Preclinical development of a chimeric antigen receptor T cell therapy targeting FGFR4 in rhabdomyosarcoma

Pediatric patients with relapsed or refractory rhabdomyosarcoma (RMS) have dismal cure rates, and effective therapy is urgently needed. The oncogenic receptor tyrosine kinase fibroblast growth factor receptor 4 (FGFR4) is highly expressed in RMS and lowly expressed in healthy tissues. Here, we describe a second-generation FGFR4-targeting chimeric antigen receptor (CAR), based on an anti-human FGFR4-specific murine monoclonal antibody 3A11, as an adoptive T cell treatment for RMS. The 3A11 CAR T cells induced robust cytokine production and cytotoxicity against RMS cell lines in vitro. In contrast, a panel of healthy human primary cells failed to activate 3A11 CAR T cells, confirming the selectivity of 3A11 CAR T cells against tumors with high FGFR4 expression. Finally, we demonstrate that 3A11 CAR T cells are persistent in vivo and can effectively eliminate RMS tumors in two metastatic and two orthotopic models. Therefore, our study credentials CAR T cell therapy targeting FGFR4 to treat patients with RMS.

A stem cell epigenome is associated with primary nonresponse to CD19 CAR T cells in pediatric acute lymphoblastic leukemia

CD19 chimeric antigen receptor T-cell therapy (CD19-CAR) has changed the treatment landscape and outcomes for patients with pre-B-cell acute lymphoblastic leukemia (B-ALL). Unfortunately, primary nonresponse (PNR), sustained CD19+ disease, and concurrent expansion of CD19-CAR occur in 20% of the patients and is associated with adverse outcomes. Although some failures may be attributable to CD19 loss, mechanisms of CD19-independent, leukemia-intrinsic resistance to CD19-CAR remain poorly understood. We hypothesize that PNR leukemias are distinct compared with primary sensitive (PS) leukemias and that these differences are present before treatment. We used a multiomic approach to investigate this in 14 patients (7 with PNR and 7 with PS) enrolled in the PLAT-02 trial at Seattle Children's Hospital. Long-read PacBio sequencing helped identify 1 PNR in which 47% of CD19 transcripts had exon 2 skipping, but other samples lacked CD19 transcript abnormalities. Epigenetic profiling discovered DNA hypermethylation at genes targeted by polycomb repressive complex 2 (PRC2) in embryonic stem cells. Similarly, assays of transposase-accessible chromatin-sequencing revealed reduced accessibility at these PRC2 target genes, with a gain in accessibility of regions characteristic of hematopoietic stem cells and multilineage progenitors in PNR. Single-cell RNA sequencing and cytometry by time of flight analyses identified leukemic subpopulations expressing multilineage markers and decreased antigen presentation in PNR. We thus describe the association of a stem cell epigenome with primary resistance to CD19-CAR therapy. Future trials incorporating these biomarkers, with the addition of multispecific CAR T cells targeting against leukemic stem cell or myeloid antigens, and/or combined epigenetic therapy to disrupt this distinct stem cell epigenome may improve outcomes of patients with B-ALL.

Abstract LB062: Profiling of pediatric neuroblastoma reveals a dynamic and clinically significant tumor immune microenvironment

Background: Neuroblastoma (NB) is the 3rd most common childhood cancer and accounts for 15% of all pediatric cancer deaths. Recently, immunotherapy using monoclonal antibodies targeting GD2 have improved survival rates for some patients with NB. Unfortunately, this response is not uniform across patients, which suggests an incomplete understanding of the underlying immune biology of this disease. Large-scale sequencing efforts of patient tumors have suggested that NB has diverse immune microenvironments (TMEs), which are associated with MYCN-amplification (A) and patient outcomes. While this is strong evidence, these results need to be further validated, specifically to determine whether the infiltrating immune cells can interact with tumor cells and if the TME is impacted by evolutionary pressures. We hypothesized the TME is dynamic, changing with therapy and metastasis, influenced by molecular subtype, and associated with patient outcomes.

Methods: To better understand the heterogeneity seen in NB TMEs, we obtained 93 clinically annotated tumors from 72 pediatric patients with neuroblastoma, consisting of high-risk primary and metastatic tumors both pre- and post- chemotherapy. We designed two highly multiplexed antibody panels targeting immune cells and performed either imaging mass cytometry (IMC) (n = 46) or NanoString GeoMx DSP (n = 47).

