189 Targeting a novel shared tumor-specific antigen with T cell receptor transduced T cells for the treatment of ovarian cancer

Background

Transgenic T cell receptor (TCR)-based T cell therapies are a powerful treatment for cancer. However, one of the greatest remaining challenges is the successful identification of tumor-specific antigens (TSAs) that are shared between patients and tumor entities and elicit strong T cell responses. The non-coding region of the genome has become a promising source of such novel TSAs. Previously, we have identified ten immunogenic shared TSAs, derived from the translation in canonical and non-canonical reading frames of non-mutated non-coding genomic regions like introns, intergenic regions and 5’-untranslated regions. In the following process, we identified several TCRs specific for these TSAs. Here we aimed at the validation of two TSA-specific TCRs in a model of ovarian cancer-derived organoids.

Methods

Freshly collected ovarian tumor and normal ovarian tissue expressing the HLA of interest were mechanically disrupted, enzymatically digested and cryopreserved. Expression of the TSA of interest in the primary tumor tissue was confirmed with RNA sequencing and mass spectrometry. Thawed single cell suspensions were used to generate tumor organoids and 2D-growing normal ovarian cell lines. To validate the generated cell lines, the presence or absence of two previously identified tumor-specific mutations was investigated by targeted Sanger sequencing in the genome of the tumor organoids, normal cell lines and primary tissues. Two TSA-specific TCRs were retrovirally transduced into CD8+ T cells of three healthy donors. Expanded TSA-specific CD8+T cells were co-cultured 24 hours with single cell suspensions of IFN-γ pre-stimulated, tumor organoids or the 2D-growing normal ovarian cell line. IFN-γ ELISA was used to assess activation of TSA-specific T cells upon co-culture.

Results

The TSA of interest was detected both at the transcriptomic and proteomic level in the primary ovarian tumor tissue. Using frozen single cell suspensions of this tumor and corresponding normal tissue, tumor organoids and 2D-growing normal cell lines were successfully established and their integrity was confirmed. Both TSA-specific TCRs were efficiently expressed on CD8+ T cells from three donors. TCR-transgenic T cells showed activation upon co-culture with tumor organoids without recognition of normal ovarian cell lines. Normal cells were only recognized after loading with the specific target peptide.

Conclusions

In conclusion, the high relevance of two TCRs identified to be specific for a novel shared tumor-specific antigen was confirmed in a model of ovarian cancer organoids. The findings support further development of these TCRs for cancer immunotherapy and implementation of tumor organoids as a relevant tool for the characterization of TSA-specific TCRs.

Ethics Approval

‘The tumor and normal tissue samples were purchased at a Biobank, collected in compliance with all applicable EU regulations and were pseudonymized.’

Abstract 1520: Targetable immunogenic tumor specific antigens can be identified in non-coding regions of the genome

CD8+ cytotoxic T cells are the main mediators of immune responses during cancer immunotherapy. Effective T cell functionality depends on the specific interaction with major histocompatibility (MHC) class I-bound peptide antigens. Significant efforts are being dedicated to the identification of novel tumor specific antigens (TSAs), investigating not only the known proteome, but also non-coding regions of the genome, that would allow for improved discrimination between cancer cells and healthy tissues. Through extensive comparisons of tumor and healthy tissues at the transcriptional and MHC-presented peptidome levels, TSAs were identified that derived from the translation in canonical and non-canonical reading frames of non-mutated non-coding genomic regions, including 5'- and 3'-untranslated regions (UTRs), introns and intergenic regions. A remarkable feature of these TSAs is that they are shared among patients and solid tumor types, thus representing ideal targets for cancer immunotherapies, including vaccines and adoptive cell therapies. To identify TSAs that can elicit T cell responses, a high throughput screening procedure was used to investigate the immunogenicity of 47 TSAs in the context of five common HLA types. Constructs harboring the TSA sequences were developed and transfected into HLA-matched monocyte-derived dendritic cells (mDCs) that were used to stimulate autologous CD8+ T cells. TSA-reactive T cells were enriched upon stimulation with antigen-positive and -negative cells using the T cell activation marker CD137 and sorted as single cells. Reactivity of individual T cell clones towards specific TSAs was confirmed by measuring cytokine release upon co-culture with HLA-matched TSA-positive and negative cell lines. Ten immunogenic TSAs were identified with this procedure, including at least one immunogenic TSA for each of the five analyzed HLAs. For some of these antigens, specific T cells were found in multiple healthy donors. The identified immunogenic TSAs derive from a variety of non-coding regions, such as introns, 5'-UTRs and non-coding RNAs. The T cell receptor (TCR) α and β chain sequences of TSA-reactive T cell clones were identified by NGS, engineered into a retroviral expression construct and transduced into CD8+ T cells. The reactivity of TCR-transgenic T cells against TSA-positive target cells was confirmed by recognition of TSA-peptide-loaded cell lines and target cells internally processing and presenting the TSAs. In conclusion, our high throughput screening approach successfully detected immunogenic TSAs. Furthermore, it can be used for the identification of TSA-reactive TCRs, thus representing a key tool in the development of novel TCR-based cancer immunotherapies targeting this novel class of TSAs.

