Embryonic expression of murine 5T4 oncofoetal antigen is associated with morphogenetic events at implantation and in developing epithelia

Trophoblast glycoprotein is a marker for efficient sorting of ventral mesencephalic dopaminergic precursors derived from human pluripotent stem cells

Successful cell therapy for Parkinson’s disease (PD) requires large numbers of homogeneous ventral mesencephalic dopaminergic (vmDA) precursors. Enrichment of vmDA precursors via cell sorting is required to ensure high safety and efficacy of the cell therapy. Here, using LMX1A-eGFP knock-in reporter human embryonic stem cells, we discovered a novel surface antigen, trophoblast glycoprotein (TPBG), which was preferentially expressed in vmDA precursors. TPBG-targeted cell sorting enriched FOXA2⁺LMX1A⁺ vmDA precursors and helped attain efficient behavioral recovery of rodent PD models with increased numbers of TH⁺, NURR1⁺, and PITX3⁺ vmDA neurons in the grafts. Additionally, fewer proliferating cells were detected in TPBG⁺ cell-derived grafts than in TPBG⁻ cell-derived grafts. Our approach is an efficient way to obtain enriched bona fide vmDA precursors, which could open a new avenue for effective PD treatment.

LRR-Containing Oncofetal Trophoblast Glycoprotein 5T4 Shapes Neural Circuits in Olfactory and Visual Systems

In mammals, the sensory experience can regulate the development of various brain structures, including the cortex, hippocampus, retina, and olfactory bulb (OB). Odor experience-evoked neural activity drives the development of dendrites on excitatory projection neurons in the OB, such as mitral and tufted cells, as well as inhibitory interneurons. OB interneurons are generated continuously in the subventricular zone and differentiate into granule cells (GCs) and periglomerular cells (PGCs). However, it remains unknown what role each type of OB interneuron plays in controlling olfactory behaviors. Recent studies showed that among the various types of OB interneurons, a subtype of GCs expressing oncofetal trophoblast glycoprotein 5T4 is required for simple odor detection and discrimination behaviors. Mouse 5T4 (also known as Tpbg) is a type I membrane glycoprotein whose extracellular domain contains seven leucine-rich repeats (LRRs) sandwiched between characteristic LRR-N and LRR-C regions. Recently, it was found that the developmental expression of 5T4 increases dramatically in the retina just before eye-opening. Single-cell transcriptomics further suggests that 5T4 is involved in the development and maintenance of functional synapses in a subset of retinal interneurons, including rod bipolar cells (RBCs) and amacrine cells (ACs). Collectively, 5T4, expressed in interneurons of the OB and retina, plays a key role in sensory processing in the olfactory and visual systems.

Expression and distribution of trophoblast glycoprotein in the mouse retina

We recently identified the leucine-rich repeat (LRR) adhesion protein, trophoblast glycoprotein (TPBG), as a novel PKCα-dependent phosphoprotein in retinal rod bipolar cells (RBCs). Since TPBG has not been thoroughly examined in the retina, this study characterizes the localization and expression patterns of TPBG in the developing and adult mouse retina using two antibodies, one against the N-terminal LRR domain and the other against the C-terminal PDZ-interacting motif. Both antibodies labeled RBC dendrites in the outer plexiform layer and axon terminals in the IPL, as well as a putative amacrine cell with their cell bodies in the inner nuclear layer (INL) and a dense layer in the middle of the inner plexiform layer (IPL). In live transfected HEK293 cells, TPBG was localized to the plasma membrane with the N-terminal LRR domain facing the extracellular space. TPBG immunofluorescence in RBCs was strongly altered by the loss of TRPM1 in the adult retina, with significantly less dendritic and axon terminal labeling in TRPM1 knockout compared to wild type, despite no change in total TPBG detected by immunoblotting. During retinal development, TPBG expression increases dramatically just prior to eye opening with a time course closely correlated with that of TRPM1 expression. In the retina, LRR proteins have been implicated in the development and maintenance of functional bipolar cell synapses, and TPBG may play a similar role in RBCs.

Expression of Oncofetal Antigen 5T4 in Murine Taste Papillae

Background: Multicellular taste buds located within taste papillae on the tongue mediate taste sensation. In taste papillae, taste bud cells (TBCs), such as taste receptor cells and taste precursor cells, and the surrounding lingual epithelium including epithelial progenitors (also called taste stem/progenitor cells) are maintained by continuous cell turnover throughout life. However, it remains unknown how the cells constituting taste buds proliferate and differentiate to maintain taste bud tissue. Based on in situ hybridization (ISH) screening, we demonstrated that the oncofetal antigen 5T4 (also known as trophoblast glycoprotein: TPBG) gene is expressed in the adult mouse tongue. Results: In immunohistochemistry of coronal tongue sections, 5T4 protein was detected at a low level exclusively in the basal part of the lingual epithelium in developing and adult mice, and at a high level particularly in foliate papillae and circumvallate papillae (CVPs). Furthermore, immunohistochemistry of the basal part of CVPs indicated that the proliferation marker PCNA (proliferating cell nuclear antigen) co-localized with 5T4. 5T4 was strongly expressed in Krt5+ epithelial progenitors and Shh+ taste precursor cells, but weakly in mature taste receptor cells. The number of proliferating cells in the CVP was higher in 5T4-knockout mice than in wild-type (WT) mice, while neither cell differentiation nor the size of taste buds differed between these two groups of mice. Notably, X-ray irradiation enhanced cell proliferation more in 5T4-knockout mice than in WT mice. Conclusion: Our results suggest that 5T4, expressed in epithelial progenitors (taste stem/progenitor cells), and taste precursor cells, may influence the maintenance of taste papillae under both normal and injury conditions.

