PRF1 and anaplastic large cell lymphoma: The resemblance of ALCL to an activated mature T cell, due to the expression of activated T-cell proteins such as CD30, granzyme B and perforin [88], has led most work to concentrate on mature subsets as the ‘normal counterpart’ of ALCL, with suggestions including IL-17-producing Th17 cells [89] or Foxp3 expressing T regs [71,90].