Histone acetylation in an Alzheimer's disease cell model promotes homeostatic amyloid-reducing pathways

Alzheimer's Disease (AD) is a disorder characterized by cognitive decline, neurodegeneration, and accumulation of amyloid plaques and tau neurofibrillary tangles in the brain. Dysregulation of epigenetic histone modifications may lead to expression of transcriptional programs that play a role either in protecting against disease genesis or in worsening of disease pathology. One such histone modification, acetylation of histone H3 lysine residue 27 (H3K27ac), is primarily localized to genomic enhancer regions and promotes active gene transcription. We previously discovered H3K27ac to be more abundant in AD patient brain tissue compared to the brains of age-matched non-demented controls. In this study, we use iPSC-neurons derived from familial AD patients with an amyloid precursor protein (APP) duplication (APPDup neurons) as a model to study the functional effect of lowering CBP/P300 enzymes that catalyze H3K27ac. We found that homeostatic amyloid-reducing genes were upregulated in the APPDup neurons compared to non-demented controls. We lowered CBP/P300 to reduce H3K27ac, which led to decreased expression of numerous of these homeostatic amyloid-reducing genes, along with increased extracellular secretion of a toxic amyloid-β species, Aβ(1-42). Our findings suggest that epigenomic histone acetylation, including H3K27ac, drives expression of compensatory genetic programs in response to AD-associated insults, specifically those resulting from APP duplication, and thus may play a role in mitigating AD pathology in neurons.

Deletion of the inhibitory co-receptor CTLA-4 enhances and invigorates chimeric antigen receptor T cells

Chimeric antigen receptor (CAR) T cell therapy targeting CD19 has achieved tremendous success treating B cell malignancies; however, some patients fail to respond due to poor autologous T cell fitness. To improve response rates, we investigated whether disruption of the co-inhibitory receptors CTLA4 or PD-1 could restore CART function. CRISPR-Cas9-mediated deletion of CTLA4 in preclinical models of leukemia and myeloma improved CAR T cell proliferation and anti-tumor efficacy. Importantly, this effect was specific to CTLA4 and not seen upon deletion of CTLA4 and/or PDCD1 in CAR T cells. Mechanistically, CTLA4 deficiency permitted unopposed CD28 signaling and maintenance of CAR expression on the T cell surface under conditions of high antigen load. In clinical studies, deletion of CTLA4 rescued the function of T cells from patients with leukemia that previously failed CAR T cell treatment. Thus, selective deletion of CTLA4 reinvigorates dysfunctional chronic lymphocytic leukemia (CLL) patient T cells, providing a strategy for increasing patient responses to CAR T cell therapy.

TOX2 coordinates with TET2 to positively regulate central memory differentiation in human CAR T cells

Chimeric antigen receptor (CAR) T cell therapy is used in treating human hematological malignancies, but its efficacy is limited by T cell exhaustion (TEX). TEX arises at the expense of central memory T cells (TCM), which exhibit robust antitumor efficacy. Reduction of the TET2 gene led to increased TCM differentiation in a patient with leukemia who experienced a complete remission. We show that loss of TET2 led to increased chromatin accessibility at exhaustion regulators TOX and TOX2, plus increased expression of TOX2. Knockdown of TOX increased the percentage of TCM. However, unexpectedly, knockdown of TOX2 decreased TCM percentage and reduced proliferation. Consistently, a TCM gene signature was reduced in the TOX2 knockdown, and TOX2 bound to promoters of numerous TCM genes. Our results thus suggest a role for human TOX2, in contrast to exhaustion regulator TOX, as a potentiator of central memory differentiation of CAR T cells, with plausible utility in CAR T cell cancer therapy via modulated TOX2 expression.