Identification of PKCα-dependent phosphoproteins in mouse retina

Adjusting to a wide range of light intensities is an essential feature of retinal rod bipolar cell (RBC) function. While persuasive evidence suggests this modulation involves phosphorylation by protein kinase C-alpha (PKCα), the targets of PKCα phosphorylation in the retina have not been identified. PKCα activity and phosphorylation in RBCs was examined by immunofluorescence confocal microscopy using a conformation-specific PKCα antibody and antibodies to phosphorylated PKC motifs. PKCα activity was dependent on light and expression of TRPM1, and RBC dendrites were the primary sites of light-dependent phosphorylation. PKCα-dependent retinal phosphoproteins were identified using a phosphoproteomics approach to compare total protein and phosphopeptide abundance between phorbol ester-treated wild type and PKCα knockout (PKCα-KO) mouse retinas. Phosphopeptide mass spectrometry identified over 1100 phosphopeptides in mouse retina, with 12 displaying significantly greater phosphorylation in WT compared to PKCα-KO samples. The differentially phosphorylated proteins fall into the following functional groups: cytoskeleton/trafficking (4 proteins), ECM/adhesion (2 proteins), signaling (2 proteins), transcriptional regulation (3 proteins), and homeostasis/metabolism (1 protein). Two strongly differentially expressed phosphoproteins, BORG4 and TPBG, were localized to the synaptic layers of the retina, and may play a role in PKCα-dependent modulation of RBC physiology. Data are available via ProteomeXchange with identifier PXD012906. SIGNIFICANCE: Retinal rod bipolar cells (RBCs), the second-order neurons of the mammalian rod visual pathway, are able to modulate their sensitivity to remain functional across a wide range of light intensities, from starlight to daylight. Evidence suggests that this modulation requires the serine/threonine kinase, PKCα, though the specific mechanism by which PKCα modulates RBC physiology is unknown. This study examined PKCα phosophorylation patterns in mouse rod bipolar cells and then used a phosphoproteomics approach to identify PKCα-dependent phosphoproteins in the mouse retina. A small number of retinal proteins showed significant PKCα-dependent phosphorylation, including BORG4 and TPBG, suggesting a potential contribution to PKCα-dependent modulation of RBC physiology.

Cancer stem cell mobilization and therapeutic targeting of the 5T4 oncofetal antigen

Cancer stem cells (CSCs) can act as the cellular drivers of tumors harnessing stem cell properties that contribute to tumorigenesis either as founder elements or by the gain of stem cell traits by the malignant cells. Thus, CSCs can self-renew and generate the cellular heterogeneity of tumors including a hierarchical organization similar to the normal tissue. While the principle tumor growth contribution is often from the non-CSC components, it is the ability of small numbers of CSCs to avoid the effects of therapeutic strategies that can contribute to recurrence after treatment. However, identifying and characterizing CSCs for therapeutic targeting is made more challenging by their cellular potency being influenced by a particular tissue niche or by the capacity of more committed cells to regain stem cell functions. This review discusses the properties of CSCs including the limitations of the available cell surface markers, the assays that document tumor initiation and clonogenicity, the roles of epithelial mesenchymal transition and molecular pathways such as Notch, Wnt, Hippo and Hedgehog. The ability to target and eliminate CSCs is thought to be critical in the search for curative cancer treatments. The oncofetal tumor-associated antigen 5T4 (TBGP) has been linked with CSC properties in several different malignancies. 5T4 has functional attributes that are relevant to the spread of tumors including through EMT, CXCR4/CXCL12, Wnt, and Hippo pathways which may all contribute through the mobilization of CSCs. There are several different immunotherapies targeting 5T4 in development including antibody-drug conjugates, antibody-targeted bacterial super-antigens, a Modified Vaccinia Ankara-basedvaccine and 5T4-directed chimeric antigen receptor T-cells. These immune therapies would have the advantage of targeting both the bulk tumor as well as mobilized CSC populations.

The Functional Role of Olfactory Bulb Granule Cell Subtypes Derived From Embryonic and Postnatal Neurogenesis

It has been shown in a variety of mammalian species that sensory experience can regulate the development of various structures, including the retina, cortex, hippocampus, and olfactory bulb (OB). In the mammalian OB, the development of dendrites in excitatory projection neurons, such as mitral and tufted cells, is well known to be dependent on odor experience. Odor experience is also involved in the development of another OB population, a subset of inhibitory interneurons that are generated in the ventricular-subventricular zone throughout life and differentiate into granule cells (GCs) and periglomerular cells. However, the roles that each type of interneuron plays in the control of olfactory behaviors are incompletely understood. We recently found that among the various types of OB interneurons, a subtype of GCs expressing the oncofetal trophoblast glycoprotein 5T4 gene is required for odor detection and discrimination behaviors. Our results suggest that embryonic-born OB interneurons, including 5T4-positive GCs, play a crucial role in fundamental olfactory responses such as simple odor detection and discrimination behaviors. By contrast, postnatal- and adult-born OB interneurons are important in the learning of more complicated olfactory behaviors. Here, we highlight the subtypes of OB GCs, and discuss their roles in olfactory processing and behavior, with a particular focus on the relative contributions of embryonically and postnatally generated subsets of GCs in rodents.

Poised for development

A new study tracks the distribution of bivalent H3K4me3/H3K27me3 chromatin in male germ cells of six vertebrate species. The results have big implications for understanding the mechanisms that specify animal development.

