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Immune checkpoint blockade (ICB) has markedly improved outcomes across a range of tumours, including metastatic melanoma (MM). However, peripheral biomarkers of response remain lacking and underlying mechanisms of action incompletely described. A number of studies have demonstrated the value of T cell receptor (TCR) repertoire analysis in determining associations with response, however identifying key groups of T cells based on their TCR usage has remained elusive. Here we performed deep sequencing of the TCR of CD8+T cells isolated from peripheral blood of patients receiving ICB for MM (n=91) at multiple time points, along with healthy control samples (n=42) and resected tumour specimens (from n=7 patients). Using the GLIPH2 algorithm to cluster TCR based on putative shared antigen specificity, we describe groups of TCR which expand post-ICB in responding patients which we term ‘Emergent Responder’ (ER) clones. We find that these ER clones are typically large and of a memory phenotype, with increased expression of genes encoding cytotoxic proteins. Analysis of tumours resected in advance of ICB demonstrates ER clones are enriched and expanded within the tumour compared to the periphery at pre-treatment. Significantly, we note the proportion of the peripheral repertoire occupied by ER clones strongly correlates with long-term clinical response. Clinical outcome further associated with HLA type and, crucially, can be validated across replication and independent datasets. This work provides the first-in-kind description of TCR-defined CD8+T cells that mediate the response to ICB in MM, demonstrating the prognostic utility of the peripheral immune repertoire with potential widespread therapeutic and prognostic applications.

Background Immune checkpoint blockers (ICBs) activate CD8+ T cells, eliciting both anti-cancer activity and immune-related adverse events (irAEs). The relationship of irAEs with baseline parameters and clinical outcome is unclear. Methods Retrospective evaluation of irAEs on survival was performed across primary (N = 144) and secondary (N = 211) independent cohorts of patients with metastatic melanoma receiving single agent (pembrolizumab/nivolumab—sICB) or combination (nivolumab and ipilimumab—cICB) checkpoint blockade. RNA from pre-treatment and post-treatment CD8+ T cells was sequenced and differential gene expression according to irAE development assessed. Results 58.3% of patients developed early irAEs and this was associated with longer progression-free (PFS) and overall survival (OS) across both cohorts (log-rank test, OS: P P = 2.8 × 10−6). Pre-treatment monocyte and neutrophil counts, but not BMI, were additional predictors of clinical outcome. Differential expression of numerous gene pathway members was observed in CD8+ T cells according to irAE development, and patients not developing irAEs demonstrating upregulated CXCR1 pre- and post-treatment. Conclusions Early irAE development post-ICB is associated with favourable survival in MM. Development of irAEs is coupled to expression of numerous gene pathways, suggesting irAE development in-part reflects baseline immune activation.

Background Unsupervised learning methods, such as Hierarchical Cluster Analysis, are commonly used for the analysis of genomic platform data. Unfortunately, such approaches ignore the well-documented heterogeneous composition of prostate cancer samples. Our aim is to use more sophisticated analytical approaches to deconvolute the structure of prostate cancer transcriptome data, providing novel clinically actionable information for this disease. Methods We apply an unsupervised model called Latent Process Decomposition (LPD), which can handle heterogeneity within individual cancer samples, to genome-wide expression data from eight prostate cancer clinical series, including 1,785 malignant samples with the clinical endpoints of PSA failure and metastasis. Results We show that PSA failure is correlated with the level of an expression signature called DESNT (HR = 1.52, 95% CI = [1.36, 1.7], P = 9.0 × 10−14, Cox model), and that patients with a majority DESNT signature have an increased metastatic risk (X2 test, P = 0.0017, and P = 0.0019). In addition, we develop a stratification framework that incorporates DESNT and identifies three novel molecular subtypes of prostate cancer. Conclusions These results highlight the importance of using more complex approaches for the analysis of genomic data, may assist drug targeting, and have allowed the construction of a nomogram combining DESNT with other clinical factors for use in clinical management.

