Immune regulation of canine tumour and macrophage PD‐L1 expression

Abstract

Expression of programmed cell death receptor ligand 1 (PD-L1) on tumor cells has been associated with immune escape in human and murine cancers, but little is known regarding the immune regulation of PD-L1 expression by tumor cells and tumor-infiltrating macrophages in dogs. Therefore, 14 canine tumor cell lines, as well as primary cultures of canine monocytes and macrophages, were evaluated for constitutive PD-L1 expression and for responsiveness to immune stimuli. We found that PD-L1 was expressed constitutively on all canine tumor cell lines evaluated, although the levels of basal expression were very variable. Significant upregulation of PD-L1 expression by all tumor cell lines was observed following IFN-γ exposure and by exposure to a TLR3 ligand. Canine monocytes and monocyte-derived macrophages did not express PD-L1 constitutively, but did significantly upregulate expression following treatment with IFN-γ. These findings suggest that most canine tumors express PD-L1 constitutively and that both innate and adaptive immune stimuli can further upregulate PD-L1 expression. Therefore the upregulation of PD-L1 expression by tumor cells and by tumor-infiltrating macrophages in response to cytokines such as IFN-γ may represent an important mechanism of tumor-mediated T-cell suppression in dogs as well as in humans.

PD‐1 expression by canine T cells and functional effects of PD‐1 blockade

“…Control antibodies included irrelevant isotype‐matched antibodies (feline Immunodeficiency virus) (Sigma‐Aldrich, St Louis, MO, USA and BioXCell, West Lebanon, NH, USA). Two antibodies specific for canine PD‐L1 (clones 4F9 and 5F12, as described recently by our group) were also used to assess expression of PD‐L1 by T cells and neutrophils and monocytes in peripheral blood.…”

“…It was also proposed that FIV infected cats could serve as a model for investigating the effects of PD‐1 blockade on control of chronic lentiviral infection . Recently it has been reported by our group and others that PD‐L1 is expressed on canine tumour cells and macrophages, both in vitro and in vivo . In dogs with visceral leishmaniasis, it was reported recently that PD‐1 signalling could induce T cell apoptosis …”

Regulation of PD-L1 expression on murine tumor-associated monocytes and macrophages by locally produced TNF-α

“…For tumor cells, IFN-γ is considered the primary cytokine reported to upregulate PD-L1 expression, as evaluated with human, murine, and canine tumor cell lines [19, 23, 24]. However, other cytokines have been found to also upregulate PD-L1 expression.…”

Emerging therapeutic approaches for canine sarcomas: Pushing the boundaries beyond the conventional

“…Blocking the PD‐1/PD‐L1 pathway with an anti‐PD‐1 or PD‐L1 antibody can restore multiple effector functions of antigen‐specific T cells, overcoming immune escape mechanisms by cancer cells . In dogs, PD‐1 and PD‐L1 expression have been reported in sarcomas, specifically hemangiosarcoma and osteosarcoma, but the therapeutic potential of PD‐1/PD‐L1blockade has not yet been fully elucidated . Recently, a novel rat‐dog chimeric anti‐PD‐L1 monoclonal antibody (c4G12) was tested in vitro and enhanced cytokine production and proliferation of dog peripheral mononuclear cells.…”

“…135,136 In dogs, PD-1 and PD-L1 expression have been reported in sarcomas, specifically hemangiosarcoma and osteosarcoma, but the therapeutic potential of PD-1/PD-L1blockade has not yet been fully elucidated. 29,30,129,133,[137][138][139] Recently, a novel rat-dog chimeric anti-PD-L1 monoclonal antibody Objective tumour responses in one dog from each tumour category were observed when c4G12 was given intravenously biweekly at 2 or 5 mg/kg. 30 PD-L1 expression was confirmed in the primary tumours of these dogs prior to enrollment.…”