A Subtype of Olfactory Bulb Interneurons Is Required for Odor Detection and Discrimination Behaviors

Neural circuits that undergo reorganization by newborn interneurons in the olfactory bulb (OB) are necessary for odor detection and discrimination, olfactory memory, and innate olfactory responses, including predator avoidance and sexual behaviors. The OB possesses many interneurons, including various types of granule cells (GCs); however, the contribution that each type of interneuron makes to olfactory behavioral control remains unknown. Here, we investigated the in vivo functional role of oncofetal trophoblast glycoprotein 5T4, a regulator for dendritic arborization of 5T4-expressing GCs (5T4 GCs), the level of which is reduced in the OB of 5T4 knock-out (KO) mice. Electrophysiological recordings with acute OB slices indicated that external tufted cells (ETCs) can be divided into two types, bursting and nonbursting. Optogenetic stimulation of 5T4 GCs revealed their connection to both bursting and nonbursting ETCs, as well as to mitral cells (MCs). Interestingly, nonbursting ETCs received fewer inhibitory inputs from GCs in 5T4 KO mice than from those in wild-type (WT) mice, whereas bursting ETCs and MCs received similar inputs in both mice. Furthermore, 5T4 GCs received significantly fewer excitatory inputs in 5T4 KO mice. Remarkably, in olfactory behavior tests, 5T4 KO mice had higher odor detection thresholds than the WT, as well as defects in odor discrimination learning. Therefore, the loss of 5T4 attenuates inhibitory inputs from 5T4 GCs to nonbursting ETCs and excitatory inputs to 5T4 GCs, contributing to disturbances in olfactory behavior. Our novel findings suggest that, among the various types of OB interneurons, the 5T4 GC subtype is required for odor detection and discrimination behaviors.

SIGNIFICANCE STATEMENT

Neuronal circuits in the brain include glutamatergic principal neurons and GABAergic interneurons. Although the latter is a minority cell type, they are vital for normal brain function because they regulate the activity of principal neurons. If interneuron function is impaired, brain function may be damaged, leading to behavior disorder. The olfactory bulb (OB) possesses various types of interneurons, including granule cells (GCs); however, the contribution that each type of interneuron makes to the control of olfactory behavior remains unknown. Here, we analyzed electrophysiologically and behaviorally the function of oncofetal trophoblast glycoprotein 5T4, a regulator for dendritic branching in OB GCs. We found that, among the various types of OB interneuron, the 5T4 GC subtype is required for odor detection and odor discrimination behaviors.

Marine Antibody-Drug Conjugates: Design Strategies and Research Progress

Antibody-drug conjugates (ADCs), constructed with monoclonal antibodies (mAbs), linkers, and natural cytotoxins, are innovative drugs developed for oncotherapy. Owing to the distinctive advantages of both chemotherapy drugs and antibody drugs, ADCs have obtained enormous success during the past several years. The development of highly specific antibodies, novel marine toxins' applications, and innovative linker technologies all accelerate the rapid R&D of ADCs. Meanwhile, some challenges remain to be solved for future ADCs. For instance, varieties of site-specific conjugation have been proposed for solving the inhomogeneity of DARs (Drug Antibody Ratios). In this review, the usages of various natural toxins, especially marine cytotoxins, and the development strategies for ADCs in the past decade are summarized. Representative ADCs with marine cytotoxins in the pipeline are introduced and characterized with their new features, while perspective comments for future ADCs are proposed.

Parallel evolution of male germline epigenetic poising and somatic development in animals

Changes in gene regulation frequently underlie changes in morphology during evolution, and differences in chromatin state have been linked with changes in anatomical structure and gene expression across evolutionary time. Here we assess the relationship between evolution of chromatin state in germ cells and evolution of gene regulatory programs governing somatic development. We examined the poised (H3K4me3/H3K27me3 bivalent) epigenetic state in male germ cells from five mammalian and one avian species. We find that core genes poised in germ cells from multiple amniote species are ancient regulators of morphogenesis that sit at the top of transcriptional hierarchies controlling somatic tissue development, whereas genes that gain poising in germ cells from individual species act downstream of core poised genes during development in a species-specific fashion. We propose that critical regulators of animal development gained an epigenetically privileged state in germ cells, manifested in amniotes by H3K4me3/H3K27me3 poising, early in metazoan evolution.

Molecular Mechanisms Regulating the Dendritic Development of Newborn Olfactory Bulb Interneurons in a Sensory Experience-Dependent Manner

Inhibitory interneurons in the olfactory bulb are generated continuously throughout life in the subventricular zone and differentiate into periglomerular and granule cells. Neural circuits that undergo reorganization by newborn olfactory bulb interneurons are necessary for odor detection, odor discrimination, olfactory memory, and innate olfactory responses. Although sensory experience has been shown to regulate development in a variety of species and in various structures, including the retina, cortex, and hippocampus, little is known about how sensory experience regulates the dendritic development of newborn olfactory bulb interneurons. Recent studies revealed that the 5T4 oncofetal trophoblast glycoprotein and the neuronal Per/Arnt/Sim domain protein 4 (Npas4) transcription factor regulate dendritic branching and dendritic spine formation, respectively, in olfactory bulb interneurons. Here, we summarize the molecular mechanisms that underlie the sensory input-dependent development of newborn interneurons and the formation of functional neural circuitry in the olfactory bulb.

Evolving Strategies for Target Selection for Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) represent a promising modality for the treatment of cancer. The therapeutic strategy is to deliver a potent drug preferentially to the tumor and not normal tissues by attaching the drug to an antibody that recognizes a tumor antigen. The selection of antigen targets is critical to enabling a therapeutic window for the ADC and has proven to be surprisingly complex. We surveyed the tumor and normal tissue expression profiles of the targets of ADCs currently in clinical development. Our analysis demonstrates a surprisingly broad range of expression profiles and the inability to formalize any optimal parameters for an ADC target. In this context, we discuss additional considerations for ADC target selection, including interdependencies among biophysical properties of the drug, biological functions of the target and strategies for clinical development. The TPBG (5T4) oncofetal antigen and the anti-TPBG ADC A1-mcMMAF are highlighted to demonstrate the relevance of the target's biological function. Emerging platform technologies and novel biological insights are expanding ADC target space and transforming strategies for target selection.

