Comparative methodologies of regulatory T cell depletion in a murine melanoma model

Abstract

There has been recent interest in the depletion of regulatory T cells (Tregs) as part of a multi-faceted approach to the immunotherapy of melanoma patients. This is in part due recent findings that convincingly show that Tregs are an integral part of regulating and even suppressing an immune response to growing tumor cells. We therefore compared three methods of Treg depletion and/or elimination, utilizing low dose cyclophosphamide (CY), a specific antibody directed against the IL-2 receptor found on Tregs (PC61) and the use of denileukin diftitox (DD), which is a fusion protein designed to have a direct cytocidal action on cells which express the IL-2 receptor. We show that CY administration resulted in the highest reduction in Tregs among the three reagents. However, the reduction in Tregs with CY was also associated with the concomitant reduction of CD8(+) T cells and a lack of tumor antigen priming. Utilization of DD resulted in a >50% Treg cell reduction without parallel cytocidal effects upon other T cell subsets but did not enhance anti-tumor immunity against B16 melanoma. Lastly, the PC61 showed a moderate reduction of Tregs that lasted longer than the other reagents, without a reduction in the total number of CD8(+) T cells. Furthermore, PC61 treatment did not abrogate tumor antigen-specific immunity elicited by dendritic cells (DC). We therefore conclude that PC61 administration was the most effective method of reducing Tregs in a murine melanoma model in addition to providing evidence of a synergistic effect when combined with DC-based immunotherapy.

Amphiregulin Confers Regulatory T Cell Suppressive Function and Tumor Invasion via the EGFR/GSK-3β/Foxp3 Axis

“…Recent studies demonstrated that AREG is involved in inflammation. Furthermore, the EGF-like growth factor AREG is expressed by activated Th2 cells, mast cells, eosinophils, and basophils (13)(14)(15)(16). These studies suggest that the function of AREG might be to regulate immune responses.…”

Dendritic Cell Vaccination in Combination with Anti-CD25 Monoclonal Antibody Treatment: A Phase I/II Study in Metastatic Melanoma Patients

“…Apparently, CD25 depletion temporarily resets the T effector/Treg balance in favor of the T effector subset. In mice several successful methodologies of Treg depletion have been described (20). This led to great interest in the depletion of Tregs as part of a multifaceted immunotherapeutic treatment of melanoma patients.…”

“…Compared with Ontak, monoclonal antibodies (mAb) against the IL-2R α-chain (CD25) are more effective in reducing Tregs in melanoma-bearing mice (20). In addition, anti-CD25 antibodies had a synergistic effect when combined with dendritic cell-based immunotherapy in mice (20).…”

“…In addition, anti-CD25 antibodies had a synergistic effect when combined with dendritic cell-based immunotherapy in mice (20). Daclizumab (F. Hoffmann-La Roche,) is a humanized antibody directed against CD25 (30).…”

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

“…Several studies have attempted to interfere with the growth of mouse transplantation tumors by PC-61 monotherapy. Usually an effect on tumor growth has been observed only in prophylactic settings when Treg were depleted before or no later than 2 days after tumor inoculation, whereas PC-61-mediated Treg depletion in animals carrying established tumors had generally no or only little effect on tumor growth [25][26][27][28]. Significant therapeutic success was only observed when complex combinatorial approaches were applied such as total body irradiation combined with adoptive T-cell transfer and vaccination [29], and additional treatment with anti-PDL1 antibody [30], but usually mice were treated when tumors were still small (3-4 days after s.c. tumor inoculation).…”