Citation Format: Tiziana Franceschetti, Qingchuan Zhao, Krystel Vincent, Claude Perreault, Slavoljub Milosevic, Daniel Sommermeyer. Targetable immunogenic tumor specific antigens can be identified in non-coding regions of the genome [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1520.

The potential role of adult stem cells in the management of the rheumatic diseases

Adult stem cells are considered as appealing therapeutic candidates for inflammatory and degenerative musculoskeletal diseases. A large body of preclinical research has contributed to describing their immune-modulating properties and regenerative potential. Additionally, increasing evidence suggests that stem cell differentiation and function are disrupted in the pathogenesis of rheumatic diseases. Clinical studies have been limited, for the most part, to the application of adult stem cell-based treatments on small numbers of patients or as a 'salvage' therapy in life-threatening disease cases. Nevertheless, these preliminary studies indicate that adult stem cells are promising tools for the long-term treatment of rheumatic diseases. This review highlights recent knowledge acquired in the fields of hematopoietic and mesenchymal stem cell therapy for the management of systemic sclerosis (SSc), systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and osteoarthritis (OA) and the potential mechanisms mediating their function.

MicroRNA-433 Dampens Glucocorticoid Receptor Signaling, Impacting Circadian Rhythm and Osteoblastic Gene Expression

Serum glucocorticoids play a critical role in synchronizing circadian rhythm in peripheral tissues, and multiple mechanisms regulate tissue sensitivity to glucocorticoids. In the skeleton, circadian rhythm helps coordinate bone formation and resorption. Circadian rhythm is regulated through transcriptional and post-transcriptional feedback loops that include microRNAs. How microRNAs regulate circadian rhythm in bone is unexplored. We show that in mouse calvaria, miR-433 displays robust circadian rhythm, peaking just after dark. In C3H/10T1/2 cells synchronized with a pulse of dexamethasone, inhibition of miR-433 using a tough decoy altered the period and amplitude of Per2 gene expression, suggesting that miR-433 regulates rhythm. Although miR-433 does not directly target the Per2 3'-UTR, it does target two rhythmically expressed genes in calvaria, Igf1 and Hif1α. miR-433 can target the glucocorticoid receptor; however, glucocorticoid receptor protein abundance was unaffected in miR-433 decoy cells. Rather, miR-433 inhibition dramatically enhanced glucocorticoid signaling due to increased nuclear receptor translocation, activating glucocorticoid receptor transcriptional targets. Last, in calvaria of transgenic mice expressing a miR-433 decoy in osteoblastic cells (Col3.6 promoter), the amplitude of Per2 and Bmal1 mRNA rhythm was increased, confirming that miR-433 regulates circadian rhythm. miR-433 was previously shown to target Runx2, and mRNA for Runx2 and its downstream target, osteocalcin, were also increased in miR-433 decoy mouse calvaria. We hypothesize that miR-433 helps maintain circadian rhythm in osteoblasts by regulating sensitivity to glucocorticoid receptor signaling.

