Background Targeted reactivation of the immune system, e.g. using immune checkpoint inhibitors (ICI), has shown great potential in the treatment of cancer. However, in vitro tools to rapidly investigate the impact of checkpoints in the context of specific T cell receptor (TCR) activation as well therapeutic effects of ICI treatment are lacking. Here, we have developed a simple method using the human papilloma virus 16 (HPV-16) E7-peptide (HLA-A2*02:01) and corresponding antigen-specific NFAT-luciferase model to assess antigen presentation and antigen-specific T cell responses and evaluate the impact of immunosuppressive factors and therapeutics that target such factors.

Methods HPV-16_E7_11-20 peptide was used as model antigen.¹ Jurkat NFAT-luciferase cell line or isolated primary T cells were modified with a previously reported TCR recognizing the E7_11-20 peptide.² HLA-A2+/- cancer cells were pulsed and incubated with Jurkat/T cells, with and without the E7_11-20-TCR. To study E7 presentation endogenously, CaSki cells were used. For the luciferase-based assay, T cell activation was correlated with the luminescence read out. For primary T cells, CD25/CD69 expression (Flow Cytometry), cytokine production (ELISA) and clustering (microscopy) were evaluated. As proof of concept for monitoring immunomodulatory events, cells were also treated with TGF-beta or modified to overexpress inhibitory immune checkpoints (e.g., HLA-G, VISTA).

Results Upon E7_11-20 pulsing of HLA-A2+ cells, an E:T ratio dependent increase in luminescence compared to non-pulsed cells (2-25 fold-increase) was observed upon coculture with Jurkat E7_11-20-TCR but not with parental Jurkat cells. Analogous experiments with CaSki yielded 30% increase in luminescence, demonstrating that the method is valid for measuring endogenous E7_11-20 processing and MHC presentation. Both HLA-A2+ pulsed cells and CaSki triggered specific T cell activation, illustrated by 5-20 fold-increase in MFI values for CD25 and CD69 expression and T cell clustering. For cytokine production, only the combination peptide: E7_11-20-TCR significantly triggered TNFa and IFNy production in HLA-A2+ pulsed cells, whereas for CaSki only higher IFNy production was observed. Overexpression of inhibitory molecules, such as HLA-G and VISTA, had a significant negative impact on TCR-induced luminescence compared to EV or non-treated cells. Moreover, treatment with immunosuppressive cytokines such as TGF-beta significantly impacted on luminescence.

Conclusions The MHC-I-specific Jurkat E7_11-20-TCR NFAT-luciferase system presented here can be used as an alternative method for the rapid evaluation of antigen-specific T cell responses in vitro. This method may be used as a rapid tool to study the impact of the TME or novel ICI in triggering effective T cell responses within the immune-oncology field.

References

1. Riemer AB, et al. A conserved E7-derived cytotoxic T lymphocyte epitope expressed on human papillomavirus 16-transformed HLA-A2+ epithelial cancers. J Biol Chem. 2010;285(38):29608–29622.

2. Jin BY, Campbell TE, Draper LM, Stevanovic S, Weissbrich B Yu, et al. Engineered T cells targeting E7 mediate regression of human papillomavirus cancers in a murine model. JCI Insight 2018. pmid:29669936