CD69 and neoplasm: We have previously reported that highly proliferative, CD69+ Treg demonstrate superior suppressive capacity37; a finding which is in line with studies demonstrating that the enhanced suppressive function of CD69+ Treg significantly increases their ability to control autoimmune disease.39 However, while the proportion of Treg expressing CD69 is significantly lower in regressor compared with non-regressor 4T1 tumors, and despite previous reports,35 administration of CD69-specific antibodies in vivo did not improve tumor control in the 4T1 model.