Immune checkpoint blockade (ICB) of PD-1 and CTLA-4 to treat metastatic melanoma (MM) has variable therapeutic benefit. To explore this in peripheral samples, we characterized CD8+ T cell gene expression across a cohort of patients with MM receiving anti-PD-1 alone (sICB) or in combination with anti-CTLA-4 (cICB). Whereas CD8+ transcriptional responses to sICB and cICB involve a shared gene set, the magnitude of cICB response is over fourfold greater, with preferential induction of mitosis- and interferon-related genes. Early samples from patients with durable clinical benefit demonstrated overexpression of T cell receptor–encoding genes. By mapping T cell receptor clonality, we find that responding patients have more large clones (those occupying >0.5% of repertoire) post-treatment than non-responding patients or controls, and this correlates with effector memory T cell percentage. Single-cell RNA-sequencing of eight post-treatment samples demonstrates that large clones overexpress genes implicated in cytotoxicity and characteristic of effector memory T cells, including CCL4, GNLY and NKG7. The 6-month clinical response to ICB in patients with MM is associated with the large CD8+ T cell clone count 21 d after treatment and agnostic to clonal specificity, suggesting that post-ICB peripheral CD8+ clonality can provide information regarding long-term treatment response and, potentially, facilitate treatment stratification. Transcriptomic analysis of peripheral CD8+ T cells in a cohort of patients with metastatic melanoma receiving checkpoint inhibitors shows that the number of large clones early post-treatment is strongly associated with six-month clinical outcome.

Although treatment with immune checkpoint blockade (ICB) has transformed outcomes for patients with melanoma (1, 2), it frequently triggers immune related adverse events (irAEs), causing serious morbidity and presenting a major hurdle to immuno-oncology (3, 4). The degree to which germline genetic variation predisposes to irAEs is unknown. Here, studying a cohort of 214 patients receiving ICB for melanoma, we observe increased risk of severe irAEs in carriers of the minor allele of rs16906115, intronic to IL7. We find rs16906115 forms a B cell specific expression quantitative trait locus to IL7 in patients only, with risk allele carriers demonstrating increased B cell IL7 expression, immunoglobulin class switching and somatic hypermutation. Notably, increased B cell IL7 expression is independently associated with risk of irAEs. Consistent with the role of IL-7 in T cell development, risk allele carriers have distinct ICB induced CD8+ T cell subset responses, with allelic effects on gene expression and clonality. Risk allele carriers display significantly reduced CD8+ T cell mitotic responses to ICB, with skewing of T cell clonality and increased counts of large clones previously associated with disease response. These observations highlight key roles for both B cells and IL-7 in ICB response and toxicity, and demonstrate the power of agnostic human genetic studies to reveal novel determinants of response to cancer immunotherapy.

The antitumor action of immune checkpoint blockade (ICB) is primarily mediated by CD8(+) T cells. How sensitivity to ICB varies across CD8(+) T cell subsets and clonotypes and the relationship of these with clinical outcome is unclear. To explore this, we used single-cell V(D)J and RNA-sequencing to track gene expression changes elicited by ICB across individual peripheral CD8(+) T cell clones, identify baseline markers of CD8(+) T cell clonal sensitivity, and chart how CD8(+) T cell transcriptional changes vary according to phenotypic subset and clonal size. We identified seven subsets of CD8(+) T cells with divergent reactivity to ICB and found that the cytotoxic effector subset showed the greatest number of differentially expressed genes while remaining stable in clonal size after ICB. At the level of CD8(+) T cell clonotypes, we found a relationship between transcriptional changes and clone size, with large clones showing a greater number of differentially regulated genes enriched for pathways including T cell receptor (TCR) signaling. Cytotoxic CD8(+) effector clones were more likely to persist following ICB and were more likely to correspond with public tumor-infiltrating lymphocyte clonotypes. Last, we demonstrated that individuals whose CD8(+) T cell pretreatment showed low cytotoxicity and had fewer expanded clones typically had worse outcomes after ICB treatment. This work further advances understanding of the molecular determinants of ICB response, assisting in the search for peripheral prognostic biomarkers and highlighting the importance of the baseline CD8(+) immune landscape in determining ICB response in metastatic melanoma.

Counting intraepithelial lymphocytes (IELs) is a key part of the assessment of duodenal biopsies. Immunohistochemistry (IHC) for CD3 can aid identification of lymphocytes in this context, but it is not evident that counts on hematoxylin and eosin (H&E) and CD3 are comparable. This study aimed to compare the IEL counts in duodenal biopsies using H&E stains and CD3 IHC, and to examine the interobserver variability. Thirty-five paired H&E and CD3 sections were reviewed by 6 pathologists who counted the number of IELs per 100 enterocytes. The counts were categorized into groups: normal (40 lymphocytes). CD3 IHC was associated with significantly higher IEL counts than H&E. Four cases with normal H&E counts had raised counts with CD3. There was moderate agreement between observers for both H&E and CD3. Lack of concordance between CD3 and H&E IEL counts suggests that counts derived from the 2 methods may not be comparable to each other and should not be considered equivalent. There was no significant improvement in interobserver variability with CD3 IHC.

