Silvia Santamaria

Will a mAb-Based Immunotherapy Directed against Cancer Stem Cells Be Feasible?

The cancer stem cell (CSC) hypothesis suggests that within a tumor, there is a small subpopulation of cells with stem cell properties responsible for tumor maintenance and metastasis generation. This hypothesis also implies that new antitumor drugs, rather than targeting the bulk of the tumor mass, would be more effective if they directly targeted the CSC subpopulation. The CSCs from several types of tumors have been identified with mAbs recognizing surface antigens in these cells; however, antigens specifically or exclusively expressed in the CSC population have not yet been identified. Thus, questioning the possibility of using therapeutic antibodies directed against the CSCs. Here, we review the possibilities of using antibodies directly targeting the CSCs as therapeutic agents in the form of naked antibodies, antibodies conjugated to nanoparticles, or antibody cocktails.

Effects of topology on robustness in ecological bipartite networks

High robustness of complex ecological systems in the face of species extinction has been hypothesized based on the redundancy in species. We explored how differences in network topology may affect robustness. Ecological bipartite networks used to be small, asymmetric and sparse matrices. We created synthetic networks to study the influence of the properties of network dimensions asymmetry, connectance and type of degree distribution on network robustness. We used two extinction strategies: node extinction and link extinction, and three extinction sequences differing in the order of species removal (least-to-most connected, random, most-to-least connected). We assessed robustness to extinction of simulated networks, which differed in one of the three topological features. Simulated networks indicated that robustness decreases when (a) extinction involved those nodes belonging to the most species-rich guild and (b) networks had lower connectance. We also compared simulated networks with different degree- distribution networks, and they showed important differences in robustness depending on the extinction scenario. In the link extinction strategy, the robustness of synthetic networks was clearly determined by the asymmetry in the network dimensions, while the variation in connectance produced negligible differences.

New Strategies Using Antibody Combinations to Increase Cancer Treatment Effectiveness

Antibodies have proven their high value in antitumor therapy over the last two decades. They are currently being used as the first-choice to treat some of the most frequent metastatic cancers, like HER2+ breast cancers or colorectal cancers, currently treated with trastuzumab (Herceptin) and bevacizumab (Avastin), respectively. The impressive therapeutic success of antibodies inhibiting immune checkpoints has extended the use of therapeutic antibodies to previously unanticipated tumor types. These anti-immune checkpoint antibodies allowed the cure of patients devoid of other therapeutic options, through the recovery of the patient’s own immune response against the tumor. In this review, we describe how the antibody-based therapies will evolve, including the use of antibodies in combinations, their main characteristics, advantages, and how they could contribute to significantly increase the chances of success in cancer therapy. Indeed, novel combinations will consist of mixtures of antibodies against either different epitopes of the same molecule or different targets on the same tumor cell; bispecific or multispecific antibodies able of simultaneously binding tumor cells, immune cells or extracellular molecules; immunomodulatory antibodies; antibody-based molecules, including fusion proteins between a ligand or a receptor domain and the IgG Fab or Fc fragments; autologous or heterologous cells; and different formats of vaccines. Through complementary mechanisms of action, these combinations could contribute to elude the current limitations of a single antibody which recognizes only one particular epitope. These combinations may allow the simultaneous attack of the cancer cells by using the help of the own immune cells and exerting wider therapeutic effects, based on a more specific, fast, and robust response, trying to mimic the action of the immune system.

Insights of the brain damage response using antibodies identifying surface antigens on neural stem cells and neuroblasts.

