CD80 and neoplasm: For example, tumor cells can express immune checkpoint molecules, sending inhibitory signals that counteract co-stimulatory signals and cause T cell anergy or apoptosis.171,172 Additionally, tumors can modulate the expression of co-stimulatory molecules on APCs by downregulating CD80 and CD86 or upregulating inhibitory receptors, thereby creating an immunosuppressive environment that impairs T cell recognition and activation.169,173 This ability of tumors to manipulate immune responses underscores their capacity to hinder effective anti-tumor immunity.