Therapeutic potential of T cell responses against tumor initiating cell-associated antigens in CRC
Final Report Abstract
The establishment of distant metastasis is an important parameter affecting the prognosis of colorectal carcinoma (CRC) patients and it has been shown by our collaborators in SP2 that these arise from a small population of long term tumor initiating cells (LT-TIC). Furthermore, the T cell infiltrate in the primary tumor of CRC patients is another major prognostic factor, suggesting the presence and the reactivity of tumor specific T cell in situ might play an important role in controlling tumor relapse, metastasis and response to treatment. Based on these observations we hypothesized that T cell responses against antigens expressed on LT-TIC might contribute to more efficient immune surveillance and might correlate with improved patients’ survival and prognosis. To date little is known about the target antigens of the spontaneous T cell responses in CRC patients. For the purpose of identifying those antigens in a systematic and unbiased manner, we utilized a two dimensional protein separation technique (PF2D) in conjunction with IFN-γ ELISpot. We have used the proteome derived from primary and metastatic tumors as well as TIC enriched spheroids as sources of potential target antigens. The immunogenic fractions derived from these proteomes have been analyzed subsequently by mass spectrometry and we generated a list of 572 potential target antigens. Since we were interested in targeting mainly tumor initiating cells we focused on 17 candidate antigens, which were specific for the TIC enriched spheroid cultures and also 10 additional ones, which were shared among all tested entities. We have shown that the newly identified antigens triggered robust T cell responses in up to 20% of CRC patients, thus underlining their importance for targeting a therapeutically relevant cell population. In addition, we have analyzed further in depth antigens identified in the first funding period, which have been shown to be differentially expressed also in TIC enriched spheroids compared to primary tissues. We have delineated the T cell epitopes for one of them namely ANXA2, which triggered predominantly CD8+ T cell responses. Identifying HLA-A2 restricted T cell epitopes to a TIC associated target antigen gave us a useful tool for identification and selection of TIC reactive T cells. We plan to isolate the TCR sequences of these TIC reactive T cells and the TCRs will be used for generation of genetically modified TIC specific T cells, which subsequently could be used in vitro and in vivo functional assays. Being able to identify and detect TIC specific T cells in blood and in situ in tumors also would help us to correlate the infiltration of TIC specific T cells with patient prognosis and thus support the relevance of these antigens for T cell based immunotherapy. Furthermore we will test the reactivity to the newly identified T cell epitopes in a bigger cohort of CRC, whose survival we can follow up, and we will correlate the T cell responses with improved survival and better prognosis. In conclusion, we have successfully identified T cell antigens, expressed by therapeutically relevant population of tumor initiating cells, which are highly immunogenic and might have an important role in tumor immune monitoring of CRC and have the potential to be a basis for the development of improved immunotherapeutic approaches.
Publications
- Tumor-specific cytotoxic T lymphocyte activity determines colorectal cancer patient prognosis. Journal of Clinical Investigation 125(2), 739-51 (2015)
Reissfelder, C., Stamova, S., Gossmann, C., Braun, M., … and Beckhove, P.
(See online at https://doi.org/10.1172/JCI74894) - Long-peptide vaccination with driver gene mutations in p53 and Kras induces cancer mutation-specific effector as well as regulatory T cell responses. Oncoimmunology 7(12):e1500671 (2018)
Quandt, J., Schlude, C., Bartoschek, M., Will, R., Cid-Arregui, A., Schölch, S., Reissfelder, C., Weitz, J., Schneider, M., Wiemann, S., Momburg, and Beckhove, P.
(See online at https://doi.org/10.1080/2162402X.2018.1500671)
