The bad and the good of mesenchymal stem cells in cancer: Boosters of tumor growth and vehicles for targeted delivery of anticancer agents

In cancer biology, mesenchymal stem cells (MSCs) display aspects that can appear contradictory. On one hand, these cells possess several features which give them the ability to specifically target and then sustain cancer cells in their ability to survive the multifaceted host response against cancer. On the other hand, due to this excellent aptitude to home-in on tumor tissues, regardless their location in the host's body, MSCs are considered to be extremely selective vehicles to reach cancer cells specifically. Recently, MSC sustainment of cancer cell growth is a hot research topic. Indeed, these cells are known to sustain tumor angiogenesis and metastasis formation, to create a microenvironment favorable for cancer cell growth and to down-modulate the immune system capabilities in the host organism. On the other hand, since scientists became able to take advantage of their extremely selective capability to target cancer cells, MSCs are now also thought of in a different light. Indeed, MSCs are now considered a promising vehicle for local expression or delivery of even particularly toxic anticancer agents, ranging from Herpes Simplex Virus to locally-acting antineoplastic drugs. On this basis, investigation is now focused on how to impair the pro-neoplastic features of MSCs on one hand whilst taking advantage of their specific tropism toward cancer cells, on the other. As with the two faces of Janus, this review will concisely explore the research activity in these two apparently conflicting fields.     

A possible model for cell-cell recognition via surface macromolecules.

Alternative possibilities for the establishment of the proper cell distribution during embryogenesis are summarized at the beginning, followed by an assessment of the examples known so far where cell-cell recognition is known to be mediated via cell surface components. In the second part the species-specific recognition process which occurs during the sorting-out of dissociated sponge cells is analysed since it may serve as a possible model for cell-cell recognition in higher animals. Three possible mechanisms for the establishment of proper cell distribution are considered. These include, first, chemotaxis: secondly, guidance of cell or cell sheet movement by extracellular matrix or by surrounding cells and thirdly, random movement followed by recognition at the final point of destination. Recognition is necessary for both of the two latter processes, i.e. for cell guidance as well as for locking the cells into their final position after random movement. Two basically different recognition mechanisms should be distinguished from each other. On the one hand cells may recognize each other with the help of macromolecules situated in or just outside of the plasmamembrane which fit to each other like enzymes and substrates or antibodies and antigens. On the other hand, cells may exchange information by exchanging cytoplasmatic components via vesicles or gap junctions. The species-specific aggregation of dissociated sponge cells is considered to be a possible model for cell-cell recognition in higher animals. A proteoglycan-like intercellular macromolecule called aggregation factor seems to mediate recognition of a given species of cells in the reaggregation process of dissociated cells. The data available at the present time suggest that a monovalent surface macromolecule (baseplate) may mediate the recognition process probably by recognizing the carbohydrate side chains of the multivalent proteoglycan aggregation factor. A cell-free system was devised to mimic this aggregation process. Addition of aggregation factor to baseplate-coated sepharose beads of approximately the size of the original sponge cells has essentially the same characteristics as the cellular system. Macromolecule-coded surface information for the recognition between cells has not been established during the embryogenesis of higher animals and remains an interesting challenge.     

Monoaminergic and cholinergic mechanisms of reproduction control in marine bivalve molluscs and echinoderms: a review.

The autoreproduction ability is one of the most important properties of living systems. Evolution of metazoans ensured their reproduction by means of such determinants as sexual cells developing in specialized organs, in gonads. In most marine invertebrates, the gonad produces tens of millions of gametes per reproductive cycle. This reproduction level guarantees the species resistance in the external environment and is provided by the whole organism, though in unfavourable ecological conditions the gonad may become a source of trophic and energy material and it can maintain the viability of organism by means or the mass, often total, lysis of sexual cells. This metabolic interaction of a part (gonad) and the whole (organism) presumes the existence of the strictly determined relations between them, on the one hand, and more or less pronounced autonomy, on the other hand. The isolated organs, including gonads, are capable of fulfilling specific functions for a short period of time by means of local regulation. However, there is no full autonomy between the gonad and the organism: the hierarchical relations set in between them.     

