The placebo treatment involved the identical preparation of the APCs, but after isolation they were immediately infused back into the patient. They were not pulsed with the gmcsf-pap antigen.
So any "placebo effect" would likely have to come from a systematic aspect of the prepration (handling, culturing ex vivo).
What is scientifically more interesting to me is how APCs pulsed with gmcsf would have performed versus gmcsf-pap... but that's just a curiosity angle.