Is there any case law where a witness was called at trial even though the prosecutor asserted privilege?

6 United States v. Coppola, 479 F.2d 1153 (10th Cir.1973), cited by defendants in their reply brief, is inapposite. There, the court reversed a conviction where a witness was called at trial even though the prosecutor knew he would assert the privilege. The prosecutor asked twenty questions which the witness refused to answer and which implied the witness's knowledge of facts which he really did not know. Defendants here do not make this contention about the grand jury questions. Moreover, the concerns animating appellate scrutiny of evidentiary rulings at trial, where the issues are honed to a determination of guilt or innocence, differ from those governing judicial review of prosecutorial conduct before the grand jury.