Gene-expression analysis of cementoblasts and osteoblasts

BACKGROUND AND OBJECTIVE

Cementum and bone are similar mineralized tissues, but cementum accumulates much more slowly than bone, does not have vasculature or innervation and does not undergo remodeling. Despite these differences, there are no well-established markers to distinguish cementoblasts from other mature mineralizing cells such as osteoblasts and odontoblasts. The purpose of this study was to assess differences in gene expression between cementoblasts and osteoblasts using gene profiling of cell populations isolated directly from osteocalcin-green fluorescent protein (OC-GFP) transgenic mice.

MATERIAL AND METHODS

OC-GFP reporter mice were used as they show labeling of cementoblasts, osteoblasts and odontoblasts, but not of periodontal ligament fibroblasts, within the periodontium. We sorted cells digested from the molar root surface to isolate OC-GFP(+) cementoblasts. Osteoblasts were isolated from calvarial digests. Microarray analysis was performed, and selected results were confirmed by real-time PCR and immunostaining or in situ hybridization.

RESULTS

Microarray analysis identified 95 genes that were expressed at least two-fold higher in cementoblasts than in osteoblasts. Our analysis indicated that the Wnt signaling pathway was differentially regulated, as were genes related to skeletal development. Real-time PCR confirmed that expression of the Wnt inhibitors Wnt inhibitory factor 1 (Wif1) and secreted frizzled-related protein 1 (Sfrp1) was elevated in cementoblasts compared with osteoblasts, and Wif1 expression was localized to the apical root region. In addition, the transcription factor BARX homeobox 1 (Barx1) was expressed at higher levels in cementoblasts, and immunohistochemistry indicated that BARX1 was expressed in apical cementoblasts and cementocytes, but not in osteoblasts or odontoblasts.

CONCLUSION

The OC-GFP mouse provides a good model for selectively isolating cementoblasts, and allowed for identification of differentially expressed genes between cementoblasts and osteoblasts.

Pathway analysis of microRNA expression profile during murine osteoclastogenesis

To design novel therapeutics against bone loss, understanding the molecular mechanisms regulating osteoclastogenesis is critical. Osteoclast formation and function are tightly regulated by transcriptional, post-transcriptional and post-translational mechanisms. This stringent regulation is crucial to prevent excessive or insufficient bone resorption and to maintain bone homeostasis. microRNAs (miRNAs) are key post-transcriptional regulators that repress expression of target mRNAs controlling osteoclast proliferation, differentiation, and apoptosis. Disruption of miRNA-mediated regulation alters osteoclast formation and bone resorption. Prior studies profiled miRNA expression in murine osteoclast precursors treated with RANKL for 24 hours. However, a more complete miRNA signature, encompassing early, mid and late stages of osteoclastogenesis, is wanting. An Agilent microarray platform was used to analyze expression of mature miRNAs in an enriched population of murine bone marrow osteoclast precursors (depleted of B220⁺ and CD3⁺ cells) undergoing 1, 3, or 5 days of RANKL-driven differentiation. Expression of 93 miRNAs, changed by >2 fold during early, mid, and late stages of osteoclastogenesis, were identified and sorted into 7 clusters. We validated the function and expression of miR-365, miR-451, and miR-99b, which were found in distinct clusters. Inhibition of miR-365 increased osteoclast number but decreased osteoclast size, while miR-99b inhibition decreased both osteoclast number and size. In contrast, overexpression of miR-451 had no effect. Computational analyses predicted mTOR, PI3 kinase/AKT, cell-matrix interactions, actin cytoskeleton organization, focal adhesion, and axon guidance pathways to be top targets of several miRNA clusters. This suggests that many miRNA clusters differentially expressed during osteoclastogenesis converge on some key functional pathways. Overall, our study is unique in that we identified miRNAs differentially expressed during early, mid, and late osteoclastogenesis in a population of primary mouse bone marrow cells enriched for osteoclast progenitors. This novel data set contributes to our understanding of the molecular mechanisms regulating the complex process of osteoclast differentiation.

