How have the courts treated immunized testimony in the context of a criminal case?

At first glance, it would seem that where the indictment is returned by the same grand jury which heard the defendant's immunized testimony, it would be virtually impossible for the Government to show that it had an independent source for the indictment's evidentiary base as "[d]espite any instructions from the judge, it would be well nigh impossible for the grand jurors to put [the immunized witness's] answers out of their minds, cf. Bruton v. United States, 391 U.S. 123, 88 S.Ct. 1620, 20 L.Ed.2d 476

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