T cell-based immunotherapies have brought great progress for cancer patients, but many questions still remain open with regard to mechanisms of action and immune regulation in the tumor microenvironment.
Methods: We setup a well-controlled co-culture system to study the dynamic T cell - cancer cell interplay. Low passage MelanA-expressing melanoma cell lines were cultured with MelanA-specific CD8+ T cells and characterized using differential gene expression analysis and flow cytometry.
Results: As expected, significant fractions of melanoma cells died in presence of melanoma-specific CD8+ T cells. However, still some melanoma cells persisted during up to three days of co-culture. Characterization of the surviving melanoma cells revealed increased mRNA levels of genes associated with antigen processing and presentation: HLA Class I-encoding genes (HLA-A and HLA-B), HLA Class 2-encoding genes (HLA-DRA and HLA-DRB) and CD74, the invariant chain that stabilizes the complex of HLA Class II α and β chains until it is loaded with a peptide, were strongly increased after co-culture, as well as TAP1 and TAP2 (encoding transporter associated with antigen presentation), responsible for peptide transfer from the cytosol to the endoplasmic reticulum (Neefjes et al., 2011). HLA-Class I and HLA-DR expression was also strongly increased at the protein level as assessed at 48h of co-culture. These gene and protein expression changes were dependent on antigen-specific interaction of CTLs with melanoma cells and were mediated by IFNγ and TNFα, two cytokines secreted by CTLs upon antigen recognition.
Discussion: So far, mainly immunosuppressive mechanisms of cancer cells upon exposure to CTLs were described, such as increased expression of IDO1 and the inhibitory receptor ligand PDL1 (Spranger et al., 2013). Here we show that further to these immunosuppressive mechanisms, melanoma cells respond to melanoma-specific CTLs with an IFNγ-driven upregulation of genes involved in antigen presentation. Increased antigen-presentation likely increases target cell recognition of CTLs. These findings may play a role in successful immunotherapy, and might explain why IFNγ blockade in situations of anti-tumor immune attack not only blocks the immunosuppressive response of melanoma cells but also the anti-tumor T cell response (McGray et al., 2013).
McGray, A.J.R., Hallett, R., Bernard, D., Swift, S.L., Zhu, Z., Teoderascu, F., VanSeggelen, H., Hassell, J.A., Hurwitz, A.A., Wan, Y., et al. (2013). Immunotherapy-induced CD8+ T Cells Instigate Immune Suppression in the Tumor. Mol Ther 22, 206-218.
Neefjes, J., Jongsma, M.L.M., Paul, P., and Bakke, O. (2011). Towards a systems understanding of MHC class I and MHC class II antigen presentation. Nat Rev Immunol 11, 823-836.
Spranger, S., Spaapen, R.M., Zha, Y., Williams, J., Meng, Y., Ha, T.T., and Gajewski, T.F. (2013). Up-Regulation of PD-L1, IDO, and Tregs in the Melanoma Tumor Microenvironment Is Driven by CD8+ T Cells. Sci Transl Med 5, 200ra116-200ra116.
Citation Format: Natalie J. Neubert, Laure Tillé, David Barras, Charlotte Soneson, Petra Baumgaertner, Donata Rimoldi, Mauro Delorenzi, Silvia A. Fuertes Marraco, Daniel E. Speiser. Melanoma cells respond to CD8+ T cell attack by upregulation of genes associated with antigen processing and presentation. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr B34.