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Table 1 Major elements influencing tumor escape from adaptive immune recognition and destruction

From: Optimal MHC-II-restricted tumor antigen presentation to CD4+ T helper cells: the key issue for development of anti-tumor vaccines

1. Tumor-related
 - Insufficient tumor antigen expression
 - Loss of MHC class I expression by tumor
 - Lack of MHC class II expression by tumor
 - Production of immunosuppressive factors for T and B cells
2. Immune cells-related
 - Insufficient lymphocyte penetration into the tumor tissue
 - Lack of T cell help
   Insufficient MHC-II-restricted antigen presentation
   Insufficient TH triggering
 - Lack or insufficient CTL activity
   Insufficient MHC-I-restricted antigen presentation
   Insufficient support by TH cells
   Scarce lytic activity
 - Extrinsic functional blocking of T cells
   Regulatory and suppressor cells
   Inhibitory cytokines