6-Thioguanine-loaded polymeric micelles deplete myeloid-derived suppressor cells and enhance the efficacy of T cell immunotherapy in tumor-bearing mice

Laura Jeanbart, Iraklis C. Kourtis, André J. van der Vlies, Melody A. Swartz, Jeffrey A. Hubbell

Research output: Contribution to journalArticle

31 Scopus citations

Abstract

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells that suppress effector T cell responses and can reduce the efficacy of cancer immunotherapies. We previously showed that ultra-small polymer nanoparticles efficiently drain to the lymphatics after intradermal injection and target antigen-presenting cells, including Ly6c<sup>hi</sup> Ly6g<sup>−</sup> monocytic MDSCs (Mo-MDSCs), in skin-draining lymph nodes (LNs) and spleen. Here, we developed ultra-small polymer micelles loaded with 6-thioguanine (MC-TG), a cytotoxic drug used in the treatment of myelogenous leukemia, with the aim of killing Mo-MDSCs in tumor-bearing mice and thus enhancing T cell-mediated anti-tumor responses. We found that 2Âdays post-injection in tumor-bearing mice (B16-F10 melanoma or E.G7-OVA thymoma), MC-TG depleted Mo-MDSCs in the spleen, Ly6c<sup>lo</sup> Ly6g<sup>+</sup> granulocytic MDSCs (G-MDSCs) in the draining LNs, and Gr1<sup>int</sup> Mo-MDSCs in the tumor. In both tumor models, MC-TG decreased the numbers of circulating Mo- and G-MDSCs, as well as of Ly6c<sup>hi</sup> macrophages, for up to 7Âdays following a single administration. MDSC depletion was dose dependent and more effective with MC-TG than with equal doses of free TG. Finally, we tested whether this MDSC-depleting strategy might enhance cancer immunotherapies in the B16-F10Âmelanoma model. We found that MC-TG significantly improved the efficacy of adoptively transferred, OVA-specific CD8<sup>+</sup> T cells in melanoma cells expressing OVA. These findings highlight the capacity of MC-TG in depleting MDSCs in the tumor microenvironment and show promise in promoting anti-tumor immunity when used in combination with T cell immunotherapies.

Original languageEnglish (US)
Pages (from-to)1033-1046
Number of pages14
JournalCancer Immunology, Immunotherapy
Volume64
Issue number8
DOIs
StatePublished - May 16 2015
Externally publishedYes

Keywords

  • 6-Thioguanine
  • Cancer
  • MDSC depletion
  • T cell therapy

ASJC Scopus subject areas

  • Cancer Research
  • Oncology
  • Immunology
  • Immunology and Allergy

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