miR-29 promotes murine osteoclastogenesis by regulating osteoclast commitment and migration

Osteoclast differentiation is regulated by transcriptional, post-transcriptional, and post-translational mechanisms. MicroRNAs are fundamental post-transcriptional regulators of gene expression. The function of the miR-29 (a/b/c) family in cells of the osteoclast lineage is not well understood. In primary cultures of mouse bone marrow-derived macrophages, inhibition of miR-29a, -29b, or -29c diminished formation of TRAP (tartrate-resistant acid phosphatase-positive) multinucleated osteoclasts, and the osteoclasts were smaller. Quantitative RT-PCR showed that all miR-29 family members increased during osteoclast differentiation, in concert with mRNAs for the osteoclast markers Trap (Acp5) and cathepsin K. Similar regulation was observed in the monocytic cell line RAW264.7. In stably transduced RAW264.7 cell lines expressing an inducible miR-29 competitive inhibitor (sponge construct), miR-29 knockdown impaired osteoclastic commitment and migration of pre-osteoclasts. However, miR-29 knockdown did not affect cell viability, actin ring formation, or apoptosis in mature osteoclasts. To better understand how miR-29 regulates osteoclast function, we validated miR-29 target genes using Luciferase 3'-UTR reporter assays and specific miR-29 inhibitors. We demonstrated that miR-29 negatively regulates RNAs critical for cytoskeletal organization, including Cdc42 (cell division control protein 42) and Srgap2 (SLIT-ROBO Rho GTPase-activating protein 2). Moreover, miR-29 targets RNAs associated with the macrophage lineage: Gpr85 (G protein-coupled receptor 85), Nfia (nuclear factor I/A), and Cd93. In addition, Calcr (calcitonin receptor), which regulates osteoclast survival and resorption, is a novel miR-29 target. Thus, miR-29 is a positive regulator of osteoclast formation and targets RNAs important for cytoskeletal organization, commitment, and osteoclast function. We hypothesize that miR-29 controls the tempo and amplitude of osteoclast differentiation.

Utilization of transgenic models in the evaluation of osteogenic differentiation of embryonic stem cells

Previous studies reported that embryonic stem cells (ESCs) can be induced to differentiate into cells showing a mature osteoblastic phenotype by culturing them under osteo-inductive conditions. It is probable that osteogenic differentiation requires that ESCs undergo differentiation through an intermediary step involving a mesenchymal lineage precursor. Based on our previous studies indicating that adult mesenchymal progenitor cells express α-smooth muscle actin (αSMA), we have generated ESCs from transgenic mice in which an αSMA promoter directs the expression of red fluorescent protein (RFP) to mesenchymal progenitor cells. To track the transition of ESC-derived MSCs into mature osteoblasts, we have utilized a bone-specific fragment of rat type I collagen promoter driving green fluorescent protein (Col2.3GFP). Following osteogenic induction in ESCs, we have observed expression of alkaline phosphatase (ALP) and subsequent mineralization as detected by von Kossa staining. After 1 week of osteogenic induction, ESCs begin to express αSMARFP. This expression was localized to the peripheral area encircling a typical ESC colony. Nevertheless, these αSMARFP positive cells did not show activation of the Col2.3GFP promoter, even after 7 weeks of osteogenic differentiation in vitro. In contrast, Col2.3GFP expression was detected in vivo, in mineralized areas following teratoma formation. Our results indicate that detection of ALP activity and mineralization of ESCs cultured under osteogenic conditions is not sufficient to demonstrate osteogenic maturation. Our study indicates the utility of the promoter-visual transgene approach to assess the commitment and differentiation of ESCs into the osteoblast lineage.

