The DNA damage-dependent expression of ligands for cytotoxic NK-cell receptors: Impact of the DNA damage response on inside out signaling in CLL

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Aim of this project is to elucidate the role of genetic lesions and the cellular DNA damage response for the immune escape mechanisms in CLL. Normal cells respond to DNA damage in two ways. One response includes cell cycle arrest followed by DNA repair or, after severe damage, by apoptosis. The other response aims at signaling the comprised state of the dangerous cells to the innate immune system. This communication occurs through the induced expression of cellular ligands for activating immune receptors such as NKG2D, NKp30 and NKp46.The expression of ligands or "danger molecules" on released vesicles (exosomes) and on the surface of affected cells allows recognition and killing of the damaged cell by NK cells. Recently, we and others observed that the activity of NK cells from CLL patients is impaired and serum levels for soluble ligands engaging NKG2D and NKp30 are significantly elevated in comparison to healthy donors. Soluble ligands cause a general NK cell inhibition and high serum levels correlate with a poor prognosis indicating that NK cells are critically involved in immunosurveillance of CLL. The molecular mechanisms directing the inducible expression of ligands for NKG2D are not fully defined but known to be ATM/ATR-dependent. To uncover the impact of the DDR for ligand upregulation in CLL we will analyze the proposed ATM-dependent induction of the ligands using RNAi technology and established knockout mice. Specifically, we will cross the TCL1 transgenic mouse with ATM, TP53 and CBP/P300 knockouts. These compound mutant mice will be compared to TCL1 transgenic counterparts to test the hypothesis that components of the DDR contribute to the inducible ligand expression and to the generation of an anti-tumor immune response. Based on previous data we expect that loss of ATM, p53 and CBP/p300 in the CLL mouse model is essential to sensitize CLL cells to the NK cell attack and promotes tumor rejection by the innate immune system.Finally we plan to restore NK cell function by a rescue of ligand expression on malignant CLL cells to prove that NK cell inhibition results from the impaired expression of NKR-ligands. We will design bispecific fusion proteins (immunoligands) of ligands for NKG2D fused to an antibody fragment detecting the B-CLL-specific antigen ROR1. The construct is used to decorate ROR1-expressing CLL cells with NKG2D ligands rendering the cells more susceptible to NK cell-mediated killing. The effect of the restored ligand expression/decoration will be evaluated in the CLL mouse models and also ex vivo using NK cells derived from healthy donors or CLL patients. We aim to derive novel, genetically-informed combination therapies consisting of frontline DNA-damaging agents with innovative approaches that harness NK cells for cancer therapy.