The vaccine has two parts, one to prime the immune system and one to boost it.

BBC: Vaccine

Medicare will not pay for all possible uses of Provenge, a cell therapy meant to prime the immune system to fight tumors.

FORBES: Medicare To Pay For Dendreon Treatment

The move shocked investors, who had already been bidding down Dendreon shares because of worries that the company will face difficulties in getting insurers and the government to pay for Provenge, which is designed to prime the immune system to attack cancer cells.

FORBES: Why Medicare Is Reviewing Provenge