Results: We confirmed that MYCN-non amplified (NA) tumors display higher frequencies of lymphocytes including CD4 (p < 0.003) and CD8 (p < 0.005) T-cells. Using nearest neighbor analysis, we found that not only are both CD4 and CD8 T-cells more frequent in MYCN-NA samples, but they are significantly closer to tumor cells compared to MYCN-A tumors (p < 2.2E-16), suggesting increased interactions. We then investigated the effects of exposure to chemotherapy on the TME and discovered that MYCN-NA tumors displayed higher frequencies of T-cells (p < 0.0041) and B-cells (p = 0.047) prior to exposure to chemotherapy. We also revealed increased frequencies of macrophages (p = 0.0193) and antigen presentation in tumors post-treatment. Interestingly, we saw increased expression of the immune checkpoints CTLA-4 (p = 0.0432) and TIM-3 (p = 2.05E-5), but not PD-1, PD-L1, or PD-L2, suggesting targeted checkpoint blockade could improve response to therapy in these patients. Notably, high expression of CD56, a marker for both NK cells and NB, was associated with increase overall survival, indicating a potential role of NK cells in improving outcomes.

Conclusions: Using two independent protein-based profiling methods, we investigated the TME in clinically annotated patient NBs. We find that the TME in NB varies with tumor subtype and changes dynamically with chemotherapy. These results can inform future trials to optimize the timing and specificity of novel immunotherapeutic approaches for these high-risk patients.

Citation Format: Katherine E. Masih, Zahin Islam, Paul Aiyetan, Igor B. Kuznetsov, Stephen M. Hewitt, Daniel Catchpoole, Jun S. Wei, William Bocik, Javed Khan. Profiling of pediatric neuroblastoma reveals a dynamic and clinically significant tumor immune microenvironment [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 LB062.

Abstract 3581: Multi-omic analysis identifies mechanisms of resistance to CD19 CAR T-cell therapy in children with acute lymphoblastic leukemia

Background: Acute lymphoblastic leukemia (ALL) is the most common childhood cancer. Despite the survival rate of 90% for newly diagnosed children with ALL, the outcome for relapsed patients is historically poor with a less than 30% survival. CD19 CAR T-cell therapy (CART19) has shown remarkable response rates, between 80-90% in relapsed/refractory disease. Little is known about antigen-independent factors that predict initial resistance to CART19. We hypothesized that leukemias that are resistant to CART19 are distinct from sensitive leukemias and that these differences can be detected prior to therapy.

Methods: To interrogate differences between resistant and sensitive leukemias, we obtained pre-treatment bone marrow aspirates (BMAs) from patients enrolled in a clinical trial at Seattle Children’s Hospital (PLAT-02). Samples were categorized based on patient response, with non-response defined as not achieving and maintaining minimal residual disease negativity at Day +63. Our study included 7 resistant and 7 sensitive leukemias as controls. We performed whole exome sequencing, bulk RNA-seq, PacBio-seq of the CD19 locus, array-based methylation, ATAC-seq, scRNA-seq, and CyTOF.

Results: We found that non-response to CART19 is independent of leukemic subtype. Despite blasts being CD19+ in all patients by flow cytometry, we identified alternative splicing of CD19 in one non-responder, while the remaining non-responders expressed high levels of wildtype CD19. We discovered a distinctive DNA methylation pattern in the non-responders characterized by hypermethylation of PRC2 targets in embryonic and cancer stem cells (p = 8.15E-25) Furthermore, using gene set enrichment analysis of ATAC-seq data, we found increased accessibility of chromatin at regions associated with stem cell proliferation (NES = 2.31; p < 0.0001) and cell cycling (NES = 2.27; p < 0.0001). We found a greater similarity between accessibility patterns of non-responders to hematopoietic progenitors, including hematopoietic stem cells (p = 0.037) and common myeloid progenitors (p = 0.047). These findings were supported by an increased frequency of cell subpopulations expressing a multi-lineage phenotype (CD19, CD20, CD33, CD34; p = 0.009). Moreover, we find decreased expression of antigen presentation and processing pathways across all leukemic cells relative to responders (p = 0.0001).

