Introduction: Currently, there are no murine chordoma cell lines nor transgenic mouse models of chordomas, which prevents us from investigating the interaction between murine chordomas and murine immune cells. Thus, to scrutinize immunotherapy (IT) against chordomas, the development of a humanized mouse model of chordomas, where human thymus and CD34+ stem cells as well as human chordomas are co-transplanted to engraft human immune system into mice, is imperative. We aimed to develop this model and investigate synergistic effect between IT and radiation therapy (RT) against chordomas using this model.
Methods: Fifteen 10-12-week-old NSG mice were sub-lethally irradiated and then implanted with human fetal thymic tissue and CD34+ stem cells, whose HLA-type is partially-matched with that of the U-CH1 chordoma cell line. Reconstitution of immune cells in NSG mice was confirmed 8 weeks post-transplantation and then each animal was injected with U-CH1 subcutaneously. Next, they were treated for 4 weeks as follows: A) control (n=3), B) anti-human-PD-1 antibodies (n=4), C) RT + isotype antibodies (n=3, 8Gy x 4), D) anti-human-PD-1 antibodies and RT (n=5). Anti-tumor activities were monitored via tumor size, flow cytometry, qRT-PCR, and immunohistochemistry.
Results: One week after the treatment, on the irradiated side, (D) demonstrated lowest tumor volume, highest number of human PBMCs, highest % of CD8+ human T cells, highest % of CD45RO+CD4+ human T cells, and lowest % of PD-1+CD8+ human T cells in the tumors via flow cytometry, and highest IFN-gamma in the tumors via qRT-PCR, compared to the other groups with statistical significance.
Conclusions: We demonstrated that this humanized mouse model could be a revolutionary platform to investigate IT against rare cancers such as chordomas, where murine equivalents are unavailable. The direct synergistic effect between IT and RT against chordoma was observed, evidenced by lowest tumor volume, highest cytotoxic T cells, and memory T cells.
Patient Care: The potential benefit of this study is not only that this combinatorial therapy could be beneficial to patients with chordomas by improving local and distant tumor control as well as decreasing toxicities of RT to adjacent normal structures, but also that this humanized mouse model itself could serve as a platform to investigate IT against other rare cancers, where murine equivalent cancer cell lines are unavailable, thereby potentially revolutionizing the field of immune-oncology.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of the development of humanized mouse models, 2) Discuss, in small groups, potential limitations of this model such as HLA-partial-mismatch, time-dependent decrease in CD14+ cells and CD19+ cells, relatively small number of regulatory T cells engrafted into NSG mice, and cost and time required to develop humanize mice as well as future directions to overcome these issues, including use of patient-derived xenografts and CD34+ stem cells from the same patients and/or NSG-SGM3 mice, 3) Identify potentially effective treatment options against rare cancers such as chordomas, including immunotherapy (PD-1/PD-L1 blockade and CD47/SIRPa blockade) and combinatorial treatment of immunotherapy and radiation therapy.