Clonal Populations Research Articles

Abstract 2012: Extrachromosomal DNA promotes drug resistance in pancreatic ductal adenocarcinoma cells

Abstract Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related deaths in Western Countries and has been predicted to become the second leading cause of cancer-related deaths by 2030. Difficulties in early detection as well as strong chemoresistance of the disease prevent the successful treatment of PDAC patients. Although we have previously identified CYP3A5 as a mediator of paclitaxel resistance, further targets remain elusive. Thus, we set out to identify these CYP3A5-independent mechanisms which could lead to the identification of novel biomarkers and drug targets to improve PDAC treatment. For this project, pancreatic cancer cell lines were derived from treatment-naive PDAC samples and exposed to increasing paclitaxel concentrations to induce resistance. The cells were characterized on a genomic and transcriptomic level using short-read sequencing as well as optical mapping to characterize potential candidate genes in vitro. In our results, multi-drug resistance protein 1 (ABCB1) was highly upregulated in our differential gene expression analysis and confirmed as a CYP3A5-independent mediator of acquired paclitaxel resistance. Its overexpression was mediated by extrachromosomal DNA (ecDNA) amplifications upon drug treatment. These circular DNAs were characterized by short-read sequencing as well as long-read optical mapping, which revealed the structures of the most abundant molecules. Furthermore, we investigated the biogenesis of the ecDNA. Current models propose different events such as chromothripsis or breakage-fusion-bridge cycles to initiate ecDNA formation, however, knowledge about the underlying mechanisms remains limited. To study the ecDNA dynamics, we generated ecDNA-negative cell clones from a paclitaxel resistant PDAC cell line. Interestingly, our clonal cell population appears to show the capacity for ecDNA de novo generation and quickly adapts to changing selective pressure such as therapy. This finding might unveil new insights into the triggers of ecDNA formation and its dynamic regulation. In conclusion, our results suggest the clinical relevance of ABCB1 as a mediator of paclitaxel resistance in PDAC and we currently validate our findings in patient samples. However, ABCB1 inhibition is associated with severe side effects. Instead, the regulatory pathways associated with enhanced ABCB1 expression and the formation of ecDNAs might provide therapeutic potential. Additionally, the characterization of ecDNA de novo generation might unveil new insights into how cancer cells adapt to changing selective pressures. Citation Format: Tim Vorberg, Manuel Reitberger, Bernardo Rodriguez-Martin, Maja Starostecka, Ornella Kossi, Vanessa Vogel, Jan Korbel, Andreas Trumpp, Martin Sprick. Extrachromosomal DNA promotes drug resistance in pancreatic ductal adenocarcinoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2012.

Abstract 3886: Analysis of clonal heterogeneity within paired primary and metastatic tumor samples of patients with solid tumors and implications for neoantigen-based personalized cancer vaccines

Abstract Background: Neoantigen-based personalized cancer vaccines carry significant promise in treating solid malignancies. However, there are uncertainties regarding the choice between the primary or the metastatic tumor for neoantigen prediction in individual patients. Here, we conducted a thorough examination of somatic variations in 676 patients who had paired primary and metastatic solid tumors. Methods: Patients were enrolled in the Total Cancer Care protocol (NCT03977402) to which patients provided an IRB-approved written informed consent within the Oncology Research Information Exchange Network (ORIEN). Whole-exome sequencing of 756 primary and metastatic tumor pairs was performed (N = 676 patients). These included Genitourinary (n=83), Gynecological (n=97), Gastrointestinal (n=213), Thoracic (n=33), Cutaneous (n=24), Breast (n=108), Endometrial (n=49), Sarcoma (n=35), Head-and-Neck (n=106) and others (n=8). The data was analyzed through the ORIEN AVATAR Molecular Analysis Pipeline for somatic mutation variant detection and variant annotation. In this analysis, we focused on somatic events that result in an in-frame alteration (such as missense, in-frame deletion and in-frame insertion) and out-of-frame protein-altering mutations (such as frameshifts, de novo start, out-of-frame, and nonstop gain). Clonal population structure was determined based on pyclone-vi. Results: For in-frame events, bladder cancer, melanoma, and gynecological cancers shared close to 75% of the mutations between paired primary and metastatic cases. In contrast, sarcoma and thyroid cancer had a low overlap (~ 25%) of variants. For out-of-frame events, these events tend to have a lower proportion of shared somatic variants between primary and metastasis than in-frame variants. Oncogenic drivers (e.g., BRAF V600E, KRAS G12A, and TP53 loss-of-function) were highly likely to be present in both paired primary and metastatic tumors. Next, we performed additional analysis on evolutionary selection of protein-coding variants via dN/dS calculation. We found no significant global shift in dN/dS ratio between paired primary and metastatic tumors across malignancies. However, we found increased selection of protein-coding variants in brain and liver metastatic sites, which correlated with increased homologous recombination deficiency within these sites. Conclusions: Our analysis demonstrates genetic variations that exist when comparing paired primary and metastatic tumors that appear to vary by histology. Variants are potentially undergoing negative selection supported by the preferential loss of out-of-frame events in metastatic tumors and positive selection in specific metastatic sites. Overall, understanding the clonal structure will be key to neoantigen prediction for effective neoantigen-based vaccines. Citation Format: Alyssa Obermayer, Timothy Shaw, Darwin Chang, Joshua Davis, Jamie K. Teer, Xiaoqing Yu, Xuefeng Wang, Dale Hedges, Aik Choon Tan, Robert Rounbehler, Abdul Rafeh Naqash, Margaret Gatti-Mays, Aakrosh Ratan, Martin McCarter, Howard Colman, Igor Puzanov, Susanne Arnold, Michelle Churchman, Patrick Hwu, William Dalton, George Weiner, Jose Conejo-Garcia, Paulo C. Rodriguez, Bodour Salhia, Ahmad A. Tarhini. Analysis of clonal heterogeneity within paired primary and metastatic tumor samples of patients with solid tumors and implications for neoantigen-based personalized cancer vaccines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3886.