Similarly to other adult tissues, a hierarchical structure has been established for the brain, where the differentiated cell types (neurons, oligodendrocytes and astrocytes) are generated from primary progenitor cells, known as type B astrocytes or neural stem cells (NSC), through one or multiple stages of amplification (transient amplifying cells) that generate precursor cells (iPC) with more restricted potential nIPCs (neural), aIPCs (astrocytes), oIPC (oligodendrocytes) (Kriegstein and Alvarez-Buylla, 2009). In the adult rodent brain, NSCs and iPCs are mainly restricted to the niches on the subventricular zone (SVZ) of the lateral ventricles (Doetsch et al., 1999; Kriegstein and Alvarez-Buylla, 2009). This hierarchical structure of the brain is critical for the understanding of brain development and adult neurogenesis, to develop new strategies for brain repair, or for the understanding of brain tumor development. Neurogenesis in the adult brain is well documented, in particular for maintaining the homeostasis of the olfactory bulb, where a continuous supply of neuroblasts, migrating from their SVZ niche to the olfactory bulb, through the rostral migratory stream (RMS). The migrating neuroblasts are required for the continuous generation of periglomerular interneurons in the olfactory bulb (Doetsch et al., 1999). However, recent data obtained by us and other laboratories demonstrate that the migration of iPCs is not restricted to the olfactory bulb. For this purpose, we took advantage of two monoclonal antibodies (mAbs) generated against mouse neurospheres (Del Valle et al., 2010) that identify surface antigens on neuroblasts (Nilo2) (Elvira et al., 2012), and NSC (type B astrocytes) in the mouse adult brain as well as radial glia in the mouse embryo (Nilo1) (Elvira et al., 2015). These antibodies were coupled to magnetic nanoglicoparticles to in vivo identify by magnetic resonance imaging (MRI) neuroblasts or NSCs in their niches, and track their migration in response to brain damage. These experiments allowed us to demonstrate in vivo that both neuroblasts and NSC are mobilized from their SVZ niches to the brain damage site, where they migrate in a fast and orderly way. In less than 3 hours from the insult, the first migrating neuroblasts and NSC start to reach the damage site. Migration of Neuroblasts and NSGs seem to be a generalized trait in response to brain damage, since it occurs during growth of a tumor, but also in response to a cryolesion, focal demyelinization, or a mechanical lesion (Figure 1) (Elvira et al., 2012, 2015). Neuroblasts and NSCs migrate to the brain damage site with similar kinetics, suggesting that both cell types respond to “damage signals” of still unknown nature, where chemoattractants or growth factors may play a role. Figure 1 Neural stem cell (NSC) response to brain damage. MRI has been previously used to monitor migration of either in vitro labeled cells that were then deposited on a recipient mouse, or endogenous neural cells after in situ endocytosis of particles (Shapiro et al., 2006; Panizzo et al., 2009; Sumner et al., 2009; Nieman et al., 2010; Vreys et al., 2010). Thus, these experiments were unable to monitor an endogenous particular progenitor subpopulation migrating in the brain. We could achieve this goal with the use of mAbs specifically identifying surface antigens on neuroblasts (Nilo2) or NSC (Nilo1). Having established the migration of NSC and neuroblasts towards a brain damage site, their physiological role at the damage site remains to be unraveled. It is enlightening, however, that i) after NSC and neuroblast migration in response to a brain puncture with a stereotaxic needle, most of the cells filling the needle track do not express NSC or neuroblast markers; and ii) in response to a focal demyelinated lesion induced by lysolecithin, remyelination could be confirmed by the presence of O4+ or myelin+ cells. Thus, NSC and neuroblasts at the damage site trigger the migration of differentiated cells towards the brain damage site, or, most likely, these cells differentiate in situ to generate the appropriate cell types, to repair the damage. Although we cannot formally distinguish between these possibilities, it is clear that the models and tools described, together with in vivo labeling of proliferating cells might allow to establish the cellular mechanism(s) involved in damage repair. In addition, migration of NSC or neuroblasts in vivo could be used as a biomarker to identify the focal sites on the brain affected by epileptic seizures or neurodegenerative processes such as Parkinsons or Alzheimers disease. NSC and neuroblats also migrate towards a tumor growth site; it is conceivable that this happens in response to the same or similar “damage signal(s)” as that in the other damage models. During tumor growth, there is no evidence of tissue repair, this may be due to the rapid growth of the tumors. Interestingly, however, the fast migration of NSCs and neuroblasts towards the tumor site could be used to precisely identify the tumor site, even before contrast agents such as gadolinium can traverse the blood-brain barrier. The most appealing finding, however, using these antibodies is the discovery that Nilo1 mAb in addition to identify mouse radial glia on the developing brain and NSC on the adult mouse, also identifies a subpopulation of cells on human gliomas. Although it is likely that Nilo1 mAb identifies the cancer stem cell population (CSC) in human gliomas, this remains to be formally demonstrated. If this is the case it might represent the first opportunity of generating an antibody against neural CSC. In this regard, the presence of CSC was first demonstrated in vivo in glioblastomas, intestinal tumors, and skin cancer, using genetic tracing of the cells (Baker, 2012). The glioblastoma experiments further demonstrated that standard chemotherapy treatments induced tumor shrinkage, but the tumors quickly returned. If chemotherapy was administered at the same time that the CSC were suppressed using a genetic trick, the tumors shrank back into “residual vestiges” that did not resemble glioblastomas (Chen et al., 2012). Thus, these data draw attention to the relevance of treatments using the neural CSC as a target, as it would be the case for Nilo1-derived drugs. In conclusion, the use of mAbs recognizing surface markers on either NSC or neuroblasts open up a series of possibilities (Figure 2), for example, they allow to purify these cells from cell suspensions, identify them in their niches, or demonstrate in vivo their migration towards damage sites. In addition allows envisaging the possibility of identifying the focal sites on epileptic brains after a seizure, or on initial stages of Parkinsons or Alzheimers diseases by the migration of NSCs towards the damage sites. Finally, if the mAb anti-NSC recognizes the CSC in human gliomas, it might turn out as the first therapeutic drug targeting neural CSC. Figure 2 Possibilities opened-up by the use of mAbs recognizing surface antigens in neural stem cells (NSC) and neuroblasts.

