TY  - GEN
AV  - public
TI  - Identification of novel tumor-associated immune modulators using a high-throughput RNAi screen
N2  - Immune surveillance by T cells is an important component of body?s defense against infection and disease, whereas the peripheral immune tolerance is important for defense against self-reactive T cells. The fine balance between the two is skewed in cancer, whereby the tumors exploit the immune tolerance mechanisms to escape recognition and elimination by the cytotoxic T lymphocytes (CTLs). One of the major routes of immune resistance of tumor cells is mediated by cell surface bound ligands that engage immune-inhibitory receptors on T cells. Targeting these immune-checkpoint ligands that inhibit immune rejection, e.g. via blocking antibodies, can restore immune surveillance and increase the efficacy of cancer immunotherapy. However, only a few such targets have been identified so far.

The aim of this thesis was to establish a high-throughput screening assay that enables a rapid and comprehensive identification of cell surface genes with immune modulatory function in selected tumors. To this end, a tumor cell-T cell co-culture assay was established which combines siRNA-based gene knockdown with a luciferase-based assessment of T cell-mediated tumor cell killing. Applied to three independent parallel screens, this study uncovered a repertoire of novel and robust immune modulatory ligands on breast cancer cells that are also abundantly expressed by other cancer types. Amongst them, CCR9 was functionally validated as a strong inhibitor of T cell function and suppressor of T cell reactivity against breast cancer, malignant melanoma and pancreatic cancer. Knockdown of CCR9 resulted in increased tumor susceptibility towards immune lysis by antigen-experienced T cells along with the increased production of effector cytokines and cytolytic enzymes. CCR9-induced gene expression changes in the encountering T cells were consistent with an enhanced effector T cell phenotype. Mechanistically, CCR9 regulated T cell effector function through differential activation of the STAT signaling pathways, thereby representing a unique example of an alternative, TCR-independent route for effective immune suppression induced by a cell surface molecule.

Additionally, the in vivo relevance of targeting CCR9 for adoptive cancer immunotherapy was explored in this study.
Taken together, this study describes a rapid, high-throughput, siRNA-based screening approach that allows a comprehensive identification of immune-modulatory genes which, as an entity, represents the ?immune modulatome? of cancer. Screening additional tumor types for their immune modulatory signatures would help in uncovering additional targets for therapeutic inhibition.
A1  - Khandelwal, Nisit
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/17429/
Y1  - 2014///
ID  - heidok17429
ER  -