Abstract 2264: Identifying and analyzing independent clonal populations in single Barrett’s esophagus biopsies

Abstract Barrett’s esophagus (BE) is a non-obligate precursor of esophageal adenocarcinoma (EAC), often measuring multiple centimeters in length and characterized by columnar epithelium replacing normal squamous epithelium in the distal esophagus. Early studies in BE suggested that all cells within a patient’s Barrett’s segment are progenies of a single founder cell. However, in recent years this previously accepted model of BE as a monoclonal disease has been retired in favor of a multiclonal model with new evidence suggesting that a patient’s Barrett’s segment can be composed of multiple independent clones with independent founder cells. Nonetheless, single BE samples are still routinely assumed to be monoclonal, leading to independent sets of genomic aberrations erroneously being analyzed as a single set in the case of multiclonal samples. Here, we utilize a previously generated whole-genome sequenced BE dataset and repurpose an established pipeline for detecting subclonal populations to identify BE samples that are comprised of multiple independent clones. Additionally, we present a novel approach for validating multiclonality from sequencing data by phasing pair-end sequencing reads using germline variants. We demonstrate that 20/80 patients have at least one multiclonal sample and that the independent clones contained in these single biopsies can have drastically different genomic profiles. Further, we speculate that these multiclonal samples capture a snapshot of clonal competition and evolution within BE. These findings highlight the importance of accounting for multiclonality when studying BE and provide the first systematic analysis of multiclonal BE samples. Citation Format: Mariya Kazachkova, Phoebe He, Ludmil B. Alexandrov. Identifying and analyzing independent clonal populations in single Barrett’s esophagus biopsies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2264.

Abstract 4343: Revealing ovarian cancer copy number variation in single cells

Abstract The mortality rate associated with ovarian cancer (OvCa) is disproportionately high in comparison to its incidence rate. This is partly due to the heterogeneous nature of the disease, which reduces treatment efficacy and contributes to high rates of relapse and chemotherapy resistance. Most OvCa are epithelial in origin and can be classified into four main subtypes: serous, mucinous, endometrioid, and clear cell. Of these, high grade serous ovarian cancer (HGSOC) is the deadliest. Epithelial ovarian carcinomas (EOC) typically exhibit widespread chromosomal and arm-level copy number abnormalities across most of the genome; in HGSOC, focal amplifications and microdeletions are especially prevalent and indicative of high genomic instability. To understand the heterogeneity of aneuploidy in EOC and HGSOC, we performed shallow single-cell whole genome sequencing on four EOC samples: two HGSOC, one clear cell, and one mixed clear cell and endometrioid. All samples were late stage and treatment naïve, and one sample had a known BRCA2 mutation. Sequencing data was processed by two complementary methods to call copy number alterations. First, we used the Cell Ranger DNA pipeline (10x Genomics) to align cell-identified sequencing reads to human reference genome GRCh38 for coverage-based copy number estimation. Resulting copy number calls were cleaned up for mappability, quality, and noisiness. Each sample was then subject to clustering and subclustering analysis using maximum likelihood genetic clustering algorithms. All samples exhibited a high level of aneuploidy, including characteristic alterations known to be associated with EOC. Two tumors contained readily distinguishable clonal populations, and all samples contained main tumor clones that could be further divided by unique subclonal characteristics. Evidence of polyploidy was also seen in all four specimens, with some tumor clusters exhibiting triploid and tetraploid baselines. In parallel, sequencing data was analyzed by the Copy-number Haplotype Inference in Single-cell by Evolutionary Links (CHISEL) algorithm. CHISEL utilizes both binned read depth ratio and B-allele frequency data to determine allele- and haplotype-specific copy numbers in single cells. Results from CHISEL confirmed the copy number calls from Cell Ranger DNA, and revealed widespread loss of heterozygosity in all samples. These findings were corroborated with allele-specific copy number data derived from matched tumor-normal whole exome sequencing. Furthermore, CHISEL detected polyploidy in one-third of the tumor cells with no preference for the A or B alleles. Overall, our findings highlight that the known heterogeneity of ovarian cancer extends to the level of aneuploidy and CNAs, shedding light on factors which pose significant barriers to effective personalized medicine implementation. Citation Format: Yuxin Jin, Rania Bassiouni, Lee D. Gibbs, Jing Qian, Solomon Rotimi, Michelle G. Webb, Seeta Rajpara, David W. Craig, Lynda D. Roman, John D. Carpten. Revealing ovarian cancer copy number variation in single cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4343.

