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Despite reports of striking outcomes, immunotherapy efficacy in melanoma is limited to subsets of patients 1, 2. Combining immunotherapies with other modalities has yielded limited improvements but also adverse events requiring cessation of treatment 1. In addition to ineffective patient stratification, efficacy can be impaired by paucity of tumor-infiltrating lymphocytes (TILs). Thus, effective strategies to safely increase TILs are urgently needed to improve immunotherapies 3. Here, we report that dietary administration of the sugar L-fucose triggers CD4+T cell-mediated increases in TILs, anti-tumor immunity, and enhanced immune checkpoint blockade responses. This is induced by the fucosylation and cell surface enrichment of the MHC-II protein HLA-DRB1 in melanoma. Single-cell immunofluorescent staining analysis of patient melanoma specimens demonstrates that fucosylation and fucosylated HLA-DRB1 is associated with intratumoral T cell abundance and anti-PD1 responder status. Our findings demonstrate that fucosylation is a key mediator of anti-tumor immunity, via regulation of melanoma cell surface HLA-DRB1 and induction of anti-tumor immunity, suggesting use of melanoma fucosylation as a novel strategy to stratify patients for immunotherapies. Importantly, our study suggests that L-fucose represents a powerful, non-toxic agent for safely increasing anti-tumor immunity and immunotherapy efficacy in melanoma.

Background Programmed cell death receptor-1 (PD-1) monotherapy is a standard treatment for advanced cutaneous melanoma, but its efficacy and toxicity are defined in white populations and remain poorly characterized in other ethnic groups, such as East Asian, Hispanic and African. Objectives To determine the efficacy and toxicity of PD-1 monotherapy in different ethnic groups. Methods Clinical data for patients with unresectable or advanced melanoma treated with anti-PD-1 monotherapy between 2009 and 2019 were collected retrospectively from five independent institutions in the USA, Australia and China. Tumour response, survival and immune-related adverse events (irAEs) were compared by ethnicity (white vs. East Asian/Hispanic/African) across different melanoma subtypes: nonacral cutaneous (NAC)/unknown primary (UP) and acral/mucosal/uveal. Results In total, 1135 patients were included. White patients had significantly higher objective response rate (ORR) [54%, 95% confidence interval (CI) 50–57% vs. 20%, 95% CI 13–28%; adjusted P < 0·001] and longer progression-free survival (14·2 months, 95% CI 10·7–20·3 vs. 5·4 months, 95% CI 4·5–7·0; adjusted P < 0·001) than East Asian, Hispanic and African patients in the NAC and UP subtypes. White ethnicity remained independently associated with a higher ORR (odds ratio 4·10, 95% CI 2·48–6·81; adjusted P < 0·001) and longer PFS (hazard ratio 0·58, 95% CI 0·46–0·74; adjusted P < 0·001) in multivariate analyses after adjustment for age, sex, primary anatomical location, metastasis stage, baseline lactate dehydrogenase level, mutational status and prior systemic treatment. White and East Asian/Hispanic/African patients shared similar ORR and progression-free survival in acral/mucosal/uveal melanomas. Similar melanoma-subtype-specific ethnic discrepancies were observed in complete response rate and overall survival. White patients had higher rates of gastrointestinal irAEs but lower rates of endocrine, liver and other rare types of irAEs. These differences in irAEs by ethnicity were not attributable to varying melanoma subtypes. Conclusions Ethnic discrepancy in clinical benefit is specific to melanoma subtype, and East Asian, Hispanic and African patients with NAC and UP melanomas have poorer clinical benefits than previously recognized. The ethnic discrepancy in toxicity observed across different melanoma subtypes warrants an ethnicity-based irAE surveillance strategy. More research is needed to elucidate the molecular and immunological determinants of these differences. What is already known about this topic? There is a great difference in response to immunotherapy between different subtypes of melanoma (cutaneous, mucosal, acral and uveal) in patients with advanced disease. What does this study add? Our data show for the first time that there are differences between different ethnic groups in terms of both response and toxicity to immunotherapy beyond the well-appreciated discrepancies due to melanoma subtype.

Despite initial responses1-3, most melanoma patients develop resistance4 to immune checkpoint blockade (ICB). To understand the evolution of resistance, we studied 37 tumor samples over 9 years from a patient with metastatic melanoma with complete clinical response to ICB followed by delayed recurrence and death. Phylogenetic analysis revealed co-evolution of seven lineages with multiple convergent, but independent resistance-associated alterations. All recurrent tumors emerged from a lineage characterized by loss of chromosome 15q, with post-treatment clones acquiring additional genomic driver events. Deconvolution of bulk RNA sequencing and highly multiplexed immunofluorescence (t-CyCIF) revealed differences in immune composition among different lineages. Imaging revealed a vasculogenic mimicry phenotype in NGFRhi tumor cells with high PD-L1 expression in close proximity to immune cells. Rapid autopsy demonstrated two distinct NGFR spatial patterns with high polarity and proximity to immune cells in subcutaneous tumors versus a diffuse spatial pattern in lung tumors, suggesting different roles of this neural-crest-like program in different tumor microenvironments. Broadly, this study establishes a high-resolution map of the evolutionary dynamics of resistance to ICB, characterizes a de-differentiated neural-crest tumor population in melanoma immunotherapy resistance and describes site-specific differences in tumor-immune interactions via longitudinal analysis of a patient with melanoma with an unusual clinical course.

