Targeting the Tumor Stroma With an Oncolytic Adenovirus Secreting a Fibroblast Activation Protein-Targeted Bispecific T-cell Engager

J Immunother Cancer. 2019 Jan 25;7(1):19. doi: 10.1186/s40425-019-0505-4.


Background: Oncolytic 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.

Methods: The 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.

Results: FBiTE 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.

Conclusions: Combination 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.

Keywords: Bispecific T-cell engager; Fibroblast activation protein; Oncolytic adenovirus; Tumor-associated stroma.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenoviridae*
  • Animals
  • Antibodies, Bispecific / administration & dosage*
  • Cancer-Associated Fibroblasts / drug effects
  • Cell Line, Tumor
  • Coculture Techniques
  • Gelatinases / antagonists & inhibitors*
  • Humans
  • Lymphocyte Activation / drug effects
  • Membrane Proteins / antagonists & inhibitors*
  • Mice
  • Neoplasms / therapy*
  • Oncolytic Virotherapy
  • Oncolytic Viruses*
  • Serine Endopeptidases
  • Single-Chain Antibodies / administration & dosage*
  • T-Lymphocytes / drug effects*
  • T-Lymphocytes / immunology


  • Antibodies, Bispecific
  • Membrane Proteins
  • Single-Chain Antibodies
  • Serine Endopeptidases
  • fibroblast activation protein alpha
  • Gelatinases