BackgroundMicrosatellite-stable (MSS) and instability-low (MSI-L) metastatic colorectal cancer (mCRC) are typically characterised as ”immune-excluded/desert” tumour microenvironments lacking T-cell infiltration. Anti-PD-1 monotherapy has little clinical benefit in MSS/MSI-L mCRC1 and knowledge of the effects of PD-1 inhibition on T-cell activation/infiltration in this population is limited. Novel combination therapies to overcome anti-PD-1 resistance are required. SPICE is a multicentre, open-label, phase 1 study of the tumour-selective chimeric Ad11/Ad3 group B oncolytic adenovirus enadenotucirev plus nivolumab in patients with metastatic/advanced epithelial tumours refractory to standard therapy. Preliminary data from patients with MSS/MSI-L mCRC demonstrated a median overall survival of 14 months, manageable tolerability and intratumoural T-cell infiltration.2 Here we characterise the immunological effects of tumour re-engineering with enadenotucirev in combination with nivolumab in patients with MSS/MSI-L mCRC.MethodsPatients received increasing doses and/or cycles of intravenous enadenotucirev followed by up to 8 cycles of nivolumab as previously described.2 Wherever possible, pre- and post-treatment (~5 weeks post-first enadenotucirev) biopsies were collected; samples were analysed using immunohistochemistry and automated image analysis. Peripheral blood mononuclear cell immunophenotyping (multiparameter flow cytometry) and serum cytokines were assessed at multiple times.Results43 patients with mCRC were treated (86% MSS/MSI-L; 14% unknown). Among the 13 patients (12/13 MSS/MSI-L; 1/13 unknown) with matched biopsies, 11 had increased intratumoural and stromal CD8+ T-cell infiltration in post-treatment biopsies (median [Q1-Q3] fold changes 6.5× [1.5–25.4] and 1.9× [1.5–3.9], respectively; figure 1). CD4+ T-cell density increased in 10/13 patients and 8/13 patients had increased proportions of PD-L1+ immune cells. Increases in CD8 T-cell proliferation (Ki67; 7/9 patients) and cytolytic activity (Granzyme B; 7/13 patients) markers were seen. 4/13 patients converted from a ”desert” to an ”inflamed” immune phenotype (pathologist scored CD8/pan-cytokeratin staining). Immunophenotyping showed trends towards increased T-cell activation (CD38+ and HLA-DR+ CD8+ T cell populations) post-treatment (9/10 patients), including in one patient who had only received enadenotucirev prior to sampling. Persistent increases in inflammatory cytokines (IFNγ, IL-12p70, IL-17a) were seen in two patients from ~Day 15, including one who achieved a sustained objective response.Abstract 342 Figure 1Tumour immune cell infiltration following treatment with enadenotucirev plus nivolumabConclusionsThese data show that intravenous enadenotucirev plus nivolumab can induce immune infiltration/activation within MSS/MSI-L mCRC. These encouraging findings suggest that immune activation can be achieved even in ”immune-excluded/desert” tumours. SPICE has been closed following completion of dose-escalation. Efforts are now focused on the development of next-generation variants of enadenotucirev designed to further re-programme the tumour microenvironment by expressing immune-enhancer transgenes (T-SIGn vectors); these studies are ongoing (NCT04830592, NCT04053283, NCT03852511).AcknowledgementsThis study was funded by PsiOxus Therapeutics Limited and Bristol Myers Squibb. Medical writing support: Lola Parfitt, MRes, of PsiOxus Therapeutics Limited.Trial RegistrationEudraCT number2017-001231-39NCT number: NCT02636036ReferencesKawazoe A, Kuboki Y, Shinozaki E, et al. Multicenter phase I/II trial of napabucasin and pembrolizumab in patients with metastatic colorectal cancer (EPOC1503/SCOOP trial). Clin Cancer Res 2020;26:5887–5894.Fakih M, Wang D, Harb W, et al. SPICE: a phase I multicenter study of enadenotucirev in combination with nivolumab in tumors of epithelial origin: an analysis of the metastatic colorectal cancer patients in the dose escalation phase. Ann Oncol 2019:30(suppl_5):v252.Ethics ApprovalThe study was approved by the WCG Institutional Review Board (study approval number 20152656), UCLA Institutional Review Board (study approval number IRB#15-002010), Vanderbilt Institutional Review Board (study approval number IRB #171453) and Henry Ford Institutional Review Board (study approval number IRB #10349).
342 Combining enadenotucirev and nivolumab increased tumour immune cell infiltration/activation in patients with microsatellite-stable/instability-low metastatic colorectal cancer in a phase 1 study