Eradication of medulloblastoma by NKG2D-specific CAR T-cells.

Abstract

2522 Background: Medulloblastoma (MB) is a cancerous malignant brain tumor, that most often occurs in young children. Standard-of-care therapies for treating pediatric MB have long-term side effects, even in children who are cured. Recently people are exploring the potential of chimeric antigen receptor T (CAR-T) cell therapy in brain tumor, yet the clinical outcome is limited. It's reported that NKG2D ligands are wildly expressed in MB cells, which supports NKG2D system might play an important role in MB therapy. Here, we take advantage of NKG2D-specific CAR-T cells (KD-025) for MB treatment. Methods: HTB186, HTB185 and HTB187 MB cell lines as well as MB cancer patient samples were evaluated for NKG2D ligands expression. The KD-025 showed antigen-specific stimulation by cytokine secretion and target cell lysis. HTB186 cells, which stably express luciferase protein, were used to establish in vivo subcutaneous and xenograft models in NSG mice. Mice received a single treatment of 10 million KD-025 intravenously. Results: NKG2D ligands were detected on HTB186 and HTB187 cells and most of screened BM patient samples. The KD-025 was generated with CD8 hinge region and transmembrane region, 4-1BB costimulatory region and CD3 zeta region. The KD-025 expression was > 50% on the surface of T cells confirmed by flow cytometry. Co-incubation of KD-025 with HTB186 cells specifically upregulates TNF-α, IFN-γ, IL-10 and IL-2 cytokines and strongly lysis tumor cells even at low E:T ratio (70-80% at 8:1). Strikingly, KD-025 markedly eliminated xenograft tumors in vivo and did not exhibit significant treatment-related toxicity in the treated mice. Regarding to T cell persistence, the CAR-T cells are barely detectable 24 days after injection, which is comparable with CD19 CAR in our experiments as well as published data. No obvious pathological changes were found in the tested organs. Conclusions: Our work with the KD-025 contributes to the growing body of research committed to discovering a novel therapy for MB. NKG2D ligands are highly expressed on human MB samples. KD-025 potently respond to MB and eliminate tumor in a xenograft mouse model with no obvious safety issues. The results support future clinical trial of KD-025 in patients with MB, where the need for effective treatment is great.