In Paul Manafort's Virginia case, prosecutors have asked the judge to seal forthcoming motions asking for "use immunity" (a type of limited immunity) for five potential trial witnesses who invoked 5th Amendment right against self-incrimination scribd.com/document/38404… 
These potential witnesses in Manafort's trial "have not been identified publicly with the case," the government writes, so it wants the "use immunity" motions sealed until these people actually testify
Per 18 U.S. Code § 6002, being compelled to testify with "use immunity" means a person's testimony can't be used against them in any criminal case, except if they're prosecuted for perjury, giving a false statement, or otherwise failing to comply with the order to testify