Phenotype of TPBG Gene Replacement in the Mouse and Impact on the Pharmacokinetics of an Antibody-Drug Conjugate

The use of predictive preclinical models in drug discovery is critical for compound selection, optimization, preclinical to clinical translation, and strategic decision-making. Trophoblast glycoprotein (TPBG), also known as 5T4, is the therapeutic target of several anticancer agents currently in clinical development, largely due to its high expression in tumors and low expression in normal adult tissues. In this study, mice were engineered to express human TPBG under endogenous regulatory sequences by replacement of the murine Tpbg coding sequence. The gene replacement was considered functional since the hTPBG knockin (hTPBG-KI) mice did not exhibit clinical observations or histopathological phenotypes that are associated with Tpbg gene deletion, except in rare instances. The expression of hTPBG in certain epithelial cell types and in different microregions of the brain and spinal cord was consistent with previously reported phenotypes and expression patterns. In pharmacokinetic studies, the exposure of a clinical-stage anti-TPBG antibody-drug conjugate (ADC), A1mcMMAF, was lower in hTPBG-KI versus wild-type animals, which was evidence of target-related increased clearance in hTPBG-KI mice. Thus, the hTPBG-KI mice constitute an improved system for pharmacology studies with current and future TPBG-targeted therapies and can generate more precise pharmacokinetic and pharmacodynamic data. In general the strategy of employing gene replacement to improve pharmacokinetic assessments should be broadly applicable to the discovery and development of ADCs and other biotherapeutics.

Understanding and exploiting 5T4 oncofoetal glycoprotein expression

Oncofoetal antigens are present during foetal development with generally limited expression in the adult but are upregulated in cancer. These molecules can sometimes be used to diagnose or follow treatment of tumours or as a target for different immunotherapies. The 5T4 oncofoetal glycoprotein was identified by searching for shared surface molecules of human trophoblast and cancer cells with the rationale that they may function to allow survival of the foetus as a semi-allograft in the mother or a tumour in its host, potentially influencing growth, invasion or altered immune surveillance of the host. 5T4 tumour selective expression has stimulated the development of 5T4 vaccine, 5T4 antibody targeted-superantigen and 5T4 antibody-drug therapies through preclinical and into clinical studies. It is now apparent that 5T4 expression is a marker of the use (or not) of several cellular pathways relevant to tumour growth and spread. Thus 5T4 expression is mechanistically associated with the directional movement of cells through epithelial mesenchymal transition, facilitation of CXCL12/CXCR4 chemotaxis, blocking of canonical Wnt/beta-catenin while favouring non-canonical pathway signalling. These processes are highly regulated in development and in normal adult tissues but can contribute to the spread of cancer cells. Understanding the differential impact of these pathways marked by 5T4 can potentially improve existing, or aid development of novel cancer treatment strategies.

Identification of Pre- and Post-Treatment Markers, Clinical, and Laboratory Parameters Associated with Outcome in Renal Cancer Patients Treated with MVA-5T4

The recent approvals of immunotherapeutic agents (Sipuleucel-T and Ipilimumab) for the treatment of different solid tumors gave a boost to the growing cancer immunotherapy field, even though few immunotherapy studies have demonstrated convincingly that there is a direct link between the predicted mode of action of an immunological compound and therapeutic benefit. MVA-5T4 (TroVax^®) is a novel vaccine combining the tumor-associated antigen 5T4 to an engineered vector-modified vaccinia Ankara (MVA). MVA helps to express the oncofetal 5T4 antigen and subsequently trigger a tumor-directed immune reaction. The safety and clinical benefit reported in multiple phase I and II clinical trials using MVA-5T4 were encouraging; immune responses were induced in almost all treated patients, and associations between 5T4-specific cellular or humoral responses and clinical benefit were reported in most of the nine phase II trials. In particular, clinical studies conducted in renal cell carcinoma (RCC) patients have demonstrated an association between 5T4-specific (but not MVA) antibody responses and enhanced survival. This review describes the clinical studies using MVA-5T4 conducted in RCC that convincingly demonstrated that an antigen-specific immune response induced by vaccination is associated with enhanced patient survival and is not simply a function of the general “health” of patients. We will also provide our expert opinions on possible future better-designed clinical trials based on relevant biomarkers. In addition, various combinations of MVA-5T4 and different and newer immunomodulator agents with promising clinical benefit will be discussed.

Evaluation of MVA-5T4 as a novel immunotherapeutic vaccine in colorectal, renal and prostate cancer

This paper reviews the development of the combination of modified vaccinia Ankara (MVA) to deliver the tumor-associated antigen 5T4 as a novel immunotherapeutic vaccine. The oncofetal antigen 5T4 is highly expressed in 80% of breast, kidney, colorectal, prostate and ovarian carcinomas, making it an ideal antigen for vaccine therapy. To date, more than 3000 doses of MVA-5T4 have been administered to colorectal, renal and prostate cancer patients, with rare occurrences of grade 3 or 4 vaccination-related adverse events being observed. Studies have demonstrated that MVA-5T4 is safe and highly immunogenic, both as monotherapy and in combination with other standard of care therapies. Although an immune response has been observed, antitumor activity has been modest or absent in clinical trials. A Phase III trial resulted in the development of an immune response surrogate that is to be applied to all future MVA-5T4 clinical trials. With minimal side effects and the ability to produce a strong immunogenic response, MVA-5T4 is a viable addition to the cancer therapy arsenal.