Monoaminergic and cholinergic mechanisms of reproduction control in marine bivalve molluscs and echinoderms: A review

The autoreproduction ability is one of the most important properties of living systems. Evolution of metazoans ensured their reproduction by means of such determinants as sexual cells developing in specialized organs, in gonads. In most marine invertebrates, the gonad produces tens of millions of gametes per reproductive cycle. This reproduction level guarantees the species resistance in the external environment and is provided by the whole organism, though in unfavourable ecological conditions the gonad may become a source of trophic and energy material and it can maintain the viability of organism by means or the mass, often total, lysis of sexual cells. This metabolic interaction of a part (gonad) and the whole (organism) presumes the existence of the strictly determined relations between them, on the one hand, and more or less pronounced autonomy, on the other hand. The isolated organs, including gonads, are capable of fulfiling specific functions for a short period of time by means of local regulation. However, there is no full autonomy between the gonad and the organism: the hierarchical relations set in between them.     

Adaptation in the face of internal conflict: the paradox of the organism revisited

The paradox of the organism refers to the observation that organisms appear to function as coherent purposeful entities, despite the potential for within-organismal components like selfish genetic elements and cancer cells to erode them from within. While it is commonly accepted that organisms may pursue fitness maximisation and can be thought to hold particular agendas, there is a growing recognition that genes and cells do so as well. This can lead to evolutionary conflicts between an organism and the parts that reside within it. Here, we revisit the paradox of the organism. We first outline its conception and relationship to debates about adaptation in evolutionary biology. Second, we review the ways selfish elements may exploit organisms, and the extent to which this threatens organismal integrity. To this end, we introduce a novel classification scheme that distinguishes between selfish elements that seek to distort transmission versus those that seek to distort phenotypic traits. Our classification scheme also highlights how some selfish elements elude a multi-level selection decomposition using the Price equation. Third, we discuss how the organism can retain its status as the primary fitness-maximising agent in the face of selfish elements. The success of selfish elements is often constrained by their strategy and further limited by a combination of fitness alignment and enforcement mechanisms controlled by the organism. Finally, we argue for the need for quantitative measures of both internal conflicts and organismality.     

Targeting of tumor cells by lymphocytes engineered to express chimeric receptor genes

Adoptive cellular immunotherapy of cancer has been limited to date mostly due to the poor immunogenicity of tumor cells, the immunocompromised status of cancer patients in advanced stages of their disease, and difficulties in raising sufficient numbers of autologous tumor-specific T lymphocytes. On the other hand, the slow tumor penetration and short half-life of exogenously administered tumor-specific monoclonal antibodies have provided major obstacles for an effective destruction of tumor cells by the humoral effector arm of the immune system. Attempts to improve the efficacy of adoptive cellular cancer immunotherapy have led to the development of novel strategies that combine advantages of T cell-based (i.e., efficient tumor penetration, cytokine release and cytotoxicity) and antibody-based (high specificity for tumor-associated antigens) immunotherapy by grafting cytotoxic T lymphocytes (CTLs) with chimeric receptors composed of antibody fragments (which recognize tumor-cell antigens) and a cellular activation motif. Antigen recognition is therefore not restricted by major histocompatibility genes, as the physiological T-cell receptor, but rather is directed to native cell surface structures. Since the requirements of major histocompatibility complex (MHC) restriction in the interaction of effector cells with target cells are bypassed, the tumor cell-binding of CTLs grafted with chimeric receptors is not affected by down-regulation of HLA class I antigens and by defects in the antigen-processing machinery. Ligand binding by the chimeric receptor triggers phosphorylation of immunoglobulin tyrosine activation motifs (ITAMs) in the cytoplasmic region of the molecule and this activates a signaling cascade that is required for the induction of cytotoxicity, cytokine secretion and proliferation. Here, the authors discuss the potential of lymphocytes grafted with chimeric antigen receptors in the immunotherapy of malignant disease.     

