title: Single dose denileukin diftitox does not enhance vaccine-induced T cell responses or effectively deplete Tregs in advanced melanoma: immune monitoring and clinical results of a randomized phase II trial.
abstract: BACKGROUND
  Depletion of CD25(+) Tregs improves anti-tumor immunity in preclinical models. Denileukin diftitox is a recombinant fusion protein of human IL-2 and diptheria toxin fragment that also can kill CD25(+) T cells. Prior clinical trials of denileukin diftitox suggested reduction of FoxP3(+) Tregs and some clinical responses.
  
  
  METHODS
  To investigate the immunologic effects of denileukin difitox on vaccine-specific immune responses in melanoma, a randomized clinical trial of single dose denileukin diftitox prior to vaccination versus vaccination alone in subjects with HLA-A2(+) metastatic melanoma was performed. Treatment included randomization to a 4-peptide vaccine (Melan-A, gp100, MAGE3 and NA17 with GM-CSF emulsified in Montanide) alone or after single dose of denileukin diftitox (18 mcg/kg). Vaccine was given every 2 weeks for 3 doses and, absent clinical progression, continued every 2 weeks. Blood and tumor biopsies were obtained pretreatment and after 3 vaccinations for immunologic assessments.
  
  
  RESULTS
  In 17 treated subjects there were no drug-related G3-4 adverse events. One partial response and 8 stable disease were observed in 9 subjects (4 DD: 5 vaccine only) with no impact of denileukin diftitox on time to progression. Total peripheral Tregs were not significantly altered, and in 1 patient biopsy intra-tumoral FoxP3 transcripts were not reduced following denileukin diftitox. ELISA for IL2R-α demonstrated no impact on outcomes by soluble CD25 level. Immune monitoring suggested the development of modest vaccine-specific CD8(+) T cell responses in the control group, however immunization efficacy was actually reduced in the denileukin diftitox group.
  
  
  CONCLUSIONS
  Our results indicate that denileukin diftitox did not effectively deplete Tregs, augment T cell responses, or improve clinical activity in melanoma. Clinicaltrials.gov ID: NCT00515528; Registered August 9, 2007.
authors.affiliation: Department of Medicine, University of Chicago, 5841 S. Maryland Ave, MC2115, Chicago, IL 60637 USA.
authors.forename: Jason J
authors.initials: JJ
authors.lastname: Luke
authors.affiliation: Department of Medicine, University of Chicago, 5841 S. Maryland Ave, MC2115, Chicago, IL 60637 USA.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Zha
authors.affiliation: Department of Medicine, University of Chicago, 5841 S. Maryland Ave, MC2115, Chicago, IL 60637 USA.
authors.forename: Karen
authors.initials: K
authors.lastname: Matijevich
authors.affiliation: Department of Medicine, University of Chicago, 5841 S. Maryland Ave, MC2115, Chicago, IL 60637 USA ; Department of Pathology, University of Chicago, 5841 S. Maryland Ave, MC2115, Chicago, IL 60637 USA.
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Gajewski
keywords: Denileukin difitox; Immunotherapy; Melanoma; Tregs; Vaccine