Regulation of autologous immunity to the mouse 5T4 oncofoetal antigen: implications for immunotherapy

Effective vaccination against tumour-associated antigens (TAA) such as the 5T4 oncofoetal glycoprotein may be limited by the nature of the T cell repertoire and the influence of immunomodulatory factors in particular T regulatory cells (Treg). Here, we identified mouse 5T4-specific T cell epitopes using a 5T4 knock out (5T4KO) mouse and evaluated corresponding wild-type (WT) responses as a model to refine and improve immunogenicity. We have shown that 5T4KO mice vaccinated by replication defective adenovirus encoding mouse 5T4 (Adm5T4) generate potent 5T4-specific IFN-γ CD8 and CD4 T cell responses which mediate significant protection against 5T4 positive tumour challenge. 5T4KO CD8 but not CD4 primed T cells also produced IL-17. By contrast, Adm5T4-immunized WT mice showed no tumour protection consistent with only low avidity CD8 IFN-γ, no IL-17 T cell responses and no detectable CD4 T cell effectors producing IFN-γ or IL-17. Treatment with anti-folate receptor 4 (FR4) antibody significantly reduced the frequency of Tregs in WT mice and enhanced 5T4-specific IFN-γ but reduced IL-10 T cell responses but did not reveal IL-17-producing effectors. This altered balance of effectors by treatment with FR4 antibody after Adm5T4 vaccination provided modest protection against autologous B16m5T4 melanoma challenge. The efficacy of 5T4 and some other TAA vaccines may be limited by the combination of TAA-specific T regs, the deletion and/or alternative differentiation of CD4 T cells as well as the absence of distinct subsets of CD8 T cells.

5T4 glycoprotein regulates the sensory input-dependent development of a specific subtype of newborn interneurons in the mouse olfactory bulb

Sensory input has been shown to regulate development in a variety of species and in various structures, including the retina, cortex, and olfactory bulb (OB). Within the mammalian OB specifically, the development of dendrites in mitral/tufted cells is well known to be odor-evoked activity dependent. However, little is known about the developmental role of sensory input in the other major OB population of the GABAgenic interneurons, such as granule cells and periglomerular cells. Here, we identified, with DNA microarray and in situ hybridization screenings, a trophoblast glycoprotein gene, 5T4, whose expression in a specific subtype of OB interneurons is dependent on sensory input. 5T4 is a type I membrane protein, whose extracellular domain contains seven leucine-rich repeats (LRR) flanked by characteristic LRR-N-flanking and C-flanking regions, and a cytoplasmic domain. 5T4 overexpression in the newborn OB interneurons facilitated their dendritic arborization even under the sensory input-deprived condition. By contrast, both 5T4 knockdown with RNAi and 5T4 knockout with mice resulted in a significant reduction in the dendritic arborization of 5T4(+) granule cells. Further, we identified the amino acid sequence in the 5T4 cytoplasmic domain that is necessary and sufficient for the sensory input-dependent dendritic shaping of specific neuronal subtypes in the OB. Thus, these results demonstrate that 5T4 glycoprotein contributes in the regulation of activity-dependent dendritic development of interneurons and the formation of functional neural circuitry in the OB.

Clinical Efficacy of TroVax in the Treatment of Progressive Castration-resistant Prostate Cancer

With approximately 240,890 new cases expected in 2011, prostate cancer remains the leading cause of non-melanoma cancer deaths in men. Immunotherapies using viral vector-based delivery systems targeting tumor-specific antigens are being studied. Viral vector-based delivery systems present tumor-targeted antigens (TAAs) to the immune system while breaking self-tolerance. Modified vaccinia ankara has been combined with the oncofetal antigen 5T4 to create TroVax for the treatment of castration-resistant prostate cancer (CRPC). The 5T4 antigen is highly expressed in a large number of carcinomas, including prostate cancer, but is rarely expressed in healthy tissue. TroVax has been demonstrated to be safe and highly immunogenic, both as monotherapy and in combination with other standard of care therapies in colorectal, renal cell, and prostate cancer. With minimal side effects and the ability to produce a strong immunogenic response, TroVax (MVA-5T4) is a viable addition to the treatment of prostate cancer.

Delineation of a cellular hierarchy in lung cancer reveals an oncofetal antigen expressed on tumor-initiating cells

Poorly differentiated tumors in non-small cell lung cancer (NSCLC) have been associated with shorter patient survival and shorter time to recurrence following treatment. Here, we integrate multiple experimental models with clinicopathologic analysis of patient tumors to delineate a cellular hierarchy in NSCLC. We show that the oncofetal protein 5T4 is expressed on tumor-initiating cells and associated with worse clinical outcome in NSCLC. Coexpression of 5T4 and factors involved in the epithelial-to-mesenchymal transition were observed in undifferentiated but not in differentiated tumor cells. Despite heterogeneous expression of 5T4 in NSCLC patient-derived xenografts, treatment with an anti-5T4 antibody-drug conjugate resulted in complete and sustained tumor regression. Thus, the aggressive growth of heterogeneous solid tumors can be blocked by therapeutic agents that target a subpopulation of cells near the top of the cellular hierarchy.

Expression of vascular endothelial growth factor receptor-3 mRNA in the rat developing forebrain and retina

Vascular endothelial growth factor receptor (VEGFR)-3, a receptor for VEGF-C and VEGF-D, is expressed in neural progenitor cells, but there has been no comprehensive study of its distribution in the developing brain. Here, the temporal and cell-specific expression of VEGFR-3 mRNA was studied in the developing rat forebrain and eye. Expression appeared along the ventricular and subventricular zones of the lateral and third ventricles showing ongoing neurogenesis as early as embryonic day 13 but was progressively down-regulated during development and remained in the subventricular zone and rostral migratory stream of the adult forebrain. VEGFR-3 expression was also detectable in some differentiating and postmitotic neurons in the developing cerebral cortex, including Cajal-Retzius cells, cortical plate neurons, and subplate neurons. Expression in the subplate increased significantly during the early postnatal period but was absent by postnatal day 14. It was also highly expressed in nonneural tissues of the eye during development, including the retinal pigment epithelium, the retinal ciliary margin, and the lens, but persisted in a subset of cells in the pigmented ciliary epithelium of the adult eye. In contrast, there was weak or undetectable expression in the early neural retina, but a subset of retinal neurons in the postnatal and mature retina showed intense signals. These unique spatiotemporal mRNA expression patterns suggest that VEGFR-3 might mediate the regulation of both neurogenesis and adult neuronal function in the rat forebrain and eye.

