TGF-ß Inhibition Improves Oncolytic Herpes Viroimmunotherapy in Murine Models of Rhabdomyosarcoma.

Oncolytic viruses are an emerging class of cancer therapeutics that couple cytotoxicity with the induction of an anti-tumor immune response. Host-virus interactions are complex and modulated by a tumor microenvironment whose immunosuppressive activities can limit the effectiveness of cancer immunotherapies. In an effort to improve this aspect of oncolytic virotherapy, we combined the oncolytic herpes virus HSV1716 with the transforming growth factor beta receptor 1 (TGF-ßR1) inhibitor A8301 to treat syngeneic models of murine rhabdomyosarcoma. Mice that received HSV1716 or A8301 alone showed little to no benefit in efficacy and survival over controls. Conversely, mice given combination therapy exhibited tumor stabilization throughout the treatment regimen, which was reflected in significantly prolonged survival times including some complete responses. In vitro cell viability and virus replication assays showed that the rhabdomyosarcoma cell lines were generally insensitive to HSV1716 and A8301. Likewise, in vivo virus replication assays showed that HSV1716 titers moderately decreased in the presence of A8301. The enhanced efficacy instead appears to be dependent on the generation of an improved anti-tumor T cell response as determined by its loss in athymic nude mice and following in vivo depletion of either CD4+ or CD8+ cells. These data suggest TGF-ß inhibition can augment the immunotherapeutic efficacy of oncolytic herpes virotherapy.

Cooperation of Oncolytic Herpes Virotherapy and PD-1 Blockade in Murine Rhabdomyosarcoma Models.

Oncolytic virotherapy is an effective immunotherapeutic approach for cancer treatment via a multistep process including direct tumor cell lysis, induction of cytotoxic or apoptosis-sensitizing cytokines and promotion of antitumor T cell responses. Solid tumors limit the effectiveness of immunotherapeutics in diverse ways such as secretion of immunosuppressive cytokines and expression of immune inhibitory ligands to inhibit antitumor T cell function. Blocking programmed cell death protein (PD)-1 signaling, which mediates T cell suppression via engagement of its inhibitory ligands, PD-L1 or PD-L2, is of particular interest due to recent successes in many types of cancer. In syngeneic murine rhabdomyosarcoma models, we found that M3-9-M (MHC I high) but not 76-9 (MHC I low) tumors respond to oncolytic herpes simplex virus-1 (oHSV-1) and PD-1 blockade combination therapy. In addition, the therapeutic outcomes in M3-9-M tumor models correlated with the increased incidence of CD4+ and CD8+ T cells but not with the CD4+CD25+Foxp3+ regulatory T cell populations in the tumor. Overall, our data suggest the combination of PD-1 blockade and oHSV-1 may be an effective treatment strategy for childhood soft tissue sarcoma.

Characterization of MHC Class I and ß-2-Microglobulin Expression in Pediatric Solid Malignancies to Guide Selection of Immune-Based Therapeutic Trials.

BACKGROUND: Over 10,000 US children are diagnosed with cancer yearly. Though outcomes have improved by optimizing conventional therapies, recent immunotherapeutic successes in adult cancers are emerging. Cytotoxic T lymphocytes (CTLs) are the primary executioners of adaptive antitumor immunity and require antigenic presentation in the context of major histocompatibility complex (MHC) class I and the associated ß-2-microglobulin (B2M). Loss of MHC I expression is a common immune escape mechanism in adult malignancies, but pediatric cancers have not been thoroughly characterized. The essential nature of MHC I expression in CTL-mediated cell death may dictate the success of immunotherapies, which rely on eliciting an adaptive response. PROCEDURE: We queried pediatric tumor microarray databases for MHC I and B2M gene expression. We detected MHC I in pediatric tumor cell lines by flow cytometry and characterized MHC I and B2M expression in patient samples by immunohistochemistry. To determine whether therapeutic approaches might enhance MHC I expression in selected models in vitro, we tested effects of exposure to IFN-γ and histone deacetylase inhibitors. RESULTS: Pediatric tumors overall, as well as samples within select individual tumor subtypes, exhibit wide ranges of MHC I and B2M gene and protein expression. For most cell lines tested, MHC I was inducible in vitro. CONCLUSIONS: MHC I and B2M expression vary among pediatric tumor types and should be evaluated as potential biomarkers, which might identify patients most likely to benefit from MHC I dependent immunotherapies. Modulation of MHC I expression may be a promising mechanism for enhancing MHC I dependent immunotherapeutic efficacy.