Introduction Histotripsy is a novel focused ultrasound tumor ablation modality with potent immunostimulatory effects. Methods To measure the spatiotemporal kinetics of local andabscopal responses to histotripsy, C57BL/6 mice bearing bilateral flank B16 melanoma or Hepa1-6 hepatocellular carcinoma tumors were treated with unilateral sham or partial histotripsy. Treated and contralateral untreated (abscopal) tumors were analyzed using multicolor immunofluorescence, digital spatial profiling, RNA sequencing (RNASeq), and flow cytometry. Results Unilateral histotripsy triggered abscopal tumor growth inhibition. Within the ablation zone, early high mobility group box protein 1 (HMGB1) release and necroptosis were accompanied by immunogenic cell death transcriptional responses in tumor cells and innate immune activation transcriptional responses in infiltrating myeloid and natural killer (NK) cells. Delayed CD8+ T cell intratumoral infiltration was spatiotemporally aligned with cancer cell features of ferroptosis; this effect was enhanced by CTLA-4 blockade and recapitulated in vitro when tumor-draining lymph node CD8+ T cells were co-cultured with tumor cells. Inoculation with cell-free tumor fractions generated by histotripsy but not radiation or freeze/thaw conferred partial protection from tumor challenge. Discussion We propose that histotripsy may evoke local necroptotic immunogenic cell death, priming systemic adaptive immune responses and abscopal ferroptotic cancer cell death.

2668 Background: Immune checkpoint inhibitors (CPI) are known to rarely cause new onset diabetes (CPI DM). While rare, this adverse event is quite challenging for patients and clinicians to manage. Therefore, it is important to identify risk factors and clinical characteristics. This is the first comprehensive, multi-institutional study of CPI-DM across multiple agents and cancer types. Methods: The NCI Cancer Therapy Program (CTEP) database of adverse events (AEs) was queried for AEs related to diabetes (Grade 3 or 4 hyperglycemia, Acidosis including Diabetic Ketoacidosis (DKA), glucose intolerance and diabetes mellitus) among 6,925 patients who had been treated with a PD-(L)1 inhibitor alone or in combination from 6/2015 to 12/2019. Each AE report was reviewed and classified as due to CPI DM, new onset type 2 diabetes mellitus (T2DM), T2DM exacerbation without medication non-compliance, existing DM with medication non-compliance, or association with steroids (SDM). CPI DM was diagnosed based on: evidence of insulin deficiency either through presentation in DKA or low c-peptide with need for long term basal bolus insulin to maintain euglycemia and/or positive islet autoantibodies. Results: In total, there were 82 cases with at least one of these AEs; 41 had CPI-DM, 22 had SDM, 1 had new T2DM, 4 had T2DM exacerbation, 3 had medication noncompliance and 11 had acidosis not attributable to diabetes or had insufficient data. After excluding non-hyperglycemic acidosis, 57.8% had CPI-DM. Furthermore, if not on steroids and in good compliance with diabetes medications, 89.1% had CPI-DM. The incidence of CPI-DM was 0.59%; it was most common on combination PD-1/CTLA-4 inhibitor therapy (0.85%, 15/1767), followed by PD-(L)1 inhibitor monotherapy (0.54%, 18/3354), followed by CPIs combined with additional agents including chemotherapy and targeted agents (0.44%, 8/1804)(p = 0.25). Hospitalization was required for 87.5% of CPI-DM cases with 74.3% of those requiring an inpatient endocrine consult. All but one CPI-DM case had an endocrine consult at as either an inpatient or outpatient. Conclusions: While rare, this cohort shows the large health care burden of CPI-DM and that any hyperglycemia, and especially marked hyperglycemia, should be treated as CPI-DM until proven otherwise. [Table: see text]

Background Histotripsy, a novel image-guided, robotically assisted sonic therapy platform, is a non-invasive and non-thermal tumor ablation modality. We have previously shown that histotripsy potentiates profound innate and adaptive anti-tumor responses in addition to direct tumor destruction.1 In this study, we sought to characterize the biomarkers of tumor cell death pathways immediately after histotripsy and after the induction of adaptive anti-tumor immune responses in preclinical settings. Methods Immunocompetent C57BL/6 mice were inoculated with bilateral subcutaneous flank injections of Hepa1-6 hepatocellular carcinoma to generate 8–10 mm tumors within 8–11 days. Unilateral subtotal histotripsy was then performed. Mice were euthanized at 6h, and 1, 3 and 10–12 days post-treatment (dpt). Tumors were measured, harvested, fixed, sectioned and studied using multicolor immunohistochemistry. Results Histotripsy decreased treated tumor growth by 50% and abscopal tumor growth by 30–40% compared to untreated tumors at 12dpt, evidencing a systemic anti-tumor immune response that inhibited growth of distant untreated tumor. Treated tumors showed immediate tissue liquefaction in the ablation zone with marked extranuclear translocation of the damage associated molecular pattern HMGB1. At 1dpt, 100% of tumor cells within the ablation zone showed HMGB1 translocation, and 70% of tumor cells at the periphery of the ablation zone showed HMGB1 translocation. Caspase 3 cleavage was not observed in the direct ablation zone, but at the junction of the ablated and non-ablated tissue ~40% cells that released HMGB1 showed cleaved Caspase 3. Caspase 9 cleavage was observed in ~50% cells that had cleaved Caspase 3, suggesting early programed cell death with mitochondrial damage and cytochrome C release 1 dpt; the presence of inflammasome integration/activation suggested pyroptosis induction. Areas of tumor well outside the zone of ablation and within untreated tumors contralateral to ablated tumors did not show early DAMP release or apoptotic cell death compared to the control tumors. However, a robust immune cell infiltration was observed in these locations at 10–12dpt, involving CD8 T-cell infiltration and areas of tumoral HMGB1 release in the vicinity of the infiltrating CD8 T cells - indicating the induction of immune rejection of treated and untreated tumors by histotripsy. Conclusions Our results indicate that histotripsy ablation promotes tumor cell destruction through both immediate mechanical disruption, as well as possible adjacent apoptotic and pyroptotic death. Systemic CD8 T-cell mobilization and immunological cell death in the treated and the contralateral tumors is a novel long term therapeutic benefit. Reference Qu S, Worlikar T, Felsted AE, Ganguly A, Beems MV, Hubbard R, Pepple AL, Kevelin AA, Garavaglia H, Dib J, Toma M, Huang H, Tsung A, Xu Z, Cho CS. Non-thermal histotripsy tumor ablation promotes abscopal immune responses that enhance cancer immunotherapy. J Immunother Cancer 2020;8:e000200.

