Immunohistochemical evaluation of immune cell infiltration in canine gliomas

Abstract

Evasion of the immune response is an integral part of the pathogenesis of glioma. In humans, important mechanisms of immune evasion include recruitment of regulatory T cells (Tregs) and polarization of macrophages toward an M2 phenotype. Canine glioma has a robust immune cell infiltrate that has not been extensively characterized. The purpose of this study was to determine the distribution of immune cells infiltrating spontaneous intracranial canine gliomas. Seventy-three formalin-fixed, paraffin-embedded tumor samples were evaluated using immunohistochemistry for CD3, forkhead box 3 (FOXP3), CD20, Iba1, calprotectin (Mac387), CD163, and indoleamine 2,3-dioxygenase (IDO). Immune cell infiltration was present in all tumors. Low-grade and high-grade gliomas significantly differed in the numbers of FoxP3+ cells, Mac387+ cells, and CD163+ cells ( P = .006, .01, and .01, respectively). Considering all tumors, there was a significant increase in tumor area fraction of CD163 compared to Mac387 ( P < .0001), and this ratio was greater in high-grade tumors than in low-grade tumors ( P = .005). These data warrant further exploration into the roles of macrophage repolarization or Treg interference therapy in canine glioma.

Tumor-Associated Macrophages in Canine Oral and Cutaneous Melanomas and Melanocytomas: Phenotypic and Prognostic Assessment

“…These results are similar to human melanoma, where CD163 expression has shown a robust association with worse overall survival (18,35). An increase in CD163 expression is similarly reported in other high-grade canine tumors, such as lymphomas and gliomas (33,46). CD163 is considered a marker for M2-polarized macrophages, hence, the presence of numerous CD163 + cells supports the hypothesis of an activation of immunosuppression and immunoescape mechanisms within the tumor microenvironment also in canine melanomas, as we previously hypothesized by testing the expression of IDO, Foxp3, and CTLA-4 (41,54).…”

“…From formalin-fixed and paraffin-embedded samples, 5-µm sections were cut and mounted on poly-L-lysinecoated slides, which were then dewaxed and dehydrated. Immunohistochemistry was performed on serial sections with antibodies raised against CD163, CD204 (44), Iba1 (45), and MAC387 (33,46,47). In cases with more available histocassettes, the most representative was chosen, avoiding samples with large necrotic areas or ulceration.…”

Safety and Efficacy of an Oncolytic Adenovirus as an Immunotherapy for Canine Cancer Patients

“…MAC387 has been identified as a marker for macrophages with an M1-like phenotype, usually associated with a pro-inflammatory and immunosuppressive TME, that favors an antitumoral response [ 56 , 57 ]. Patients with an overall MST higher than that expected with conventional treatment (PSit02 and PSit04) showed an increase in MAC387+ cells in the primary tumor tissue after the administration of the OV, suggesting that ICOCAV15 could have an effect on the TME, further suggesting that the infiltration of these cells could improve survival.…”

Intracranial Virotherapy for a Canine Hemangioma

“…After each intracranial administration of ICOCAV15, the infiltration of MAC387+ and Iba1+ cells in the tumor increased, suggesting that ICOCAV15 can induce a change in the tumor microenvironment (TME) [ 36 ]. M1 macrophages (MAC387+) and activated microglia (Iba1+) have a proinflammatory behavior and trigger antitumoral responses; therefore, an increased number of these cells could favor a more immunoreactive TME [ 37 ]. Furthermore, the increase in the infiltration of CD3+ (reduction in regulatory FoxP3+ subset) and CD20+ lymphocytes after the administration of ICOCAV15 might support the TME’s proinflammatory/antitumor state.…”