753 An open-label, phase 1a/b study of AB248, a CD8+ selective IL-2 mutein fusion protein, alone or in combination with pembrolizumab in patients with advanced solid tumors by Costantine Albany, Andrea Pirzkall, Michael Chisamore, Jennifer Visich, Elizabeth I Buchbinder, Xiaohan Liu, David R Spigel, Kelly D Moynihan, Christopher DelNagro, Matt Axt, Mark Sayles