Keeping up a masquerade for the sake of a plot twist

So in my cyperpunk/biopunk story the main character is an artificial/genetically engineered human who has escaped from the lab he was..um grown. This was a few years before the story begins and is largely hidden from the reader until the halfway mark where it's revealed in a kind of twist.

The story begins with him in a team of misfits who are out to take down the corporation that built him (cliched I know, but this is largely simplified here).

The problem is that I dunno why he would keep this a secret from the fellow team mates. I mean maybe he wants to hide it so that the MegaCorp doesn't figure it out and start sending their best to hunt him but early on (like second chapter) another of the genetically engineered people is helped to escape from a lab and join the team.

This person doesn't hide it, and the MegaCorp tracks this other character down anyway by the end of the first arc so I don't see why my main character should be hiding it. The more I try to keep up the masquerade the more flimsy the premise sounds.

Is this really worth the plot twist?

You could always have him try really hard to be 'normal' but litter clues and Suspiciously Specific Denials through out and leave it as more an on going question than a twist out of nowhere.

The guy could always be in denial about his true nature (especially if there's some major drawback).

Society's disaproval of the idea of genetic whatsit-making (if they disaprove?) might lead your character to believe that society would be similarly hostile towards the results.

This is not a Masquerade (organized, large-scale deception), it's more of a single character not wanting to reveal his background. Which is perfectly plausible. Maybe he is paranoid, maybe there is a prejudice towards tank-bred humans, maybe he's just embarrassed about his own nature. Maybe there is a girl in the team whom he secretly likes but who has said prejudice against tank-breds and he doesn't want her to know about his origin. And he hides it from everyone else to minimize the risk of her learning about it. :)

And it's not much a Plot Twist if the audience knows about it before the reveal.

The obvious reason, it seems to me, is that the rest of the team would suspect him of being a spy for the corporation. He wouldn't necessarily be a conscious, willing spy, either. They built him, they could have put in any number of monitoring devices. You might include someone like that as an antagonist to make the point before revealing that one of the protagonists is also like that. Whether his monitoring devices are still active could go either way.

Yeah, Masquerade's the wrong word. And it's hidden from the audience, the plot twist is mainly for them.

Only 2 people in the team of 7ish know about it.

I guess this is definitely a case where I can justify it. I was just worried that it'd be a case of Poor Communication Kills and I was just hiding it from the audience because it'd be more shocking that way.

I'll have to rewrite his character to work in the paranoia and embarassment and stuff but that just makes him more interesting as a character I think. Thanks heaps guys.