The Combination of TIM3-Based Checkpoint Blockade and Oncolytic Virotherapy Regresses Established Solid Tumors.

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.

Initial dose of oncolytic myxoma virus programs durable antitumor immunity independent of in vivo viral replication.

BACKGROUND: Oncolytic therapy uses live-replicating viruses to improve the immunological status of treated tumors. Critically, while these viruses are known to self-amplify in vivo, clinical oncolytic therapies still appear to display a strong dose dependence and the mechanisms mediating this dose dependence are not well understood. METHODS: To explore this apparent contradiction, we investigated how the initial dose of oncolytic myxoma virus affected the subsequent ability of treatment to alter the immunological status of tumors as well as synergize with programmed cell death protein 1 (PD1) blockade. RESULTS: Our results indicate that, due to viral self-amplification in vivo, the overall load of myxoma virus rapidly normalizes within treated tumors despite up to 3-log differences in inoculating dose. Because of this, therapeutic efficacy in the absence of checkpoint blockade is largely dose independent. Despite this rapid normalization, however, treatment with high or low doses of myxoma virus induces distinct immunological changes within treated tumors. Critically, these changes appear to be durably programmed based on the initial oncolytic dose with low-dose treatment failing to induce immunological improvements despite rapidly achieving equivalent viral burdens. Finally, due to the distinct immunological profiles induced by high and low myxoma virus doses, oncolytic efficacy resulting from combination with PD1 blockade therapy displays a strong dose dependence. CONCLUSIONS: Taken together, these data suggest that the ability of oncolytic myxoma virus to immunologically reprogram treated tumors is dependent on initial viral dose. Additionally, this work could provide a possible mechanistic explanation for clinical results observed with other oncolytic viruses.

Genome-wide inference of natural selection on human transcription factor binding sites.

For decades, it has been hypothesized that gene regulation has had a central role in human evolution, yet much remains unknown about the genome-wide impact of regulatory mutations. Here we use whole-genome sequences and genome-wide chromatin immunoprecipitation and sequencing data to demonstrate that natural selection has profoundly influenced human transcription factor binding sites since the divergence of humans from chimpanzees 4-6 million years ago. Our analysis uses a new probabilistic method, called INSIGHT, for measuring the influence of selection on collections of short, interspersed noncoding elements. We find that, on average, transcription factor binding sites have experienced somewhat weaker selection than protein-coding genes. However, the binding sites of several transcription factors show clear evidence of adaptation. Several measures of selection are strongly correlated with predicted binding affinity. Overall, regulatory elements seem to contribute substantially to both adaptive substitutions and deleterious polymorphisms with key implications for human evolution and disease.