Multiple myeloma (MM) is the second most common hematologic malignancy and remains incurable despite the advent of numerous new drugs such as proteasome inhibitors (PIs), immunomodulatory agents (IMiDs), and monoclonal antibodies. There is an unmet need to develop novel therapies for refractory/relapsed MM. In the past few years, chimeric antigen receptor (CAR)-modified T cell therapy for MM has shown promising efficacy in preclinical and clinical studies. Furthermore, the toxicities of CAR-T cell therapy are manageable. This article summarizes recent developments of CAR-T therapy in MM, focusing on promising targets, new technologies, and new research areas. Additionally, a comprehensive overview of antigen selection is presented along with preliminary results and future directions of CAR-T therapy development.

Immune cells play critical functions in cancer, and mice with intact immune systems are vital to understanding tumor immunology. Both genetically engineered mouse models (GEMMs) and syngeneic cell transplant approaches use immunocompetent mice to define immune-dependent events in tumor development and progression. Due to their rapid and reproducible nature, there is expanded interest in developing new syngeneic tools from established primary tumor models. However, few studies have examined the extent that syngeneic tumors reflect the immune profile of their originating primary models. Here, we describe comprehensive immunophenotyping of two well-established GEMMs and four new syngeneic models derived from these parental primary tumors. To our knowledge, this is the first systematic analysis comparing immune landscapes between primary and orthotopic syngeneic tumors. These models all use the same well-defined human-relevant driver mutations, arise at identical orthotopic locations, and are generated in mice of the same background strain. This allows for a direct and focused comparison of tumor immune landscapes in carefully controlled mouse models. We identify key differences between the immune infiltrate of GEMM models and their corresponding syngeneic tumors. Most notable is the divergence of T cell populations, with different proportions of CD8+ T cells and regulatory T cells across several models. We also observe immune variation across syngeneic tumors derived from the same primary model. These findings highlight the importance of immune variance across mouse modeling approaches, which has strong implications for the design of rigorous and reproducible translational studies.

Rhabdomyosarcoma (RMS) is an aggressive form of cancer that accounts for half of all pediatric soft tissue sarcomas. Little progress has been made in improving survival outcomes over the past three decades. Mouse models of rhabdomyosarcoma are a critical component of translational research aimed at understanding tumor biology and developing new, improved therapies. Though several models exist, many common mutations found in human rhabdomyosarcoma tumors remain unmodeled and understudied. This study describes a new model of embryonal rhabdomyosarcoma driven by the loss of Nf1 and Ink4a/Arf, two mutations commonly found in patient tumors. We find that this new model is histologically similar to other previously-published rhabdomyosarcoma models, although it substantially differs in the time required for tumor onset and in tumor growth kinetics. We also observe unique sex-dependent phenotypes in both primary and newly-developed orthotopic syngeneic allograft tumors that are not present in previous models. Using in vitro and in vivo studies, we examined the response to vincristine, a component of the standard-of-care chemotherapy for RMS. The findings from this study provide valuable insight into a new mouse model of rhabdomyosarcoma that addresses an ongoing need for patient-relevant animal models to further translational research.

The histone methyltransferase PRC2 plays a complex role in cancer. Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive sarcomas with frequent loss-of-function mutations in PRC2 that are associated with poor outcome. Here, we identify a critical role for PRC2 loss in driving MPNST metastasis. PRC2-dependent metastatic phenotypes include increased collagen-dependent invasion, upregulation of matrix remodeling enzymes, and elevated lung metastasis in orthotopic mouse models. Furthermore, clinical sample analysis determines that PRC2 loss correlates with metastatic disease, increased fibrosis, and decreased survival in MPNST patients. These results may have broad implications for PRC2 function across multiple cancers and provide a strong rationale for investigating potential therapies targeting ECM remodeling enzymes and tumor fibrosis to improve outcomes in MPNST patients.

The DNA methyltransferase inhibitor decitabine has classically been used to reactivate silenced genes and as a pre-treatment for anti-cancer therapies. In a new variation of this idea, this study explores the concept of adding low-dose decitabine following administration of chemotherapy to bolster therapeutic efficacy. We find that addition of decitabine following treatment with the chemotherapy agent gemcitabine improves survival and slows tumor growth in a mouse model of high-grade sarcoma. Unlike prior studies in epithelial tumor models, low-dose decitabine did not induce a robust anti-tumor T cell response in sarcoma. Furthermore, low-dose decitabine synergizes with gemcitabine independently of the immune system. Mechanistic analyses demonstrate that the combination therapy induces bi-phasic cell cycle arrest and apoptosis. Therapeutic efficacy was found to be sequence dependent, with gemcitabine priming cells for treatment with decitabine through inhibition of ribonucleotide reductase. This study identifies a unique application of low-dose decitabine to augment the cytotoxic effects of conventional chemotherapy in an immune-independent manner.The concepts explored in this study represent a promising new paradigm for cancer treatment by augmenting chemotherapy through addition of low-dose decitabine to increase tolerability and improve patient response. These findings have widespread implications for the treatment of sarcomas and other aggressive malignancies.

