Dreyer, T. F., Kuhn, S., Stange, C., Heithorst, N., Schilling, D., Jelsma, J., Sievert, W., Seitz, S., Stangl, S., Hapfelmeier, A., Noske, A., Wege, A. K., Weichert, W., Ruland, J., Schmitt, M., Dorn, J., Kiechle, M., Reuning, U., Magdolen, V., Multhoff, G., Bronger, H. (2021). Cancer Immunol Res 9, 779-789.
A crucial mode of action of trastuzumab is the labeling of HER2-positive (HER2+) tumor cells for the eradication by natural killer (NK) cells, a process called antibody-dependent cellular cytotoxicity (ADCC). However, despite widespread HER2 expression among cancer entities, only a fraction, with robust HER2 overexpression, benefits from trastuzumab therapy. ADCC requires both sufficient lymphocytic infiltration and close binding of the immune cells to the antibody-tagged tumor cells. We hypothesized that the chemokine CX3CL1 could improve both processes, as it is synthesized as a membrane-bound, adhesive form that is eventually cleaved into a soluble, chemotactic protein. Here, we show that CX3CL1 overexpression is a positive prognostic marker in breast cancer. CX3CL1 overexpression attracted tumor-suppressive lymphocytes, including NK cells, and inhibited tumor growth and lung metastasis in the syngeneic 4T1 breast cancer mouse model. In HER2+ SKBR3, MDA-MB-453, and HT-29 tumor cells, CX3CL1 overexpression increased NK cell–mediated cytotoxicity in vitro and acted synergistically with trastuzumab. Even though CX3CL1 did not further improve trastuzumab efficacy in vivo in the trastuzumab-sensitive MDA-MB-453 model, it compensated for NK-cell depletion and prolonged survival. In the HER2 low–expressing HT-29 model, however, CX3CL1 overexpression not only prolonged survival time but also overcame trastuzumab resistance in a partly NK cell–dependent manner. Taken together, these findings identify CX3CL1 as a feasible pharmacologic target to enable trastuzumab therapy in HER2 low–expressing cancers and render it a potential predictive biomarker to determine therapy responders.