<p>Figure S1; the AC29 mesothelioma tumor model has a more dominant TAM phenotype compared to the AB1 tumor model. Figure S2; GM-CSF cultured dendritic cells are minimally affected by PLX3397. Figure S3; Gating of immune cell subsets in the blood of mice during therapy. Figure S4; CD4/CD8 Double positive T cells are most abundant after DC- TAM-depletion combination therapy and highest in proliferation marker Ki-67 compared to single positive CD8+ T cells. Figure S5; Similar patterns in myeloid and lymphoid cell dynamics in response to treatment were made in the BALB/c (AB1) tumor model compared to the CBA/j (AC29) model. The TME immune contexture at day 15 post tumor injection is differentially modulated by PLX3397 and DC-therapy. Figure S7; TAM-depletion improves CD8+ T-cell exhaustion status characterized by decreased PD1, LAG3, TIM3 and CD8 expression</p>
ARTICLE ABSTRACT
New immunotherapeutic strategies are needed to induce effective antitumor immunity in all cancer patients. Malignant mesothelioma is characterized by a poor prognosis and resistance to conventional therapies. Infiltration of tumor-associated macrophages (TAM) is prominent in mesothelioma and is linked to immune suppression, angiogenesis, and tumor aggressiveness. Therefore, TAM depletion could potentially reactivate antitumor immunity. We show that M-CSFR inhibition using the CSF-1R kinase inhibitor PLX3397 (pexidartinib) effectively reduced numbers of TAMs, circulating nonclassical monocytes, as well as amount of neoangiogenesis and ascites in mesothelioma mouse models, but did not improve survival. When combined with dendritic cell vaccination, survival was synergistically enhanced with a concomitant decrease in TAMs and an increase in CD8+ T-cell numbers and functionality. Total as well as tumor antigen–specific CD8+ T cells in tumor tissue of mice treated with combination therapy showed reduced surface expression of the programmed cell death protein-1 (PD-1), a phenomenon associated with T-cell exhaustion. Finally, mice treated with combination therapy were protected from tumor rechallenge and displayed superior T-cell memory responses. We report that decreasing local TAM-mediated immune suppression without immune activation does not improve survival. However, combination of TAM-mediated immune suppression with dendritic cell immunotherapy generates robust and durable antitumor immunity. These findings provide insights into the interaction between immunotherapy-induced antitumor T cells and TAMs and offer a therapeutic strategy for mesothelioma treatment. Cancer Immunol Res; 5(7); 535–46. ©2017 AACR.