Discovery of Possible Gene Relationships through the Application of Self-Organizing Maps to DNA Microarray Databases

DNA microarrays and cell cycle synchronization experiments have made possible the study of the mechanisms of cell cycle regulation of Saccharomyces cerevisiae by simultaneously monitoring the expression levels of thousands of genes at specific time points. On the other hand, pattern recognition techniques can contribute to the analysis of such massive measurements, providing a model of gene expression level evolution through the cell cycle process. In this paper, we propose the use of one of such techniques –an unsupervised artificial neural network called a Self-Organizing Map (SOM)–which has been successfully applied to processes involving very noisy signals, classifying and organizing them, and assisting in the discovery of behavior patterns without requiring prior knowledge about the process under analysis. As a test bed for the use of SOMs in finding possible relationships among genes and their possible contribution in some biological processes, we selected 282 S. cerevisiae genes that have been shown through biological experiments to have an activity during the cell cycle. The expression level of these genes was analyzed in five of the most cited time series DNA microarray databases used in the study of the cell cycle of this organism. With the use of SOM, it was possible to find clusters of genes with similar behavior in the five databases along two cell cycles. This result suggested that some of these genes might be biologically related or might have a regulatory relationship, as was corroborated by comparing some of the clusters obtained with SOMs against a previously reported regulatory network that was generated using biological knowledge, such as protein-protein interactions, gene expression levels, metabolism dynamics, promoter binding, and modification, regulation and transport of proteins. The methodology described in this paper could be applied to the study of gene relationships of other biological processes in different organisms.     

Clinical evaluation of systemic and local immune responses in cancer: time for integration

The immune system has a dual role in cancer development and progression. On the one hand, it can eradicate emerging malignant cells, but on the other hand, it can actively promote growth of malignant cells, their invasive capacities and their ability to metastasize. Immune cells with predominantly anti-tumor functionality include cells of the innate immune system, such as natural killer cells, and cells of adaptive immunity, such as conventional dendritic cells and cytotoxic T lymphocytes. Immune cells with predominantly pro-tumor functionality include a broad spectrum of cells of the innate and adaptive immune system, such as type 2 neutrophils and macrophages, plasmacytoid DC, myeloid-derived suppressor cells and regulatory T lymphocytes. The presence of immune cells with tumor-suppressive and tumor-promoting activity in the cancer microenvironment and in peripheral blood is usually associated with good clinical outcomes and poor clinical outcomes, respectively. Significant advances in experimental and clinical oncoimmunology achieved in the last decade open an opportunity for the use of modern morphologic, flow cytometric and functional tests in clinical practice. In this review, we describe an integrated approach to clinical evaluation of the immune status of cancer patients for diagnostic purposes, prognostic/predictive purposes (evaluation of patient prognosis and response to treatment) and for therapeutic purposes.     

Recruitment of endogenous neural progenitor cells by malignant neoplasms of the central nervous system

It is proposed here that malignancies of the central nervous system (CNS) are capable of recruiting non-malignant CNS precursor cells and that doing so worsens the course of the disease. In particular, the argument is put forward that such tumors can activate resident neural stem cells, attract them or their progeny to the tumor site, and induce them to proliferate. What begins as a normal wound repair response by the recruited cells can eventually result in augmentation of the tumor. In support of this hypothesis, evidence consistent with the ideas proposed is presented. Since these recruited cells are non-malignant, it should be possible to interfere with this process. This would not necessarily remove the threat posed by the cancer, but could beneficially impact patients by slowing progression. Interfering with recruitment could simultaneously serve to block autocrine stimulation by tumor cells. In contrast, introducing exogenous stem cells could exacerbate the recruitment process unless measures are taken to preclude this possibility. Finally, it is worth noting that the situation described in the current hypothesis might apply to a variety of other stem and precursor cell-containing systems throughout the body.     

On the kinetics and optimal specificity of cytotoxic reactions mediated by T-lymphocyte clones

Using the chromium release assay and the single cell assay in agarose, we study the cytotoxic reaction of the MHC-restricted T lymphocyte clones P89:15 and P1:3, which recognize distinct but specific tumour antigens on the surface of syngeneic P815 mastocytoma cells. We propose a mathematical model which describes these experiments, accounts for the strongly non-Michaelian behaviour of the reaction and permits us to estimate the kinetic parameters characterizing effector-target conjugation and lethal hit delivery. The results show that the binding and lytic activity of effector cells is modulated by the number of targets bound to them. The binding of a second target by an effector having already a target bound is facilitated; on the other hand, an effector having bound two targets delivers a lethal hit more slowly than one with a single target bound. We investigate the role of these kinetic properties in the competition between the process of tumour progression due to cancer cell replication and the process of tumour regression due to T lymphocyte cytotoxic activity. For both clones, we estimate the effector-target ratio beyond which rejection prevails. This ratio is nine times larger for P1:3 than for P89:15. Furthermore, our analysis suggests that there exists an optimal specificity minimizing this ratio. Deviations from this optimum, be it in the sense of an increase or decrease of specificity, tendsto stabilize the tumoural state: a situation which in the broader context of the immune response evolution and regulation can be viewed as animmune response dilemma.     

