The figure illustrates that there are circulating T cells that can induce GVL (in blue) and GVHD (in yellow) which are both constrained by CTLA-4.  With the introduction of ipilumumab, a CTLA-4 inhibitor, the authors showed evidence of 3 types of responses. Some patients had robust AML response with expansion of CD8 T cells (blue) and induction of epitope spreading (red and green cells in upper right), and/or GVHD with expansion of these T cells (yellow cells that attack healthy tissues [liver shown], in middle right section), or no response with PD-1 positive T cells present (lower right). Professional illustration by Somersault18:24.