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.

Facilitated expansion of Th17 cells in lupus nephritis patients

“…Such heterogeneity is due probably to a natural variance in LN, or may arise from enrolment of patients at different disease stages or treatment modes. Conversely, T reg cells were found to be extremely sensitive to CTX-mediated apoptosis [50]. As in our study patients were not treated with CTX in the recent past (< 6 months), this result suggests that previous courses of induction immunosuppressive therapy might have a far-reaching effect on the differentiation of Th17 and T reg cells and their respective balance.…”

Compromised DNA Repair and Signalling in Human Granulocytes

“…Thus, in view of the short lifespan of granulocytes in the peripheral blood it is conceivable that DNA repair is not needed anymore. For the different subpopulations of T cells, we have data at hand to show that they are quite radiation sensitive, responding in a similar way to IR, although regulatory T cells exhibit a specific sensitivity to cyclophosphamide [32]. Although terminally differentiated, T cell populations have quite a long lifespan and, therefore, they obviously need DNA repair in order to survive, given the 40,000 DNA lesions induced per genome per day spontaneously [33].…”

An extract ofUlmus macrocarpaimproves cellular immunity in immuno-suppressed models

“…CY has a cytotoxic effect on splenocytes in a dosedependent manner CY has often been used as a type of immune suppressive agent (Pyo et al 2001;Yoon et al 2010;Heylmann et al 2013). Several studies were designed to elucidate systematically the ex vivo and in vivo immuno-enhancement effects of plant extracts in immunosuppressed models induced by the CY treatment (Zhai et al 2007;Gupta et al 2010); thus, we tried to study the immune-enhancement effects of the water-soluble fraction of U. macrocarpa by designing similar models.…”