70 Background: Human CD274 receptor, known as programmed cell death 1 ligand 1 (RefSeq NP_054862.1), is an inhibitory ligand for Programmed cell death protein 1 (PD1). We aimed in this bioinformatic experiment to identify a homologous PDL-1 protein in plants. Methods: We chose to use tBLASTn because it compares a protein query sequence against a nucleotide sequence database dynamically translated in all six reading frames (both strands). We chose the EST database and restricted our search to plants (Viridiplantae). Results: Using the FASTA sequence of PDL-1 protein, the tBLASTn of the CD274 protein produced a single hit to Nicotiana tabacum (Common tobacco) cDNA, accession number FG181602.1 with E value of 2e-13 and score of 75.9. We translated the FASTA FG181602.1 through ExPASy and after inspecting the results of the 6 open reading frames (ORFs) in comparison with the matching homologous plant protein obtained through tBLASTn above, we found this “novel” protein which we named "PDL1LI". It has the following amino acid sequence: MHAVRRHRGEMHKVALLHNSFLIISILGSYADDFRVMVPTRRLTAARGHSVVLGCEFSPHFGPNPDLSSLVLTWQRQEDSRVVHSFYYERDQLAKQSSAYRNRTALFVTELSKGNASVRIENVGVTDAGRYLCTVSTNQGTNKAELQLDYGAFYTEPRLTINVNSSDVLLQYETEGFPAPVVIWKGEDGENLTDRMKTSVQSNEEMGLYYIKSSYTAPNTPLSLTFTLENHLLHQYLQRPVSYTGGQNSCFYQFIAPVVVS Gor4 shows that our novel PDL1LI protein is 181 amino acids long with 36% alpha helix, 18% extended strand and 46% random coil sequence. According to BLASTp, this protein contains an immunoglobulin domain found in the Ig superfamily in the first half of the protein, and specific domain hits to the Ig_HHLA2, V-set, and IGv domains, with e-values of 1.37e-28, 2.23e-08, and 1.73e-06. Conclusions: Of all the plants, we found a single homology for our original protein PDL1 only in Nicotiana tabacum. We named this novel protein PDL1LI. Tobacco has been implicated in the etiology of several cancers including lung cancer, bladder cancer, head and neck cancers, etc. A wet lab experiment is underway to isolate our novel protein PDL1LI and to study its properties including any possible inhibitory actions on T cells. If confirmed, then we would have elucidated a new carcinogenic mechanism of tobacco.

BackgroundDeveloping the ability to use tumor-directed therapies to trigger potentially therapeutic immune responses against cancer antigens remains a high priority for cancer immunotherapy. We hypothesized that histotripsy, a novel non-invasive, non-thermal ablation modality that uses ultrasound-generated acoustic cavitation to disrupt tissues, could engender adaptive immune responses to tumor antigens.MethodsImmunocompetent C57BL/6 mice inoculated with flank melanoma or hepatocellular carcinoma tumors were treated with histotripsy, thermal ablation, radiation therapy, or cytotoxic T lymphocyte-associated protein-4 (CTLA-4) blockade checkpoint inhibition. Lymphocyte responses were measured using flow cytometric and immunohistochemical analyses. The impact of histotripsy on abscopal immune responses was assessed in mice bearing bilateral tumors, or unilateral tumors with pulmonary tumors established via tail vein injection.ResultsHistotripsy ablation of subcutaneous murine melanoma tumors stimulated potent local intratumoral infiltration of innate and adaptive immune cell populations. The magnitude of this immunostimulation was stronger than that seen with tumor irradiation or thermal ablation. Histotripsy also promoted abscopal immune responses at untreated tumor sites and inhibited growth of pulmonary metastases. Histotripsy was capable of releasing tumor antigens with retained immunogenicity, and this immunostimulatory effect was associated with calreticulin translocation to the cellular membrane and local and systemic release of high mobility group box protein 1. Histotripsy ablation potentiated the efficacy of checkpoint inhibition immunotherapy in murine models of melanoma and hepatocellular carcinoma.ConclusionsThese preclinical observations suggest that non-invasive histotripsy ablation can be used to stimulate tumor-specific immune responses capable of magnifying the impact of checkpoint inhibition immunotherapy.