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 OVs by forming a barrier that blocks efficient viral penetration and spread. Moreover, the stroma plays a critical role in progression and immunosuppression 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 anti-tumor immunity to improve therapeutic activity.
The BiTE 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.
FBiTE expression from the OAd ICO15K did not decrease the infectivity and replication potency in vitro. T-cells activation and proliferation, leading to T-cells-mediated cytotoxicity of FAP-positive cells was successfully achieved after FBiTE-mediated binding of both CD3+cells and FAP+ cells. 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 OAd was superior to the parental virus.
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.
IDIBELL.
Ministerio de Economía y Competividad and Generalitat de Catalunya.
All authors have declared no conflicts of interest.