Abstract 3602: Mechanisms of CAR T cell dysfunction and identification of transcription factors that drive the exhaustion phenotype

Chimeric antigen receptor (CAR) T cell immunotherapy is FDA approved for the treatment of a subset of B cell malignancies but has shown limited clinical success in solid tumor therapy. T cell exhaustion is an important factor involved in treatment failure, and can, in part, result from continuous stimulation of the CAR by tumor cells expressing the cognate antigen. To gain deeper understanding of CAR T cell exhaustion induced by chronic antigen exposure (CAE), we developed and validated a robust in vitro model, in which mesothelin-redirected CAR T cells (M5CAR) were continuously stimulated with mesothelin-expressing AsPC-1 pancreatic tumor cells such that tumor cells were never cleared, and we characterized these CAE CAR T cells by gene expression at population and single-cell levels, and by epigenetic analyses.

CAE M5CAR T cells recapitulate the hallmarks of T cell exhaustion, including reduced proliferation, down-modulation of surface CAR, decreased cytokine production, and reduced cytotoxicity. In addition, CAR T cells undergoing CAE have a transcriptional signature and an epigenetic landscape consistent with exhaustion. Further, transcriptomic analysis revealed that CAE M5CAR T cells undergo a transition from T cells to a post-thymic NK-like T cell phenotype. This plasticity was confirmed by TCR lineage tracing and was also detected in CD19 CAR T cells analyzed from post-infusion blood from DLBCL patients and in M5CAR T cells infiltrating relapsed tumors derived from a xenograft NSG/AsPC-1 mouse model. The dysfunctional signature and the NK phenotype were further detected in vivo by transcriptomic analysis in Ly95 TCR-specific TILs infiltrating NY-ESO-1 tumors. Among the genes included in the dysfunctional signature, the transcription factors SOX4 and ID3 were identified as potential regulators of dysfunction by differential gene expression and pathway analyses. To determine their role in the establishment of a dysfunctional phenotype, we generated ID3KO.M5 and SOX4KO.M5 CAR T cells using CRISPR technology in primary human lymphocytes. The cytotoxic potential of the M5 CAR T cell product generated was not modified by the genetic disruption of the transcription factors. However, when CAR T cells were challenged with chronic antigen stimulation, KO CAR T cells showed a significant reduction of the dysfunctional signature and the NK-like T cell gene expression. Importantly, CAE KO CAR T cells exhibit improved cytotoxicity as compared to Mock.M5CAR T cells.

In summary, we have developed a robust in vitro model that recapitulates the hallmarks of T cell exhaustion and that facilitated the identification of a gene signature defining CAR dysregulation, a T-to-NK-like-T cell transition as a novel feature of CAR T cell dysfunction and the transcription factors SOX4 and ID3 as key regulators of CAR T cell exhaustion.

Citation Format: M. Angela Aznar, Charly R. Good, Shunichiro Kuramitsu, Parisa Samareh, Sangya Agarwal, Greg Donahue, Kenichi Ishiyama, Nils Wellhausen, Austin K. Rennels, Yujie Ma, Lifeng Tian, Sonia Guedan, Katherine A. Alexander, Zhen Zhang, Philipp C. Rommel, Nathan Singh, Karl M. Glastad, Max W. Richardson, Keisuke Watanabe, Janos L. Tanyi, Mark H. O’Hara, Marco Ruella, Simon F. Lacey, Edmund K. Moon, Stephen J. Schuster, Steven M. Albelda, Lewis L. Lanier, Regina M. Young, Shelley L. Berger, Carl H. June. Mechanisms of CAR T cell dysfunction and identification of transcription factors that drive the exhaustion phenotype [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3602.

Reverse Transcriptase Inhibition Disrupts Repeat Element Life Cycle in Colorectal Cancer

Altered RNA expression of repetitive sequences and retrotransposition are frequently seen in colorectal cancer, implicating a functional importance of repeat activity in cancer progression. We show the nucleoside reverse transcriptase inhibitor 3TC targets activities of these repeat elements in colorectal cancer preclinical models with a preferential effect in p53-mutant cell lines linked with direct binding of p53 to repeat elements. We translate these findings to a human phase II trial of single-agent 3TC treatment in metastatic colorectal cancer with demonstration of clinical benefit in 9 of 32 patients. Analysis of 3TC effects on colorectal cancer tumorspheres demonstrates accumulation of immunogenic RNA:DNA hybrids linked with induction of interferon response genes and DNA damage response. Epigenetic and DNA-damaging agents induce repeat RNAs and have enhanced cytotoxicity with 3TC. These findings identify a vulnerability in colorectal cancer by targeting the viral mimicry of repeat elements.

