Role and therapeutic modulation of the RANK-RANKL molecule system in the NK cell immune surveillance of malignant hematopoietic diseases

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NK cells play an important role in the immunosurveillane of tumors and, due to their ability to potently mediate antibody-dependent cellular cytotoxicity (ADCC), largely contribute to the clinical efficacy of therapeutic antibodies like Rituximab. Accordingly, multiple strategies presently aim to increase the potential of antibodies to induce ADCC of NK cells against tumor cells. Both the direct anti-tumor reactivity and ADCC of NK cells are influenced by the various ligands for receptors expressed by NK cells, and neutralization of inhibitory molecules thus serves well to increase constitutive and therapeutically-induced NK cell anti-tumor immunity. In the last funding period we demonstrated that the TNFR family member RANK (mainly known for its role in bone metabolism) is expressed by NK cells while its counterpart RANKL is expressed by malignant hematopoietic cells. We found that RANKL is capable to transduce signals into the ligand-expressing malignant cells (reverse signaling) which lead to release of cytokines that act as autocrine/paracrine growth and survival factors in the malignant diseases. In addition, the factors released upon RANKL signaling impaired the anti-tumor reactivity of NK cells and induced RANK expression on NK cells, The latter was further found to transduce signals into NK cells that impair their anti-tumor reactivity thereby facilitating immune escape of the RANKL-expressing malignant cells. Based on these findings we developed Fc-engineered RANK-Ig fusion proteins that are capable to neutralize the detrimental function of RANKL on anti-tumor immunity while at the same time potently stimulating NK cell ADCC by targeting of the malignant cells.In the second funding period we aim to elucidate the signaling pathways that mediate the induction of cytokine release and metabolic activity in malignant hematopoietic cells following RANKL signaling. Moreover, we aim to determine the molecular mechanisms by which RANK mediates the observed differential inhibition of NK cell cytotoxicity and cytokine production. Based on our findings regarding the differential susceptibility of human and murine NK cells for ADCC-induction observed in syngeneic mouse tumor models, the focus of the upcoming studies is to establish suitable humanized mouse models to further preclinically characterize our Fc-engineered RANK-Ig fusion proteins. Such models are envisaged to finally validate our strategy to dually reinforce NK reactivity against malignant hematopoietic cells by neutralizing the inhibitory effects of RANKL and simultaneously targeting the RANKL-expressing malignant cells for NK cells ADCC. After the preclinical validation, we envisage our constructs to be produced in an University-owned production unit according to GMP guidelines with the aim to enable rapid clinical testing in cancer patients.