Merkel cell carcinoma is a rare cutaneous neuroendocrine carcinoma with a high rate of regional and distant metastasis and mortality. Here, we report a novel case of Merkel cell carcinoma which presented as a primary lesion to the left cheek with regional lymph node involvement and was treated with pembrolizumab and radiation. Widely metastatic disease eventually revealed on autopsy clinically mimicked immune-related organ insult leading to management with immunosuppressants. The patient also had a biopsy-confirmed immune-related cutaneous adverse event during admission. The case highlights a rare circumstance in which disease progression masqueraded as multiple immune-related end-organ adverse events. Contribution of on-target anti-PD-1 toxicity remains a possibility.

Cancer immunotherapy with immune checkpoint blockade (ICB) has transformed the treatment of melanoma, although intrinsic or acquired resistance develops in nearly half of patients. Tumor-infiltrating CD8+ T lymphocytes (TILs) are key determinants of anti-tumor immunity in melanoma and other cancers, and single-cell RNA-sequencing has identified T cell states associated with improved clinical response to ICB, as well as adoptive T cell therapy (ACT). Despite these advances, strategies to identify and analyze tumor-reactive TILs in ICB-resistant patients remain limited. Here, we demonstrate that TILs from ICB-resistant melanoma patients can recognize and eliminate autologous tumor cells independent of class I HLA-TCR interactions. TILs eliminated matched melanoma cells in a time and dose-dependent fashion associated with secretion of effector cytokines. Strikingly, the deletion of B2M (resulting in loss of class I HLA surface expression) did not alter the activity of these TILs. Immunophenotyping studies confirmed that TILs are largely (>95%) effector memory (Tem) CD8 T cells (CD45RA-CD45RO+CCR7-) and give rise to terminal effector cells after co-culture with matched melanoma cells. Further, the elimination of melanoma cells by TILs required intact JAK1/2 signaling, although interferon-gamma (IFNγ) was neither necessary nor sufficient for tumor cell elimination. Together, these findings demonstrate that expanded TILs from ICB-resistant melanoma patients are capable of eliminating melanoma cells via a novel, class I MHC-independent mechanism. Citation Format: Hongyan Xie, Aiping Jiang, Anne Jenney, Yi Sun, Tatyana Sharova, Moshe Sade-Feldman, Or-yam Revach, Angelina Cicerchia, Martin Q. Rasmussen, Nir Hacohen, Robert T. Manguso, Russell W. Jenkins. Class I HLA-independent lysis of immunotherapy-resistant melanoma by CD8 T cells. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4072.

Therapeutic blockade of co-inhibitory immune receptors PD-1 and CTLA-4 has revolutionized oncology, but treatments are limited by immune-related adverse events (IRAEs). IRAE Colitis (irColitis) is the most common, severe IRAE affecting up to 25% of patients on dual PD-1 and CTLA-4 inhibition. Here, we present a systems biology approach to define the cell populations and transcriptional programs driving irColitis. We collected paired colon mucosal biopsy and blood specimens from 13 patients with irColitis, 8 healthy individuals, and 8 controls on immune checkpoint inhibitors (ICIs), and analyzed them with single-cell/nuclei RNA sequencing with paired TCR and BCR sequencing, multispectral fluorescence microscopy, and secreted factor analysis (Luminex). We profiled 299,407 cells from tissue and blood and identified 105 cell subsets that revealed significant tissue remodeling in active disease. Colon mucosal immune populations were dominated by tissue-resident memory (TRM) ITGAE-expressing CD8 T cells representing a phenotypic spectrum defined by gene programs associated with T cell activation, cytotoxicity, cycling, and exhaustion. CD8 TRM and effector CD4 T cells upregulated type 17 immune programs (IL17A, IL26) and Tfh-like programs (CXCL13, PDCD1). We also identified for the first time an increased abundance of two KLRG1 and ITGB2-expressing CD8 T cell populations with circulatory cell markers, including a GZMK TRM-like population and a CX3CR1 population that is predicted to be intravascular. These two populations were more abundant in irColitis patients treated with dual PD-1/CTLA-4 inhibition than those receiving anti-PD-1 monotherapy. They also had significant TCR sharing with PBMCs, suggesting a circulatory origin. In irColitis we observed significant epithelial turnover marked by fewer LGR5-expressing stem cells, more transit amplifying cells, and upregulation of apoptotic and DNA-sensing programs such as the cGAS-STING pathway. Mature epithelial cells with top crypt genes upregulated interferon-stimulated pathways, CD274 (PD-L1), anti-microbial genes, and MHC-class II genes, and downregulated aquaporin and solute-carrier gene families, likely contributing to epithelial cell damage and absorptive dysfunction. Mesenchymal remodeling was defined by increased endothelial cells, both in irColitis patients and specifically in patients on dual PD-1/CTLA-4 blockade. Cell-cell communication analysis identified putative receptor-ligand pairs that recruit CD8 T cells from blood to inflamed endothelium and positive feedback loops such as the CXCR3 chemokine system that retain cells in tissue. This study highlights the cellular and molecular drivers underlying irColitis and provides new insights into the role of CTLA-4 and PD-1 signaling in maintaining CD8 TRM homeostasis, regulating CD8 T recruitment from blood, and promoting epithelial-immune crosstalk critical to gastrointestinal immune tolerance and intestinal barrier function.

