Anti-PD-1 Blockade and Stereotactic Radiation Produce Long-Term Survival in Mice With Intracranial Gliomas

Abstract

Purpose Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults, and radiation is one of the main treatment modalities. However, cure rates remain low despite best available therapies. Immunotherapy is a promising modality that could work synergistically with radiation, which has been shown to increase antigen presentation and promote a proinflammatory tumor microenvironment. Programmed-death-1 (PD-1) is a surface receptor expressed on activated and exhausted T cells, which mediate T cell inhibition upon binding with its ligand PD-L1, expressed on many tumor types including human GBMs. We tested the combination of anti-PD-1 immunotherapy with stereotactic radiosurgery in a mouse orthotopic GBM model. Methods and Materials We performed intracranial implantation of mouse glioma cell line GL261 transfected with luciferase into C57BL/6 mice. Mice were stratified into 4 treatment groups: (1) control; (2) radiation only; (3) anti-PD-1 antibody only; and (4) radiation plus anti-PD-1 antibody. Overall survival was quantified. The mice were killed on day 21 after implantation to assess immunologic parameters in the brain/tumor, cervical lymph nodes, and spleen. Results Improved survival was demonstrated with combination anti-PD-1 therapy plus radiation compared with either modality alone: median survival was 25 days in the control arm, 27 days in the anti-PD-1 antibody arm, 28 days in the radiation arm, and 53 days in the radiation plus anti-PD-1 therapy arm (P<.05 by log-rank Mantle-Cox). Long-term survival was seen only in the combined treatment arm, with a fraction (15%–40%) of animals alive at day 180+ after treatment. Immunologic data on day 21 after implantation showed increased tumor infiltration by cytotoxic T cells (CD8+/interferon-γ+/tumor necrosis factor-α+) and decreased regulatory T cells (CD4+/FOXP3) in the combined treatment group compared with the single modality arms. Conclusions The combination of PD-1 blockade and localized radiation therapy results in long-term survival in mice with orthotopic brain tumors. These studies provide strong preclinical evidence to support combination trials in patients with GBM.

TIGIT and PD-1 dual checkpoint blockade enhances antitumor immunity and survival in GBM

“…36-42 Furthermore, single and combinatorial checkpoint blockade have also shown promise in both preclinical and clinical settings. 10 , 12 , 43-48 In our study, we identify a significant survival benefit with the use of combination PD-1 and TIGIT blockade in the murine GBM model through modulations of both the T cell and myeloid compartments. Our data suggests that anti-TIGIT therapy may be a valuable addition to the management of GBM.…”

“…The treatment effect of anti-PD-1 has been previously described in multiple murine GBM studies. 12 , 43 Combination therapy using anti-TIGIT and anti-PD-1 antibodies further conferred a greater survival benefit in all anti-TIGIT treatment schedules, implying a synergistic mechanism following interruption of the two inhibitory checkpoints. This improvement in therapeutic efficacy following dual blockade of the TIGIT and PD-1 pathways has been demonstrated in the murine colorectal model.…”

Contrasting impact of corticosteroids on anti-PD-1 immunotherapy efficacy for tumor histologies located within or outside the central nervous system

“…To investigate this question, a well-established anti-PD-1-responsive, intracranial GL261-Luc tumor model (N = 80) was utilized (Figure 4A). 19–21 Single therapy with Dex-1, Dex-2, or Dex-Cont did not appear to improve survival compared to control mice (Figure 4B through 4D). In accordance with previous studies, anti-PD-1 monotherapy significantly prolonged survival compared to untreated controls in the intracranial tumor model ( P  = 0.020).…”

“…In accordance with previous studies, anti-PD-1 monotherapy significantly prolonged survival compared to untreated controls in the intracranial tumor model ( P  = 0.020). 19–21 Combination anti-PD-1 and dexamethasone therapy prolonged survival compared to untreated mice (anti-PD-1 + Dex-1: P  = 0.0047, anti-PD-1 + Dex-2: P  = 0.020, anti-PD-1 + Dex-Cont: P  = 0.0061). There were no significant differences in survival between the anti-PD-1 monotherapy and combination treatment groups.…”

“…19 Briefly, mice were properly anesthetized prior to procedure with a ketamine (5 mg/mL, Henry Schein)/xylazine (0.5 mg/mL, Akorn) solution in 0.9% saline. A small midline incision was made, and a burr hole was then placed on the left-side 1 mm anterolateral to bregma.…”