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Winger Campbell-Ryce, 28, has moved back to east London from Bristol City for the rest of the season having had a spell on loan with the O's eight years ago.
Midfielder Reed, 20, has signed a similar deal from Sunderland and both players could be added to the squad to face Tranmere on Saturday.
Manager Russell Slade told the club website: "There was competition for Jamal so we are delighted he has decided to join us.
"Adam had a very successful spell with Brentford last season. He's technically very sound and has a combative side to his game too, so he will be a big asset to us."
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