Immature osteoblast lineage cells increase osteoclastogenesis in osteogenesis imperfecta murine

This study addressed the role of impairment of osteoblastic differentiation as a mechanism underlying pathophysiology of the osteogenesis imperfecta (OI). We hypothesized that combination of impaired osteogenic differentiation with increased bone resorption leads to diminished bone mass. By introducing visual markers of distinct stages of osteoblast differentiation, pOBCol3.6GFP (3.6GFP; preosteoblast) and pOBCol2.3GFP (2.3GFP; osteoblast/osteocytes), into the OIM model, we assessed osteoblast maturation and the mechanism of increased osteoclastogenesis. Cultures from oim/oim;2.3GFP mice showed a marked reduction of cells expressing GFP relative to +/+;2.3GFP littermates. No significant difference in expression of 3.6GFP between the +/+ and oim/oim mice was observed. Histological analysis of the oim/oim;3.6GFP mice showed an increased area of GFP-positive cells lining the endocortical surface compared with +/+;3.6GFP mice. In contrast GFP expression was similar between oim/oim;2.3GFP and +/+;2.3GFP mice. These data indicate that the osteoblastic lineage is under continuous stimulation; however, only a proportion of cells attain the mature osteoblast stage. Indeed, immature osteoblasts exhibit a stronger potential to support osteoclast formation and differentiation. We detected a higher Rankl/Opg ratio and higher expression of TNF-alpha in sorted immature osteoblasts. In addition, increased osteoclast formation was observed when osteoclast progenitors were cocultured with oim/oim-derived osteoblasts compared with osteoblasts derived from +/+ mice. Taken together, our data indicate that osteoblast lineage maturation is a critical aspect underlying the pathophysiology of OI.

SLUG: a new target of lymphoid enhancer factor-1 in human osteoblasts

Background

Lymphoid Enhancer Factor-1 (Lef-1) is a member of a transcription factor family that acts as downstream mediator of the Wnt/β-catenin signalling pathway which plays a critical role in osteoblast proliferation and differentiation. In a search for Lef-1 responsive genes in human osteoblasts, we focused on the transcriptional regulation of the SLUG, a zinc finger transcription factor belonging to the Snail family of developmental proteins. Although the role of SLUG in epithelial-mesenchymal transition and cell motility during embryogenesis is well documented, the functions of this factor in most normal adult human tissues are largely unknown. In this study we investigated SLUG expression in normal human osteoblasts and their mesenchymal precursors, and its possible correlation with Lef-1 and Wnt/β-catenin signalling.

Results

The experiments were performed on normal human primary osteoblasts obtained from bone fragments, cultured in osteogenic conditions in presence of Lef-1 expression vector or GSK-3β inhibitor, SB216763. We demonstrated that the transcription factor SLUG is present in osteoblasts as well as in their mesenchymal precursors obtained from Wharton's Jelly of human umbilical cord and induced to osteoblastic differentiation. We found that SLUG is positively correlated with RUNX2 expression and deposition of mineralized matrix, and is regulated by Lef-1 and β-catenin. Consistently, Chromatin Immunoprecipitation (ChIP) assay, used to detect the direct Lef/Tcf factors that are responsible for the promoter activity of SLUG gene, demonstrated that Lef-1, TCF-1 and TCF4 are recruited to the SLUG gene promoter "in vivo".

Conclusion

These studies provide, for the first time, the evidence that SLUG expression is correlated with osteogenic commitment, and is positively regulated by Lef-1 signal in normal human osteoblasts. These findings will help to further understand the regulation of the human SLUG gene and reveal the biological functions of SLUG in the context of bone tissue.

Influence of obstetric factors on osteogenic potential of umbilical cord-derived mesenchymal stem cells

