Bartee, Eric

T-cell immunoglobulin and mucin domain 3 (TIM3) is emerging as a potential target for antibody-based checkpoint blockade. However, the efficacy of TIM3 blockade in combination with other treatment modalities, has not been extensively studied. In the current work we combined TIM3 blockade with myxoma virus-based oncolytic virotherapy (OV). Our results demonstrate that myxoma virus’s ability to initiate an immense antitumor immune response complements the ability of TIM3 blockade to shift the tumor microenvironment to a more proinflammatory state. As a result, the combination of TIM3 blockade and OV is able to completely eradicate established disease, while neither monotherapy is effective. These data represent the first demonstration that OV can enhance the efficacy of TIM3 blockade and suggest that this treatment may need to be incorporated into more aggressive, combinatorial regimens in order to fulfill its potential as an immunotherapeutic.

Background Oncolytic virotherapy (OV) represents a method to treat a variety of solid tumors by inducing antitumor immune responses. While this therapy has been extremely efficacious in preclinical models, translating these successes into human patients has proven challenging. One of the major reasons for these failures is the existence of immune-regulatory mechanisms, which dampen the efficacy of virally induced antitumor immunity. Unfortunately, the full extent of these immune-regulatory pathways remains unclear. Methods To address this issue, we generated a doubly recombinant, oncolytic myxoma virus which expresses both a soluble fragment of programmed cell death protein 1 (PD1) and an interleukin 12 (IL-12) fusion protein (vPD1/IL-12 (virus-expressing PD1 and IL-12)). We then tested the molecular impact and therapeutic efficacy of this construct in multiple models of disseminated disease to identify novel pathways, which are associated with poor therapeutic outcomes. Results Our results demonstrate that vPD1/IL-12 causes robust inflammation during therapy including inducing high levels of tumor necrosis factor (TNF). Surprisingly, although expression of TNF has generally been assumed to be beneficial to OV, the presence of this TNF appears to inhibit therapeutic efficacy by reducing intratumoral T-cell viability. Likely because of this, disruption of the TNF pathway, either through genetic knockout or antibody-based blockade, significantly enhances the overall outcomes of vPD1/IL-12-based therapy that allows for the generation of complete cures in normally non-responsive models. Conclusions These data suggest that some aspects of OV-induced inflammation might represent a double-edged sword during therapy and that specific blockade of TNF might enhance the efficacy of these treatments.