This protocol describes the dissociation of primary human colorectal cancer (CRC) resection specimens into single cell suspensions for single cell RNA-seq applications. It was successfully used for droplet-based single cell RNA-seq of more than 60 patient specimens using the 10x Genomics platform, including 21 HTAPP CRC cohort samples. It can also be used upstream of other single cell RNA-seq approaches such as plate-based SS2 single cell RNA-seq protocols.

Purpose: Programmed cell death receptor-1 (PD-1) inhibitors are frontline therapy in advanced melanoma. Severe immune-related adverse effects (irAEs) often require immunosuppressive treatment with glucocorticoids (GCCs), but GCC use and its correlation with patient survival outcomes during anti–PD-1 monotherapy remains unclear. Experimental Design: In this multicenter retrospective analysis, patients treated with anti–PD-1 monotherapy between 2009 and 2019 and detailed GCC use, data were identified from five independent cohorts, with median follow-up time of 206 weeks. IrAEs were tracked from the initiation of anti–PD-1 until disease progression, initiation of a new therapy, or last follow-up. Correlations between irAEs, GCC use, and survival outcomes were analyzed. Results: Of the entire cohort of 947 patients, 509 (54%) developed irAEs. In the MGH cohort [irAE(+) n = 90], early-onset irAE (within 8 weeks of anti–PD-1 initiation) with high-dose GCC use (≥60-mg prednisone equivalent once a day) was independently associated with poorer post-irAE PFS/OS (progression-free survival/overall survival) [post-irAE PFS: HR, 5.37; 95% confidence interval (CI), 2.10–13.70; P < 0.001; post-irAE OS: HR, 5.95; 95% CI, 2.20–16.09; P < 0.001] compared with irAEs without early high-dose GCC use. These findings were validated in the combined validation cohort [irAE(+) n = 419, post-irAE PFS: HR, 1.69; 95% CI, 1.04–2.76; P = 0.04; post-irAE OS: HR, 1.97; 95% CI, 1.15–3.39; P = 0.01]. Similar findings were also observed in the 26-week landmark analysis for post–irAE-PFS but not for post–irAE-OS. A sensitivity analysis using accumulated GCC exposure as the measurement achieved similar results. Conclusions: Early high-dose GCC use was associated with poorer PFS and OS after irAE onset. Judicious use of GCC early during anti–PD-1 monotherapy should be considered. Further prospective randomized control clinical trials designed to explore alternative irAE management options are warranted.

BackgroundAlthough the Society for Immunotherapy of Cancer (SITC) Immunotherapy Resistance Taskforce recently defined primary and secondary resistance to anti-programmed cell death protein 1 (anti-PD-1) therapy, there is lack of real-world data regarding differences in these resistance subtypes with respect to radiological dynamics and clinical manifestations.MethodsWe performed single-blind re-evaluations of radiological images by independent radiologists on a retrospectively assembled cohort of patients with advanced melanoma (n=254, median follow-up 31 months) receiving anti-PD-1 monotherapy at Massachusetts General Hospital and Peking University Cancer Hospital. Radiological characteristics and timing at multiple crucial time points were analyzed and correlated with each other and with survival. Primary and secondary resistance was defined as per the SITC Immunotherapy Resistance Taskforce definitions.ResultsThe most significant target lesion measurement change took place within the first 3 months after anti-PD-1 initiation. Patients with stable disease with versus without tumor shrinkage at the initial evaluation exhibited distinct disease trajectory, as the rate of further upgrade to a partial or complete remission (CR/PR) was 44% and 0%, respectively. Eleven per cent of PR patients ultimately achieved a CR. In multivariate analyses, deeper response depth was independently associated with a more limited progression pattern, fewer involved organs, lower tumor burden, slower growth rate at disease progression (PD) (all p≤0.001), and longer post-progression survival (PPS) (bivariate analysis, p=0.005). Compared with primary resistance, secondary resistance was associated with less widespread PD pattern, lower tumor burden and slower tumor growth (all p≤0.001). Patients with secondary resistance were less likely to receive further systemic therapy (28% vs 57%, pConclusionsRadiological dynamics were variable, yet significantly correlated with survival outcomes. SITC-defined primary and secondary resistance are distinct clinical manifestations in patients with melanoma, suggesting the possibility of resistance-type-based therapeutic decision-making and clinical trial design, once further validated by future prospective studies.

Summary Objectives: Cachexia is a systemic metabolic disorder characterized by loss of fat and muscle mass, which disproportionately impacts patients with gastrointestinal malignancies such as pancreatic cancer. While the immunologic shifts contributing to the development of other adipose tissue (AT) pathologies such as obesity have been well described, the immune microenvironment has not been studied in the context of cachexia. Methods: We performed bulk RNA-sequencing, cytokine arrays, and flow cytometry to characterize the immune landscape of visceral AT (VAT) in the setting of pancreatic and colorectal cancers. Results: The cachexia inducing factor IL-6 is strongly elevated in the wasting VAT of cancer bearing mice, but the regulatory type 2 immune landscape which characterizes healthy VAT is maintained. Pathologic skewing toward Th1 and Th17 inflammation is absent. Similarly, the VAT of patients with colorectal cancer is characterized by a Th2 signature with abundant IL-33 and eotaxin-2, albeit also with high levels of IL-6. Conclusions: Wasting AT during the development of cachexia may not undergo drastic changes in immune composition like those seen in obese AT. Our approach provides a framework for future immunologic analyses of cancer associated cachexia., Graphical Abstract Graphical Abstract