Wharton's jelly from the umbilical cord is a noncontroversial source of mesenchymal stem cells (WJMSCs) with high plasticity, proliferation rate and ability to differentiate towards multiple lineages. WJMSCs from different donors have been characterized for their osteogenic potential. Although there is large evidence of WJMSCs plasticity, recently scientific debate has focused on MSCs selection, establishing predictable elements to discriminate the cells with most promising osteoprogenitor cell potential.In the present study a comparative study between the presence of osteoblastic markers and different parameters that pertain to both the newborn and the mother was performed. Umbilical cords were collected after all patients signed the informed consent and local ethical commettee approved the study. Obstetric parameters, including baby's gender and birth weight, mother's age at delivery, gestational stage at parturition and mode of delivery were examined. After characterization and expansion, WJMSCs were analyzed for two osteoblastic markers, alkaline phosphatase (ALP) activity, and the expression level of RUNX-2 transcription factor, and for their ability to deposit mineralized matrix after osteogenic induction.We found that osteoblastic potential was not influenced by baby's gender and mode of delivery. On the contrary, the highest degree of osteoblastic potential has been shown by WJMSCs with RUNX-2 high basal levels, selected from umbilical cords of the heaviest term babies.Even if further evaluation is required, our hypothesis is that our findings may help in selecting the optimal umbilical cord donors and in collecting high potential Wharton's jelly-derived osteoprogenitors efficiently.

Identification of differentially expressed genes between osteoblasts and osteocytes

Osteocytes represent the most abundant cellular component of mammalian bones with important functions in bone mass maintenance and remodeling. To elucidate the differential gene expression between osteoblasts and osteocytes we completed a comprehensive analysis of their gene profiles. Selective identification of these two mature populations was achieved by utilization of visual markers of bone lineage cells. We have utilized dual GFP reporter mice in which osteocytes are expressing GFP (topaz) directed by the DMP1 promoter, while osteoblasts are identified by expression of GFP (cyan) driven by 2.3 kb of the Col1a1 promoter. Histological analysis of 7-day-old neonatal calvaria confirmed the expression pattern of DMP1GFP in osteocytes and Col2.3 in osteoblasts and osteocytes. To isolate distinct populations of cells we utilized fluorescent activated cell sorting (FACS). Cell suspensions were subjected to RNA extraction, in vitro transcription and labeling of cDNA and gene expression was analyzed using the Illumina WG-6v1 BeadChip. Following normalization of raw data from four biological replicates, 3444 genes were called present in all three sorted cell populations: GFP negative, Col2.3cyan(+) (osteoblasts), and DMP1topaz(+) (preosteocytes and osteocytes). We present the genes that showed in excess of a 2-fold change for gene expression between DMP1topaz(+) and Col2.3cyan(+) cells. The selected genes were classified and grouped according to their associated gene ontology terms. Genes clustered to osteogenesis and skeletal development such as Bmp4, Bmp8a, Dmp1, Enpp1, Phex and Ank were highly expressed in DMP1topaz(+)cells. Most of the genes encoding extracellular matrix components and secreted proteins had lower expression in DMP1topaz(+) cells, while most of the genes encoding plasma membrane proteins were increased. Interestingly a large number of genes associated with muscle development and function and with neuronal phenotype were increased in DMP1topaz(+) cells, indicating some new aspects of osteocyte biology. Although a large number of genes differentially expressed in DMP1topaz(+) and Col2.3cyan(+) cells in our study have already been assigned to bone development and physiology, for most of them we still lack any substantial data. Therefore, isolation of osteocyte and osteoblast cell populations and their subsequent microarray analysis allowed us to identify a number or genes and pathways with potential roles in regulation of bone mass.

Slug gene expression supports human osteoblast maturation

This study aims to define the function of Slug transcription factor in human normal osteoblasts (hOBs). To date, Slug is considered exclusively a marker of malignancy in bone tissue. Here, we identified, for the first time, a role for Slug in hOBs using a knockdown approach. We demonstrated that Slug is positively correlated with osteoblast markers, including Runx2, osteopontin, osteocalcin, Collagen type 1, Wnt/beta-catenin signaling mediators, and mineral deposition. At the same time, Slug silencing potentiates the expression of Sox-9, a factor indispensable for chondrogenic development. These data, with the finding that Slug is in vivo recruited by the promoters of Runx2 and Sox-9 genes, suggest that, in hOBs, Slug may act both as positive and negative transcriptional regulator of Runx2 and Sox-9 genes, respectively. In summary, our results support the hypothesis that Slug functions as a novel regulator of osteoblast activity and may be considered a new factor required for osteoblast maturation.