Trillium Therapeutics Inc. is a clinical stage immuno-oncology company developing innovative therapies for the treatment of cancer. Trillium has two SIRPαFc fusion proteins, TTI-621 and TTI-622, in clinical development. Both consist of the extracellular CD47-binding domain of human signal regulatory protein alpha, or SIRPα, linked to an Fc region of a human immunoglobulin (IgG). They are designed to activate the anti-tumor activity of macrophages by blocking the inhibitory (“don’t eat me”) signal from CD47 and simultaneously delivering a pro-phagocytic (“eat”) signal through the Fc region. The two molecules differ in the identity of the Fc region; TTI-621 delivers a strong pro-phagocytic signal through its IgG1 Fc, whereas TTI-622 delivers a more modest pro-phagocytic signal through its IgG4 Fc region. Both TTI-621 and TTI-622 are currently in phase 1 dose escalation studies.