Abstract 2296: Liquid biopsy of cerebrospinal fluid in breast to brain metastases

Abstract Up to 30% of patients with breast cancers will develop brain metastases, and this risk is especially high with HER2-positive cancers. For patients with central nervous system metastases, cerebrospinal fluid (CSF) liquid biopsies are a promising opportunity to monitor disease, inform treatment, and predict prognosis. This study explores the CSF liquid biopsy analytes from 3 patients with central nervous system metastases analyzed with the third generation non-enrichment high-definition single cell assay (HDSCA3.0) workflow. The detection of cellular analytes was compared between the CSF and matched peripheral blood (PB) samples. Circulating tumor cells (CTCs) were detected in the CSF but not the PB and were subsequently molecularly characterized by single cell genomics and targeted multiplexed proteomics to reveal a clonal population of phenotypically heterogeneous cells. There was a lack of concordance between CTCs and cfDNA of the CSF in the copy number alteration profiles. In an extracellular vesicle surface marker analysis of the CSF, there was a high signal among tetraspanin CD9/CD63/CD81, with CD81 signal the highest across all 3 patients. The data indicates that the CSF may be used as a diagnostic or potentially prognostic tool to measure and characterize disease burden. Citation Format: Stephanie N. Shishido, Amelia Marvit, Saul Priceman, Jana Portnow, Peter Kuhn. Liquid biopsy of cerebrospinal fluid in breast to brain metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2296.

Abstract 1610: Elucidating tumor evolution and heterogeneity in metastatic bladder cancer from rapid autopsies

Abstract Background: Bladder Cancer is a highly prevalent cancer with staggering mortality of about 20%. Metastatic BLCA (mBLCA) with variant histologies are aggressive and have a poor prognosis. The extent and impact of tumor heterogeneity in these variant subtypes are not fully understood. This work explores the intricate characterization of intra-patient and inter-patient tumor heterogeneity through genomic and transcriptomic analyses, drawing insights from a unique rapid autopsy cohort comprising 20 patients. The resulting revelations provide critical perspectives on heterogeneity and clonal evolution in mBLCA, underscoring the essential role of understanding these dynamics for the development of personalized treatment strategies. Approach: Our research focuses on the genetic and molecular characteristics of these tumors, including the vast landscape of tumor heterogeneity, clonal evolution, genomic alterations, mutational signatures, and structural variants. Within the tumor microenvironment, we identified diverse cell populations with distinct genetic profiles. A detailed examination of mutational signatures sheds light on the specific processes underlying genetic alterations, while the investigation of structural variants elucidates their consequential role in cancer development and progression. Advanced bioinformatics tools are deployed to process and interpret the vast genomic and transcriptomic datasets, facilitating the identification of clonal populations, their genetic features, and the trajectory of clonal evolution. Furthermore, statistical models are employed to discern correlations between mutational signatures, treatment responses, and clinical outcomes. Summary: The study unveils substantial inter-patient heterogeneity and discernible differences in mutational signatures, revealing intriguing correlations with treatment responses. These variations are intricately connected to underlying genomic alterations, copy number alterations, and gene expression patterns, offer a detailed perspective on the molecular landscape of mBLCA. Conclusion: This multi-omics exploration stands as the most extensive study of its kind, leveraging rapid autopsy samples of metastatic variant histology BLCA. The research provides unprecedented resolution of genomic alterations and intra- and inter-patient tumor heterogeneity. The exploration of clonal evolution enhances our appreciation of the temporal dynamics of tumor progression, establishing a robust foundation for future therapeutic interventions precisely targeting evolving tumor clones. As we advance into an era of personalized medicine, these findings pave the way for tailored therapeutic strategies in the challenging landscape of metastatic variant histology Bladder Cancer. Citation Format: Pushpa Itagi, Sonali Arora, Thomas Persse, Michael Yang, Patricia Galipeau, Yixin Lin, Funda Vakar-Lopez, John K. Lee, Petros Grivas, Robert B. Montgomery, Jonathan L. Wright, Hung-Ming Lam, Andrew Hsieh, Gavin Ha. Elucidating tumor evolution and heterogeneity in metastatic bladder cancer from rapid autopsies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1610.

Genetic Knock-Ins of Endogenous Fluorescent Tags in RAW 264.7 Murine Macrophages Using CRISPR/Cas9 Genome Editing.