SIGNIFICANCE

Colorectal cancers express abundant repeat elements that have a viral-like life cycle that can be therapeutically targeted with nucleoside reverse transcriptase inhibitors (NRTI) commonly used for viral diseases. NRTIs induce DNA damage and interferon response that provide a new anticancer therapeutic strategy. This article is highlighted in the In This Issue feature, p. 1397.

An NK-like CAR T cell transition in CAR T cell dysfunction

Chimeric antigen receptor (CAR) T cell therapy has achieved remarkable success in hematological malignancies but remains ineffective in solid tumors, due in part to CAR T cell exhaustion in the solid tumor microenvironment. To study dysfunction of mesothelin-redirected CAR T cells in pancreatic cancer, we establish a robust model of continuous antigen exposure that recapitulates hallmark features of T cell exhaustion and discover, both in vitro and in CAR T cell patients, that CAR dysregulation is associated with a CD8+ T-to-NK-like T cell transition. Furthermore, we identify a gene signature defining CAR and TCR dysregulation and transcription factors, including SOX4 and ID3 as key regulators of CAR T cell exhaustion. Our findings shed light on the plasticity of human CAR T cells and demonstrate that genetic downmodulation of ID3 and SOX4 expression can improve the efficacy of CAR T cell therapy in solid tumors by preventing or delaying CAR T cell dysfunction.

Abstract 60: Induction of T cell dysfunction and NK-like T cell differentiation in vitro and in patients after CAR T cell treatment

Chimeric antigen receptor (CAR) T cell therapy has achieved remarkable success in hematological malignancies but remains largely ineffective in solid tumors. A major factor leading to the reduced efficacy of CAR T cell therapy is T cell dysfunction, and the mechanisms mediating this dysfunction are under investigation. Here we establish a robust model to study dysfunction of mesothelin-redirected CAR T cells in pancreatic cancer. Continuous antigen exposure results in hallmark features of exhaustion including reduced proliferation capacity and cytotoxicity, and severe defects in cytokine production. Here we identified a transcriptional signature at both population and single-cell levels in CAR T cells after continuous antigen exposure. In addition, TCR lineage tracing revealed a CD8+ T-to-NK-like T cell plasticity that results in reduced tumor cell killing. The transcription factors SOX4 and ID3 are specifically expressed in the dysfunctional CAR NK-like T cells and are predicted to be master regulators of the dysfunction gene expression signature and the post-thymic acquisition of an NK-like T cell fate. Finally, we identified the emergence of NK-like CAR T cells in a subset of patients after infusion of CAR T cells. The findings gleaned from this study shed light on the plasticity of human CAR T cells and suggest new approaches to improve the efficacy of CAR T cell therapy in solid tumors by preventing or revitalizing CAR T cell dysfunction.

Citation Format: Charly R. Good, Shunichiro Kuramitsu, Parisa Samareh, Greg Donahue, Kenichi Ishiyama, Yujie Ma, Nils Wellhausen, Lifeng Tian, Sangya Agarwal, Sonia Guedan, M. Angela Aznar, Katherine A. Alexander, Zhen Zhang, Nathan Singh, Max W. Richardson, Keisuke Watanabe, Janos L. Tanyi, Mark H. O'Hara, Marco Ruella, Simon F. Lacey, Edmund K. Moon, Stephen J. Schuster, Steven M. Albelda, Lewis L. Lanier, Regina M. Young, Shelley L. Berger, Carl H. June. Induction of T cell dysfunction and NK-like T cell differentiation in vitro and in patients after CAR T cell treatment [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 60.

