Dendritic cell vaccination in combination with anti-CD25 monoclonal antibody treatment: A phase I/II study in metastatic melanoma patients

Abstract

Purpose: The success of cancer immunotherapy depends on the balance between effector T cells and suppressive immune regulatory mechanisms within the tumor microenvironment. In this study we investigated whether transient monoclonal antibody-mediated depletion of CD25high regulatory T cells (Treg) is capable of enhancing the immunostimulatory efficacy of dendritic cell vaccines. Experimental Design: Thirty HLA-A2.1+ metastatic melanoma patients were vaccinated with mature dendritic cells pulsed with tumor peptide and keyhole limpet hemocyanin (KLH). Half of the patients were pretreated with daclizumab, a humanized antibody against the interleukin-2 (IL-2) receptor α-chain (CD25), either four or eight days before dendritic cell vaccinations. Clinical and immunologic parameters were determined. Results: Daclizumab efficiently depleted all CD25high immune cells, including CD4+FoxP3+CD25high cells, from the peripheral blood within four days of administration. Thirty days after administration, daclizumab was cleared from the circulation and all CD25+ cells reappeared. The presence of daclizumab during dendritic cell vaccinations prevented the induction of specific antibodies in vivo but not the presence of antigen-specific T cells. Daclizumab, however, did prevent these CD25 + T cells from acquiring effector functions. Consequently, significantly less patients pretreated with daclizumab developed functional, vaccine-specific effector T cells and antibodies compared with controls. Daclizumab pretreatment had no significant effect on progression-free survival compared with the control group. Conclusions: Although daclizumab depleted the CD4+FoxP3+CD25high Tregs from the peripheral circulation, it did not enhance the efficacy of the dendritic cell vaccine. Residual daclizumab functionally suppressed de novo induced CD25+ effector cells during dendritic cell vaccinations. Our results indicate that for immunotherapeutic benefit of transient Treg depletion, timing and dosing as well as Treg specificity are extremely important. ©2010 AACR.