Table 1.

Obstacles to protective immune reactivity to tumor

Direct immune inhibition by tumor:	References
PGE2	[63, 84]
TGF-β	[44, 59, 84]
IL-6	[48]
IL-10	[68]
Indirect immune inhibition	References
Blockage of dendritic cell maturation	[3, 24, 56]
Skewing toward Th2 reactivity	[55, 64, 76]
Th2-skewing monocytes / dendritic cells	[34, 91]
Mobilization of CD34+ precursor cells	[57, 74, 83, 85]