Abstract
The aim of the study was to assess the expression of the immune checkpoint inhibitor programmed death-ligand 1 (PD-L1) in equine sarcoids (ES). Programmed death-ligand 1 is expressed by various cancer cells to block T cell–mediated elimination of tumor cells. Antibodies targeting human PD-L1 were tested by immunohistochemistry for their cross-reactivity with equine PD-L1 using formalin-fixed, paraffin-embedded tissues. Our results do not support an important role of PD-L1-mediated immune evasion in ES disease and hence do not offer a rationale for anti-PD-1/PD-L1-based immunotherapy against ES.
Highlights
Equine sarcoids (ES) are the most common tumors in equids and account for more than half of all skin tumors in this species [1,2]
The number of examined tumors is low, this pilot experiment suggests that programmed death-ligand 1 (PD-L1) is not generally expressed by ES-derived transformed equine fibroblasts and PD-1 blockade is unlikely a general mechanism of immune evasion in ES disease
We focused on the quantification of PD-L1-positive transformed fibroblasts that are readily differentiated from immune cells, based on morphological criteria
Summary
Equine sarcoids (ES) are the most common tumors in equids and account for more than half of all skin tumors in this species [1,2]. The physiologic role of immune checkpoints is to maintain self-tolerance and protect tissues from self-damage, for instance while responding to an infection [6,7,8] The dysregulation of these immune checkpoint proteins can be observed in various cancers, and represents an important mechanism for tumor cells to evade the immune system [6,9]. PD-L1 is expressed na by various cancer cells to block T cell-mediated elimination of the tumor cells by binding to programmed cell death protein 1 (PD-1) at the surface of T lymphocytes This mechanism of immune evasion can be prevented by using specific antibodies against PD-L1 or PD-1 [6]
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