5T4-modified vaccinia Ankara: progress in tumor-associated antigen-based immunotherapy

IMPORTANCE OF THE FIELD

The expression and biology of the tumor-associated antigen (TAA) 5T4 suggest it is an effective target for cancer immunotherapy.

AREAS COVERED IN THIS REVIEW

Development of a vaccine comprising highly attenuated modified vaccinia Ankara virus encoding 5T4 (MVA-5T4, a.k.a. TroVax).

WHAT THE READER WILL GAIN

Preclinical studies demonstrated that MVA-5T4 is safe and effective in prophylactic and active treatment of syngeneic murine tumor models. Over 700 doses of MVA-5T4 have been administered to over 200 patients to date. Results from clinical trials on metastatic colorectal, metastatic renal and hormone-refractory prostate cancer patients demonstrate that MVA-5T4 is safe and immunogenic as a monotherapy and in combination with standard-of-care therapies. MVA-5T4 induced potent and sustained immune responses in approximately 95% of tested patients. Post hoc analyses have noted a correlation between anti-5T4 immune responses and indicators of clinical benefit. A Phase III randomized, placebo controlled study, which investigated MVA-5T4 added to first line standard of care to evaluate whether vaccination prolonged survival of patients with metastatic clear cell renal cell cancer did not meet the primary endpoint (overall survival).

TAKE HOME MESSAGE

With its minimal side effects and ability to produce immune responses MVA-5T4 is a promising addition to the cancer therapy arsenal.

CXCR4 mediated chemotaxis is regulated by 5T4 oncofetal glycoprotein in mouse embryonic cells

5T4 oncofetal molecules are highly expressed during development and upregulated in cancer while showing only low levels in some adult tissues. Upregulation of 5T4 expression is a marker of loss of pluripotency in the early differentiation of embryonic stem (ES) cells and forms an integrated component of an epithelial-mesenchymal transition, a process important during embryonic development and metastatic spread of epithelial tumors. Investigation of the transcriptional changes in early ES differentiation showed upregulation of CXCL12 and down-regulation of a cell surface protease, CD26, which cleaves this chemokine. CXCL12 binds to the widely expressed CXCR4 and regulates key aspects of development, stem cell motility and tumour metastasis to tissues with high levels of CXCL12. We show that the 5T4 glycoprotein is required for optimal functional cell surface expression of the chemokine receptor CXCR4 and CXCL12 mediated chemotaxis in differentiating murine embryonic stem cells and embryo fibroblasts (MEF). Cell surface expression of 5T4 and CXCR4 molecules is co-localized in differentiating ES cells and MEF. By contrast, differentiating ES and MEF derived from 5T4 knockout (KO) mice show only intracellular CXCR4 expression but infection with adenovirus encoding mouse 5T4 restores CXCL12 chemotaxis and surface co-localization with 5T4 molecules. A series of chimeric constructs with interchanged domains of 5T4 and the glycoprotein CD44 were used to map the 5T4 sequences relevant for CXCR4 membrane expression and function in 5T4KO MEF. These data identified the 5T4 transmembrane domain as sufficient and necessary to enable CXCR4 cell surface expression and chemotaxis. Furthermore, some monoclonal antibodies against m5T4 can inhibit CXCL12 chemotaxis of differentiating ES cells and MEF which is not mediated by simple antigenic modulation. Collectively, these data support a molecular interaction of 5T4 and CXCR4 occurring at the cell surface which directly facilitates the biological response to CXCL12. The regulation of CXCR4 surface expression by 5T4 molecules is a novel means to control responses to the chemokine CXCL12 for example during embryogenesis but can also be selected to advantage the spread of a 5T4 positive tumor from its primary site.

Maintenance of pluripotency and self-renewal ability of mouse embryonic stem cells in the absence of tetraspanin CD9

We have previously demonstrated that the tetraspanin CD9 is necessary for membrane fusion between sperm and oocyte during fertilization. While knockout mice for CD9 are viable, CD9(-/-) females are sterile due to the inability of their oocytes to fuse with sperm. While CD9 is not essential for subsequent development, a role in embryonic stem (ES) cell self-renewal was hypothesised on the basis of two observations: CD9 is highly expressed in murine and human ES cells and the CD9-blocking antibody inhibits mouse ES cell colony formation and survival. To investigate whether CD9 has a direct effect on ES cells, we generated and characterised several CD9 knockout murine ES cell lines. These CD9(-/-) ES cell lines exhibited equivalent morphology and growth properties to wild-type ES cells. Furthermore, the CD9(-/-) ES cell lines also displayed similar expression of pluripotency factors Oct3/4, Sox2 and Nanog. CD9(-/-) ES cells were found to be pluripotent in vivo, as their cells injected into immunocompromised mice gave rise to teratomas consisting of tissues representative of all three germ layers. Additionally several high contribution mouse chimeras were generated by blastocyst injection with several CD9(-/-) ES cell lines. Taken together, our results reveal that CD9 is dispensable for mouse ES cell self-renewal and pluripotency. The generation of CD9(-/-) ES cells should prove to be a useful tool with which to study the function of this protein and a range of other associated cellular processes.

