These Tregs, through their high expression of CTLA-4, not only suppress CTL activity but also modulate the function of APCs, reduce their ability to deliver antigens, and generate the essential co-stimulatory signals for T cell activation.296,297 This creates a feedback loop in which the immunosuppressive environment is maintained and even enhanced, allowing the tumor to grow and escape immune destruction. Here, CTLA4 is linked to neoplasm.