Abstract 2713: Novel anti-PD-L1-IL-15 diabody immunocytokine in combination with radiation therapy improves response rates in immune-resistant murine head and neck cancer

Abstract Purpose: The purpose of this study was to develop a new anti-programmed death-ligand 1 (αPD-L1) interleukin-15 (IL-15) diabody (Db) immunocytokine to improve the efficacy of combination radiation therapy (RT) and immune checkpoint inhibition (ICI) treatment in head and neck cancer. Background ICI has revolutionized cancer care by increasing survival in patients with metastatic cancer, yet many patients with poorly immunogenic tumors have limited response to this therapy. To improve the efficacy of ICI, we developed a new immunocytokine combining an αPD-L1 Db with an effector immune cell agonist, IL-15. We hypothesized that our αPD-L1-IL-15 Db construct in combination with immunostimulatory radiation will lead to improved tumor responses and survival from ICI-resistant tumors. Methods: Production in-vitro: αPD-L1-IL-15 Db construct was transfected into Expi-CHO™ cells and isolated with HiTrap™ Protein L affinity column. The molecular weight was confirmed via SDS-PAGE, and surface plasmon resonance sensorgram kinetics revealed high affinity of the immunocytokine to mouse isoform PD-L1 (KD 10 nM). Splenocyte proliferation and HEK-Blue™ reporter assays showed the IL-15 component to be functionally active. Testing in-vivo: 80-100 mm3 mouse oral carcinoma-2 (MOC-2) tumors were established in C57BL/6 mice. Groups of 6 mice with tumors were treated with rat IgG isotype control, αPD-L1 Db, and αPD-L1-IL-15 Db w/wo 8 Gy of tumor-localized beam RT to upregulate PD-L1. Mice were tracked for tumor growth via tumor measurements and overall survival until the tumor burden endpoint was reached. Results: We found αPD-L1 Db w/wo RT had an insignificant impact on survival or tumor growth delay in this tumor model in comparison to IgG w/wo RT. However, αPD-L1-IL-15 Db significantly improved survival compared to αPD-L1 Db treatment (p = 0. 004) and IgG (p = 0. 0013) in the presence of RT. We also saw significantly increased mean tumor growth delay with αPD-L1-IL-15 Db treatment compared to αPD-L1 Db (p = 0. 0164) and IgG (p = 0. 0252), on days 25 and 18 respectively, in the presence of RT. However, in the absence of RT, αPD-L1-IL-15 Db yielded no significant difference in mean tumor growth delay or survival when compared to IgG and αPD-L1 Db w/o RT. Conclusion: Our results demonstrate that our αPD-L1-IL-15 Db immunocytokine with RT significantly improved tumor response and increased survival in aggressive, ICI-resistant mouse oral carcinoma, as compared to αPD-L1 Db with RT. However, this observation no longer persisted in the absence of RT. Hence, this suggests a synergy between radiation therapy and ICI-cytokine therapy in immunotherapy-resistant tumors. Further correlative and mechanistic tumor microenvironment profiling studies are underway to further elucidate mechanisms of immune activation with our combination of αPD-L1-IL-15 Db and radiation treatment. Citation Format: Abhay R. Sheeri, Robert S. Edinger, Harikrishnan Rajkumar, Ravi B. Patel. Novel anti-PD-L1-IL-15 diabody immunocytokine in combination with radiation therapy improves response rates in immune-resistant murine head and neck cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2713.