CRISPR/Cas9 genome editing is a widely used tool for creating genetic knock-ins, which allow for endogenous tagging of genes. This is in contrast with random insertion using viral vectors, where expression of the inserted transgene changes the total copy number of a gene in a cell and does not reflect the endogenous chromatin environment or any trans-acting regulation experienced at a locus. There are very few protocols for endogenous fluorescent tagging in macrophages. Here, we describe a protocol to design and test CRISPR guide RNAs and donor plasmids, to transfect them into RAW 264.7 mouse macrophage-like cells using the Neon transfection system and to grow up clonal populations of cells containing the endogenous knock-in at various loci. We have used this protocol to create endogenous fluorescent knock-ins in at least six loci, including both endogenously tagging genes and inserting transgenes in the Rosa26 and Tigre safe harbor loci. This protocol uses circular plasmid DNA as the donor template and delivers the sgRNA and Cas9 as an all-in-one expression plasmid. We designed this protocol for fluorescent protein knock-ins; it is best used when positive clones can be identified by fluorescence. However, it may be possible to adapt the protocol for non-fluorescent knock-ins. This protocol allows for the fairly straightforward creation of clonal populations of macrophages with tags at the endogenous loci of genes. We also describe how to set up imaging experiments in 24-well plates to track fluorescence in the edited cells over time. Key features • CRISPR knock-in of fluorescent proteins in RAW 264.7 mouse macrophages at diverse genomic loci. • This protocol is optimized for the use of the Neon transfection system. • Includes instructions for growing up edited clonal populations from single cells with one single-cell sorting step and efficient growth in conditioned media after cell sorting. • Designed for knocking in fluorescent proteins and screening transfected cells by FACS, but modification for non-fluorescent knock-ins may be possible.

An Enterobacteriaceae bloom in aging animals is restrained by the gut microbiome.

The gut microbiome plays important roles in host function and health. Core microbiomes have been described for different species, and imbalances in their composition, known as dysbiosis, are associated with pathology. Changes in the gut microbiome and dysbiosis are common in aging, possibly due to multi-tissue deterioration, which includes metabolic shifts, dysregulated immunity, and disrupted epithelial barriers. However, the characteristics of these changes, as reported in different studies, are varied and sometimes conflicting. Using clonal populations of Caenorhabditis elegans to highlight trends shared among individuals, we employed 16s rRNA gene sequencing, CFU counts and fluorescent imaging, identifying an Enterobacteriaceae bloom as a common denominator in aging animals. Experiments using Enterobacter hormaechei, a representative commensal, suggested that the Enterobacteriaceae bloom was facilitated by a decline in Sma/BMP immune signaling in aging animals and demonstrated its potential for exacerbating infection susceptibility. However, such detrimental effects were context-dependent, mitigated by competition with commensal communities, highlighting the latter as determinants of healthy versus unhealthy aging, depending on their ability to restrain opportunistic pathobionts.

Borreliella burgdorferi factor H-binding proteins are not required for serum resistance and infection in mammals.

The causative agent of Lyme disease (LD), Borreliella burgdorferi, binds factor H (FH) and other complement regulatory proteins to its surface. B. burgdorferi B31 (type strain) encodes five FH-binding proteins (FHBPs): CspZ, CspA, and the OspE paralogs OspEBBN38, OspEBBL39, and OspEBBP38. This study assessed potential correlations between the production of individual FHBPs, FH-binding ability, and serum resistance using a panel of infectious B. burgdorferi clonal populations recovered from dogs. FHBP production was assessed in cultivated spirochetes and by antibody responses in naturally infected humans, dogs, and eastern coyotes (wild canids). FH binding specificity and sensitivity to dog and human serum were also assessed and compared. No correlation was observed between the production of individual FHBPs and FH binding with serum resistance, and CspA was determined to not be produced in animals. Notably, one or more clones isolated from dogs lacked CspZ or the OspE proteins (a finding confirmed by genome sequence determination) and did not bind FH derived from canines. The data presented do not support a correlation between FH binding and the production of individual FHBPs with serum resistance and infectivity. In addition, the limited number and polymorphic nature of cp32s in B. burgdorferi clone DRI85A that were identified through genome sequencing suggest no strict requirement for a defined set of these replicons for infectivity. This study reveals that the immune evasion mechanisms employed by B. burgdorferi are diverse, complex, and yet to be fully defined.

Streamlined, single-step non-viral CRISPR-Cas9 knockout strategy enhances gene editing efficiency in primary human chondrocyte populations

BackgroundCRISPR-Cas9-based genome engineering represents a powerful therapeutic tool for cartilage tissue engineering and for understanding molecular pathways driving cartilage diseases. However, primary chondrocytes are difficult to transfect and rapidly dedifferentiate during monolayer (2D) cell culture, making the lengthy expansion of a single-cell-derived edited clonal population not feasible. For this reason, functional genetics studies focused on cartilage and rheumatic diseases have long been carried out in cellular models that poorly recapitulate the native molecular properties of human cartilaginous tissue (e.g., cell lines, induced pluripotent stem cells). Here, we set out to develop a non-viral CRISPR-Cas9, bulk-gene editing method suitable for chondrocyte populations from different cartilaginous sources.MethodsWe screened electroporation and lipid nanoparticles for ribonucleoprotein (RNP) delivery in primary polydactyly chondrocytes, and optimized RNP reagents assembly. We knocked out RELA (also known as p65), a subunit of the nuclear factor kappa B (NF-κB), in polydactyly chondrocytes and further characterized knockout (KO) cells with RT-qPCR and Western Blot. We tested RELA KO in chondrocytes from diverse cartilaginous sources and characterized their phenotype with RT-qPCR. We examined the chondrogenic potential of wild-type (WT) and KO cell pellets in presence and absence of interleukin-1β (IL-1β).ResultsWe established electroporation as the optimal transfection technique for chondrocytes enhancing transfection and editing efficiency, while preserving high cell viability. We knocked out RELA with an unprecedented efficiency of ~90%, confirming lower inflammatory pathways activation upon IL-1β stimulation compared to unedited cells. Our protocol could be easily transferred to primary human chondrocytes harvested from osteoarthritis (OA) patients, human FE002 chondroprogenitor cells, bovine chondrocytes, and a human chondrocyte cell line, achieving comparable mean RELA KO editing levels using the same protocol. All KO pellets from primary human chondrocytes retained chondrogenic ability equivalent to WT cells, and additionally displayed enhanced matrix retention under inflamed conditions.ConclusionsWe showcased the applicability of our bulk gene editing method to develop effective autologous and allogeneic off-the-shelf gene therapies strategies and to enable functional genetics studies in human chondrocytes to unravel molecular mechanisms of cartilage diseases.