Background The SITC Immunotherapy Resistance Taskforce recently defined primary and secondary resistance to anti-PD-1 therapy,1 yet there is little data that compares these two scenarios. In particular, detailed radiological dynamics of the different resistance types remain undescribed. Methods We performed independent single-blind reevaluations of available radiological image data on a retrospectively assembled cohort of advanced melanoma patients (n=254, median follow-up 31.3 months, figure 1) treated with anti-PD-1 monotherapy initiated between Sept 2009 and Aug 2018 at both Massachusetts General Hospital and Peking University Cancer Hospital. Radiological characteristics and timing at multiple crucial radiological landmarks were analyzed and correlated with each other and with survival. As per the SITC Taskforce, primary resistance was defined as a best response of stable disease (SD) lasting less than six months or disease progression (PD), secondary as PD following an initial partial or complete response (PR/CR) or SD lasting 6 months or greater.1 Results The most dramatic tumor reduction occurred within the first 3 months after anti-PD-1 initiation. A subpopulation of patients who had SD (28.6%, all with tumor shrinkage) experienced further tumor reduction and upgraded to CR/PR and 11.1% of patients with initial PR upgraded to CR. No patients without tumor shrinkage at the initial evaluation ultimately responded. Baseline tumor burden, response depth, timing of maximal response and PD pattern demonstrated great variation and were significantly correlated with each other and with survival. In multivariate analyses, deeper response depth was independently associated with a less widespread progression pattern, less involved organs, smaller target lesion size and slower tumor growth rate (all P≤.001) at PD, and longer post progression survival (PPS) (P=0.005). Compared to primary resistance, secondary resistance was correlated with less broad progression pattern, less tumor burden and slower tumor growth (all P≤.001). Patients with secondary resistance were more likely to receive further local/regional therapy (46.5% vs. 30.9%, P=0.07) rather than systemic therapy (27.9% vs. 56.9%, P Conclusions Radiological dynamics were heterogeneous, yet significantly correlated with survival. Patterns of progression and PPS of the SITC Immunotherapy Resistance Taskforce defined primary and secondary resistance are different. This distinction may be important for the design of clinical trials targeting a PD-1 resistant population. Ethics Approval This study has been conducted in compliance with local Institutional Review Board policies. Consent NA. Reference Kluger H, Tawbi H, Ascierto M, et al. Defining tumor resistance to PD-1 pathway blockade: recommendations from the first meeting of the SITC Immunotherapy Resistance Taskforce. J Immunother Cancer. 2020; 8:3000398.

In many areas of oncology, we lack sensitive tools to track low-burden disease. Although cell-free DNA (cfDNA) shows promise in detecting cancer mutations, we found that the combination of low tumor fraction (TF) and limited number of DNA fragments restricts low-disease-burden monitoring through the prevailing deep targeted sequencing paradigm. We reasoned that breadth may supplant depth of sequencing to overcome the barrier of cfDNA abundance. Whole-genome sequencing (WGS) of cfDNA allowed ultra-sensitive detection, capitalizing on the cumulative signal of thousands of somatic mutations observed in solid malignancies, with TF detection sensitivity as low as 10−5. The WGS approach enabled dynamic tumor burden tracking and postoperative residual disease detection, associated with adverse outcome. Thus, we present an orthogonal framework for cfDNA cancer monitoring via genome-wide mutational integration, enabling ultra-sensitive detection, overcoming the limitation of cfDNA abundance and empowering treatment optimization in low-disease-burden oncology care. A new approach for whole-genome sequencing of plasma circulating tumor DNA allows for dynamic monitoring of disease burden and ultra-sensitive detection of minimal residual disease.

Immune responses to cancer are highly variable, with mismatch repair-deficient (MMRd) tumors exhibiting more anti-tumor immunity than mismatch repair-proficient (MMRp) tumors. To understand the rules governing these varied responses, we transcriptionally profiled 371,223 cells from colorectal tumors and adjacent normal tissues of 28 MMRp and 34 MMRd individuals. Analysis of 88 cell subsets and their 204 associated gene expression programs revealed extensive transcriptional and spatial remodeling across tumors. To discover hubs of interacting malignant and immune cells, we identified expression programs in different cell types that co-varied across tumors from affected individuals and used spatial profiling to localize coordinated programs. We discovered a myeloid cell-attracting hub at the tumor-luminal interface associated with tissue damage and an MMRd-enriched immune hub within the tumor, with activated T cells together with malignant and myeloid cells expressing T cell-attracting chemokines. By identifying interacting cellular programs, we reveal the logic underlying spatially organized immune-malignant cell networks.

This protocol describes the dissociation of primary human colorectal cancer (CRC) resection specimens into single cell suspensions for single cell RNA-seq applications. It was successfully used for droplet-based single cell RNA-seq of more than 60 patient specimens using the 10x Genomics platform, including 20 HTAPP CRC cohort samples. It can also be used upstream of other single cell RNA-seq approaches such as plate-based SS2 single cell RNA-seq protocols.

