CTLA4 (CD152) has been in the centre of attention for its pivotal role in autoimmunity and cancer. Although not fully understood, CTLA4 with no doubt plays an important role in the maintenance of the immune response by its expression on activated and regulatory T cells. CTLA4 has many variants and polymorphic forms, some present in regulatory positions, some in 3' UTR and the most important one in the leader sequence (+49 A/G).CTL-associated antigen 4 (CTLA4) is a well-established immune checkpoint for antitumor immune responses. The protumorigenic function of CTLA4 is believed to be limited to T-cell inhibition by countering the activity of the T-cell costimulating receptor CD28.