Abstract A028: Subclonal lineage recording in glioblastoma using CRISPR base editing

Abstract Novel lineage tracing approaches are needed to undercover lineage relationships between diverse cells in complex tumors such as glioblastoma (GBM). Intratumoral heterogeneity in GBM drives treatment resistance and recurrence. This intratumoral heterogeneity is reflected by multiple cellular states seen within tumors and across patients. Unfortunately, little is known about their lineage relationships and shared origins. Here we’ve developed a novel lineage tracing technology to track the clonal and subclonal evolution in patient-derived GBM models. Our adenine base editor lineage tracing (ABELT) system uses a Cas9 adenine base editor (ABE) to induce heritable single-nucleotide changes in the 3’ untranslated region of endogenous transcripts. These heritable marks distinguish individual clonal populations and can be used to trace the relationship between progeny within each clone. We demonstrate our system's in vitro lineage tracing capacity and show that the ABELT system faithfully records lineage, which is recoverable with unmodified single-cell RNA sequencing approaches. We then track the relationships between evolving cellular states across multiple divisions in an evolving GBM model. Our ABELT technology enables the rapid engineering and lineage tracing of cancer models incompatible with previous approaches. This novel approach will enable our group and others to explore GBM intratumoral heterogeneity with subclonal resolution to determine transcriptional plasticity that ultimately leads to treatment resistance. Citation Format: Abigail C. Marshall, Aaron McKenna. Subclonal lineage recording in glioblastoma using CRISPR base editing [abstract]. In: Proceedings of the AACR Special Conference on Brain Cancer; 2023 Oct 19-22; Minneapolis, Minnesota. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_1):Abstract nr A028.

Advances in Nonresponsive and Refractory Celiac Disease

Nonresponsive celiac disease (CeD) is relatively common. It is generally attributed to persistent gluten exposure and resolves after correction of diet errors. However, other complications of CeD and disorders clinically mimicking CeD need to be excluded. Novel therapies are being evaluated to facilitate mucosal recovery, which might benefit patients with nonresponsive CeD. Refractory CeD (RCeD) is rare and is divided into 2 types. The etiology of type I RCeD is unclear. A switch to gluten-independent autoimmunity is suspected in some patients. In contrast, type II RCeD represents a low-grade intraepithelial lymphoma. Type I RCeD remains a diagnosis of exclusion, requiring ruling out gluten intake and other nonmalignant causes of villous atrophy. Diagnosis of type II RCeD relies on the demonstration of a clonal population of neoplastic intraepithelial lymphocytes with an atypical immunophenotype. Type I RCeD and type II RCeD generally respond to open-capsule budesonide, but the latter has a dismal prognosis due to severe malnutrition and frequent progression to enteropathy-associated T-cell lymphoma; more efficient therapy is needed.

Treatment with the apoptosis inhibitor Asunercept reduces clone sizes in patients with lower risk Myelodysplastic Neoplasms

In low-risk Myelodysplastic Neoplasms (MDS), increased activity of apoptosis-promoting factors such as tumor necrosis factor (TNFα) and pro-apoptotic Fas ligand (CD95L) have been described as possible pathomechanisms leading to impaired erythropoiesis. Asunercept (APG101) is a novel therapeutic fusion protein blocking CD95, which has previously shown partial efficacy in reducing transfusion requirement in a clinical phase I trial for low-risk MDS patients (NCT01736436; 2012-11-26). In the current study we aimed to evaluate the effect of Asunercept therapy on the clonal bone marrow composition to identify potential biomarkers to predict response. Bone marrow samples of n = 12 low-risk MDS patients from the above referenced clinical trial were analyzed by serial deep whole exome sequencing in a total of n = 58 time points. We could distinguish a mean of 3.5 molecularly defined subclones per patient (range 2–6). We observed a molecular response defined as reductions of dominant clone sizes by a variant allele frequency (VAF) decrease of at least 10% (mean 20%, range: 10.5–39.2%) in dependency of Asunercept treatment in 9 of 12 (75%) patients. Most of this decline in clonal populations was observed after completion of 12 weeks treatment. Particularly early and pronounced reductions of clone sizes were found in subclones driven by mutations in genes involved in regulation of methylation (n = 1 DNMT3A, n = 1 IDH2, n = 1 TET2). Our results suggest that APG101 could be efficacious in reducing clone sizes of mutated hematopoietic cells in the bone marrow of Myelodysplastic Neoplasms, which warrants further investigation.

