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Emerging evidence indicates a link between the increased proportion of regulatory T cells (Tregs) and reduced survival in patients who have been diagnosed with cancer. Cancer stem cells (CSCs) have been indicated to play a vital role in tumour initiation, drug resistance and recurrence. However, the relationship between Tregs and CSCs remains largely unknown. Here, we sorted out ovarian cancer stem-like side population (SP) cells and CD133+ cells to investigate the influence of ovarian CSCs on Tregs. Among the various immune-related molecules that we assessed, C-C motif chemokine ligand 5 (CCL5) was the most elevated in ovarian CSCs relative to that in the non-CSCs. The expression of its receptor, C-C motif chemokine receptor 5 (CCR5), was also increased on the surface of Tregs in ovarian cancer patients. This receptor-ligand expression profile indicated that ovarian CSCs recruit Tregs via CCL5-CCR5 interactions. We further assessed the expression of interleukin (IL)-10 in Tregs cultured with different cancer cells. Tregs cultured in conditioned medium (CM) from ovarian CD133+ cells expressed a higher level of IL-10 than Tregs cultured in CM from CD133- cells, indicating that Tregs exert pronounced immune-inhibitory functions in CSC-rich environments. Furthermore, co-culture with ovarian cancer cell lines induced the expression of matrix metalloproteinase-9 (MMP9) in Tregs which, in turn, enhanced the degradation of the extracellular matrix and enabled the invasion of tumour cells, thereby facilitating tumour metastasis. For the first time, to our knowledge, our findings describe the relationship between ovarian CSCs and Tregs, and demonstrated that these two cell populations co-operate to promote tumour immune tolerance and enhance tumour progression. [ABSTRACT FROM AUTHOR]

Malignant transformation of normal hematopoietic transplants induced by residual leukemia cells is considered as a pivotal mechanism of donor cell leukemia (DCL). The effects of leukemia cell-derived microvesicles (MVs) in this transformation were examined. We found that MVs derived from K562 leukemia cells contained the breakpoint cluster region-Abelson leukemia gene human homolog 1 (BCR-ABL1) mRNA. Following incubation with BCR-ABL1-positive MVs, mononuclear cells derived from normal transplants exhibited a leukemia-like malignant phenotype both in vitro and in vivo. Horizontal transfer of BCR-ABL1 mRNA from MVs into the recipient cells was critical to the transformation. Relative genomic instability was observed and considered the main mechanism in the recipient cells. MVs contributed to genomic instability by two distinct pathways: via consequent overexpression of activation-induced cytidine deaminase and reactive oxygen species, which mediated DNA breakage and recombination; and via upregulation of methyltransferases and global DNA hypermethylation. We demonstrated that BCR-ABL1-positive MVs could initiate malignant transformation of normal hematopoietic transplants through genomic instability, which might serve as a convenient and operable model for investigating leukemogenesis, especially for DCL. Furthermore, MVs themselves could act as an early warning indicator and a novel tool to detect and prevent the occurrence of DCL. [ABSTRACT FROM AUTHOR]

Gemcitabine is the first-line chemotherapeutic agent for advanced adenocarcinoma of the pancreas; however, chemoresistance to gemcitabine remains a major cause of failure for the clinical treatment of this disease. Polo-like kinase 1 (Plk-1) is highly expressed in pancreatic cancer cell lines and pancreatic tumour tissues, and is involved in a wide variety of cell cycle processes. Nevertheless, its biological role and implication for gemcitabine resistance are not clearly defined. In this study, we used RNA-interference (RNAi)-mediated depletion of Plk-1 to determine its potential for sensitizing pancreatic tumour cells to gemcitabine. We showed that the level of Plk-1 protein was correlated significantly with gemcitabine resistance in human pancreatic adenocarcinoma cells and that overexpression of Plk-1 reduced sensitivity to gemcitabine in these cells. In addition, small interfering RNA (siRNA)-mediated knockdown of Plk-1 caused cell cycle arrest at G2/M and the reduction of cellular proliferation. More importantly, the treatment of pancreatic cancer cells with Plk-1 siRNA followed by exposure to gemcitabine dramatically decreased cell viability and increased cellular apoptosis, as compared with treatment with either agent alone. These observations indicate that down-regulation of Plk-1 expression by RNAi enhances gemcitabine sensitivity and increases gemcitabine cytotoxicity in pancreatic tumour cells. This is the first demonstration that the combination of Plk-1 gene therapy and gemcitabine chemotherapy has synergistic anti-tumour activity against pancreatic carcinoma in vitro. This combination treatment warrants further investigation as an effective therapeutic regimen for patients with resistant pancreatic cancer and other tumours. [ABSTRACT FROM AUTHOR]