Vaccination of renal cell cancer patients with modified vaccinia ankara delivering tumor antigen 5T4 (TroVax) administered with interleukin 2: a phase II trial

PURPOSE

The attenuated vaccinia virus modified vaccinia ankara (MVA) has been engineered to deliver the tumor antigen 5T4 (TroVax). TroVax has been evaluated in an open-label phase II trial in metastatic renal cell cancer patients in which the vaccine was administered in combination with interleukin-2 (IL-2). The safety, immunologic, and clinical efficacy of TroVax in combination with IL-2 was determined.

EXPERIMENTAL DESIGN

Twenty-five patients with metastatic renal cell cancer were treated with TroVax plus IL-2. 5T4-specific cellular and humoral responses were monitored throughout the study. Clinical responses were assessed by measuring changes in tumor burden by computed tomography or magnetic resonance imaging scan.

RESULTS

TroVax was well tolerated with no serious adverse event attributed to vaccination. Of 25 intention-to-treat patients, 21 mounted 5T4-specific antibody responses. Two patients showed a complete response for > 24 months and one a partial response for > 12 months. Six patients had disease stabilization from 6 to > 21 months. Median progression-free survival (PFS) and overall survival (OS) were > 3.37 months (range, 1.50- > 24.76) and > 12.87 months (range, 1.90- > 24.76), respectively. A statistically significant relationship was detected between the magnitude of 5T4-specific antibody responses and PFS and OS.

CONCLUSION

TroVax in combination with IL-2 was safe and well tolerated in all patients. The high frequency of 5T4-specific immune responses and good clinical response rate are encouraging and warrant further investigation.

Epithelial-mesenchymal transition events during human embryonic stem cell differentiation

Epithelial-mesenchymal transition (EMT) occurs during embryonic development and may also be associated with the metastatic spread of epithelial tumors. During EMT, E-cadherin is down-regulated and this correlates with increased motility and invasion of cells. We show that differentiation of human embryonic stem (ES) cells in monolayer culture is associated with an E- to N-cadherin switch, increased vimentin expression, up-regulation of E-cadherin repressor molecules (Snail and Slug proteins), and increased gelatinase (matrix metalloproteinases; MMP-2 and MMP-9) activity and cellular motility, all characteristic EMT events. The 5T4 oncofetal antigen, previously shown to be associated with early human ES cell differentiation, is also part of this process. Abrogation of E-cadherin-mediated cell-cell contact in undifferentiated ES cells using neutralizing antibody (nAb) SHE78.7 resulted in increased cellular motility, altered actin cytoskeleton arrangement and a mesenchymal phenotype together with presentation of the 5T4 antigen at the cell surface. nAb-treated ES cells remained in an undifferentiated state, as assessed by OCT-4 protein expression, and did not express EMT-associated transcripts. Removal of nAb from ES cells resulted in the restoration of cell-cell contact, absence of cell surface 5T4, decreased mesenchymal cellular morphology and motility, and enabled the differentiation of the cells to the three germ layers upon their removal from the fibroblast feeder layer. We conclude that E-cadherin functions in human ES cells to stabilize the cortical actin cyoskeletal arrangement and this prevents cell surface localization of the 5T4 antigen. Furthermore, human ES cells represent a useful model system with which to study EMT events relevant to embryonic development and tumor cell metastasis.

5T4-modified vaccinia ankara: progress in tumor-associated antigen-based immunotherapy

Both the expression and biology of the tumor-associated antigen (TAA) 5T4 suggest that it is an effective target for cancer immunotherapy. This paper reviews the development of a novel immunotherapeutic vaccine comprising the highly attenuated modified vaccinia ankara virus encoding 5T4 (MVA-5T4, aka TroVax). Preclinical studies have demonstrated that MVA-5T4 is safe and highly effective in both the prophylactic and active treatment of syngeneic murine tumor models. More importantly, > 700 doses of MVA-5T4 have been administered to > 200 patients to date. Reported results from clinical trials in metastatic colorectal, metastatic renal and hormone-refractory prostate cancer patients demonstrate that MVA-5T4 is safe and highly immunogenic, both as a monotherapy and in combination with standard-of-care therapies including irinotecan, oxaliplatin, IFN-alpha and IL-2. These studies demonstrate that MVA-5T4 induces potent and sustained immune responses in approximately 95% of tested patients. In addition, post-hoc analyses of these studies have noted a correlation between anti-5T4 immune responses and indicators of clinical benefit. With its minimal side effects and demonstrated ability to produce strong immune responses in patient populations, MVA-5T4 is a promising addition to the cancer therapy arsenal.

Novel vectors for homologous recombination strategies in mouse embryonic stem cells: an ES cell line expressing EGFP under control of the 5T4 promoter

The use of gene mutation/knock-out strategies in mouse embryonic stem (ES) cells has revolutionized the study of gene function in ES cells and embryonic development. However, the construction of vectors for homologous recombination strategies requires considerable expertise and time. We describe two novel vectors that can generate site specific knock-out or EGFP knock-in ES cells within 6 weeks from construct design to identification of positive ES cell clones. As proof-of-principle, we have utilized the knock-out targeting vector to modify the NEIL2 locus in ES cells. In addition, using the knock-in vector, we have inserted EGFP downstream of the 5T4 oncofetal antigen promoter in ES cells (5T4-GFP ES cells). Undifferentiated 5T4-GFP ES cells lack EGFP and maintain expression of the pluripotent markers OCT-4 and NANOG. Upon differentiation, EGFP expression is increased in 5T4-GFP ES cells and this correlates with 5T4 transcript expression of the unmodified allele, loss of Nanog and Oct-4 transcripts and upregulation of differentiation-associated transcripts. Furthermore, we demonstrate that fluorescent activated cell sorting of 5T4-GFP ES cells allows isolation of pluripotent or differentiated cells from a heterogeneous population. These vectors provide researchers with a rapid method of modifying specific ES cell genes to study cellular differentiation and embryonic development.

