TP53 is the most frequently mutated gene in human cancers. In Acute Myeloid Leukemia (AML) and Clonal Hematopoiesis of Indeterminate Potential (CHIP), it is one of several recurrent genetic alterations. Despite multiple recent therapeutic advances for AML, TP53 mutated AML is associated with resistance to currently approved therapies and thus, a very poor prognosis. Emerging evidence suggests that mutations in TP53 may be a predictor of positive response to immunotherapy. To model cell - extrinsic consequences of hematopoietic p53 loss, we generated bone marrow chimeric mice bearing p53 -/- and congenic wild type cells. Following reconstitution, we observed increased levels of wild type CD8+ and CD4+ T cells in mice transplanted with p53 -/- hematopoietic cells compared to controls. In addition, we observed a change in the frequency of T cell subsets in p53 -/- chimeras including an increase in Tregs. To determine if these alterations were mirrored in the leukemic setting, we next generated p53 -/- ; nRas G12D leukemia. While the bone marrow of p53 -/- ; nRas G12D leukemia showed the presence of both T and B lymphocytes, MLL-AF9 showed a near complete absence of lymphocytes, akin to ‘immune-infiltrated’ and ‘immune-desert’ phenotypes seen in solid tumors. These data clearly demonstrate a causal cell-extrinsic effect of hematopoietic p53 loss on the immune system, both in the context of leukemia and preleukemic states. Modeling AML genetics in murine models serves as a powerful tool to define the association between genetic drivers and immune subtypes of AML towards precise patient stratification critical for the application of emerging targeted and immune therapies. Statement of Significance TP53 mutations are frequent in both AML and CHIP, and are associated with both resistance to therapy as well as very poor prognosis. We provide evidence to investigate the immunotherapy as a treatment option for this subgroup of AML.

Abstract Lung cancer represents one of the most significant and lethal diseases worldwide. Advances in treatment protocols, the development of targeted agents, and our comprehensive understanding of the genetics and mechanisms driving this disease, have helped identify novel agents with therapeutic promise, yet mortality remains high. Thus, there is a real need to identify new therapeutic options that can target this disease to improve patient outcome. BMI-1 (B cell-specific Moloney murine leukemia virus integration site 1), a key component of the epigenetic Polycomb Repressive Complex 1, plays a substantial role in many solid tumors, including NSCLC. It represents a compelling therapeutic target for NSCLC cancer patients as the majority of NSCLCs (~75%) display positive BMI-1 protein expression. Several compounds that reduce levels of the oncogene BMI-1 protein have been discovered by PTC Therapeutics i.e., PTC596 and a related analog PTC-028. PTC596 completed Ph1 trials and is currently being further tested in Ph1b trials. By using xenografts and established murine models of NSCLC, we are investigating BMI-1 as a novel therapeutic target in lung cancer, the mechanisms through which BMI-1 confers tumorigenicity, and determine the efficacy of BMI-1 inhibition in in vivo models of lung cancer at the single cell level. One critical aspect of cancer development lies in the 3-dimensional network of interactions that occurs between cells within their microenvironment. Therefore, by means of droplet-based molecular barcoding techniques we are analyzing single cell transcripts and identifying the population clusters within the heterogeneous tumor cellular milieu, to determine which cellular populations exist within tumors and how they respond to anti-BMI-1 treatment. Our data show that mutant EGFR and K-Ras driven lung cancer transgenic mice, as well as xenograft mice, express high levels of BMI-1 protein. In addition, we show that tumor growth of both models is affected by PTC596 treatment, with a more rapid response than that of currently available therapeutics. Tumor growth was measured at different time-points by magnetic resonance imaging. Transcriptional deconvolution of single cell sequencing data has enabled us to identify tumor-associated pulmonary subpopulations displaying epithelial, immune, fibroblast, and endothelial features. Importantly, tumor associated epithelial cells display a positive BMI-1 signature, which we also identified in primary NSCLC samples, underscoring the beneficial effects of anti-BMI-1 therapy in NSCLC patients. Citation Format: Indira Krishnan, Giorgia Maroni, Sean Clohessy, Virginia Savova, Mahmoud Bassal, Rapolas Zilionis, Eva Csizmadia, Clara M. Kerwin, Sun Choi, Claire V. Meyerovitz, Nicole Pandell, Chee W. Fhu, Junyan Zhang, Daniela S. Basseres, Cristina M. Magli, Julian Goggi, Robert S. Welner, Allon M. Klein, Marla Weetall, Art Branstrom, Raphael Bueno, Azhar Ali, Daniel G. Tenen, Elena Levantini. Novel anti-BMI-1 therapy in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5864.