698 PD-L1 targeted CD28 costimulatory bispecific antibodies enhance T cell activation in solid tumors by Jing Qi, Gregory Moore, Michael Hedvat, Christine Bonzon, Rumana Rashid, Umesh Muchhal, John Desjarlais, Irene Leung, Veronica Zeng, Juan Diaz, Kendra Avery, Charles Bakhit, Matthew Dragovich, Ruschelle Love, Michael Hackett, Norman Barlow