15353-j-veluchamy

4 NK cell ADCC enhances treatment efficacy in colorectal cancer | 97 Introduction Epidermal Growth Factor Receptor (EGFR) is expressed on cell surfaces in normal tissues and binding to its ligands activates two important pathways, the RAS-RAF-MAPK and PI3K-PTEN- AKT pathway, which both control cell proliferation, survival and motility 1 . Dysregulation of the EGFR signaling cascade can result in rapid cell division ultimately supporting tumor growth. Several solid tumors show elevated EGFR expression levels, which were shown to be related to poor prognosis 2 . Cetuximab (IgG 1 chimeric) and panitumumab (IgG 2 fully humanized) are clinically approved anti-EGFR mAbs that bind to the extracellular domain of EGFR thereby blocking EGFR dimerization, resulting in apoptosis and preventing tumor growth 3 . Regrettably, mutations in the EGFR downstream signaling pathway (e.g. RAS mutations), can lead to constitutive RAS signaling, resulting in unresponsiveness to anti-EGFR therapy 4-6 . The fact that in about 40% of patients with metastatic colorectal cancer (mCRC) mutations in the RAS gene can be observed, means that anti-EGFR therapy is applicable in only half of the mCRC patients 7 . Therefore, several approaches have been proposed and are currently tested to increase the efficacy of anti-EGFR mAb therapy by overcoming the inhibitory effect of RAS mutation, e.g. by immune effector cell-mediated antibody dependent cell- mediated cytotoxicity (ADCC) 8,9 . Several immune effector cells in the body have the ability to recognize target molecules on the tumor cell surface, like EGFR on CRC cells, through their FcR-mediated binding of antibodies directed against these targets, leading to potent antitumor immunity. However, due to cytotoxic treatment regimens in solid tumor patients, the immune system can be temporarily dysfunctional, signified by a decrease in immune effector cell subsets 10,11 . This limitation may be overcome by cellular immunotherapy, such as the adoptive transfer of activated cytolytic Natural Killer (NK) cells. NK cells are part of the innate immune defense, with the ability to kill tumor cells. NK cells comprise of two subsets, fromwhich the majority (about 90%) are phenotypically CD56 dim CD16 bright and exert mainly cytolytic functions, whereas the other subset of CD56 bright CD16 dim NK cells primarily exert immune regulatory functions 12 . CD16a (FcγRIIIa), a low affinity Fc receptor, preferably binds to IgG 1 antibodies and can actively mediate ADCC 13,14 . This study aims to prove that NK cells are able to induce strong ADCC responses in combination with therapeutic EGFR-targeting mAbs and can thereby overcome the potential limitations of stand-alone anti-EGFR therapy. Therefore, activated PBNK cells were combined with cetuximab or panitumumab to test their ADCC efficacy on EGFR + / - , RAS wt / mut , BRAF mut cell lines and primary tumor cells from patients with CRC.