It has been rumored repeatedly that Naughty Dog have begun work a sequel to The Last of Us. But the producer Neil Druckmann says this isn't true, even though he admits that the studio has been brainstorming new ideas for the game, one of the ideas involves using a brand new cast of characters:
"We were brainstorming ideas for The Last Of Us 2 with new characters; ideas for Joel and Ellie; ideas for a sci-fi game; ideas for a fantasy game, and building prototypes for each one of those ideas. So, I guess Nolan North was kind of right in that we were working on stuff, but we don't know what we're doing next and we won't know until probably a few months after we finish Uncharted 4."
Thanks, Official PlayStation Magazine (via Games Radar).