gms | German Medical Science

Background: Anti-tumor therapy with immune checkpoint inhibitors for programmed-death 1 receptor (PD1), such as nivolumab is often accompanied by immune-related adverse events (irAE). The cellular and molecular mechanisms underlying this phenomenon are not defined yet. Interaction of PD-1 with its ligand (PD-L1) mediates potent inhibitory signals to hinder proliferation and effector function of T cells. Interruption of PD1:PD-L1 interaction by nivolumab during treatment regiment might therefore amplify T cell receptor (TCR) signalling and facilitate the development of a pro-inflammatory autoimmune responses. Here we investigated the impact of PD1 inhibition on intracellular signalling mechanisms down-stream of TCR such as calcium (Ca2+) influx and activation of mitogen-activated protein kinases (MAPK) pathway and assessed the effect of PD1 inhibition on T cell effector function by evaluating the cytokine profile and glucose metabolism of nivolumab-treated T cells.

Methods: CD4 T cells were stimulated in the presence of nivolumab. Intracellular Ca2+ influx was assessed by flow cytometry. mRNA expression was determined by real-time PCR. Phosphorylation of extracellular signal-regulated kinase 1 and 2 (Erk1/2), cytokine profile and glucose uptake was determined by intracellular flow cytometry.

Results: Treatment of CD4 T cells with nivolumab led to a pronounced increase of the ionomycin-mediated Ca2+ influx. At the same time expression of store-operated Ca2+ entry (SOCE) proteins, STIM1 and orai1, was significantly up regulated in the nivolumab-treated cells. Phosphorylation of ERK1/2 in response to short anti-CD3/CD28 restimulation was increased in CD4 T cells cultured with nivolumab. The long-term nivolumab treatment led to higher frequencies of IL-17-producing T cells (Th17 cells) and to an increase in glucose uptake. Analysis of CD4 T cells from nivolumab-treated carcinoma patients suffering from irAEs revealed increased levels of ERK1/2 phosphorylation as compared to healthy controls. Interestingly the ERK phosphorylation levels were similar to that in RA patients.

Conclusion: Interruption of PD1:PD-L1 interaction by nivolumab activate SOCE and promote Erk1/2 activation. Both T cell signalling pathways are essential for a proper mounting an immune response. Their deregulation might therefore precede an abnormal T cell response as shown for example by increased Th17 cell frequency and enhanced metabolism and facilitate the onset of autoimmune phenomena such as irAE in nivolumab-treated carcinoma patients.