Innate and adaptive immunity play important roles in immunosurveillance and tumor destruction.
However increasing evidence suggests that tumor-infiltrating immune cells may have a dual
function: inhibiting or promoting tumor growth and progression. Although regulatory T (Treg)
cells induce immune tolerance by suppressing host immune responses against self- or non
self-antigens thus playing critical roles in preventing autoimmune diseases they might
inhibit antitumor immunity and promote tumor growth. Recent studies demonstrate that elevated
proportions of Treg cells are present in various types of cancers and suppress antitumor
immunity. Furthermore tumor-specific Treg cells can inhibit immune responses only when they
are exposed to antigens presented by tumor cells. Therefore Treg cells at tumor sites have
detrimental effects on immunotherapy directed to cancer.
