Description

Radiotherapy in combination with aOX40 and aCTLA-4 immunotherapy is capable of both preventing and reversing functional exhaustion within tumor-specific CD8 T cells

Joshua M Walker¹, Melissa J Kasiewicz², Courtney L Mick² and William L Redmond^2*

¹Oregon Health & Science University Department of Radiation Medicine; ²Earle A. Chiles Research Institute, Providence Portland Medical Center

^*Corresponding Author

Re-stimulation of functionally exhausted and anergic effector CD8 T cell cells using systemic immunotherapy (IT) alone remains a challenge. Here we show that the addition of ionizing radiotherapy (RT) to IT with agonist aOX40 & blocking aCTLA-4 antibodies (aOX40/aCTLA-4) prevents development of CD8 T cell functional exhaustion. Additionally, combined aOX40/aCTLA-4/RT results in increased T cell receptor (TCR) signaling and cytokine production within exhausted CD8 T cells.

CT26 tumor-bearing mice were treated with a single 20 Gy fraction of RT, aOX40/aCTLA-4, or combined IT/RT. The frequency and function of tumor-specific (AH1) CD8 T cells was monitored in the blood, spleen, lymph node, and tumor. The addition of RT to aOX40/aCTLA-4 significantly increased the frequency of AH1 CD8 T cells within the tumor, spleen, and lymph nodes of CT26 tumor-bearing mice compared to IT alone. The addition of RT resulted in up to a 4-fold increase in the frequency of AH1-specific CD8 T cells within the TIL. Combination therapy prevented development of functional exhaustion, leading to a more polyfunctional cytokine profile compared to IT alone.

We also characterized the onset of antigen-specific CD8 T cell functional exhaustion in tumor-bearing mice and found that OT-I cells become functionally exhausted 18-21 days after adoptive transfer. Combination therapy with aOX40/aCTLA-4 and RT resulted in increased TCR stimulation in exhausted OT-I T cells compared to IT alone, as measured using Nur77-GFP OT-I transgenic T cells which express green fluorescent protein in response to TCR ligation. The addition of RT to treatment with aOX40/aCTLA-4 also resulted in increased effector cytokine polyfunctionality within the OT-I cell compartment compared to IT alone.