Conclusions: This study, one of the most comprehensive multi-omic analyses of samples from patients treated with CAR T-cells, identified resistance mechanisms that can be detected prior to treatment. We report the novel association of a stem cell phenotype, lineage plasticity, and decreased antigen presentation with resistance. These results support further refinement of eligibility for CART19 for children with leukemia and highlights the need for alternative of complimentary approaches for these patients.

Citation Format: Katherine E. Masih, Rebecca Gardner, Hsien-Chao Chou, Abdalla Abdelmaksoud, Young K. Song, Luca Mariani, Vineela Gangalapudi, Berkley E. Gryder, Ashley Wilson, Serifat O. Adebola, Benjamin Z. Stanton, Chaoyu Wang, Xinyu Wen, Gregoire Altan-Bonnet, Michael C. Kelly, Jun S. Wei, Martha L. Bulyk, Michael C. Jensen, Rimas J. Orentas, Javed Khan. Multi-omic analysis identifies mechanisms of resistance to CD19 CAR T-cell therapy in children with acute lymphoblastic leukemia [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 3581.

Immuno-transcriptomic profiling of extracranial pediatric solid malignancies

We perform an immunogenomics analysis utilizing whole-transcriptome sequencing of 657 pediatric extracranial solid cancer samples representing 14 diagnoses, and additionally utilize transcriptomes of 131 pediatric cancer cell lines and 147 normal tissue samples for comparison. We describe patterns of infiltrating immune cells, T cell receptor (TCR) clonal expansion, and translationally relevant immune checkpoints. We find that tumor-infiltrating lymphocytes and TCR counts vary widely across cancer types and within each diagnosis, and notably are significantly predictive of survival in osteosarcoma patients. We identify potential cancer-specific immunotherapeutic targets for adoptive cell therapies including cell-surface proteins, tumor germline antigens, and lineage-specific transcription factors. Using an orthogonal immunopeptidomics approach, we find several potential immunotherapeutic targets in osteosarcoma and Ewing sarcoma and validated PRAME as a bona fide multi-pediatric cancer target. Importantly, this work provides a critical framework for immune targeting of extracranial solid tumors using parallel immuno-transcriptomic and -peptidomic approaches.

Consequences of hemophagocytic lymphohistiocytosis-like cytokine release syndrome toxicities and concurrent bacteremia

Serious bacterial infections (SBI) can lead to devastating complications with CD19 CAR T cells and cytokine release syndrome (CRS). Little is known about consequences of and risk factors for SBI with novel CAR T-cell constructs or with CRS complicated by HLH-like toxicities. We report on three patients with B-cell acute lymphoblastic leukemia treated with CD22 CAR T cells who developed SBI and CRS-associated HLH. Serum cytokine profiling revealed sustained elevations well beyond CRS resolution, suggesting ongoing systemic inflammation. Heightened inflammatory states converging with SBI contribute to poor outcomes, and recognition and prevention of extended inflammation may be needed to improve outcomes.

ZFTA Translocations Constitute Ependymoma Chromatin Remodeling and Transcription Factors

ZFTA (C11orf95)-a gene of unknown function-partners with a variety of transcriptional coactivators in translocations that drive supratentorial ependymoma, a frequently lethal brain tumor. Understanding the function of ZFTA is key to developing therapies that inhibit these fusion proteins. Here, using a combination of transcriptomics, chromatin immunoprecipitation sequencing, and proteomics, we interrogated a series of deletion-mutant genes to identify a tripartite transformation mechanism of ZFTA-containing fusions, including: spontaneous nuclear translocation, extensive chromatin binding, and SWI/SNF, SAGA, and NuA4/Tip60 HAT chromatin modifier complex recruitment. Thereby, ZFTA tethers fusion proteins across the genome, modifying chromatin to an active state and enabling its partner transcriptional coactivators to promote promiscuous expression of a transforming transcriptome. Using mouse models, we validate further those elements of ZFTA-fusion proteins that are critical for transformation-including ZFTA zinc fingers and partner gene transactivation domains-thereby unmasking vulnerabilities for therapeutic targeting. SIGNIFICANCE: Ependymomas are hard-to-treat brain tumors driven by translocations between ZFTA and a variety of transcriptional coactivators. We dissect the transforming mechanism of these fusion proteins and identify protein domains indispensable for tumorigenesis, thereby providing insights into the molecular basis of ependymoma tumorigenesis and vulnerabilities for therapeutic targeting.This article is highlighted in the In This Issue feature, p. 2113.

