Targeting the tumor stroma with an oncolytic adenovirus secreting a fibroblast activation protein-targeted bispecific T-cell engager

Abstract

BackgroundOncolytic virus (OV)-based therapies have an emerging role in the treatment of solid tumors, involving both direct cell lysis and immunogenic cell death. Nonetheless, tumor-associated stroma limits the efficacy of oncolytic viruses by forming a barrier that blocks efficient viral penetration and spread. The stroma also plays a critical role in progression, immunosuppression and invasiveness of cancer. Fibroblast activation protein-α (FAP) is highly overexpressed in cancer-associated fibroblasts (CAFs), the main cellular component of tumor stroma, and in this study we assessed whether arming oncolytic adenovirus (OAd) with a FAP-targeting Bispecific T-cell Engager (FBiTE) could retarget infiltrated lymphocytes towards CAFs, enhancing viral spread and T cell-mediated cytotoxicity against the tumor stroma to improve therapeutic activity.MethodsThe bispecific T-cell Engager against FAP was constructed using an anti-human CD3 single-chain variable fragment (scFv) linked to an anti-murine and human FAP scFv. This FBiTE was inserted in the oncolytic adenovirus ICOVIR15K under the control of the major late promoter, generating the ICO15K-FBiTE. ICO15K-FBiTE replication and potency were assessed in HT1080 and A549 tumor cell lines. The expression of the FBiTE and the activation and proliferation of T cells that induced along with the T cell-mediated cytotoxicity of CAFs were evaluated by flow cytometry in vitro. In vivo, T-cell biodistribution and antitumor efficacy studies were conducted in NOD/scid/IL2rg−/− (NSG) mice.ResultsFBiTE expression did not decrease the infectivity and replication potency of the armed virus. FBiTE-mediated binding of CD3+ effector T cells and FAP+ target cells led to T-cell activation, proliferation, and cytotoxicity of FAP-positive cells in vitro. In vivo, FBiTE expression increased intratumoral accumulation of T cells and decreased the level of FAP, a marker of CAFs, in tumors. The antitumor activity of the FBiTE-armed adenovirus was superior to the parental virus.ConclusionsCombination of viral oncolysis of cancer cells and FBiTE-mediated cytotoxicity of FAP-expressing CAFs might be an effective strategy to overcome a key limitation of oncolytic virotherapy, encouraging its further clinical development.Electronic supplementary materialThe online version of this article (10.1186/s40425-019-0505-4) contains supplementary material, which is available to authorized users.

Concise Review: Targeting Cancer Stem Cells and Their Supporting Niche Using Oncolytic Viruses

“…EMT [68][69][70][71]. In recent studies, a fibroblast-activating protein-CD3 BiTE has been encoded in an oncolytic vaccinia virus or adenovirus to target immunosuppressive stromal cells [62,72,73]. Due to their roles in tumor progression, CAFs may prove to be a valuable CSC-related target in transforming the TME toward tumor suppression.…”

“…A major challenge to many therapies involves overcoming CAF‐mediated effects in the TME, such as their promotion of tumor growth, angiogenesis, extracellular matrix degradation and EMT . In recent studies, a fibroblast‐activating protein‐CD3 BiTE has been encoded in an oncolytic vaccinia virus or adenovirus to target immunosuppressive stromal cells . Due to their roles in tumor progression, CAFs may prove to be a valuable CSC‐related target in transforming the TME toward tumor suppression.…”

Effect of Transgene Location, Transcriptional Control Elements and Transgene Features in Armed Oncolytic Adenoviruses

“…The IIIa splicing unit and splice enhancer (3VDE) was the first one to be studied in detail [68]. We have used this sequence to express GFP, TK, hyaluronidase, and bispecific T-cell engagers as transgenes after the fiber, as a L6 unit [46,60,[69][70][71]. Ad40 and Ad41 express two fibers simultaneously from two SA, thus exploring the SA from these fibers was highly attractive to arm Ad5 with transgenes after the fiber.…”

“…An OAd armed with an EGFR-targeting BiTE showed promising results alone [70] or in combination with CAR-T cell therapy [143]. OAds expressing BiTEs against Epcam [144] or FAP [71] antigens were also reported. NG-641 (Table 1) currently in a clinical trial is armed with 4 transgenes: Interferon alpha (IFNα) to drive dendritic cell priming, CXCL9 and CXCL10 to recruit T-cells and FAP-BiTE to redirect them.…”

Modeling the Efficacy of Oncolytic Adenoviruses In Vitro and In Vivo: Current and Future Perspectives

“…However, due to the heterogenous and complex nature of most solid tumors, OAd-mediated lysis is not sufficient to fully eliminate disease. Therefore, many studies have taken advantage of the well-characterized adenoviral vector to deliver immunostimulatory transgenes to the tumor site to further augment host immune activation, destroy stromal components, and prolong T-cell persistence [7][8][9].…”