EP001/#442 The effect of mild hyperthermia on immune evasion actors PD-L1 and NLRC5 in ovarian cancer

Objectives

Multiple preclinical studies have demonstrated the benefit of augmenting immunotherapy with hyperthermia (HT) considering the proven ability of HT to enhance immune cell immunogenicity and to stimulate an antitumor immune response primarily via heat shock proteins (HSP). However, antitumor immune responses are often invalidated by immune evasion mechanisms such as the overexpression of programmed death-ligand 1 (PD-L1) and the loss of MHC class I expression. In this context, we sought to investigate the effects of HT on PD-L1 and the transcriptional activator of MHC class I genes NLRC5 and their interplay in ovarian cancer.

Methods

A co-culture of ovarian cancer cell lines (IGROV1 and SKOV3) with peripheral blood mononuclear cells was set up. Culture media conditioned with IGROV1 or SKOV3 subjected to HT were tested on untreated cell cultures. Knockdown of HSPA1 and HSPB1 and inhibition of STAT3 activation were performed. Expression levels of PD-L1, NLRC5, proinflammatory cytokines and HSP were measured. The correlation between PD-L1 and NLRC5 expression in ovarian cancer was evaluated using data from The Cancer Genome Atlas (TCGA) database.

Results

HT produced a significant concomitant decrease of PD-L1 and NLRC5 expression in co-culture. Notably, however the conditioned media by heat shocked cells increased their expression. Knockdown of the HSPB1 gene reversed this increase, an effect enhanced by STAT3 activation inhibition. Correlation analysis showed a positive correlation between NLRC5 and PD-L1 (r=0.54, p-value <0.001) in TCGA database.

Conclusions

Our results revealed that HSP27 induces a concomitant upregulation of PD-L1 and NLRC5 expression through the activation of a common regulator ‘STAT3’.