Impaired Death Receptor Signaling in Leukemia Causes Antigen-Independent Resistance by Inducing CAR T-cell Dysfunction

Primary resistance to CD19-directed chimeric antigen receptor T-cell therapy (CART19) occurs in 10% to 20% of patients with acute lymphoblastic leukemia (ALL); however, the mechanisms of this resistance remain elusive. Using a genome-wide loss-of-function screen, we identified that impaired death receptor signaling in ALL led to rapidly progressive disease despite CART19 treatment. This was mediated by an inherent resistance to T-cell cytotoxicity that permitted antigen persistence and was subsequently magnified by the induction of CAR T-cell functional impairment. These findings were validated using samples from two CAR T-cell clinical trials in ALL, where we found that reduced expression of death receptor genes was associated with worse overall survival and reduced T-cell fitness. Our findings suggest that inherent dysregulation of death receptor signaling in ALL directly leads to CAR T-cell failure by impairing T-cell cytotoxicity and promoting progressive CAR T-cell dysfunction. SIGNIFICANCE: Resistance to CART19 is a significant barrier to efficacy in the treatment of B-cell malignancies. This work demonstrates that impaired death receptor signaling in tumor cells causes failed CART19 cytotoxicity and drives CART19 dysfunction, identifying a novel mechanism of antigen-independent resistance to CAR therapy.See related commentary by Green and Neelapu, p. 492.

Impaired Death Receptor Signaling in Leukemia Causes Antigen-Independent Resistance by Inducing CAR T-cell Dysfunction

Primary resistance to CD19-directed chimeric antigen receptor T-cell therapy (CART19) occurs in 10% to 20% of patients with acute lymphoblastic leukemia (ALL); however, the mechanisms of this resistance remain elusive. Using a genome-wide loss-of-function screen, we identified that impaired death receptor signaling in ALL led to rapidly progressive disease despite CART19 treatment. This was mediated by an inherent resistance to T-cell cytotoxicity that permitted antigen persistence and was subsequently magnified by the induction of CAR T-cell functional impairment. These findings were validated using samples from two CAR T-cell clinical trials in ALL, where we found that reduced expression of death receptor genes was associated with worse overall survival and reduced T-cell fitness. Our findings suggest that inherent dysregulation of death receptor signaling in ALL directly leads to CAR T-cell failure by impairing T-cell cytotoxicity and promoting progressive CAR T-cell dysfunction. SIGNIFICANCE: Resistance to CART19 is a significant barrier to efficacy in the treatment of B-cell malignancies. This work demonstrates that impaired death receptor signaling in tumor cells causes failed CART19 cytotoxicity and drives CART19 dysfunction, identifying a novel mechanism of antigen-independent resistance to CAR therapy.See related commentary by Green and Neelapu, p. 492.

Demethylator phenotypes in acute myeloid leukemia

Acute myeloid leukemia (AML) often harbors mutations in epigenetic regulators, and also has frequent DNA hypermethylation, including the presence of CpG island methylator phenotypes (CIMPs). Although global hypomethylation is well known in cancer, the question of whether distinct demethylator phenotypes (DMPs) exist remains unanswered. Using Illumina 450k arrays for 194 patients from The Cancer Genome Atlas, we identified two distinct DMPs by hierarchical clustering: DMP.1 and DMP.2. DMP.1 cases harbored mutations in NPM1 (94%), FLT3 (71%) and DNMT3A (61%). Surprisingly, only 40% of patients with DNMT3A mutations were DMP.1, which has implications for mechanisms of transformation by this mutation. In contrast, DMP.2 AML was comprised of patients with t(8;21), inv(16) or t(15;17), suggesting common methylation defects connect these disparate rearrangements. RNA-seq revealed upregulated genes functioning in immune response (DMP.1) and development (DMP.2). We confirmed these findings by integrating independent 450k data sets (236 additional cases), and found prognostic effects by DMP status, independent of age and cytogenetics. The existence of DMPs has implications for AML pathogenesis and may augment existing tools in risk stratification.

