Regulatory T cells (Tregs) have been implicated as key players in immune tolerance as well as suppression of antitumor responses. The chemotherapeutic alkylating agent cyclophosphamide (CY) is widely used in the treatment of tumors and some autoimmune conditions. Although previous data has demonstrated that Tregs may be preferentially affected by CY, its relevance in promoting autoimmune conditions has not been addressed. The nonobese diabetic mouse spontaneously develops type-1 diabetes (T1D). We demonstrate in this study that CY targets CD4+CD25+Foxp3+ Tregs in vivo. CD4+CD25+ T cells isolated from CY-treated mice display reduced suppressive activity in vitro and increased expression of apoptotic markers. Although Treg numbers rapidly recovered to pretreatment levels in the peripheral lymphoid tissues, Tregs failed to recover proportionally within pancreatic infiltrates. T1D progression was effectively prevented by adoptive transfer of a small number of islet Ag-specific CD4+CD25+ Tregs to CY-treated recipients. Prevention of T1D was associated with reduced T cell activation and higher Treg proportions in the pancreas. We conclude that acceleration of T1D by CY is associated with a reduction in CD4+CD25+Foxp3+ Tregs and can be prevented by transfer of CD4+CD25+ Tregs.

Cyclophosphamide (CTX) is an alkylating cytotoxic drug that primarily affects proliferating lymphocytes. CTX has been extensively used as a chemotherapeutic and disease-modifying agent against certain solid tumors, lymphomas, and some autoimmune conditions. Depending on its dose and timing of administration, CTX can also enhance immune responses. These opposing immune functions of CTX have been investigated in numerous animal models and recent clinical studies. Administration of CTX augments delayed type 1 hypersensitivity (DTH) reactions, can precipitate type 1 diabetes, and boosts antitumor responses in both vaccination and adoptive cell transfer models. Although the mechanisms by which CTX elicits these effects are not fully understood, CTX treatment has a differential effect on lymphocyte compartments, rapidly depleting B and T cells. This is followed by a recovery phase characterized by extensive proliferation and bone marrow mobilization. The proposed underlying mechanisms of augmentation of immune responses include the facilitation of homing and homeostatic proliferation by the creation of space, the skewing of Th2/Th1 responses due to the cytokine storm during the recovery phase, and the removal or inhibition of a suppressor cell population. With the identification of naturally occurring and peripheral regulatory T cells, recent studies have re-evaluated these hypotheses and suggest that CTX inhibits the function of Foxp3+ regulatory T cells. In this review, we critically evaluate relevant historical and recent data on CTX-mediated immunomodulation and discuss the resulting implications for immunotherapy.

Solute carrier family 11 member a1 (Slc11a1; formerly Nramp1) encodes a late endosomal/lysosomal protein/ divalent cation transporter that regulates iron homeostasis in macrophages. During macrophage activation, Slc11a1 has multiple pleiotropic effects on gene regulation and function, including gamma interferon-induced class II expression and antigen-presenting cell function. The wild-type allele at Slc11a1 has been associated with a bias in Th1 cell function in vivo, which is beneficial in resistance to infection against intracellular macrophage pathogens but detrimental in contributing to development of type 1 diabetes. The extent to which this depends on macrophage versus dendritic cell (DC) function is not known. Here we show that Slc11a1 is expressed in late endosomes and/or lysosomes of CD11c ؉ DCs. DCs from mutant and congenic wild-type mice upregulate interleukin-12 (IL-12) and IL-10 mRNA in response to lipopolysaccharide (LPS) stimulation, but the ratio of IL-10 to IL-12 is higher in unstimulated DCs and DCs stimulated for 15 h with LPS from mutant mice than from wild-type mice. DCs from wild-type mice upregulate major histocompatibility complex class II in response to LPS more efficiently than DCs from mutant mice. Unstimulated DCs from wild-type and mutant mice present ovalbumin (OVA) peptide with an efficiency equivalent to that of an OVA-specific CD4 T-cell line, but DCs from wild-type mice are more efficient at processing and presenting OVA or Leishmania activator of cell kinase (LACK) protein to OVA-and LACK-specific T cells. These data indicate that wild-type Slc11a1 expressed in DCs may play a role both in determining resistance to infectious disease and in susceptibility to autoimmune disease such as type 1 diabetes.