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Patient characteristics of the whole breast cancer cohort used for CX3CL1 expression analysis (n=250)

CX3CL1 mRNA expression is associated with improved recurrence-free, distant-metastasis free, and overall survival in human breast cancer.

Figure S2. Impact of Cx3cl1 overexpression on tumor cell growth in vitro, Cx3cl1 serum concentrations, and myeloid cell tumor infiltration in the 4T1 breast cancer model.

Impact of Cx3cl1 overexpression in the HT-29 xenograft model.

Impact of soluble CX3CL1 and ADAM17 inhibition by TAPI-2 on NK cell-mediated tumor cell lysis in vitro.

Impact of Cx3cl1 overexpression in the MDA-MB 453 xenograft model.

Modulation of CXCL10 secretion from human HER2-positive cancer cell lines upon stimulation with TNF-α and TAPI-2.

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.

CX3CL1 overexpression in HER2 overexpressing human breast cancer.

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.

A crucial mode of action of trastuzumab is the labeling of HER2-positive (HER2