Whole genome sequence-based characterization of Campylobacter isolated from broiler carcasses over a three-year period in a big poultry slaughterhouse reveals high genetic diversity and a recurring genomic lineage of Campylobacter jejuni

Campylobacter is among the most frequent agents of bacterial gastroenteritis in Europe and is primarily linked to the consumption of contaminated food. The aim of this study was to assess genomic diversity and to identify antimicrobial resistance and virulence genes of 155 Campylobacter isolated from broiler carcasses (neck skin samples) in a large-scale Swiss poultry abattoir over a three-year period. Samples originated from broilers from three different types of farming systems (particularly animal-friendly stabling (PAFS), free-range farms, and organic farms).Campylobacter jejuni (n = 127) and Campylobacter coli (n = 28) were analysed using a whole genome sequencing (WGS) approach (MiniSeq; Illumina). Sequence types (STs) were determined in silico from the WGS data and isolates were assigned into complex types (CTs) using the cgMLST SeqSphere+ scheme. Antimicrobial resistance genes were identified using the Resistance Gene Identifier (RGI), and virulence genes were identified using the virulence factor database (VFDB).A high degree of genetic diversity was observed. Many sequence types (C. jejuni ST19, ST21, ST48, ST50, ST122, ST262 and C. coli ST827) occurred more than once and were distributed throughout the study period, irrespective of the year of isolation and of the broiler farming type. Antimicrobial resistance determinants included blaOXA and tet(O) genes, as well as the T86I substitution within GyrA. Virulence genes known to play a role in human Campylobacter infection were identified such as the wlaN, cstIII, neuA1, neuB1, and neuC1. Subtyping of the Campylobacter isolates identified the occurrence of a highly clonal population of C. jejuni ST21 that was isolated throughout the three-year study period from carcasses from farms with geographically different locations and different farming systems.The high rate of genetic diversity observed among broiler carcass isolates is consistent with previous studies. The identification of a persisting highly clonal C. jejuni ST21 subtype suggests that the slaughterhouse may represent an environment in which C. jejuni ST21 may survive, however, the ecological reservoir potentially maintaining this clone remains unknown.

A complete workflow for single cell mtDNAseq in CHO cells, from cell culture to bioinformatic analysis.

Chinese hamster ovary (CHO) cells have a long history in the biopharmaceutical industry and currently produce the vast majority of recombinant therapeutic proteins. A key step in controlling the process and product consistency is the development of a producer cell line derived from a single cell clone. However, it is recognized that genetic and phenotypic heterogeneity between individual cells in a clonal CHO population tends to arise over time. Previous bulk analysis of CHO cell populations revealed considerable variation within the mtDNA sequence (heteroplasmy), which could have implications for the performance of the cell line. By analyzing the heteroplasmy of single cells within the same population, this heterogeneity can be characterized with greater resolution. Such analysis may identify heterogeneity in the mitochondrial genome, which impacts the overall phenotypic performance of a producer cell population, and potentially reveal routes for genetic engineering. A critical first step is the development of robust experimental and computational methods to enable single cell mtDNA sequencing (termed scmtDNAseq). Here, we present a protocol from cell culture to bioinformatic analysis and provide preliminary evidence of significant mtDNA heteroplasmy across a small panel of single CHO cells.

Extraction of the CDRH3 sequence of the mouse antibody repertoire selected upon influenza virus infection by subtraction of the background antibody repertoire.

As specific interactions between antigens and cell-surface antibodies trigger the proliferation of B-cell clones, the frequency of each antibody sequence in the samples reflects the size of each clonal population. Nevertheless, it is extremely difficult to extract antigen-specific antibody sequences from the comprehensive bulk antibody sequences obtained from blood samples due to repertoire bias influenced by exposure to dietary antigens and other infectious agents. This issue can be addressed by subtracting the background noise from the post-immunization or post-infection repertoire data. In the present study, we propose a method to quantify repertoire data from comprehensive repertoire data. This method allowed subtraction of the background repertoire, resulting in more accurate extraction of expanded antibody repertoires upon influenza virus infection. This accurate extraction of antigen- or infection-specific repertoire information is a useful tool for vaccine evaluation.