Immune checkpoint blockers (ICB) exert their anti-cancer effects via CD8+ T cells, although how responses vary over sub-populations and across clones is incompletely understood. We performed single-cell RNA-sequencing of CD8+ T cells and their receptors pre- and post-ICB across eight patients, integrating results with bulk-sequencing data (n=209). We identify seven subsets with divergent responses to ICB, finding the effector cluster demonstrates the most pronounced changes. Likewise, transcriptomic response to ICB relates to clone size, with large clones demonstrating increased numbers of regulated genes of higher immunological pertinence. Cytotoxic effector clones were more likely to persist long-term following ICB and overlapped with public tumour-infiltrating lymphocyte clonotypes. Notably, pre-treatment CD8+ cytotoxicity associated with progression-free survival, highlighting the importance of the baseline CD8+ immune landscape in long-term response. This work further advances understanding of the molecular determinants of ICB response and assists in the search for peripheral prognostic biomarkers.ONE SENTENCE SUMMARYUsing single-cell and bulk RNA sequencing we explore checkpoint immunotherapy activity on peripheral CD8+ T cells in metastatic melanoma; demonstrating that cell subset and clone size determine gene expression responses to treatment, and that pre-treatment cytotoxicity and clonality of peripheral CD8+ T cells is clinically prognostic.

1Abstract1.1BackgroundImmune checkpoint blockers (ICBs) activate CD8+ T cells to elicit anti-cancer activity but frequently lead to immune-related adverse events (irAEs). The relationship of irAE with baseline parameters and clinical outcome is unclear. We investigated associations between irAE development, CD8+ T cell receptor diversity and expression and clinical outcome in a non-trial setting.1.2MethodsPatients ≥18 years old with metastatic melanoma (MM) receiving combination ICB (ipilimumab plus nivolumab – cICB, n=60) or single-agent ICB (nivolumab/pembrolizumab – sICB, n=78) were prospectively recruited. We retrospectively evaluated the impact of irAEs on survival. This analysis was repeated in an independent cohort of MM patients treated at a separate institution (n=210, cICB:74, sICB:136). We performed RNA sequencing of CD8+ T cells isolated from patients prior to treatment, analysing T cell receptor clonality differential transcript expression according to irAE development.1.3Results48.6% of patients experienced treatment-related irAEs within the first 5 cycles of treatment. Development of irAE prior to the 5th cycle of ICB was associated with longer progression-free and overall survival (PFS, OS) in the primary cohort (log-rank test, PFS: P=0.00034; OS: PP=0.00064). Across cohorts median survival for those patients not experiencing irAE was 14.4 (95% CI:9.6-19.5) months vs not-reached (95% CI:28.9 - Inf), P=3.0×10−7. Pre-treatment performance status and neutrophil count, but not BMI, were additional predictors of clinical outcome. Analysis of CD8+ T cells from 128 patients demonstrated irAE development was associated with increased T cell receptor diversity post-treatment (P=4.3×10−5). Development of irAE in sICB recipients was additionally associated with baseline differential expression of 224 transcripts (FDRCYP4F3 and PTGS2.1.4ConclusionsEarly irAE development post-ICB is strongly associated with favourable survival in MM and increased diversity of peripheral CD8+ T cell receptors after treatment. irAE post-sICB is associated with pre-treatment upregulation of inflammatory pathways, indicating irAE development may reflect baseline immune activation states.Key messageImmune-related adverse events (irAEs) commonly occur in patients with metastatic melanoma treated with immune checkpoint blockade (ICB) therapy. In real world setting we find development of early irAEs post-ICB treatment is associated with survival benefit, indicative of a shared mechanism with anti-tumour efficacy. CD8+ T cells from patients who develop irAE show increased receptor diversity, and pre-treatment samples from patients who develop irAE post single-agent anti-PD1 show over-expression of inflammatory pathways, indicating baseline immune state can determine irAE development.

Metaplastic carcinomas of the breast are a rare but morphologically heterogeneous group of tumours with a distinct immunoprofile. We describe a case of metaplastic carcinoma with mesenchymal differentiation in a patient who presented with a left breast lump. These tumours are typically composed of metaplastic cartilaginous, osseous or rhabdomyoid elements, usually with a malignant epithelial component. Here we outline the current WHO classification of metaplastic carcinomas of the breast, key clinical features and some diagnostic challenges.