Intrinsic cues and hormones control mouse mammary epithelial tree size

Organ size control is a long‐standing question in biology. In mammals, using conditional cell ablation, two mutually exclusive mechanisms involving either intrinsic or extrinsic programs have been described to control organ size. The mammary gland is an ideal model for such studies, since it undergoes size and morphological changes during puberty and pregnancy. The role of stem cells in controlling mammary epithelial tree size is unclear, although mammary stem cells are able to reconstitute a functional organ on transplantation. Here, we show that mammary gland cellularity was strictly dependent on mammary stem cell number, even following a 20‐fold expansion of the mammary stem cell pool at puberty and transient 3‐fold expansions with each pregnancy. In addition, the expansion of the mammary stem cell pool was hormone dependent, as demonstrated by female bilateral ovariectomies during puberty and transplants of male‐derived cells into female recipients. In these transplants, apart from a mammary stem cell expansion, we also observed the donor cells reconstituting functional mammary glands, developing alveolar structures, and secreting milk after the recipients parturition. Taken together, these data suggest that in the mammary gland, there is a third organ size control mechanism, combining intrinsic cues throughout the organisms lifetime, with extrinsic hormone signals at particular developmental windows (puberty, pregnancy), where an expansion of the mammary stem cell pool occurs. This mechanism might have strong implications for the understanding of mammary tumorigenesis, since the expansion of the mammary stem cell pool precedes the generation of breast tumors.—Diaz‐Guerra, E., Lillo, M. A., Santamaria, S., Garcia‐Sanz, J. A. Intrinsic cues and hormones control mouse mammary epithelial tree size. FASEB J. 26, 3844–3853 (2012). www.fasebj.org

XV Reunión científica anual de ECOFLOR

Delgado L.A. 2018. Landscape Heterogeneity and tree species diversity in a tropical forest. Development and validation of a methodological proposal. Ecosistemas 27(1): 105-115. Doi.: 10.7818/ECOS.1475 Many landscapes exist as unstable spatial-temporal mosaics where changes in patterns of biodiversity are affected by nature processes and the dynamic interaction between social and ecological factors. It is a consequence of the natural dynamics of socio-economic systems that regulate man-made tropical forests. However, a significant proportion of studies have made generalizations about the relative values of biodiversity, without taking into account the high levels of internal heterogeneity in the biophysical properties and land uses of each site. The purpose of this study is to propose and validate a methodology to delimit the heterogeneity of the landscape based on criteria that integrate the coupling of human-ecological systems such as: space-time dynamics of deforestation and fragmentation; complexity of the landscape structure; current and historical land use and biophysical variability. For this, the use of satellite images, landscape metrics, field work, documentary review and multivariate analysis were combined. The proposed methodology is intended to help guide the empirical delimitation of landscape heterogeneity as a prerequisite for the selection of similar landscapes and forest patches in studies of the diversity of tree species, in order to provide an opportunity to control the possible difficulties caused by variability in the proportion of forests, landscape configuration and successional states, in estimating its effects on forest richness and floristic composition.

92R Monoclonal Antibody Inhibits Human CCR9+ Leukemia Cells Growth in NSG Mice Xenografts

CCR9 is as an interesting target for the treatment of human CCR9+-T cell acute lymphoblastic leukemia, since its expression is limited to immature cells in the thymus, infiltrating leukocytes in the small intestine and a small fraction of mature circulating T lymphocytes. 92R, a new mouse mAb (IgG2a isotype), was raised using the A-isoform of hCCR9 as immunogen. Its initial characterization demonstrates that binds with high affinity to the CCR9 N-terminal domain, competing with the previously described 91R mAb for receptor binding. 92R inhibits human CCR9+ tumor growth in T and B-cell deficient Rag2−/− mice. In vitro assays suggested complement-dependent cytotoxicity and antibody-dependent cell-mediated cytotoxicity as possible in vivo mechanisms of action. Unexpectedly, 92R strongly inhibited tumor growth also in a model with compromised NK and complement activities, suggesting that other mechanisms, including phagocytosis or apoptosis, might also be playing a role on 92R-mediated tumor elimination. Taken together, these data contribute to strengthen the hypothesis of the immune system’s opportunistic nature.