Abstract A11: A comprehensive and integrative omic analysis of multiply relapsed refractory pediatric pre-B cell acute lymphoblastic leukemia predicts response to CD19 CAR T-cell therapy

Acute lymphoblastic leukemia (ALL) is the most common childhood cancer with a peak incidence at 3-5 years of age. Despite the improved survival rate of 90% for newly diagnosed children with ALL, the outcome for patients with relapsed disease is poor with a less than 30% overall survival. CD19 CAR T-cell therapy has shown remarkable response rates in relapsed/refractory disease. Long-term survival analysis has shown that initial response rates exceed 80%. However, durable response rates at one year are closer to 40%. Little is known about factors predicting durable response to CAR T therapy. We hypothesize that patients with CD19 CAR T-cell resistant ALL have a distinct disease compared to responders to therapy that can be identified in pretreatment leukemia. Utilizing advanced genomic, epigenetic, proteomic, and single-cell (sc) techniques, we characterized patient bone marrow aspirates (BMA) to identify mechanisms of resistance. Patients enrolled in PLAT-02 at Seattle Children’s Hospital were categorized according to the durability of their response to CD19 CAR T therapy. To characterize the molecular and genomic alterations specific to the therapy-resistant ALLs, we performed comprehensive analyses on pre-treatment therapy-resistant and sensitive BMAs using whole-exome sequencing, RNA- BMAs seq, scRNA-seq, sc B cell receptor (BCR)-seq, methylation array, H3K27ac ChIP-seq, ATAC-seq, and CyTOF. Additionally, we developed murine patient-derived xenografts (PDXs) for future studies. Initial mutation analyses revealed 5 hotspot mutations (ABL1, 2 x KRAS, IKZF1, and EP300) and actionable fusion (2 ABL1, 2 ETV6, 2 ETV5, KMT2A). Interestingly, we identified a KMT2A-AFF1 fusion in a sensitive leukemia, which has been demonstrated to predispose patients to CD19 CAR T resistance through lineage switching. Additionally, we identified a novel CREBBP-fusion in leukemias resistant to CD19 CAR T-induced B-cell aplasia. Alterations of CREBBP have previously been associated with ALL that is refractory to conventional therapies. Integrated gene expression and epigenetic analyses are ongoing to identify genes or pathways associated with resistant disease. scRNA- and scBCR-seq data are being analyzed and integrated with CyTOF analyses to detect mixed lineage and gene expression-based heterogeneity that may predict clonal selection by CAR T pressure. Finally, we developed and genetically analyzed murine PDXs for 64% of the patient samples, establishing a valuable resource for future studies and developing novel therapies for resistant leukemias. This study is one of the most integrative and comprehensive genomic profiling approaches to identify the molecular traits of therapy-resistant ALL in patient samples. We hope to identify and develop crucial biomarkers predicting responsiveness to CAR T-cell therapy.

Citation Format: Katherine E. Masih, Rebecca Gardner, Berkley E. Gryder, Abdalla Abdelmaksoud, Ashley Wilson, Serifat Adebola, Benjamin Z. Stanton, Young K. Song, Justin Lack, Chaoyu Wang, Xinyu Wen, Zachary Rae, Adam Cheuk, Gregoire Altan-Bonnet, Michael Kelly, Jun S. Wei, Michael C. Jensen, Rimas J. Orentas, Javed Khan. A comprehensive and integrative omic analysis of multiply relapsed refractory pediatric pre-B cell acute lymphoblastic leukemia predicts response to CD19 CAR T-cell therapy [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr A11.

