Anti-GD2 antibody therapy alters the neuroblastoma tumor microenvironment and extends survival in TH-MYCN mice

BackgroundNeuroblastoma is a commonly lethal solid tumor of childhood and intensive chemoradiotherapy treatment cures ~50% of children with high-risk disease. The addition of immunotherapy using dinutuximab, a monoclonal antibody directed against the GD2 disialoganglioside expressed on neuroblasts, improves survival when incorporated into front-line therapy and shows robust activity in regressing relapsed disease when combined with chemotherapy. Still, many children succumb to neuroblastoma despite receiving dinutuximab-based immunotherapy, and efforts to counteract the immune suppressive signals responsible are warranted. Animal models of human cancers provide useful platforms to study immunotherapies. TH-MYCN transgenic mice are immunocompetent and develop neuroblastomas at autochthonous sites due to enforced MYCN expression in developing neural crest tissues. However, GD2-directed immunotherapy in this model has been underutilized due to the prevailing notion that TH-MYCN neuroblasts express insufficient GD2 to be targeted. MethodsTH-MYCN mice were treated with 14G2a (anti-GD2 antibody), isotype antibody, or phosphate buffered saline from day 14 of life until day 100 or signs of morbidity. Survival was recorded, and tumors were isolated in terminal surgeries for analysis of GD2 expression and immune cell frequencies. Tumors from untreated mice were explanted for generation into cell lines, and GD2 expression was recorded with serial passage in tissue culture. Immunocytology and immunoblotting were performed to evaluate for adrenergic and mesenchymal markers of neuroblasts. Survival curves compared using Kaplan-Meier method with a log-rank test for significance. Unpaired two-tailed Students t-tests used for comparison of groups in flow cytometry analysis. Results14G2a markedly extends survival in such TH-MYCN mice. Additionally, neuroblasts in 14G2a-treated mice have reduced GD2 expression and fewer macrophage and myeloid-derived suppressor cells in their tumor microenvironments. Neuroblasts in TH-MYCN-driven tumors express GD2 at levels comparable to human neuroblastomas but rapidly lose GD2 expression when explanted ex vivo to establish tumor cell lines. The loss of GD2 expression ex vivo is associated with a transition from an adrenergic to mesenchymal state that is maintained when reimplanted in vivo. ConclusionsOur findings support the utility of the TH-MYCN model to inform GD2-directed immunotherapy approaches for neuroblastoma as well as opportunities to investigate drivers of adrenergic to mesenchymal fate decisions.