Mesenchymal stem cells: biology and clinical potential in type 1 diabetes therapy

Mesenchymal stem cells (MSCs) can be derived from adult bone marrow, fat and several foetal tissues. In vitro , MSCs have the capacity to differentiate into multiple mesodermal and non-mesodermal cell lineages. Besides, MSCs possess immunosuppressive effects by modulating the immune function of the major cell populations involved in alloantigen recognition and elimination. The intriguing biology of MSCs makes them strong candidates for cell-based therapy against various human diseases. Type 1 diabetes is caused by a cell-mediated autoimmune destruction of pancreatic β-cells. While insulin replacement remains the cornerstone treatment for type 1 diabetes, the transplantation of pancreatic islets of Langerhans provides a cure for this disorder. And yet, islet transplantation is limited by the lack of donor pancreas. Generation of insulin-producing cells (IPCs) from MSCs represents an attractive alternative. On the one hand, MSCs from pancreas, bone marrow, adipose tissue, umbilical cord blood and cord tissue have the potential to differentiate into IPCs by genetic modification and/or defined culture conditions In vitro . On the other hand, MSCs are able to serve as a cellular vehicle for the expression of human insulin gene. Moreover, protein transduction technology could offer a novel approach for generating IPCs from stem cells including MSCs. In this review, we first summarize the current knowledge on the biological characterization of MSCs. Next, we consider MSCs as surrogate β-cell source for islet transplantation, and present some basic requirements for these replacement cells. Finally, MSCs-mediated therapeutic neovascularization in type 1 diabetes is discussed.     

Recognition of the fungal cell wall by innate immune receptors

Human cells have a variety of receptors that innately recognize conserved structures on the fungal cell wall. Major receptors include dectin-1, which recognizes β1,3-glucans; mannose receptors, which recognize mannans, and Toll-like receptors 2 and 4. The fungal cell wall is a potent activator of complement, which results in deposition of fragments of the third component of complement that serve as ligands for complement receptors. The nature of the innate immune response is dictated by the relative amount each of these receptors is stimulated. Innate recognition can lead to destruction of the invading fungus and/or initiation of an adaptive immune response. Fungi have a variety of strategies to avoid innate recognition, including masking of ligands and changing their surface properties by phase transition.     

Theory of the continuity of germ plasma according to the findings of modern biology

The main principles on the theory of germ plasma by A. Weismann are briefly presented; a number of his genetic-embryological hypotheses proved to be prophetic. Modern notions on the germ plasma are critically discussed, as well as the resulting from them the conception on continuity of totipotent cells (the source of germ cells) in the line of generations, that is historically connected with M. Nussbaum--A. Weismann's notions on continuity of the embryonic pathway. The term totipotency is sometimes used inaccurately; it means ability to formation of a whole organism. In Metazoa zygota and isolated blastomeres, at a regulative type of development, and groups of somatic cells or fragments of the organism, at an asexual reproduction and somatic embryogenesis, possess this ability. In ontogenesis totipotency is lost both by the somatic and by the germ cells because of their specialization and is recreated with the beginning of every ontogenesis when zygota is formed. The germ cells are always a product of the organism--unicellular or multicellular, and their specialization in all its manifestations is the result of integrative influences of the organism as a whole of them. Certain reasons are presented for supporting ideas on germ cells as one of the lines of cell differentiation. The main, if not the only contradiction in the problem concerning relation of the germ and somatic cells is, at the present time, the thesis on continuity of totipotent cells in the line of generations.     