As the largest branch of the autonomic nervous system, the enteric nervous system (ENS) controls the entire gastrointestinal tract, but remains incompletely characterized. Here, we develop RAISIN RNA-seq, which enables the capture of intact single nuclei along with ribosome-bound mRNA, and use it to profile the adult mouse and human colon to generate a reference map of the ENS at a single-cell resolution. This map reveals an extraordinary diversity of neuron subsets across intestinal locations, ages, and circadian phases, with conserved transcriptional programs that are shared between human and mouse. These data suggest possible revisions to the current model of peristalsis and molecular mechanisms that may allow enteric neurons to orchestrate tissue homeostasis, including immune regulation and stem cell maintenance. Human enteric neurons specifically express risk genes for neuropathic, inflammatory, and extra-intestinal diseases with concomitant gut dysmotility. Our study therefore provides a roadmap to understanding the ENS in health and disease.

The enteric nervous system (ENS) coordinates diverse functions in the intestine but has eluded comprehensive molecular characterization because of the rarity and diversity of cells. Here we develop two methods to profile the ENS of adult mice and humans at single-cell resolution: RAISIN RNA-seq for profiling intact nuclei with ribosome-bound mRNA and MIRACL-seq for label-free enrichment of rare cell types by droplet-based profiling. The 1,187,535 nuclei in our mouse atlas include 5,068 neurons from the ileum and colon, revealing extraordinary neuron diversity. We highlight circadian expression changes in enteric neurons, show that disease-related genes are dysregulated with aging, and identify differences between the ileum and proximal/distal colon. In humans, we profile 436,202 nuclei, recovering 1,445 neurons, and identify conserved and species-specific transcriptional programs and putative neuro-epithelial, neuro-stromal, and neuro-immune interactions. The human ENS expresses risk genes for neuropathic, inflammatory, and extra-intestinal diseases, suggesting neuronal contributions to disease.

9530 Background: Ultraviolet (UV)-induced high tumor mutation burden (TMB) of NACM is associated with response to anti-PD-1 monotherapy (aPD-1). Anatomic location of the primary lesion (reflecting UV exposure) and race (reflecting eumelanin level) may serve as surrogates for TMB and be associated with varying response and irAE patterns. Methods: Pts with advanced NACM receiving aPD-1 between 2009-2019 were retrospectively analyzed from 5 institutions in the US, Australia and China. Best response, survival (PFS and OS), and organ/system-specific irAEs were compared by race (Caucasian [C] vs non-Caucasian [NC]) and primary anatomic site. Results: Among 697 patients, 616 were C, 81 were NC. Complete response rate (CRR) was 24.8% (95%CI, 21.4-28.4) and 2.6% (95%CI, 0.3-9.1) and ORR was 54.9% (95%CI, 50.9-58.9) and 15.6% (95%CI, 8.3-25.6) in C and NC, respectively (both P

9538 Background: Percutaneous image-guided cryoablation (cryo) is an established minimally invasive oncologic treatment that modulates the immune microenvironment. We hypothesized that cryo can augment anti-tumor responses in melanoma patients progressing on immune checkpoint inhibitors (ICI). Methods: In this non-randomized phase II single-center study, subjects with unresectable melanoma progressing on ICI underwent cryo of an enlarging lesion and ICI continuation for a minimum of 2 additional cycles. Computed tomography was performed at 6-8 weeks following cryo to determine tumor response in non-ablated lesions per RECIST1.1, with confirmatory scans at 8-12 weeks. The primary endpoint was safety and feasibility. Secondary endpoints were overall response rate (ORR) and disease control rate (DCR) with DCR defined as the percentage of pts who achieve complete response (CR), partial response (PR), and stable disease (SD). Correlative analyses on pre- and post-cryo tumor biopsy and blood samples were performed. Results: From May 2018 through July 2020, 20 pts were screened, 18 enrolled and 17 treated per protocol. All pts received prior PD-1/PD-L1 monotherapy and 12 (67%) experienced primary resistance to ICI. Median follow-up was 8.5 months. Ablated lesions included lymph nodes (n = 4), lung/pleura (n = 4), soft tissue/bone (n = 3), adrenal (n = 3), chest wall (n = 1), and kidney (n = 1). Peri-procedural events occurred in 3 cases (pneumothorax, diaphragm puncture, osteomyelitis). One pt. with underlying ICI-induced hypophysitis experienced an adrenal crisis post-procedure, which rapidly corrected with stress-dose steroid administration; there were no de novo immune-related adverse events post-ablation and there were no grade 4/5 events. In evaluable pts (n = 17), ORR was 18% and DCR was 47% (3 PR, 5 SD). To investigate the inflammatory state of the tumor microenvironment prior to cryo, PD-1, CD8+ TIL IHC, was performed and will be presented at the meeting. Additional exploratory analyses (serial ctDNA analysis, single cell RNA sequencing, HLA-subtyping) are ongoing. Conclusions: Cryoablation in patients with unresectable melanoma following progression on ICI is feasible with an acceptable side effect profile. Efficacy data of this potentially synergistic approach in metastatic melanoma is encouraging. Correlative analyses are underway to identify biomarkers of response to this novel strategy. Clinical trial information: NCT03290677. [Table: see text]

