Pharmacological inhibition of perforin dampens CD8+ T cell-mediated beta cell destruction in autoimmune diabetes in mice.

AIMS/HYPOTHESIS: CD8⁺ T cells are key mediators of beta cell destruction in type 1 diabetes, employing the perforin/granzyme and Fas/Fas ligand pathways. Evidence from our studies and others indicates that perforin plays a dominant role in CD8⁺ T cell mediated beta cell destruction in non-obese diabetic (NOD) mice. As perforin is indispensable for delivering pro-apoptotic granzymes into the cytosol of target cells, pharmacological inhibition of perforin may potentially protect beta cells against CD8+ T cell cytotoxicity. Such a strategy will slow down beta cell loss and the progression to autoimmune diabetes. Small molecule perforin inhibitors recently becoming available provided an opportunity to test this hypothesis.

METHODS

The new small molecule perforin inhibitor SN34960 was evaluated for its ability to protect the beta cells of non-obese diabetic mice upon attack by autoreactive cytotoxic T lymphocytes, both in vitro and in vivo.

RESULTS

In vitro, perforin inhibitor SN34960 protected isolated pancreatic islets from CD8+ T cell-mediated destruction (p<0.001). In vivo, a single dose of SN34960 reduced the death of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) peptide-loaded target cells by ~50% over 16 h compared with non-peptide-loaded control cells (p<0.05). Furthermore, prediabetic NOD mice treated with perforin inhibitor for 7 days had a reduced incidence of diabetes when autoimmune attack was accelerated by anti-PDL1 blockade (91.2% vs 58.4%, p<0.05). Pharmacological perforin inhibition with SN34960 did not alter the activation or differentiation status of pathogenic cytotoxic T lymphocyte infiltrating the pancreas; instead, its mode of action is specifically to block the membrane-disruptive and pro-apoptotic effects of perforin following its secretion into the synaptic cleft.

CONCLUSIONS/INTERPRETATION: Our results suggest that pharmacological perforin inhibition may represent a novel approach to protect beta cells from destruction by autoreactive CD8+ T cells.