ROS and oncogenesis with special reference to EMT and stemness

Elevation of the level of intracellular reactive oxygen species (ROS) has immense implication in the biological system. On the one hand, ROS promote the signaling cascades for the maintenance of normal physiological functions, the phenomenon referred to as redox biology, and on the other hand increased ROS can cause damages to the cellular macromolecules as well as genetic material, the process known as oxidative stress. Oxidative stress acts as an etiological factor for wide varieties of pathologies, cancer being one of them. ROS is regarded as a “double-edged sword” with respect to oncogenesis. It can suppress as well as promote the malignant progression depending on the type of signaling pathway it uses. Moreover, the attribution of ROS in promoting phenotypic plasticity as well as acquisition of stemness during neoplasia has become a wide area of research. The current review discussed all the aspects of ROS in the perspective of tumor biology with special reference to epithelial-mesenchymal transition (EMT) and cancer stem cells.     

Beyond DNA origami: the unfolding prospects of nucleic acid nanotechnology

Nucleic acid nanotechnology exploits the programmable molecular recognition properties of natural and synthetic nucleic acids to assemble structures with nanometer-scale precision. In 2006, DNA origami transformed the field by providing a versatile platform for self-assembly of arbitrary shapes from one long DNA strand held in place by hundreds of short, site-specific (spatially addressable) DNA 'staples'. This revolutionary approach has led to the creation of a multitude of two-dimensional and three-dimensional scaffolds that form the basis for functional nanodevices. Not limited to nucleic acids, these nanodevices can incorporate other structural and functional materials, such as proteins and nanoparticles, making them broadly useful for current and future applications in emerging fields such as nanomedicine, nanoelectronics, and alternative energy.     

Identification of a protein that binds to the Ho endonuclease recognition sequence at the yeast mating type locus.

Mating type switching in Saccharomyces cerevisiae initiates when Ho endonuclease makes a site-specific double-stranded break at MAT, the yeast mating type locus. To identify other proteins involved in this process, we examined whether extracts prepared from ho- mutants contain additional factors that bind near the recognition sequence for Ho. Using an electrophoretic mobility shift assay, we isolated a chromatographic fraction that contains an activity, named YZbp, which binds to two sequences flanking the recognition sequence at MATalpha and to one sequence overlapping it at MATa. MAT plasmids carrying mutations in the YZbp recognition sequence are cleaved by purified Ho at wild-type efficiencies in an in vitro assay. These same plasmids, however, are not cleaved by Ho inside cells, demonstrating that YZbp acts as a positive activator of in vivo cleavage. YZbp is present in all cell types, even those not undergoing mating type switching, suggesting that it has additional cellular functions.     

Antigen processing defects in cervical carcinomas limit the presentation of a CTL epitope from human papillomavirus 16 E6.

Human papillomavirus (HPV) infection, particularly type 16, is causally associated with the development of cervical cancer. The E6 and E7 proteins of HPV are constitutively expressed in cervical carcinoma cells making them attractive targets for CTL-based immunotherapy. However, few studies have addressed whether cervical carcinomas can process and present HPV E6/E7-derived Ags for recognition by CTL. We generated HLA-A*0201-restricted CTL clones against HPV16 E6(29-38) that recognized HPV16 E6 Ags transfected into B lymphoblastoid cells. These CTL were unable to recognize HLA-A*0201(+) HPV16 E6(+) cervical carcinoma cell lines even when the level of endogenous HPV16 E6 in these cells was increased by transfection. This defect in presentation of HPV16 E6(29-38) correlated with low level expression of HLA class I, proteasome subunits low molecular mass protein 2 and 7, and the transporter proteins TAP1 and TAP2 in the cervical carcinoma cell lines. The expression of all of these proteins could be up-regulated by IFN-gamma, but this was insufficient for CTL recognition unless the level of HPV16 E6 Ag was also increased by transfection. CTL recognition of the HPV16 E6(29-38) epitope in 721.174 B cells was dependent on TAP expression but independent of immunoproteasome expression. Collectively, these findings suggest that presentation of the HPV16 E6(29-38) epitope in cervical carcinoma cell lines is limited both by the level of TAP expression and by the low level or availability of the source HPV E6 oncoprotein. These observations place constraints on the use of this, and potentially other, HPV-derived CTL epitopes for the immunotherapy of cervical cancer.     