Abstract LB-056: An integrated genomic, epigenetic, proteomic, and single cell analysis of pediatric B cell acute lymphoblastic leukemia to elucidate resistance mechanisms to CD19 CAR T cell therapy

Background

Acute lymphoblastic leukemia (ALL) is the most common childhood cancer with a peak incidence at 3-5 years of age. Despite the improved survival rate of 90% for newly diagnosed children with ALL, the outcome for patients with relapsed disease is poor with a less than 30% overall survival. CD19 CAR T cell therapy has shown impressive response rates in relapsed/refractory disease. However, long-term survival analysis has shown that despite initial response rates exceeding 80%, durable response rates at one year are closer to 40%. Currently, little is known about molecular factors predicting durable response to CAR T therapy. We hypothesized that patients with CD19 CAR T therapy resistant ALL have a molecularly distinct disease compared to patients who respond to therapy, which can be identified in pre-treatment leukemia samples. Utilizing advanced genomic, epigenetic, proteomic, and single-cell techniques, we characterized the bone marrow of patients that were resistant or sensitive to therapy to identify mechanisms of resistance.

Methods

Patients enrolled in a phase I clinical trial at Seattle Children’s Hospital (PLAT-02) were categorized according to the durability of their response to CD19 CAR T therapy. Bone marrow aspirates from patients with leukemias resistant to therapy (4 pre-treatment with 2 paired post-treatment) were analyzed and compared to patients with therapy sensitive leukemias (5 pre-treatment). We performed bulk whole-exome sequencing and RNA-seq, single cell (sc) RNA-seq, scB cell receptor (BCR)-seq, methylation array, H3K27ac ChIP-seq, and ATAC-seq.

Results

Initial genomic analysis revealed a total of 5 previously reported recurrent hotspot mutations in ABL1, 2 x KRAS (Q61H), IKZF1, and EP300. RNA-seq analyses identified actionable fusions in 2 x ABL1, 2 x ETV6, 2 x ETV5, and 1x KMT2A with variable partners. Interestingly, a therapy-sensitive leukemia harbored a KMT2A-AFF1fusion that was previously shown to predispose patients treated with blinatumomab to leukemic plasticity and lineage switching. Additionally, we identified in-frame CREBBP-fusions in all leukemias that failed to achieve CD19 CAR T cell induced B cell aplasia. CREBBP perturbations have previously been associated with relapsed and refractory ALL. Integrated gene expression and epigenetic analyses identified several pathways associated with resistant disease. ATAC-seq and methylation data are being analyzed for lineage specification. Similarly, scRNA- and scBCR-seq data are being analyzed for the existence of mixed lineage and gene expression-based heterogeneity that may predict clonal selection under CAR T pressure.

Conclusions

This study establishes one of the most comprehensive approaches to genomic profiling for leukemia patient samples. Although our analysis is preliminary and sample number is small, in-depth analyses are highlighting crucial differences in leukemia that will allow improved prediction of responsiveness to CAR T therapy.

Citation Format: Katherine E. Masih, Rebecca Gardner, Berkley E. Gryder, Justin Lack, Benjamin Z. Stanton, Ashley Wilson, Olivia Finney, Sivasish Sindiri, Young Song, Zachary Rae, Michael Kelly, Chaoyu Wang, Xinyu Wen, Adam Cheuk, Jun S. Wei, Michael Jensen, Rimas Orentas, Javed Khan. An integrated genomic, epigenetic, proteomic, and single cell analysis of pediatric B cell acute lymphoblastic leukemia to elucidate resistance mechanisms to CD19 CAR T cell therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-056.

Genomic subtyping and therapeutic targeting of acute erythroleukemia

Acute erythroid leukemia (AEL) is a high-risk leukemia of poorly understood genetic basis, with controversy regarding diagnosis in the spectrum of myelodysplasia and myeloid leukemia. We compared genomic features of 159 childhood and adult AEL cases with non-AEL myeloid disorders and defined five age-related subgroups with distinct transcriptional profiles: adult, TP53 mutated; NPM1 mutated; KMT2A mutated/rearranged; adult, DDX41 mutated; and pediatric, NUP98 rearranged. Genomic features influenced outcome, with NPM1 mutations and HOXB9 overexpression being associated with a favorable prognosis and TP53, FLT3 or RB1 alterations associated with poor survival. Targetable signaling mutations were present in 45% of cases and included recurrent mutations of ALK and NTRK1, the latter of which drives erythroid leukemogenesis sensitive to TRK inhibition. This genomic landscape of AEL provides the framework for accurate diagnosis and risk stratification of this disease, and the rationale for testing targeted therapies in this high-risk leukemia.