BackgroundThe use of T cell-engaging CD3-bispecific antibodies (CD3-bsAbs) is a promising immunotherapeutic strategy for cancer. Although this therapy has reached clinical practice for hematological malignancies, the absence of sufficient infiltrating T cells is a major barrier for efficacy in solid tumors.1 Oncolytic viruses are emerging as anti-cancer therapeutics, and accumulating evidence demonstrates their applicability to sensitize tumors for immune checkpoint immunotherapy.2 In this study, we exploited oncolytic reovirus as a strategy to enhance the efficacy of CD3-bsAbs in immune-silent, solid tumors.MethodsThe mutant p53 and K-ras induced murine pancreatic cancer model KPC3 resembles human pancreatic ductal adenocarcinomas with a desmoplastic tumor microenvironment, low T cell density, and resistance to immunotherapy. Immune-competent mice with established, subcutaneous KPC3 tumors were intratumorally injected with an optimized regimen of oncolytic reovirus (type 3 Dearing strain) and the reovirus-induced changes in the tumor microenvironment and lymphoid organs were analyzed over time by NanoString analysis, RT-qPCR and multicolor flow cytometry. The efficacy of combination with systemically injected CD3-bsAbs was evaluated in KPC3 and B16.F10 murine tumor models and the close-to-patient HER2+ BT474 breast cancer model with cell surface-expressed TRP1 and HER2 as target antigens, respectively. Primary outcome was tumor size, measured with caliper three times a week in a blinded-manner.ResultsReplication-competent reovirus induced an early IFN-signature, followed by a strong influx of CD8+ T cells (2.6-fold increase, p=0.0092). Viral replication declined after seven days and was associated with systemic activation of lymphocytes. Tumor-infiltrating T cells were mostly reovirus-specific and served as effector cells for the subsequently systemically administered CD3-bsAbs. The combination of reovirus and CD3-bsAbs induced regressions up to 70% in all mice with large, established KPC3, B16.F10, and BT474 tumors and significantly prolonged survival. Importantly, the employment of reovirus as a pre-conditioning regimen performed significantly better than the simultaneous or preceding administration of bsAbs. This combination treatment also induced regressions of non-injected distant lesions, suggesting that this therapy might be effective for metastatic disease.Abstract 590 Figure 1Reovirus sensitizes tumors for CD3-bsAb therapyReovirus-induced interferon signaling leads to increased T cell influx and subsequent effective CD3-bispecific antibody therapy in solid tumorsConclusionsOncolytic reovirus administration represents an effective strategy to induce a local IFN response and strong T cell influx, thereby sensitizing the tumor microenvironment for subsequent CD3-bsAb therapy (figure 1). Our data advocate for the inclusion of oncolytic viruses as a pre-conditioning strategy in T cell engaging antibody trials for solid tumors. Since both CD3-bispecific antibodies and oncolytic viruses are in advanced clinical development as monotherapies, efficient translation of this combination seems feasible.AcknowledgementsThis work was financially supported by the Dutch Cancer Society Bas Mulder Award 11056 (to NvM), a PhD fellowship from Leiden University Medical Center (to CG) and the Support Casper campaign by the Dutch foundation ‘Stichting Overleven met Alvleesklierkanker’ (supportcasper.nl) project numbers SOAK 17.04 and 19.03.Ethics ApprovalAll mouse studies were approved by the institutional Animal Welfare Body of Leiden University Medical Center and carried out under project licenses AVD1160020187004 or AVD116002015271, issued by the competent authority on animal experiments in the Netherland (named CCD).ReferencesBenonisson H, Altıntaş I, Sluijter M, Verploegen S, Labrijn AF, Schuurhuis DH, Houtkamp MA, Verbeek JS, Schuurman J and van Hall T. CD3-Bispecific antibody therapy turns solid tumors into inflammatory sites but does not install protective memory. Mol Cancer Ther 2019; 18(2):312–322.Groeneveldt, C, van Hall, T, van der Burg, SH, ten Dijke, P and van Montfoort, N. Immunotherapeutic potential of TGF-β inhibition and oncolytic viruses. Trends Immunol 2020; 41(5):406–420.
590 Pre-conditioning of the tumor microenvironment with oncolytic reovirus converts CD3-bispecific antibody treatment into effective immunotherapy