Background: Although immune-related adverse effects (irAEs) are commonly seen in anti-PD-1 monotherapy-treated patients, their predictive biomarkers are still lacking. Methods: In this retrospective analysis, clinical data were collected from 141 advanced melanoma patients treated with anti-PD-1 monotherapy at Massachusetts General Hospital from Sept. 2009 to Dec. 2017. Demographic characteristics, baseline, and early-on-treatment (median 3 weeks after anti-PD-1 monotherapy initiation) routine laboratory variables were collected and correlated with occurrence of irAEs in both univariate and multivariate analyses. Results: 80/141 (56.7%) patients developed irAEs after anti-PD-1 monotherapy initiation. Significant independent predictive variables (P < 0.05) in favor of the occurrence of irAEs included the following: with no distant metastasis (Stage M0) before treatment initiation, high baseline neutrophils, and high early-on-treatment neutrophil-to-lymphocyte ratio (NLR). High baseline monocytes, high baseline basophils, and high early-on-treatment WBCs were of borderline significance (P < 0.1) in multivariate analyses. An irAE risk scoring model (total scale: 0-6) comprising these 6 factors (all as dichotomous variables) was established (HR 1.781, 95% CI 1.450 – 2.187, P < 0.001). Risks of developing at least one irAE within 12 weeks after anti-PD-1 monotherapy initiation were 0%, 21%, 21%, 39%, 30%, and 63%; within 48 weeks were 0%, 41%, 57%, 68%, 77%, and 100%, for patients with scores of 0 to 5 (no patient scored 6 within this cohort), respectively. Conclusions: Scoring system based on simple, easily accessible, and routinely tested biomarkers could be used to help predict the risk of irAEs occurrence in anti-PD-1 monotherapy-treated advanced melanoma patients. Citation Format: Xue Bai, Michelle S. Kim, Gyulnara Kasumova, Justine Cohen, Donald Lawrence, Christine Freedman, Riley Fadden, Krista Rubin, Tatyana Sharova, Keith Flaherty, Ryan Sullivan, Genevieve Boland. Demographic characteristics and peripheral blood clinical laboratory variables predict irAE occurrence in patients with advanced melanoma receiving anti-PD-1 monotherapy [abstract]. In: Proceedings of the AACR Special Conference on Melanoma: From Biology to Target; 2019 Jan 15-18; Houston, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(19 Suppl):Abstract nr B25.

Summary Checkpoint blockade with antibodies specific for the PD-1 and CTLA-4 inhibitory receptors can induce durable responses in a wide range of human cancers. However, the immunological mechanisms responsible for severe inflammatory side effects remain poorly understood. Here we report a comprehensive single-cell analysis of immune cell populations in colitis, a common and severe side effect of checkpoint blockade. We observed a striking accumulation of CD8 T cells with highly cytotoxic and proliferative states and no evidence of regulatory T cell depletion. T cell receptor (TCR) sequence analysis demonstrated that a substantial fraction of colitis-associated CD8 T cells originated from tissue-resident populations, explaining the frequently early onset of colitis symptoms following treatment initiation. Our analysis also identified cytokines, chemokines, and surface receptors that could serve as therapeutic targets for colitis and potentially other inflammatory side effects of checkpoint blockade.

10020 Background: Programmed cell death receptor-1 (PD-1) monotherapy is the standard first line therapy for advanced cutaneous melanoma, with efficacy, toxicity, and their correlations well established. Yet these remain poorly characterized for non-Caucasians and for certain rarer melanoma subtypes. Methods: Clinical data from melanoma patients treated with anti-PD-1 monotherapy between 2009 and 2018 was collected retrospectively from three independent institutions from the US and China. Tumor response, survival outcome, and organ/system-specific immune-related adverse effects (irAEs) were directly compared between different subgroups. Results: Among 626 patients, 411 were Caucasian, 214 non-Caucasian; 369 had cutaneous melanoma, and 257 other subtypes. Both ethnicity and melanoma subtype were independently associated with benefit and irAEs. In multivariate analyses, Caucasians had significantly higher objective response rate (ORR) (OR 2.0, 95% CI 1.1-3.5), but this did not translate into a survival advantage (PFS, HR 0.8, 95% CI 0.6-1.1; OS, HR 1.0, 95% CI 0.7-1.4); melanoma of unknown primary shared similar response and survival profile with cutaneous, while acral (ORR, OR 0.4, 95% CI 0.2-0.9; PFS, HR 1.6, 95% CI 1.1-2.2; OS, HR 1.3, 95% CI 0.8-1.9), mucosal (ORR, OR 0.4, 95% CI 0.2-0.9; PFS, HR 1.4, 95% CI 1.0-2.0; OS, HR 1.7, 95% CI 1.1-2.6) and ocular (ORR, OR 0.1, 95% CI 0-0.6; PFS, HR 2.3, 95% CI 1.4-3.6; OS, HR 2.2, 95% CI 1.3-3.6) melanomas had inferior outcomes. Non-Caucasian cutaneous patients had a significantly worse ORR than Caucasians with cutaneous melanoma (P < .01). Distinct irAE patterns were observed, exemplified by lower incidence of most irAEs (although more frequent pneumonitis) in Caucasians, and higher and lower liver irAE incidence in ocular and mucosal melanomas, respectively. Endocrine, musculoskeletal and skin irAEs were associated with improved PFS and OS across ethnicities and nearly all melanoma subtypes, whereas heterogeneity existed for other irAE types. Conclusions: Ethnicity and melanoma subtype are associated with distinct response patterns, survival outcomes, and irAE profiles in the setting of anti-PD-1 monotherapy. More research is needed to elucidate the molecular and immunologic determinants of these variable outcomes.