A novel isoform of TET1 that lacks a CXXC domain is overexpressed in cancer

TET1 oxidizes methylated cytosine into 5-hydroxymethylcytosine (5hmC), resulting in regulation of DNA methylation and gene expression. Full length TET1 (TET1FL) has a CXXC domain that binds to unmethylated CpG islands (CGIs). This CXXC domain allows TET1 to protect CGIs from aberrant methylation, but it also limits its ability to regulate genes outside of CGIs. Here, we report a novel isoform of TET1 (TET1ALT) that has a unique transcription start site from an alternate promoter in intron 2, yielding a protein with a unique translation start site. Importantly, TET1ALT lacks the CXXC domain but retains the catalytic domain. TET1ALT is repressed in embryonic stem cells (ESCs) but becomes activated in embryonic and adult tissues while TET1FL is expressed in ESCs, but repressed in adult tissues. Overexpression of TET1ALT shows production of 5hmC with distinct (and weaker) effects on DNA methylation or gene expression when compared to TET1FL. TET1ALT is aberrantly activated in multiple cancer types including breast, uterine and glioblastoma, and TET1 activation is associated with a worse overall survival in breast, uterine and ovarian cancers. Our data suggest that the predominantly activated isoform of TET1 in cancer cells does not protect from CGI methylation and likely mediates dynamic site-specific demethylation outside of CGIs.

Abstract 5382: A DNMT3A-independent hypomethylator phenotype is a unifying epigenetic signature of AML with good risk cytogenetics

Background: Acute myeloid leukemia (AML) causes the most leukemia-related deaths in the United States, and has frequent mutations in epigenetic regulators, including DNMT3A, IDH, and TET2. Such aberrations have been proposed to transform the epigenetic state in cancer, often involving DNA hypomethylation, however, the genomic specificity, causes, and clinical consequences of such methylation changes in AML remain unclear.

Methods: We queried genome-wide CpG methylation using The Cancer Genome Atlas (TCGA) AML samples (n=194) run on Illumina 450k arrays. We used RNA-seq data to study gene expression changes associated with hypomethylator phenotypes (HP). Analysis was done using R.

Results: Genome-wide analysis of CpG sites that are highly methylated in normal blood, and variably methylated in AML (β-value standard deviation in AML > 0.2; average β-value in normal blood > 0.8) revealed two distinct HPs by hierarchical clustering: Good-risk (GR) HP which included favorable cytogenetics, and DNMT-HP, which was enriched for DNMT3A mutations. We refined DNA methylation signatures of each HP cluster by differential methylation analysis and re-classified patients accordingly. Strikingly, all patients with t(8;21), inv(16), or t(15;17) belonged to the GR-HP+ group, suggesting that a common epigenetic thread connects these otherwise disparate genetic aberrations. From a clinical perspective GR-HP+ patients were younger than GR-HP- patients, and had significantly longer overall survival (median OS, years: GR-HP+ = Not reached; GR-HP- = 1.00; P < 0.001). In contrast, DNMT-HP+ cases were statistically equivalent to DNMT-HP- except for an enrichment for higher WBC counts, including no difference in survival (median OS, years: DNMT-HP+ = 0.92; DNMT-HP- = 1.34; P = 0.27). From an epigenetic perspective the two HP clusters harbored distinct DNA methylation changes; although both favored hypomethylation within non-CpG islands relative to CpG islands, the enrichment was more pronounced for DNMT-HP (Odds ratio: hypomethylated CpG islands/hypomethylated non-CpG islands, GR-HP = 0.64; DNMT-HP = 0.18). Genetic analysis revealed that GR-HP+ leukemia had wild-type IDH, DNMT3A, and NPM1 genes. In contrast, DNMT-HP+ AML had significantly more FLT3, NPM1, and DNMT3A mutations compared to DNMT-HP- patients. RNA-seq revealed significant up-regulation of genes in both HP phenotypes (216, and 150 genes for GR-HP and DNMT-HP, respectively at FDR < 0.01 and FC > 2). Pathway analysis of these genes revealed enrichments for ion channels and the complement pathway in DNMT-HP, and for nervous system and developmental genes in GR-HP.

Conclusions: Our data suggest that two HPs exist in AML with unique epigenetic and transcriptomic signatures. The striking association between GR-HP and different favorable cytogenetic changes suggests that a common set of epigenetic features may contribute to improved survival in these patients.