This work was funded by the Bob Champion Cancer Trust, The Masonic Charitable Foundation successor to The Grand Charity, The King Family, and The University of East Anglia. We acknowledge support from Movember, from Prostate Cancer UK, Callum Barton, and from The Andy Ripley Memorial Fund. We would like to acknowledge the support of the National Institute for Health Research which funds the Cambridge Bio-medical Research Centre, Cambridge UK. Background : A critical problem in the clinical management of prostate cancer is that it is highly heterogeneous. Accurate prediction of individual cancer behaviour is therefore not achievable at the time of diagnosis leading to substantial overtreatment. It remains an enigma that, in contrast to breast cancer, unsupervised analyses of global expression profiles have not currently defined robust categories of prostate cancer with distinct clinical outcomes. Objective: To devise a novel classification framework for human prostate cancer based on unsupervised mathematical approaches. Design, setting, and participants: Our analyses are based on the hypothesis that previous attempts to classify prostate cancer have been unsuccessful because individual samples of prostate cancer frequently have heterogeneous compositions. To address this issue, we applied an unsupervised Bayesian procedure called Latent Process Decomposition to four independent prostate cancer transcriptome datasets obtained using samples from prostatectomy patients and containing between 78 and 182 participants. Outcome measurements and statistical analysis: Biochemical failure was assessed using log-rank analysis and Cox regression analysis. Results and limitations: Application of Latent Process Decomposition identified a common process in all four independent datasets examined. Cancers assigned to this process (designated DESNT cancers) are characterized by low expression of a core set of 45 genes, many encoding proteins involved in the cytoskeleton machinery, ion transport, and cell adhesion. For the three datasets with linked prostate-specific antigen failure data following prostatectomy, patients with DESNT cancer exhibited poor outcome relative to other patients (p = 2.65 × 10−5, p = 4.28 × 10−5, and p = 2.98 × 10−8). When these three datasets were combined the independent predictive value of DESNT membership was p = 1.61 × 10−7 compared with p = 1.00 × 10−5 for Gleason sum. A limitation of the study is that only prediction of prostate-specific antigen failure was examined. Conclusions: Our results demonstrate the existence of a novel poor prognosis category of human prostate cancer and will assist in the targeting of therapy, helping avoid treatment-associated morbidity in men with indolent disease. Patient Summary: Prostate cancer, unlike breast cancer, does not have a robust classification framework. We propose that this failure has occurred because prostate cancer samples selected for analysis frequently have heterozygous compositions (individual samples are made up of many different parts that each have different characteristics). Applying a mathematical approach that can overcome this problem we identify a novel poor prognosis category of human prostate cancer called DESNT. Publisher PDF

Background Immune Checkpoint blockade for the treatment of metastatic melanoma is associated with highly variable clinical outcomes between individuals in terms of both oncological benefit and immune-related adverse events. Early markers of response are urgently sought. Whereas numerous intra-tumoural determinants of sensitivity to immunotherapy are known, the identification of peripheral predictors of response is limited. We aimed to characterize the CD8+ T-cell transcriptomic and clonal changes to treatment across a large cohort of patients in an effort to gain further insight into the peripheral markers of response. Methods We performed paired-end 75bp read RNA-sequencing to assay the peripheral CD8+ response at baseline and across multiple cycles of treatment (n = 105 patients, 69 controls, 315 separate transcriptomes). We validated identified clonal subsets indicative of response using 10X Chromium single cell sequencing (16 samples, 8 patients), flow-cytometry and targeted PCR. Results After adjusting for multiple testing, we identify >5,800 transcripts induced by treatment. These fall into discrete gene modules, with several markedly diverging between combination immunotherapy and anti-PD1 alone. Patients demonstrating a durable radiological response to checkpoint immunotherapy (absence of progression at 6 months) have significantly increased numbers of large peripheral CD8+ circulating clones by day 21 after treatment, compared to non-responders and controls. We replicate this observation in a separately recruited cohort. Large peripheral clones have a distinct gene expression profile, characterized by high expression of CCL5, BCL2L1and NKG7 amongst other genes. Conclusions We identify robust and reproducible predictors of 6 month clinical and radiological responses to immune checkpoint blockade in the transcriptomes of peripheral circulating CD8+ T-cells from metastic melanoma patients after 21 days of treatment. These observations can be used to further our understanding of determinants of patient response, and may provide a mechanism for early treatment stratification of patients with a non-favourable peripheral profile. Legal entity responsible for the study Oxford Radcliffe Biobank. Funding Wellcome Trust, Oxford NIHR Biomedical Research Centre, Cancer Research UK. Disclosure All authors have declared no conflicts of interest.