can be considered as a “salvage” therapeutic tool in very selected patients and diseases.

Mesenchymal stem cells migration homing and tracking

In this review, we discuss the migration and homing ability of mesenchymal stem cells (MSCs) and MSC-like cells and factors influencing this. We also discuss studies related to the mechanism of migration and homing and the approaches undertaken to enhance it. Finally, we describe the different methods available and frequently used to track and identify the injected cells in vivo.