Purpose: Malignant peripheral nerve sheath tumors (MPNSTs) are lethal, Ras-driven sarcomas that lack effective therapies. We investigated effects of targeting CDK4/6, MEK, and/or programmed death-ligand 1 (PD-L1) in preclinical MPNST models. Experimental Design: Patient-matched MPNSTs and precursor lesions were examined by FISH, RNAseq, IHC, and Connectivity-Map analyses. Antitumor activity of CDK4/6 and MEK inhibitors was measured in MPNST cell lines, patient-derived xenografts (PDXs), and de novo mouse MPNSTs, with the latter used to determine anti-PD-L1 response. Results: Patient tumor analyses identified CDK4/6 and MEK as actionable targets for MPNST therapy. Low-dose combinations of CDK4/6 and MEK inhibitors synergistically reactivated the retinoblastoma (RB1) tumor suppressor, induced cell death, and decreased clonogenic survival of MPNST cells. In immune-deficient mice, dual CDK4/6-MEK inhibition slowed tumor growth in 4 of 5 MPNST PDXs. In immunocompetent mice, combination therapy of de novo MPNSTs caused tumor regression, delayed resistant tumor outgrowth, and improved survival relative to monotherapies. Drug-sensitive tumors that regressed contained plasma cells and increased cytotoxic T cells, whereas drug-resistant tumors adopted an immunosuppressive microenvironment with elevated MHC II-low macrophages and increased tumor cell PD-L1 expression. Excitingly, CDK4/6-MEK inhibition sensitized MPNSTs to anti-PD-L1 immune checkpoint blockade (ICB) with some mice showing complete tumor regression. Conclusions: CDK4/6-MEK inhibition induces a novel plasma cell-associated immune response and extended antitumor activity in MPNSTs, which dramatically enhances anti-PD-L1 therapy. These preclinical findings provide strong rationale for clinical translation of CDK4/6-MEK-ICB targeted therapies in MPNST as they may yield sustained antitumor responses and improved patient outcomes.

<p>Supplementary Table S3. Cluster of differentiation (CD) markers used to delineate immune cell populations after gating on CD45+ live cells.</p>

Epigenetic reprogramming alters gene transcription in response to different cellular cues and can occur at both the DNA level as well as histone post-translational modifications. Polycomb repressive complex 2 (PRC2) is a common epigenetic modifier that is responsible for adding methyl groups to the twenty-seventh lysine of histone 3. This modification is associated with decreased gene transcription and recruits complexes that further compact chromatin. PRC2 mutations have been implicated in the tumorigenesis of many cancer types; however, the role that PRC2 plays in tumorigenesis is complex and not well understood. PRC2 loss-of-function mutations have been identified in malignant peripheral nerve sheath tumors (MPNST), an aggressive sarcoma. PRC2 mutations are found in the EED and SUZ12 subunits in 70-92% of tumors. There are currently no effective therapies for MPNSTs resulting in a poor prognosis for individuals with inoperable tumors. Using a CRISPR/Cas9 system to delete EED or SUZ12, we developed in vitro and in vivo models to further study the biology of PRC2 loss in MPNSTs. Our data suggests that loss of PRC2 subunits increases the expression of extra-cellular matrix (ECM) remodeling genes, promotes cell migration in vitro, and increases pulmonary metastasis in vivo. We also observed that loss of either EED or SUZ12 increases collagen handling and a clustering metastatic phenotype. Additionally, loss of H3K27me3 was correlated with increased ECM and ECM remodeling genes as well as metastasis and overall survival in patient RNA-seq and tumor microarray data, respectively. Further characterization of the underlying mechanisms of PRC2-dependent metastasis will allow us to better understand the role of PRC2 in MPNST biology and test novel therapies for these patients. Citation Format: Qierra R. Brockman, Amanda Scherer, Gavin R. McGivney, Wade R. Gutierrez, Andrew Voigt, Alexandra Isaacson, Emily A. Laverty, Grace Roughton, Vickie Knepper-Adrian, Benjamin Darbro, Munir R. Tanas, Christopher Stipp, Rebecca D. Dodd. PRC2 loss drives MPNST metastasis and matrix remodeling. [abstract]. In: Proceedings of the AACR Special Conference: Cancer Epigenomics; 2022 Oct 6-8; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_2):Abstract nr A024.