A major focus of new treatment strategies is to enlist the aid of the immune system, particularly the development of prostate cancer vaccines. There has been a number of studies using dendritic cell based vaccines and the treatment has been well tolerated. Specific T-cell immune responses have been observed and occasional evidence for tumor regression. A reduction in serum prostate-specific antigen (PSA) has been observed as well. Lengthening the time-to-progression and delays in the onset of bone pain have been observed in subsets of patients with HRPC.