Playing Hide and Seek with Glioblastoma: Using epigenetic modulators to increase Cancer Testis and Neoantigen expression


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Ruichong Ma, Margarida Rei, Katherine Ferris, Isaac Woodhouse, Hashem Koohy, Puneet Plaha, Vincenzo Cerundolo

Abstract

Background

Glioblastoma (GBM) is the most common and malignant primary brain tumour in adults and propers a median survival of only 14-24 months despite best management. The inevitable progression of GBM is thought to be facilitated by an immunosuppressive microenvironment, which weakens the ability of the central nervous system to mount an effective and tumour-eradicating response. However, despite numerous trials, clinical response to immunotherapy is modest, due, in part, to the low number of mutations in GBM. Epigenetic regulation of tumours is becoming increasingly recognised as an important factor in tumour immune escape. Here, we examine the effect of a decitabine (DAC), a DNA methyl-transferase inhibitor, on the expression of both cancer testis antigens (CTA) and neoantigens (NAg) in GBM.

Method

Primary GBM cell lines were created through culture of fresh tumour specimens using defined media. NAg from primary and U87MG cell lines were predicted using whole exome sequencing data. Differential expression of CTA and NAg following DAC treatment was determined by RNA sequencing. Peptide specific T cells were isolated from autologous and healthy donors using fluorescence labelled peptide-MHC class I tetramers. T cell functionality was tested through intracellular cytokine staining and/or LDH release killing assay.

Results

Many potential NAg-encoding mutations and CTA were significantly up-regulated following DAC treatment. We were able to establish NAg and CTA specific T cells. These T cell clones are able to recognise and kill the specific cell lines in a TCR-MHC dependent fashion. Furthermore, we show that T cells specific to NAgs and CTA upregulated by DAC show increased activation and killing against cell lines treated with DAC.

Conclusion

Here we show for the first time that a large spectrum of CTAs as well as several NAgs are up-regulated in GBM following DAC treatment. We show that increased expression of NAg and CTA leads to increased T cell mediated killing. 

Impact statement

We have identified a novel mechanism for increasing expression of immunogenic antigens to enhance the immunogenicity of an otherwise immune cold tumour. This offers the possibility of unlocking the potential of current immunotherapies, which offer limited success.