Focal Radiation Therapy Combined with 4-1BB Activation and CTLA-4 Blockade Yields Long-Term Survival and a Protective Antigen-Specific Memory Response in a Murine Glioma Model

Abstract

BackgroundGlioblastoma (GBM) is the most common malignant brain tumor in adults and is associated with a poor prognosis. Cytotoxic T lymphocyte antigen -4 (CTLA-4) blocking antibodies have demonstrated an ability to generate robust antitumor immune responses against a variety of solid tumors. 4-1BB (CD137) is expressed by activated T lymphocytes and served as a co-stimulatory signal, which promotes cytotoxic function. Here, we evaluate a combination immunotherapy regimen involving 4-1BB activation, CTLA-4 blockade, and focal radiation therapy in an immune-competent intracranial GBM model.MethodsGL261-luciferace cells were stereotactically implanted in the striatum of C57BL/6 mice. Mice were treated with a triple therapy regimen consisted of 4-1BB agonist antibodies, CTLA-4 blocking antibodies, and focal radiation therapy using a small animal radiation research platform and mice were followed for survival. Numbers of brain-infiltrating lymphocytes were analyzed by FACS analysis. CD4 or CD8 depleting antibodies were administered to determine the relative contribution of T helper and cytotoxic T cells in this regimen. To evaluate the ability of this immunotherapy to generate an antigen-specific memory response, long-term survivors were re-challenged with GL261 glioma en B16 melanoma flank tumors.ResultsMice treated with triple therapy had increased survival compared to mice treated with focal radiation therapy and immunotherapy with 4-1BB activation and CTLA-4 blockade. Animals treated with triple therapy exhibited at least 50% long-term tumor free survival. Treatment with triple therapy resulted in a higher density of CD4+ and CD8+ tumor infiltrating lymphocytes. Mechanistically, depletion of CD4+ T cells abrogated the antitumor efficacy of triple therapy, while depletion of CD8+ T cells had no effect on the treatment response.ConclusionCombination therapy with 4-1BB activation and CTLA-4 blockade in the setting of focal radiation therapy improves survival in an orthotopic mouse model of glioma by a CD4+ T cell dependent mechanism and generates antigen-specific memory.

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

“…12 , 26 Based on these findings, we hypothesized that anti-PD-1 and anti-TIGIT dual therapy would be more effective than either monotherapy alone. However, there has been no established anti-TIGIT treatment schedule for GBM.…”

Preclinical efficacy of immune-checkpoint monotherapy does not recapitulate corresponding biomarkers-based clinical predictions in glioblastoma

“…Studies were excluded because of following reasons: (1) not sufficient survival data reported, (2) letters, reviews, commentary, perspectives, case reports, conference abstracts, editorials or expert opinion, (3) studies reporting xenograft results in immunodeficient or humanized mice. Overall these search criteria helped short-list 15 research articles 12,15,16,[50][51][52][53][54][55][56][57][58][59][60][61] mentioned in Box S1.…”

Irradiation and immunotherapy: From concept to the clinic

“…In addition, in a glioma model, the combination of RT plus CTLA-4 blockade significantly improved survival compared with untreated animals, whereas CTLA-4 blockade alone had no impact. 30 Furthermore, adding an agonist antibody to the costimulatory immune-checkpoint 4-1BB resulted in further improvement. The synergistic effect did not appear to depend on the timing of RT relative to drug therapy, Review Article and it is noteworthy that it appeared to be primarily CD4-positive T-cell mediated.…”

“…The synergistic effect did not appear to depend on the timing of RT relative to drug therapy, Review Article and it is noteworthy that it appeared to be primarily CD4-positive T-cell mediated. 30 RT Synergy With Programmed Cell Death 1/Programmed Death-Ligand 1 Directed Therapy…”