3, 5, 7-Trihydroxy-4'-methoxy-8-(3-hydroxy-3- methylbutyl)–flavone (ICT) is a novel derivative of Icariin (ICA), the major active ingredient of Herba Epimedii, a herb used in traditional Chinese and alternative medicine. We previously demonstrated its anti-inflammatory effect in murine innate immune cells and activated human PBMCs. We report herein that ICA or ICT treatment reduces the expression of MRP8/MRP14 and toll-like receptor 4 (TLR4) on human PBMCs. Administration of ICA or ICT inhibited tumor growth in 4T1-Neu tumor-bearing mice and considerably decreased MDSC numbers in the spleen of these mice. Further, we saw a restoration of IFN-γ production by CD8+ T cells in tumor bearing mice when treated with ICA or ICT. ICA and ICT significantly decreased the amounts of nitric oxide and reactive oxygen species in MDSC in vivo. When MDSC were treated in vitro with ICT, we saw a significant reduction in the percent of these cells with concomitant differentiation into dendritic cells and macrophages. Concomitant with this cell type conversion was a down-regulation of IL-10, IL-6 and TNF-α production. Decreased expression of S100A8/9 and inhibition of activation of STAT3 and AKT may in part be responsible for the observed results. In conclusion, our results showed that ICA, and more robustly, ICT, directly modulate MDSC signaling and therefore altered the phenotype and function of these cells, in vitro and in vivo.

Response to immunosuppressive therapy (IST) in younger patients with myelodysplastic syndrome (MDS) has been linked to a T-cell-dominant autoimmune process that impairs hematopoiesis. Analysis of the age-adjusted CD4:CD8 ratio in 76 MDS patients compared with 54 healthy controls showed that inadequate CD4+, rather than expansion of CD8+ T cells, was associated with a lower ratio in a group that included both lower and higher risk MDS patients defined by the International Prognostic Scoring System. In younger MDS patients, naive and memory phenotypes defined by CD45RA and CD62L display showed depletion of naive CD4+ and CD8+ T cells, suggesting a possible relationship to IST responsiveness. To determine the correlation between T-cell subset distribution, T-cell turnover and autoimmunity, a cohort of 20 patients were studied before and after IST. The CD4:CD8 ratio correlated inversely with the proliferative T-cell index before treatment in IST-responsive patients, suggesting that proliferation may be linked to accelerated CD4+ T-cell turnover and hematopoietic failure. Our data show seminal findings that both CD4+ and CD8+ T-cell subsets are dysregulated in MDS. Association between these T-cell defects and response to IST suggests that aberrant T-cell homeostasis and chronic activation are critical determinants influencing autoimmune hematopoietic suppression in younger patients.

The relationship between telomere length (TL) and predisposition to myelodysplastic syndromes (MDS) remains unclear. We compared peripheral blood leukocyte (PBL) TL among cases of histologically-confirmed MDS (n=65) who were treatment-naive with no prior cancer history to age-matched controls (n=63). Relative TL was measured in PBL and saliva by quantitative PCR and in CD15+ and CD19+ cells by Flow-FISH. Human telomerase reverse transcriptase gene (hTERT) mutations were assessed by PCR. After adjustment for age and sex, relative TLs were reduced in PBL (p=0.02), CD15+ (p=0.01), CD19+ (p=0.25) and saliva (p=0.13) in MDS cases versus controls, although only PBL and CD15+ results were statistically significant. Among MDS cases, CD15+ and CD19+ cell TLs positively correlated (p=0.03). PBL TL was reduced among those occupationally exposed to paints and pesticides, but was not associated with hTERT genotype. Future studies are needed to further investigate constitutional telomere attrition as a possible predisposing factor for MDS.