58 Background: Systemic immune checkpoint blockade therapy anti-PD1 nivolumab combined with anti-CTLA-4 ipilimumab is an effective therapy for metastatic melanoma. The treatment, however, has a high frequency of immune related adverse events. Interestingly, immune-related adverse events in anti-PD1 and anti-CTLA4 monotherapy have been associated with an improved overall survival in melanoma. Whether immune-related events correlate with enhanced outcomes in ipilimumab/nivolumab combination therapy is unknown. Methods: Clinical data from patients diagnosed with untreated cutaneous stage IV melanoma receiving ipilimumab/nivolumab combination therapy between 2015-2018 at the Massachusetts General Hospital (MGH) and have been analyzed retrospectively. Tumor response was measured using RECIST criteria. Primary endpoints were frequencies and characteristics of immune-related adverse events, overall survival, and response to therapy. Results: A total of 57 patients received ipilimumab/nivolumab combination therapy. During a mean follow-up period of 26 months, 28 (49%) patients completed the therapy. Immune-related adverse events were observed in 45 (79%) patients, with rash (28%), colitis (23), hepatitis (21%) and fever (21%) being the most frequent. Overall survival was 29 months in patients with immune-adverse related events and 14 months in the group without any adverse events (p-value < 0.01). The onset of hypophysitis correlated with tumor response (p = 0.02) and hepatitis showed a trend in a correlation to response of therapy (p = 0.06). Conclusions: Our study demonstrates the association between improved overall survival and the onset of immune-related adverse events in ipilimumab/nivolumab combination therapy. A trend correlated with improved outcomes and onset of immune-related adverse events was seen in hepatitis and was significantly associated with hypophysitis, however these results must be interpretated carefully as larger studies must confirm our findings. Despite small study size, we are the first to describe an association between immune-related adverse events in ipilimumab/nivolumab combination therapy.

Immune checkpoint blockade (ICB) has revolutionized the treatment of metastatic melanoma, however, cases of resistance have now begun to emerge. We report here a case of acquired resistance by melanoma phenotypic transformation in a patient treated on a Phase 1b/2 clinical trial (NCT02437136) with anti-PD1 (Pembrolizumab) and a histone deacetylase (HDAC) inhibitor (Entinostat). The patient presented to MGH with metastatic melanoma confirmed by core-needle biopsy of a liver lesion. A PET/CT scan one month after starting the trial revealed interval regression of liver and bone lesions, however, four months later the patient presented with disease progression. A tumor debulked from the L2 vertebral body at that time revealed the presence of a pleomorphic rhabdomyosarcoma. The patient was started on anti-CTLA4 (Ipilumimab) with further disease progression, and surgical specimens thereafter revealed either melanoma or rhabdomyosarcoma. Tumor tissue was evaluated for markers by immunohistochemistry. All tumors (5 specimens in total) were subjected to whole exosome sequencing (WES), RNA-sequencing (RNAseq) and epigenomic sequencing (ATACseq). WES revealed 844 mutations were shared between all tumors, suggesting a common ancestor including driver mutations in NRAS (G13D), NF1 (E1121* and W1314*) and the TERT2 promoter, among others. The pre-treatment melanoma biopsy had positive staining for S100 and MART-1, nuclear staining patterns for SOX10 and MITF, and were BRAF V600E negative. Importantly, 80% of the tumor cells had strong staining for PD-L1 expression and CD8 CTL infiltration was associated with 25% of the tumor. The post-treatment rhabdomyosarcoma biopsy was notable for diffusely positive staining for Desmin and MyoD1, and multifocal positivity for myogenin. The tumor stained negative for S100 and SOX10, and there was no PD-L1 staining and less than 5% tumor CD8 CTL infiltration. Gene expression analysis revealed distinct expression patterns between melanoma and rhabdomyosarcoma samples, with 150 differentially expressed genes implicated in processes such as antigen presentation, T cell activation, cell death and protein metabolism. In addition, each tumor was found to have a unique immune cell composition and T-cell receptor repertoire, suggesting an interplay between phenotypic transformation and immune response. Results from epigenomic sequencing are pending, but may shed light on the mechanisms of transformation leading to resistance. These data therefore elucidate a previously undescribed mechanism of acquired resistance to ICB through melanoma phenotypic transformation to a rhabdomyosarcoma. Whereas these tumors were genetically similar, they expressed distinct gene expression patterns suggestive of underlying epigenomic differences in the setting of an HDAC inhibitor. Citation Format: Arnav Mehta, David Liu, Alvin Shi, Dennie T. Frederick, Li-Lun Ho, Ana B. Larque, Benchun Miao, Rumya S. Raghavan, Tatyana Sharova, John H. Shin, Nicola Rinaldi, Ivan A. Chebib, Manolis Kellis, Eliezer Van Allen, Nir Hacohen, Keith T. Flaherty, Genevieve M. Boland, Ryan J. Sullivan. Acquired resistance to immune checkpoint inhibition by melanoma phenotypic transformation [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 3013.

