Blockade of DC-SIGNthorn Tumor-Associated Macrophages Reactivates Antitumor Immunity and Improves Immunotherapy in Muscle-Invasive Bladder Cancer

Tumor-associated macrophages (TAM) play an indispensable role in the modulation of the cancer immune microenvironment. Despite the fact that TAMs may exert both antitumor and protumor activities, the molecular mechanisms involved remain poorly understood. Here, we characterized a subpopulation of TAMs expressing dendritic cell-specific C-type lectin (DC-SIGN) and investigated its relevance to the prognosis and immune microenvironment of muscle-invasive bladder cancer (MIBC). DC-SIGN(+) TAMs were abundant in a significant proportion of human MIBC specimens. High levels of DC-SIGN(+) TAMs were associated with dismal prognosis and unresponsiveness to adjuvant chemotherapy in MIBC. Notably, multiple anti-inflammatory cytokines were enriched in DC-SIGN(+) TAMs. RNA-seq analysis revealed that multiple M2-like signaling pathways were significantly upregulated in DC-SIGN(+) TAMs. High infiltration of DC-SIGN(+) TAMs was associated with CD8(+) T-cell tolerance in MIBC. Moreover, abrogating DC-SIGN function using a neutralizing antibody led to impaired expression of anti-inflammatory cytokines and augmented PD-1 inhibitor pembrolizumab-mediated cytotoxic effects of CD8(+) T cells toward MIBC cells. In summary, these results suggest that DC-SIGN(+) TAM infiltration is closely linked to a protumor immune microenvironment and may serve as a promising therapeutic target in the immunotherapy of MIBC. Significance: DC-SIGN(+) TAMs have an immunosuppressive and tumor-promoting function and may serve as a prognostic indicator and therapeutic target in MIBC.