APL-509 is a novel IgG1 humanized monoclonal antibody against the cytotoxic T-lymphocyte associated protein 4 (CTLA-4) receptor.

CTLA-4 is a protein expressed exclusively on T cells (a type of immune cell) that helps the body’s immune responses stay in check. Some anticancer drugs, called immune checkpoint inhibitors, are used to block CTLA-4. When this protein is blocked, the “brakes” on the immune system are released and the ability of T cells to kill cancer cells is increased.

Apollomics retains worldwide rights to APL-509.