title: Human CD4+CD25+ regulatory T cells are sensitive to low dose cyclophosphamide: implications for the immune response.
abstract: Regulatory T cells (Treg) play a pivotal role in the immune system since they inhibit the T cell response. It is well known that cyclophosphamide applied at low dose is able to stimulate the immune response while high dose cyclophosphamide exerts inhibitory activity. Data obtained in mice indicate that cyclophosphamide provokes a reduction in the number of Treg and impairs their suppressive activity, resulting in immune stimulation. Here, we addressed the question of the sensitivity of human Treg to cyclophosphamide, comparing Treg with cytotoxic T cells (CTL) and T helper cells (Th). We show that Treg are more sensitive than CTL and Th to mafosfamide, which is an active derivative of cyclophosphamide, which does not need metabolic activation. The high sensitivity of Treg was due to the induction of apoptosis. Treg compared to CTL and Th were not more sensitive to the alkylating drugs temozolomide and nimustine and also not to mitomycin C, indicating a specific Treg response to mafosfamide. The high sensitivity of Treg to mafosfamide resulted not only in enhanced cell death, but also in impaired Treg function as demonstrated by a decline in the suppressor activity of Treg in a co-culture model with Th and Helios positive Treg. Treatment of Treg with mafosfamide gave rise to a high level of DNA crosslinks, which were not repaired to the same extent as observed in Th and CTL. Also, Treg showed a low level of γH2AX foci up to 6 h and a high level 24 h after treatment, indicating alterations in the DNA damage response. Overall, this is the first demonstration that human Treg are, in comparison with Th and CTL, hypersensitive to cyclophosphamide, which is presumably due to a DNA repair defect.
authors.affiliation: Department of Toxicology, University Medical Center, Mainz, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Heylmann
authors.affiliation: Department of Toxicology, University Medical Center, Mainz, Germany.
authors.forename: Martina
authors.initials: M
authors.lastname: Bauer
authors.affiliation: Department of Toxicology, University Medical Center, Mainz, Germany.
authors.forename: Huong
authors.initials: H
authors.lastname: Becker
authors.affiliation: Pediatric Neuro-Oncology, University Hospitals, Leuven, Belgium.
authors.forename: Stefaan
authors.initials: S
authors.lastname: van Gool
authors.affiliation: Department of Dermatology, University Medical Center, Mainz, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Bacher
authors.affiliation: Department of Dermatology, University Medical Center, Mainz, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Steinbrink
authors.affiliation: Department of Toxicology, University Medical Center, Mainz, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Kaina
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D003520:Cyclophosphamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D053645:Interleukin-2 Receptor alpha Subunit / Q000378:metabolism*; D009336:Necrosis / Q000139:chemically induced; D050378:T-Lymphocytes, Regulatory / Q000166:cytology / Q000187:drug effects* / Q000276:immunology* / Q000378:metabolism
chemical_list: D007166:Immunosuppressive Agents; D053645:Interleukin-2 Receptor alpha Subunit; C048341:mafosfamide; D003520:Cyclophosphamide