Neoadjuvant chemotherapy induces IL-34 signaling and promotes chemoresistance via tumor-associated macrophage polarization in esophageal squamous cell carcinoma.

The tumor microenvironment (TME) plays a key role in the efficacy of neoadjuvant chemotherapy (NAC) in solid tumors including esophageal squamous cell carcinoma (ESCC). However, the TME profile of ESCC treated with NAC is not fully understood. In this study, we investigated the effect of NAC on the TME especially tumor-associated macrophages (TAMs), the important immune-suppressive components of the TME, in ESCC. We quantified the expression of CD163, a crucial marker of TAM, in pre-therapeutic biopsy and surgically resected ESCC specimens from patients who received NAC (n=33) or did not receive NAC (n=12). We found that NAC dramatically increased the expression of CD163 on TAMs in ESCC. Colony-stimulating factor-1 (CSF-1) and interleukin-34 (IL-34) are crucial cytokines that recruit monocytes into tumor sites and differentiate them into TAMs. Interestingly, NAC significantly up-regulated the expression of IL-34 but not CSF-1 on tumor cells, and the frequencies of CD163+ TAMs were significantly correlated with IL-34 expression in ESCC after NAC. The expression of IL-34 in NAC-nonresponsive patients was significantly higher than that in NAC-responsive patients, and patients with IL-34-high ESCC exhibited worse prognosis as compared with patients with IL-34-low ESCC. We also demonstrated that 5-fluorouracil (5-FU)/cisplatin (CDDP) preferentially increased mRNA expression of IL-34 on human ESCC cell lines. Human peripheral blood monocytes co-cultured with ESCC cells treated with 5-FU/CDDP increased the expression of CD163, which was attenuated by the treatment with CSF-1R inhibitors. These data suggest that IL-34 expression by NAC shifts the TME toward CD163+ TAMs-rich immunosuppressive and chemo-insensitive microenvironment in ESCC. Implications: The blockade of IL-34 signaling may offer a novel therapeutic strategy against chemoresistance in ESCC by inhibiting M2-TAM polarization.