Abstract A010: Longitudinal histology and spatial transcriptomics profiling in targeted treatment of melanoma patient-derived models interrogates persister and resistant cell populations

Abstract Over half of BRAF-mutant melanoma patients with initial response to targeted therapy will recur with resistant disease. It is thought that recurrence arises from the ability of resistant clonal populations to enter and exit a slow-cycling persister state, evading treatment in quiescence before returning to a proliferative state. However, clonal transcriptional profiles and their spatial relationships in the tumor environment are not well characterized. Through longitudinal profiling of tumors from pre-treatment through the growth of resistant tumors, we track clonal lineages and transcriptional state changes to identify recurrent evolutionary patterns. BRAF mutant patient-derived melanoma xenografts were treated with BRAF/MEK inhibitors through maximum tumor size reduction and re-growth. Spatial transcriptomics (ST) and H&E histological staining were performed at five timepoints across 94 and 133 days of PDX models WM4237 and WM4007 treatment, tracking clonal populations with intact tissue structure. Deep learning feature extraction on high-resolution H&E-stained images allowed the detection of histological features that co-localize with expression levels. A novel computational workflow performed integration of samples across time points, pathway enrichment analysis, and pseudotemporal ordering, allowing spatial recreation of copy number variation based clonal phylogenies and cell fate trajectory inference during the treatment course. We characterize the clonal populations by the burden of accumulated copy number variations and establish clonal phylogeny. With the added temporal resolution, ST profiling during melanoma treatment enables observation of a global shift where all lineages begin the transition into the persister transcriptional state. The drug-sensitive cells are eliminated due to treatment, and distinct transcriptional states arise due to metabolic plasticity regardless of the lineage of origin. The clones of the transient persister state constitute the minimal residual disease, where melanoma cells have an increase in invasive capacity and a slowing of the cell cycle. The ability to survive through the persister state and re-emerge into a proliferating clone where the cell cycle is upregulated varies by lineage. We observe that the transcriptional changes during emergence from dormancy show decreased invasiveness and continued reliance on oxidative respiration versus glycolysis. We compare the re-emerged resistant cell populations and pre-treatment samples to pinpoint the changes in the transcriptional state of the MAPK signaling pathway and find that sets of upregulated genes differ by the model, WM4237 and WM4007. We connect deep learning imaging features extracted from longitudinal histology profiling to ST profiles to associate histology data with the cell cycle activation, invasiveness, hypoxia state, and metabolic mode across the timepoints. We observe that the imaging features alone can be potentially used to track the evolution of the tumor cell population phenotypes during drug treatment. Citation Format: Sergii Domanskyi, Todd B. Sheridan, Brian J. Sanderson, SungHee Park, Jessica Kaster, Haiyin Li, Olga Anczukow, Meenhard Herlyn, Jeffrey H. Chuang, Jill C. Rubinstein. Longitudinal histology and spatial transcriptomics profiling in targeted treatment of melanoma patient-derived models interrogates persister and resistant cell populations [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Cancer Evolution and Data Science: The Next Frontier; 2023 Dec 3-6; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_2):Abstract nr A010.

Abstract PR009: Tick tock trees: Reconstructing the evolutionary dynamics of human tissues using fluctuating methylation clocks

Abstract The development of cancer from healthy somatic cells is fundamentally an evolutionary process. Understanding this process is vital to improving its clinical management and developing new treatment strategies. Tracing individual human cells’ fates would simultaneously advance somatic evolutionary theory and our understanding of normal tissue function and its change through development, aging, and cancer progression. We cannot use human cell-labeling techniques in vivo. Still, population genetic and phylogenetic models can leverage the information recorded in heritable alterations to reconstruct the unobserved somatic cells’ history. Most such methods are limited by the few parameters they can estimate and restricted to neoplastic samples due to the lack of adequate evolutionary signal in healthy somatic cells. Gabbutt et al. recently ameliorated this limitation by introducing fluctuating methylation clocks (FMCs)—tissue-specific CpG sites that randomly change their methylation state—and a model that uses them to reconstruct the evolution of a clonal stem-cell population. In this application, all FMCs in a bulk sample are interrogated using a single standard methylation array to yield estimates of rates of methylation, demethylation and cell replacement, and the size of the stem-cell niche. This technique is especially suited to studying stem-cell niche dynamics in healthy or pre-malignant tissues organized in clonal cell populations where the whole population can be sampled together, like crypts (e.g., intestine, Barrett’s esophagus) and glands (e.g., endometrium). We have developed a multi-sample extension of this model that simultaneously reconstructs the evolutionary dynamics of stem cells within a niche and the niches within the tissue. This phylodynamic model produces additional estimates like ancestral relationships between sampled clonal populations, their calendar divergence times, the number of effective evolutionary niches, and how some of these parameters change over time. Here, we will present the method, demonstrate its validity, characterize its accuracy under a broad simulation parameter space, and showcase its application in analyzing human data from the following tissues: colon, small intestine, endometrium, and Barrett’s esophagus. We will also discuss the current model's limitations and future improvements that will discern between mechanisms of stem-cell-niche reproduction and incorporate geographical information. The stochastic nature of neoplastic progression makes it unlikely for any particular somatic alteration to be highly predictive of its outcome. This can explain why developing reliable traditional biomarkers has been so difficult. Alternatively, evolutionary biomarkers measure the characteristics of the process itself and thus should apply to all neoplasms. Parametric phylogenetic reconstruction models like the one introduced here will enable us to develop such universal biomarkers. Our ultimate goal is for evolutionary biomarkers to join evolutionary therapies in the revolution of the clinical management of cancer. Citation Format: Diego Mallo, Pablo Bousquets-Muñoz, Heather E. Grant, Darryl Shibata, Trevor A. Graham, Carlo C. Maley, Calum Gabbutt. Tick tock trees: Reconstructing the evolutionary dynamics of human tissues using fluctuating methylation clocks [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Cancer Evolution and Data Science: The Next Frontier; 2023 Dec 3-6; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_2):Abstract nr PR009.