The role of peroxiredoxin 6 in neutralization of X-ray mediated oxidative stress: effects on gene expression,preservation of radiosensitive tissues and postradiation survival of animals

Peroxiredoxins are redox-sensing multifunctional enzymes, among them peroxiredoxin 6 (Prx6) can neutralize the most broadest range of hydroperoxides and play an important role in maintaining the redox homeostasis of the cell. In the present study, radioprotective and signaling regulatory effects of Prx6 were demonstrated and characterized. Intravenously administered exogenous Prx6 protects the organism of mice from the destructive action of ionizing radiation in the lethal dose range of 5–10?Gy. Dose reduction factor of 1.4 Prx6 injection reduces the severity of radiation-induced leuko- and thrombopenia in irradiated animals, also preventing the destruction of epithelial cells in the small intestine. Injecting exogenous Prx6 also as its mutated form of Prx6–C47S lacking peroxidase activity affects the expression of genes involved in antioxidant response, DNA reparation, apoptosis and inflammatory processes, in bone marrow cells both in intact animals and in those subjected to ionizing radiation. The radioprotective properties of Prx6 are based, on the one hand, on the capability for ROS neutralization, and on the other hand – on the potentiality for activation of reparation processes of the cell under oxidative stress conditions. Prx6 can be considered as a potentially perspective radioprotective agent for the reduction of risks from the damaging action of ionizing radiation on the mammalian organism.     

An induced fit hypothesis for antigen recognition by T lymphocytes: a role for specific antigen retention structures on antigen-presenting cells

The nature of T lymphocyte recognition of foreign antigens is not known, despite recent advances in elucidating the cellular structures that may be involved in the specific interactions. The central difficulty in this process is that T cells respond to foreign antigen only in the context of major histocompatibility complex (MHC) antigens expressed by another antigen-presenting cell. In addition, T cells that interact with class II MHC antigens do not bind foreign protein antigens in their native form, but seem to recognize only proteolytic peptide fragments as the relevant antigen. The simplest explanation for these observations is that the class II MHC antigens themselves bind antigenic peptides to form the appropriate determinant that interacts with the antigen-specific T cell receptor. However, to date no such antigenic complex has been found with MHC antigens despite rigorous attempts at their demonstration. One alternative explanation described here is that there is no preexisting foreign antigen-MHC antigen complex prior to interaction with T cells, and it is the T cells that cause the two moieties to become associated for recognition by a single antigen-specific T cell receptor. Central to this mechanism is that foreign antigenic peptides must be associated with specific antigen retention structures (SARS) expressed by antigen-presenting cells which retain and protect the peptide on the cell surface. These SARS, upon interaction with T cell membrane moieties, would subsequently associate with MHC antigens. A hypothesis to describe this mechanism is developed to account for published observations of antigen processing by antigen-presenting cells and T cell antigen recognition, and makes several predictions that are experimentally testable. This mechanism is also generally applicable to other cellular interactions in which soluble peptide mediators may become associated with surface components of one cell type, and this newly formed complex is in turn recognized by a receptor on a second cell type to deliver functional signals.     

Functional polymorphism of the KIR3DL1/S1 receptor on human NK cells

NK cells express both inhibitory and activatory receptors that allow them to recognize target cells through HLA class I Ag expression. KIR3DL1 is a receptor that recognizes the HLA-Bw4 public epitope of HLA-B alleles. We demonstrate that polymorphism within the KIR3DL1 receptor has functional consequences in terms of NK cell recognition of target. Inhibitory alleles of KIR3DL1 differ in their ability to recognize HLA-Bw4 ligand, and a consistent hierarchy of ligand reactivity can be defined. KIR3DS1, which segregates as an allele of KIR3DL1, has a short cytoplasmic tail characteristic of activatory receptors. Because it is very similar to KIR3DL1 in the extracellular domains, it has been assumed that KIR3DS1 will recognize a HLA-Bw4 ligand. In this study, we demonstrate that KIR3DS1 is expressed as a protein at the cell surface of NK cells, where it is recognized by the Z27 Ab. Using this Ab, we found that KIR3DS1 is expressed on a higher percentage of NK cells in KIR3DS1 homozygous compared with heterozygous donors. In contrast to the inhibitory KIR3DL1 allotypes, KIR3DS1 did not recognize HLA-Bw4 on EBV-transformed cell lines.