E-cadherin inhibits cell surface localization of the pro-migratory 5T4 oncofetal antigen in mouse embryonic stem cells

Epithelial-mesenchymal transition (EMT) events occur during embryonic development and are important for the metastatic spread of epithelial tumors. We show here that spontaneous differentiation of mouse embryonic stem (ES) cells is associated with an E- to N-cadherin switch, up-regulation of E-cadherin repressor molecules (Snail and Slug proteins), gelatinase activity (matrix metalloproteinase [MMP]-2 and -9), and increased cellular motility, all characteristic EMT events. The 5T4 oncofetal antigen, previously shown to be associated with very early ES cell differentiation and altered motility, is also a part of this coordinated process. E- and N-cadherin and 5T4 proteins are independently regulated during ES cell differentiation and are not required for induction of EMT-associated transcripts and proteins, as judged from the study of the respective knockout ES cells. Further, abrogation of E-cadherin-mediated cell-cell contact in undifferentiated ES cells using neutralizing antibody results in a reversible mesenchymal phenotype and actin cytoskeleton rearrangement that is concomitant with translocation of the 5T4 antigen from the cytoplasm to the cell surface in an energy-dependent manner. E-cadherin null ES cells are constitutively cell surface 5T4 positive, and although forced expression of E-cadherin cDNA in these cells is sufficient to restore cell-cell contact, cell surface expression of 5T4 antigen is unchanged. 5T4 and N-cadherin knockout ES cells exhibit significantly decreased motility during EMT, demonstrating a functional role for these proteins in this process. We conclude that E-cadherin protein stabilizes cortical actin cytoskeletal arrangement in ES cells, and this can prevent cell surface localization of the promigratory 5T4 antigen.

The Lectin Dolichos Biflorus Agglutinin Recognizes Glycan Epitopes on the Surface of Murine Embryonic Stem Cells: A New Tool for Characterizing Pluripotent Cells and Early Differentiation

Cell surface markers are key tools that are frequently used to characterize and separate mixed cell populations. Existing cell surface markers used to define murine embryonic stem cells (mESCs) such as stage-specific embryonic antigen 1 (SSEA1), Forssman antigen (FA), alkaline phosphatase (AP), and CD9 are limiting, however, because they do not unambiguously define the pluripotent state and are not reliable indicators of differentiation commitment. To identify glycan cell surface markers that would circumvent this problem, we used a panel of 18 lectins to identify epitopes specifically elevated on the surface of mESCs, which, during differentiation, decrease with kinetics that precede currently used markers such as CD9, SSEA1, FA, and AP. The anticipated outcome of this analysis was to identify glycans that have utility as reliable mESC markers and high-resolution readouts for early differentiation commitment. Here, we show that the lectin Dolichos biflorus agglutinin (DBA) recognizes alpha-N-acetylgalactosamine (GalNAc) cell surface epitopes on mESCs (CD9(high) SSEA1(high) AP(high) DBA(high)). These glycan epitopes decline markedly in cells undergoing the first definable step of differentiation, the transition from mESCs to primitive ectoderm (CD9(high) SSEA1(high) AP(high) DBA(low)). Loss of GalNAc epitopes is, therefore, the earliest cell surface change that can be assigned to differentiating cells, and the only cell surface marker known to be tightly associated with the pluripotent state. The lectin DBA is, therefore, a useful tool to characterize mESC cultures by nondestructive approaches, an indicator of differentiation commitment, and a predictor of developmental potency.

Cell surface 5T4 antigen is transiently upregulated during early human embryonic stem cell differentiation: effect of 5T4 phenotype on neural lineage formation

The 5T4 oncofoetal antigen is a cell surface glycoprotein that is transiently expressed during mouse ES cell differentiation and correlates with decreased pluripotency of such cells. We show that 5T4 antigen is transiently unregulated during HES4 and H1 human ES cell differentiation and its expression correlates with loss of the pluripotent markers OCT-4 and Tra-1-60 and upregulation of transcript markers associated with the three primary germ layers. To confirm that absence of cell surface 5T4 antigen represents a pluripotent hES cell phenotype, we performed mechanical transfer of either 5T4-ve or 5T4+ve HES4 colonies identified using live cell staining. 5T4-ve transfers maintained expression of OCT-4 in over 90% of resultant colonies, whereas 5T4+ve transfers exhibited significantly lower numbers of OCT-4-expressing colonies (92 +/- 1.4 vs. 2.9 +/- 2.0%). Interestingly, low cell density 5T4-ve colony transfers exhibited increased numbers of OCT-4-expressing colonies compared to large 5T4-ve transfers (92 +/- 1.4 vs. 63.2 +/- 1.9%). 5T4-ve and 5T4+ve HES4 and H1 ES cell lines expressed markers representative of neuroectoderm lineages, and we assessed the formation of neural lineages from these phenotypes in serum-containing medium and N2B27 medium. Expression of 5T4 was found to be inversely related to the yield of tyrosine-hydroxylase (TH+)-expressing neurons in N2B27 medium, with additional mesoderm and endoderm transcript markers detected. Homogeneous glial cell populations were derived from low cell density 5T4-ve colony transfers cultured in serum-containing medium, with TH+ neuronal formation inhibited in a cell-density-dependent manner. We conclude that the 5T4 antigen is a transient marker of hES cell differentiation and that 5T4 phenotype, colony seeding density and culture conditions significantly influence the maintenance of pluripotent hES cells and their differentiation to neural lineages.