Citation Format: Andrew D. Kelly, Jozef Madzo, Priyanka Madireddi, Patricia Kropf, Charly R. Good, Jaroslav Jelinek, Jean-Pierre J. Issa. A DNMT3A-independent hypomethylator phenotype is a unifying epigenetic signature of AML with good risk cytogenetics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5382. doi:10.1158/1538-7445.AM2017-5382

Abstract 2659: A novel isoform of TET1 that lacks a CXXC domain is overexpressed in cancer

TET1 is a DNA demethylase that regulates DNA methylation, hydroxymethylation and gene expression patterns. It has a catalytic domain that oxidizes methylated cytosine into 5-hydroxymethylcytosine and can then be further oxidized or converted to un-methylated cytosine. TET1 has a CXXC domain that allows it to recognize and bind to long stretches of CpG dinucleotides, known as CpG islands (CGIs). Our previous work found TET1 to protect CGIs from aberrant methylation and that the CXXC domain limits its ability to regulate genes outside of CGIs. However, many of the methylation changes in cancer are outside CGIs. To determine if TET1 could possibly play a role in this hypomethylation, we searched for alternatively spliced forms of the protein. We identified a novel isoform of TET1 (TET1ALT) that lacks the CXXC domain but retains the demethylase domain. TET1ALT has a unique transcription start site from a strong alternate promoter upstream of exon 3, yielding a protein with a unique translation start site. We confirmed promoter activity using Luciferase constructs, and confirmed TET1ALT translation and function through overexpression experiments. Gene expression analyses by qPCR found that TET1ALT is silenced in mESCs but becomes activated in select embryonic and adult tissues while full length TET1 is favored in mESCs, but is repressed in adult tissues. Thus, there is an isoform switch during differentiation and TET1ALT is the major isoform expressed in adult cells. TET1ALT is over expressed in several cancer cell lines, including breast cancer. In conclusion, we have identified a novel isoform of TET1 that has the potential to regulate DNA methylation outside of CGIs and is the predominant isoform expressed in adult cells. We are investigating the hypothesis that TET1ALT may contribute to the methylation changes observed in cancer outside of CGIs, such as in gene bodies and in enhancers.

Citation Format: Charly R. Good, Jozef Madzo, Shinji Maegawa, Nora Engel, Jaroslav Jelinek, Jean-Pierre Issa. A novel isoform of TET1 that lacks a CXXC domain is overexpressed in cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2659.

Tolerability of oral loading of divalproex sodium in child psychiatry inpatients

OBJECTIVE

To determine a well-tolerated oral load of divalproex sodium that quickly and reliably achieves therapeutic drug levels in child psychiatry inpatients.

METHODS

A retrospective chart review revealed that during a 6-month period, divalproex sodium therapy was initiated in 16 male inpatients (ages 5-14 years). The patients were divided into two groups based on the initial dosing regimen. The first group received approximately 15 mg/kg/day based on actual weight, and the second group received approximately 15 mg/kg/day based on an adjusted ideal body weight (IBW). Weight was adjusted in these patients according to the following formula: IBW + 40% (Observed Weight - IBW). A trough blood level was obtained on day 5 of therapy.

RESULTS

Initial drug levels ranged from 46-146 ug/mL (mean = 90.6), of which 13 of 16 (81.3%) were considered within therapeutic range (50-120 ug/mL). Eight of 16 patients (50%) had reported side effects, including sedation and gastrointestinal upset. The majority of these side effects occurred in patients with drug levels > or = 90 ug/mL and were noted to improve with 1-2 days of therapy +/- dosage adjustment. Overweight patients (> or = 15% above IBW) who received the unadjusted 15 mg/kg oral load had significantly higher drug levels than their normal weight counterparts and overweight children who received weight-adjusted dosing (p < 0.003).

CONCLUSION

A 15 mg/kg/day oral load of divalproex sodium resulted in therapeutic drug levels on day 5 of treatment and is well tolerated in normal weight children. Overweight children are significantly more likely to experience supratherapeutic drug levels on this regimen, which may affect tolerability. Overweight children appear to benefit from weight-adjusted oral loading.