Activation of interferon regulatory factor 3 by replication-competent vaccinia viruses improves antitumor efficacy mediated by T cell responses

Abstract

Recently, oncolytic vaccinia viruses (VACVs) have shown their potential to provide for clinically effective cancer treatments. The reason for this clinical usefulness is not only the direct destruction of infected cancer cells but also activation of immune responses directed against tumor antigens. For eliciting a robust antitumor immunity, a dominant T helper 1 (Th1) cell differentiation of the response is preferred, and such polarization can be achieved by activating the Toll-like receptor 3 (TLR3)-interferon regulatory factor 3 (IRF3) signaling pathway. However, current VACVs used as oncolytic viruses to date still encode several immune evasion proteins involved in the inhibition of this signaling pathway. By inactivating genes of selected regulatory virus proteins, we aimed for a candidate virus with increased potency to activate cellular antitumor immunity but at the same time with a fully maintained replicative capacity in cancer cells. The removal of up to three key genes ( C10L , N2L , and C6L ) from VACV did not reduce the strength of viral replication, both in vitro and in vivo , but resulted in the rescue of IRF3 phosphorylation upon infection of cancer cells. In syngeneic mouse tumor models, this activation translated to enhanced cytotoxic T lymphocyte (CTL) responses directed against tumor-associated antigens and neo-epitopes and improved antitumor activity.

Improving poxvirus-mediated antitumor immune responses by deleting viral cGAMP-specific nuclease

“…Tumor volume ( b , d ) and overall survival ( c , e ) are plotted for 9–14 mice per group +SEM. Data shown in ( b ) for the control groups PBS and WR/TK– is the same as published in [ 23 ] as both studies were done in the same experiment following the principle of the 3Rs. * p < 0.05; ** p < 0.01, *** p < 0.001.…”

“…For instance, A46 binds and inhibits TRIF [ 36 ], B19 is a soluble type I interferon receptor [ 37 ], and K7 binds DDX3 [ 38 ]. Previously, we attempted to activate the IRF3 pathway by deleting several of these proteins [ 23 ]. We demonstrated that combining a deleted thymidine kinase gene with truncations in immunomodulatory proteins C6 (interacts with NAP1, TANK, and SINTBAD [ 39 ]), N2 (blocks nuclear translocation of P-IRF3 [ 40 ]), or C10 (prevents dsDNA recognition by DNA-PK [ 41 ]) did not translate into IRF3 phosphorylation after cell infection; these three deletions needed to be combined in one virus (named WR/TK-/3Δ) in order detect IRF3 activation and subsequent type I interferon expression.…”

“…All replication-competent recombinant VACV used or constructed in this work are based on the VACV strain Western Reserve (WR). Construction of WR/TK- (VACV strain WR with a truncated viral thymidine kinase (TK) gene and expressing mCherry under the VACV-specific late promoter P11) was previously described [ 23 ]. The B2R gene was inactivated in WR/TK- by guided homologous recombination replacing the original gene sequence with a synthetic construct containing 350 bp upstream and 350 bp downstream of the B2R genomic site.…”

Molecular Circuits of Immune Sensing and Response to Oncolytic Virotherapy

“…Genetically engineered Sendai Virus carrying the IL-2 gene stimulates antitumor effects by modulating immune cell populations [88]. Oncolytic vaccinia viruses, armed with immunomodulatory molecules play a crucial role in activating molecular immune responses against cancer [89][90][91][92][93][94][95][96][97][98]. These viruses enhance antitumor efficacy by stimulating the activation of CD4+ and CD8+ T cells, promoting immune cell infiltration, and augmenting immune-based antitumoral activity through the delivery of chemokines and immunomodulatory antibodies.…”

Tumor Tropism of DNA Viruses for Oncolytic Virotherapy

“…A recent study demonstrated that deleting three key immune-evasion gene products (C10L, N2L, and C6L) from VACV preserved its replication ability in cancer cells [30]. Proteins encoded by VACV, including C10, A46, N2L, and C6, acted as antagonists in the TLR3-IRF3 signaling pathway in various stages [31].…”