Table 1.

Opposite functions of pDCs in tumors.

Function in Tumors	Phenotypes and Mechanisms	References
Negative role in anti-tumor immune responses	Accumulation of pDCs correlated with poor diagnosis in multiple tumors. Potential mechanisms include induction of regulatory T cells through ICOSL- or IDO-dependent pathways.	[29,30,74,75,76,77,78]
Positive role in anti-tumor immunity	Tumor-infiltrated pDCs correlate with survival in human colon cancer, and activation pDCs lead to enhance anti-tumor immunity. Possible mechanisms include: IFN-I-dependent enhancement of function of NK cells and T cells, as well as cross-priming by cDCs; enhanced direct cross-priming. However, the exact contributions of IFN-I versus pDC-mediated cross-priming remain poorly understood.	[64,79,80,81,82,83,84,85,86]
Tumoricidal activity	Activated pDCs directly kill tumor cells through TRAIL- and Granzyme B-dependent mechanisms leading to tumor regression.	[95,96,97,98]