e14243 Background: Image-guided percutaneous cryoablation is an established minimally invasive oncologic treatment. Through direct modulation of the tumor, it is theorized that this local therapy may modify the immune microenvironment. We hypothesized that it can augment an anti-tumor response when used concurrently with ICI. Methods: In this phase II single-arm study, pts with advanced lung cancer or melanoma progressing on ICI undergo cryo of an enlarging lesion and ICI is continued for a minimum 2 additional cycles. Computed tomography is performed at 4-6 weeks following cryo to determine tumor response in non-ablated lesions per RECIST1.1, with confirmatory scans at 8-10 weeks. The primary endpoint is safety and feasibility. Secondary endpoints are overall response rate (ORR) and disease control rate (DCR) with DCR defined as the percentage of pts who achieve complete response (CR), partial response (PR), and stable disease (SD). Correlative analysis on pre- and post-cryo biopsy specimen, when evaluable, will be performed. A planned analysis to document preliminary safety and feasibility in the first 11 patients was performed. Results: 11 pts (out of planned 40) have been enrolled. 8 with melanoma, 3 with lung cancer. All pts received prior PD-1/PD-L1 monotherapy with 8 pts treated with pembrolizumab, 2 with nivolumab and 1 with atezolizumab. Treated lesions were in lung (n = 4), bone (n = 3), lymph nodes (n = 2), liver (n = 1) and adrenal gland (n = 1). No immune related adverse events occurred. There was one treatment-related CTCAE grade 3 event (osteomyelitis) but no grade 4/5 events. One pt. experienced grade 3 hyponatremia, unrelated to cryo. In evaluable pts (n = 10), ORR was 10% and DCR was 50% (4 SD, 1 PR). Conclusions: During this scheduled safety analysis, cryo following progression on ICI was feasible and had an acceptable side effect profile. Early efficacy data of this potentially synergistic approach is encouraging but warrants further investigation. Clinical trial information: NCT03290677. [Table: see text]

9552 Background: Melanoma is notorious for its high degree of heterogeneity with the implication that metastases in different sites react differently to immunotherapy. We aimed to explore the site-specific response pattern in anti-PD-1 monotherapy treated advanced melanoma patients. Methods: Clinical data was collected retrospectively from advanced melanoma patients treated with anti-PD-1 monotherapy at Massachusetts General Hospital (MGH) from Sept 2009 to Dec 2017. Radiological evaluations were carried out by radiologists from the MGH Tumor Imaging Metrics Core using irRECIST 1.1. Statistical analysis was carried out using ANOVA test. Results: Among 61 evaluated patients, 56 (91.8%) had at least one measurable target lesion(s) at baseline, including 35 (57.4%) patients with measurable lymph nodes (LN)/subcutaneous lesion(s), 25 (50.0%) with lung lesion(s), and 21 (34.4%) with liver lesion(s). At week-12 radiological evaluation after anti-PD-1 monotherapy initiation, lesions at different sites responded differently at marginal statistical significance (P = 0.071), namely mean percent changes compared with baseline were 3.75%, 5.12%, and -30.95% for LN/subcutaneous, liver, and lung lesions, respectively. Among patients who had disease under control (CR/PR/SD) (n = 37, 60.7%) by week-12 evaluation, the mean tumor percentage change at week-24 compared with week-12 were -8.94%, -12.18%, and -5.91% for LN/subcutaneous, liver, and lung lesions, respectively (P = 0.479). Conclusions: Although our small sample size limits definitive discrimination in organ site-specific response differences, it appears that lung lesions respond more quickly and to a greater extent compared with LN/subcutaneous and liver lesions in advanced melanoma patients treated with anti-PD-1 monotherapy. We will explore this in a larger, multicenter cohort.

133 Background: Anti-PD-1 monotherapy has dramatically improved the outcomes of patients with advanced melanoma, yet the majority of patients develop therapeutic resistance. A prognostic model is needed to optimally select patients who are most and least likely to benefit. Methods: We performed a retrospective analysis of 141 advanced melanoma patients treated with anti-PD-1 monotherapy at Massachusetts General Hospital from Sept 2009 to Dec 2017. Demographic and clinical characteristics, baseline and early-on-treatment (median 3 weeks after anti-PD-1 monotherapy initiation) routine laboratory variables, and prognostic data were collected and correlated in both univariate and multivariate analyses. Results: Median progression free survival (PFS) and overall survival (OS) were 7.6 months (95% CI 2.3-12.9) and 57.3 months (95% CI 33.3-81.3), respectively. In multivariate analyses, significant independent prognostic variables ( P < 0.05) in favor of longer PFS included cutaneous subtype, low baseline lactic acid dehydrogenase (LDH); low early-on-treatment derived neutrophil-to-lymphocyte ratio (dNLR); high early-on-treatment albumin, basophil, and red blood cell counts (RBCs); those in favor of longer OS included BRAF V600 mutation; low baseline LDH and neutrophil-to-lymphocyte ratio (NLR); low early-on-treatment LDH; high early-on-treatment total protein, basophil, and lymphocyte counts. Prognostic scoring models (total scale: 0-6) were established based on these independent prognostic factors as dichotomous variables, for both PFS (HR 0.555, 95% CI 0.481-0.641, P

e21569Background: Mechanisms underlying immune checkpoint inhibition (ICI) efficacy and toxicity have yet to be fully elucidated and, to date, there are no reliable biomarkers predictive of the dev...