Augmentation of Dendritic Cell-Based Vaccines in Melanoma Patients by Depletion of Regulatory T Cells in Stage IV Melanoma Patients

Dendritic cells (DC) are the professional antigen presenting cells of the immune system. Multiple distinct DC lineage's exist and it is now well appreciated that the DC subset and the maturation stage of the DC determines the type of immune response, ranging from a TH1 or TH2 response to immune tolerance. The extremely potent capacity of mature DC to initiate immune responses can be exploited to fight infectious diseases and cancer. Others and we are currently using tumor antigen loaded mature DC in clinical vaccination studies against cancer, and clinical as well as immunological responses have been observed.

Exciting new insights accompany the revival of suppressor T cells, now referred to as regulatory T cells (Treg), and implicate that also Treg play a key role in the control of immunity. Treg constitute a sub-population of CD4+ T cells constitutively expressing the IL-2R alpha-chain (CD25). Treg show remarkably suppressive activities on different components of the immune system, including T lymphocytes and dendritic cells, suggesting they act both at the initiation phase (DC) and at the effector phase (activated T cells) of the immune response. Interestingly, temporal depletion of Treg has been shown to enhance anti-tumor immune responses and in case of prolonged absence of Treg even autoimmunity. Furthermore, data in mouse tumor models indicate that temporal depletion of Treg also results in improved vaccine efficiency in the therapeutic setting, e.g. in mice with a pre-existing tumor. These data imply that in tumor bearing patients depletion of Treg prior to vaccination will improve vaccine efficacy.

In this study we investigate the effect of regulatory T cell (Treg) depletion on the efficacy of DC-based anti-tumor vaccines in a clinical study using melanoma associated antigens tyrosinase and gp100-loaded DC and a depleting anti-CD25 mononuclear antibody (Daclizumab). Our primary objective in this study is the induction of an effective anti-tumor immune response. Our secondary objective is the induction of a clinical response.