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In vivo depletion of CD25+ cells prior to LRAST increases therapeutic efficacy in a murine melanoma model
© Kovács et al.; licensee BioMed Central Ltd. 2014
Published: 6 November 2014
Lymphodepletion, immune reconstitution and active- specific tumor cell vaccination (LRAST) have proven to benefit the activation of tumor-specific T cells in mice during homeostatic proliferation. Immunoregulatory mechanisms like the induction of regulatory T cells may counteract this beneficial effect. To further clarify the role of regulatory T cells (Treg) during LRAST, we inhibited CD25+ cells in donor mice and/or in recipient mice in vivo, using the monoclonal anti-CD25 antibody PC61. We investigated the induction of an anti-tumor immune response by analyzing tumor growth and the induction of tumor-specific T cells following LRAST.
C57BL/6 recipient mice were pre-treated with a monoclonal anti-CD25 antibody (PC61, 250µg i.p.) or a corresponding isotype control (anti-βGal, 260µg, i.p.) twice before tumor inoculation with murine melanoma cells (D5, 5x104 cells s.c.). Three days later, lymphopenia was induced by injection of cyclophosphamide (200 mg/kg). The next day, mice were reconstituted with spleen cells from a congenic mouse strain (C57BL6-Ly5.1, 2x107 cells i.v.) either pre-treated with anti-CD25 or the isotype antibody. The effect of the anti-CD25 antibody on CD45+CD4+CD25+Foxp3+ (Treg) levels in the peripheral blood was analyzed by flow cytometry. Tumor growth was monitored and the induction of tumor-specific T cells was analyzed by IFN-γ cytokine release assay.
Three of five (60%) of the mice treated with anti-CD25 antibody and reconstituted with spleen cells from Treg-depleted donor mice showed a prolonged survival in comparison to mice treated with isotype antibody and reconstituted with spleen cells from naïve donors. Treg-depleted hosts reconstituted with cells from donor mice treated with an isotype control showed the highest release of tumor-specific IFN-γ in tumor-draining lymph node cells. Interestingly, reconstitution with anti-CD25-depleted spleen cells significantly reduced tumor-specific IFN-γ release in tumor-draining lymph node cells.
Treg inactivation with anti-CD25 antibody prior to LRAST increases therapeutic efficacy. These results suggest that CD25 depletion of the host, but not of the donor, is advantageous for the induction of a tumor-specific immune response. Whether this treatment protocol results in a therapeutic immune response and further improves survival is currently under investigation.
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.