Depletion of CD4⁺CD25⁺ human regulatory T cells in vivo: Kinetics of Treg depletion and alterations in immune functions in vivo and in vitro

Abstract

The aim of this study was to investigate whether depletion of CD4 1 CD251 regulatory T cells (Treg) from melanoma patients affects immune responses against tumors. By application of recombinant IL-2-diphteria toxin fusion protein, also known as ONTAK, we were able to significantly reduce the frequency of Treg in peripheral blood, whereas other cell populations remained unaffected. The reduction of Treg started immediately after the first bolus of ONTAK with a dose of 5 lg ONTAK per kg bodyweight and lasted for 13 days with subsequent recovery thereafter. Successive ONTAK treatments further reduced the number of circulating Treg. Using the contact sensitizer DCP we show that all patients developed vast eczema after Treg depletion, whereas no or only mild eczematous reactions were detectable before ONTAK treatment. Corresponding induction of DCP-specific CD4 1 and CD8 1 T cells were detectable. Moreover, after immunization of ONTAK treated patients with tumor antigen peptides, MelanA/ MART-1 and gp100, significant induction of peptide specific CD8 1 T cells could be observed in 90% of the patients treated. These cells displayed effector functions, as they were able to lyse peptide-pulsed target cells and secreted IFNc upon restimulation. In aggregate, our data indicate that ONTAK depletes Treg in vivo significantly, resulting in enhanced immune functions and substantial development of antigen-specific CD8 1 T cells in vaccinated individuals. ' 2007 Wiley-Liss, Inc.

T-regulatory cell modulation: the future of cancer immunotherapy?

“…Diftitox administration in advanced renal cell carcinoma (RCC) patients before dendritic cell vaccination resulted in a reduction in the peripheral Tregs and Treg-mediated immunosuppression. This effect on solid tumours was further corroborated in melanoma patients for whom enhanced antigen-specific CD8 Tcell activity was seen (Mahnke et al, 2007). However, a study evaluating the treatment of melanoma patients with diftitox not only failed to show any favourable clinical improvement, but also showed no change in number or suppressive properties of peripheral Tregs .…”

Immunomodulatory Effect of Imiquimod Through CCL22 Produced by Tumor-associated Macrophages in B16F10 Melanomas

“…Indeed, both MDSCs, which are known as immunosuppressive immature macrophages, and Tregs determine the prognosis of advanced melanoma patients (30). In addition, Mahnke et al reported that Treg depletion by denileukin diftitox (Ontak ® , Eisai Medical Research, Tokyo, Japan) in melanoma patients resulted in the substantial development of antigen-specific CD8 + T cells in vaccinated individuals (31). Another report also suggested that Treg depletion had a significant clinical effect in unresectable stage IV melanoma patients (32).…”

Efficient Treg depletion induces T‐cell infiltration and rejection of large tumors

“…For Treg depletion in humans, several reagents are employed such as CY [35], the IL-2 DT fusion protein Denileukin diftitox or ONTAK [36][37][38][39], but the degree of Treg depletion is still limited (about 50%). There also exist antibodies directed against the human CD25 molecule, e.g.…”

“…The present study, together with the above mentioned works by Ganss et al [32] and Hamzah and co-workers [12] would add T cells to the list of cancer treatment modalities that benefit from normalization of the tumor vasculature. However, it remains a major challenge to unravel the cellular and molecular processes involved in re-modeling of the tumor vasculature and the mechanism by which changes in the vasculature regulate T-cell infiltration.For Treg depletion in humans, several reagents are employed such as CY [35], the IL-2 DT fusion protein Denileukin diftitox or ONTAK [36][37][38][39], but the degree of Treg depletion is still limited (about 50%). There also exist antibodies directed against the human CD25 molecule, e.g.…”