The Last of Us is what it is—a Children of Men-esque story about the zombie apocalypse starring one man and his quest to aid a young girl immune to the effects of the zombie virus that gnaws at the flesh of humanity.
Before the game became what it is today, the game went through many different iterations, one of which was as a game called "Mankind", where the only humans afflicted by the flesh-eating zombie virus spread by cordyceps fungi were women. Except for Ellie, that is. Unlike every other woman in the game, Ellie was immune to the virus. The idea was, as you can imagine, arguably misogynistic, which lead its developers to rethink the whole concept of the game.
As Jonathan Holmes notes on Destructoid, a concept of a game in which you killed only women would have made Resident Evil 5's early builds in which all the zombies were black people pretty tame by comparison.
Source: "The Power of Failure: Making The Last of Us" on The Verge