Fig 1.

Antigen presenting cells such as dendritic cells can process antigens such as peptides or whole tumor cells, can become infected by viral vectors which then express tumor associated antigens for presentation, or can be ex vivo pulsed with peptides then injected. These antigen presenting cells present to the T-cell causing activation of the T-cell. Upon activation, CTLA4 is upregulated and inhibits activation of the T-cell. Antibodies to CTLA4 can block the inhibitory signals and cause prolonged activation. (Figure courtesy of NIH Medical Arts.)