SP 5

Therapeutic potential of T cell responses against tumor initiating cell-associated antigens in CRC

The prognosis of colorectal carcinoma (CRC) patients is dependent on the establishment of distant metastases, which  according to the recent findings of KFO SP2 arise from a small population of  long term tumor initiating cells (LT-TIC), located in the primary tumor tissue, in the bone marrow and in metastatic lesions.

The extent of the T cell infiltrates in the primary tumors is the major prognostic parameter in CRC, hinting that tumor specific T cell immune surveillance plays a critical role in the control of tumor relapse, formation of metastases and response to treatment. We have demonstrated that tumor specific T cell responses occur in CRC patients and population of tumor antigen specific T cells are responsible for the infiltration in the tumors and for the effector functions observed in situ. Based on these observations we hypothesize that T cell responses against tumor antigens expressed on LT-TIC might trigger more efficient immune surveillance and correlate with improved CRC prognosis. Boosting pre-existing T cell responses against these antigens may improve the efficiency of tumor immunotherapy. The identification of such antigens will allow a selective therapeutic targeting of T cell responses against the populations of LT-TIC e.g. by vaccination or adoptive T cell therapy.

The activation and function of tumor specific effector T cells can be inhibited by regulatory T cells (Treg), thus underlying the important role they have in T cell based immune surveillance and control of CRC progression.

In order to lay the foundations for TIC-specific T cell based immunotherapy of CRC and for improved algorithms for prediction of CRC prognosis we are aiming to identify CRC progression-associated target antigens of spontaneous T cell and Treg responses. For this purpose we have established a whole proteome-based technology, which allowed us to identify in an unbiased manner new tumor associated target antigens of spontaneous T cell responses which are differentially expressed throughout the metastatic cascade, and for some of them we have already shown selective expression on the LT-TIC population. Furthermore we have observed that the T cell responses to these newly identified antigens were more abundant and of higher frequency than T cell responses against "canonical" tumor antigens described in the past. We have established a new method for systemic identification of target antigens triggering spontaneous Treg responses in CRC patients, which will help us to characterize the repertoire of major target antigens of tumor-specific regulatory T cells and thus will allow us to investigate their impact on the activity of tumor antigen reactive memory T cells.

We are currently working on expanding the gained information on LT-TIC associated CRC antigens and we will investigate the hypothesis that high T cell infiltrates in primary and metastatic CRC are associated with increased numbers of LT-TIC specific T cells. Their presence will be determined by utilizing HLA-multimers for selected TIC-specific antigens. Moreover we will use single cell T cell receptor (TCR)-CDR3 sequencing to identify and quantify the TIC specific TCRs. Using these two approaches we are aiming to build up a database of LT-TIC specific T cell numbers in situ and in the blood and bone marrow for consecutive correlation with patient prognosis.

Furthermore we will apply the knowledge obtained on LT-TIC associated antigens to generate LT-TIC specific CTL clones. Together with the SP2 partner we will use these clones alongside with CTL clones targeting "canonical" tumor antigens for treatment of NOD/Scid mice orthotopically transplanted with LT-TIC enriched tumor spheroids to test our hypothesis that only the LT-TIC specific CTL clones have the capability to reduce the metastatic potential and tumorigenicity of the xenotransplanted TIC spheroids and thus we will evaluate their therapeutic potential in vivo.

Team SP5

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