Abstract A036: Macropinocytosis mediates metabolic resistance to loss of glutamine transport in triple-negative breast cancer

Abstract Introduction Although a nonessential amino acid in normal cells, the demand for glutamine is dramatically increased throughout malignant transformation, supporting a range of metabolic processes including mitochondrial ATP production, protein synthesis, purine and pyrimidine biosynthesis. We previously shown that triple-negative breast cancer (TNBC) cells rely on glutamine uptake by the amino acid transporter ASCT2 to sustain their unique glutamine metabolism, thereby supporting in vitro growth and in vivo tumour formation. However, it is known that TNBC cells can also utilise non-transporter mediated nutrient uptake facilitated by processes such as macropinocytosis. Methods We examined proliferation of human breast cancer cell lines after ASCT2 CRISPR/Cas9 knockout (clonal and polyclonal populations) and shRNA knockdown. Proteomics and mRNAseq analysis further examined cellular and adaptive changes to ASCT2 knockout. Cellular changes were further analysed by western blotting, with macropinocytosis examined using 70kDa dextran-FITC uptake. Metabolic changes were assessed using targeted metabolomics approaches including 13C-labelled substrate tracing and liquid chromatography coupled tandem-mass spectrometry (LC-MS/MS) to determine intracellular levels of key tricarboxylic acid (TCA) cycle intermediates, glycolytic metabolites, fatty acid precursors, nucleotides, and amino acids in human TNBC cell lines in vitro. Results Despite our previous data showing a significant reduction in cell growth after ASCT2 knockdown, ASCT2 knockout was well-tolerated by both TNBC and Luminal A breast cancer cell lines, with proliferation rates similar to non-targeted CRISPR/Cas9 control cells. This adaptation to ASCT2 knockout was not due to the high glutamine levels present in culture media, as the knockout cells could be cloned in media containing either standard 2 mM glutamine or physiological 0.5 mM glutamine. Previous data have shown that TNBC cell lines can undergo constitutive macropinocytosis, and that this can be enhanced when cells are cultured in low nutrient conditions. Indeed, not only did the TNBC cell line HCC1806 undergo constitutive macropinocytosis, the amount of macropinocytosis was significantly increased (5-10 fold) in 5 separate ASCT2 knockout clones tested. By comparison, the ASCT2 shRNA knockdown cell line, which are published to have a significant proliferation deficit, showed a modest 2-fold increase in macropinocytosis, which may explain why they maintain a growth phenotype compared to the knockout lines. Despite in-depth analysis of gene and protein levels by mRNAseq and proteomics, ASCT2 knockout cells showed only a few significant changes in known macropinocytotic genes. There was, however, a substantial upregulation of Ser473-Akt phosphorylation which may drive the adaptive macropinocytosis in TNBC. Conclusion These data suggest that the constitutive macropinocytosis present in TNBC cell lines provides a novel resistance mechanism to strategies targeting glutamine uptake alone. Citation Format: Kanu Wahi, Natasha Freidman, Qian Wang, Yi Fang Guan, Jeff Holst. Macropinocytosis mediates metabolic resistance to loss of glutamine transport in triple-negative breast cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr A036.

Abstract A019: The role of tumor transcriptional variability in evading acute CD8+ T cell exposure in melanoma

Abstract Throughout melanoma progression and immunotherapy treatment, melanoma cells often develop an ability to evade the immune system. Thus, there is a pressing need to identify and target the melanoma cell-intrinsic mechanisms underlying immune evasion. Our laboratory has pioneered the identification of transcriptional pathways that underlie melanoma progression. We have found that within even clonal melanoma cell populations, subclones of cells demonstrate tremendous heterogeneity in their transcriptional state. We previously demonstrated that these varying transcriptional states correspond to varying sensitivities of melanoma cells to stressors such as targeted therapies, and that these states can be stable across multiple cell divisions. We hypothesize that varying transcriptional states also correspond to cells that have differing abilities to evade CD8+ T cells, which are major effector cells against melanoma. To study the interactions between melanoma cells and CD8+ T cells, we engineered an ovalbumin antigen and OT-I T cell receptor system using mouse melanoma cell lines. We combined this system with DNA barcoding, which enables us to track subclones of cells undergoing immune selection. When cocultured together in vitro, ovalbumin-expressing melanoma cells are effectively killed by OT-I cells. However, we find that subclones of melanoma cells consistently possess different sensitivity to OT-I cells, and these differences are not due to their genetic background nor their ability to express and present ovalbumin. We then leveraged our DNA barcoding system with single cell RNA sequencing (scRNA-seq) to link the lineage and transcriptional state of single melanoma cells that persist through OT-I coculture. By expanding on these preliminary results, we aim to identify novel melanoma cell targets to decrease immune evasion. Citation Format: Raymond W.S. Ng, Sydney M Shaffer. The role of tumor transcriptional variability in evading acute CD8+ T cell exposure in melanoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Cancer Evolution and Data Science: The Next Frontier; 2023 Dec 3-6; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_2):Abstract nr A019.