Phase I: intended to determine a loose range of safe doses for patients. Subjects enrolled in Phase I clinical trials are informed that it is unlikely for the drug to benefit them. Normally, subjects are healthy volunteers that are put into buckets of different doses to determine the Maximal Tolerated Dose (MTD).
Phase II: Intended to characterize the efficacy of the drug (on a small scale). There are several methods of conducting Phase II trials; some are simply longitudinal case studies, and others are structured more like randomized controlled trials (the type of clinical trial generally considered the most valid [i.e. maintains the highest internal validity]).
Phase III: Randomized controlled trial. Patients are randomized into the test group vs. placebo/current standard of care to determine whether the new drug is effective. The best RCTs are double-blinded though this is not always the case.
This drug, a monoclonal antibody intended to alter the immune response, was halted in the Phase I clinical trial.