Inability of a Fusion Protein of IL-2 and Diphtheria Toxin (Denileukin Diftitox, DAB389IL-2, ONTAK) to Eliminate Regulatory T Lymphocytes in Patients With Melanoma

Abstract

SummaryElimination of regulatory T lymphocytes may provide a way to break self-tolerance and unleash the anti-tumor properties of circulating lymphocytes. The use of fusion proteins, which link cytotoxic molecules to receptor targets, provides one approach to this problem. This study examined the ability of a fusion protein of interleukin-2 (IL-2) and diphtheria toxin (Denileukin Diftitox, DAB 389 IL-2, ONTAK) to eliminate regulatory T lymphocytes based on their expression of high-affinity IL-2 receptors. Thirteen patients (12 with metastatic melanoma, 1 with metastatic renal cell carcinoma) were treated at one of the two Food and Drug Administration-approved doses of Denileukin Diftitox (seven patients at 9 μg/kg, six patients at 18 μg/kg). None of the patients experienced an objective clinical response. Foxp3 expression did not decrease significantly overall, although it did decrease minimally among patients receiving 18 μg/kg (−2.01 ± 0.618 copies of Foxp3/10 3 copies of β-actin; P = 0.031). Denileukin Diftitox did not decrease the suppressive ability of CD4 + CD25 + cells as quantified by an in vitro co-culture suppression assay. Furthermore, the increased numbers of lymphocytes in patients resulting from treatment with IL-2 were not susceptible to Denileukin Diftitox. Administration of Denileukin Diftitox does not appear to eliminate regulatory T lymphocytes or cause regression of metastatic melanoma.

Skin Melanoma Development in ret Transgenic Mice Despite the Depletion of CD25+Foxp3+ Regulatory T Cells in Lymphoid Organs

“…These results might be partly due to the observed insufficient Treg depletion in mouse tumors, where Treg can directly inhibit tumorspecific T cells (41). Our data are in agreement with recently published data from clinical trials showing that the treatment of melanoma patients with the fusion protein of IL-2 and diphtheria toxin (Ontak) did not result in the decrease of Treg numbers and function as well as in objective clinical responses (42,43). After the Treg depletion in ret transgenic mice without macroscopic skin tumors, we found only a little, statistically nonsignificant antitumor effect.…”

Dynamic Behavior and Function of Foxp3+ Regulatory T Cells in Tumor Bearing Host

“…Several published reports show that administration of Ontak in patients results in reduction of CD25 + Foxp3 + Tregs in peripheral blood, which correlates with heightened DTH response and increase of antigenspecific CTLs in response to tumor antigen immunization (105)(106)(107). However, the effect of Ontak on Treg depletion may not be consistent, as there is no significant reduction in certain caner patients (108). Furthermore, like chemotherapeuitc agents discussed in the previous section, depletion incurred by Ontak appears to be transient, and Treg populations are restored rapidly after the treatment cessation (105)(106)(107) 109).…”

Peripheral T-Cell Tolerance Associated with Prostate Cancer Is Independent from CD4+CD25+ Regulatory T Cells

“…Dannull et al (47) reported that in renal cancer patients pretreated with the recombinant IL-2 diphteria toxin conjugate denileukin, Treg were selectively eliminated and a vaccine-mediated antitumor immunity was enhanced. However, another group reported no reduction in the number of Treg or their function in melanoma patients receiving denileukin (48). Furthermore, depletion is only transient, and Treg rapidly repopulate the human body (49).…”