Who could grant immunity to Comey? Mueller can’t, he’s investigating Russia collusion. He is not involved in Hillary’s e-mail investigation.
Immunity is not a pardon. Immunity would only cover testimony or evidence provided under grant of immunity. If the government finds evidence from other sources, then they can certainly prosecute.
Now, regarding Mueller’s Russia collusion investigation...Comey most likely testified to Mueller under grant of immunity which may protect Comey from being prosecuted for leaking his classified notes. However, Comey’s book tour might be his downfall. Also, in his testimony to the Senate (I believe), Comey admitted to the leaks. His testimony would be public record.
So, bottom line is I believe Comey & DOJ/FBI personnel involved in Hillary’s e-mail investigation don’t have immunity.
That makes sense—thanks.