The tumour microenvironment is believed to be involved in development, growth, metastasis, and therapy resistance of many cancers. Here we show survivin, a member of the inhibitor of apoptosis protein (IAP) family, implicated in apoptosis inhibition and the regulation of mitosis in cancer cells, exists in a novel extracellular pool in tumour cells. Furthermore, we have constructed stable cell lines that provide the extracellular pool with either wild-type survivin (Surv-WT) or the previously described dominant-negative mutant survivin (Surv-T34A), which has proven pro-apoptotic effects in cancer cells but not in normal proliferating cells. Cancer cells grown in conditioned medium (CM) taken from Surv-WT cells absorbed survivin and experienced enhanced protection against genotoxic stresses. These cells also exhibited an increased replicative and metastatic potential, suggesting that survivin in the tumour microenvironment may be directly associated with malignant progression, further supporting survivin's function in tumourigenesis. Alternatively, cancer cells grown in CM taken from the Surv-T34A cells began to apoptose through a caspase-2-and caspase-9-dependent pathway that was further enhanced by the addition of other chemo-and radiotherapeutic modalities. Together our findings suggest a novel microenvironmental function for survivin in the control of cancer aggressiveness and spread, and should result in the genesis of additional cancer treatment modalities.

To ensure their survival, a number of bacterial and plant species have evolved a common strategy to capture energy from other biological systems. Being imperfect pathogens, organisms synthesizing multi-subunit AB toxins are responsible for the mortality of millions of people and animals annually. Vaccination against these organisms and their toxins has proved rather ineffective in providing long-term protection from disease. In response to the debilitating effects of AB toxins on epithelial cells of the digestive mucosa, mechanisms underlying toxin immunomodulation of immune responses have become the focus of increasing experimentation. The results of these studies reveal that AB toxins may have a beneficial application as adjuvants for the enhancement of immune protection against infection and autoimmunity. Here, we examine similarities and differences in the structure and function of bacterial and plant AB toxins that underlie their toxicity and their exceptional properties as immunomodulators for stimulating immune responses against infectious disease and for immune suppression of organ-specific autoimmunity.

Antigen presenting cells, specifically dendritic cells (DCs) are a focal point in the delicate balance between T cell tolerance and immune responses contributing to the onset of type I diabetes (T1D). Weak adjuvant proteins like the cholera toxin B subunit when linked to autoantigens may sufficiently alter the balance of this initial immune response to suppress the development of autoimmunity. To assess adjuvant enhancement of autoantigen mediated immune suppression of Type 1 diabetes, we examined the cholera toxin B subunit (CTB)-proinsulin fusion protein (CTB-INS) activation of immature dendritic cells (iDC) at the earliest detectable stage of the human immune response. In this study, Incubation of human umbilical cord blood monocyte-derived immature DCs with CTB-INS autoantigen fusion protein increased the surface membrane expression of DC toll-like receptor (TLR-2) while no significant upregulation in TLR-4 expression was detected. Inoculation of iDCs with CTB stimulated the biosynthesis of both CD86 and CD83 co-stimulatory factors demonstrating an immunostimulatory role for CTB in both DC activation and maturation. In contrast, incubation of iDCs with proinsulin partially suppressed CD86 co-stimulatory factor mediated DC activation, while incubation of iDCs with CTB-INS fusion protein completely suppressed iDC biosynthesis of both CD86 and CD83 costimulatory factors. The incubation of iDCs with increasing amounts of insulin did not increase the level of immune suppression but rather activated DC maturation by stimulating increased biosynthesis of both CD86 and CD83 costimulatory factors. Inoculation of iDCs with CTB-INS fusion protein dramatically increased secretion of the immunosuppressive cytokine IL-10 and suppressed synthesis of the pro-inflammatory cytokine IL12/23 p40 subunit protein suggesting that linkage of CTB to insulin (INS) may play an important role in mediating DC guidance of cognate naïve Th0 cell development into immunosuppressive T lymphocytes. Taken together, the experimental data suggests Toll like receptor 2 (TLR-2) plays a dominant role in CTB mediated INS inhibition of DC induced type 1 diabetes onset in human Type 1 diabetes autoimmunity. Further, fusion of CTB to the autoantigen was found to be essential for enhancement of immune suppression as codelivery of CTB and insulin did not significantly inhibit DC costimulatory factor biosynthesis. The experimental data presented supports the hypotheses that adjuvant enhancement of Author to whom correspondence should be addressed: William Langridge; Tel.: +1-909 558-1000 (81362); Fax: +1-909-558-0177 (Center for Health Disparities and Molecular Medicine, Loma Linda University, School of Medicine, Loma Linda, CA. 92354). Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its fina...

Dendritic cells are the largest population of antigen presenting cells in the body. One of their main functions is to regulate the delicate balance between immunity and tolerance responsible for maintenance of immunological homeostasis. Disruption of this delicate balance often results in chronic inflammation responsible for initiation of organ specific autoimmune diseases such as rheumatoid arthritis, multiple sclerosis and type I diabetes. The cholera toxin B subunit (CTB) is a weak mucosal adjuvant known for its ability to stimulate immunity to antigenic proteins. However, conjugation of CTB to many autoantigens can induce immunological tolerance resulting in suppression of autoimmunity. In this study, we examined whether linkage of CTB to a 5 kDa C-terminal protein fragment of the major diabetes autoantigen glutamic acid decarboxylase (GAD35), can block dendritic cell (DC) functions such as biosynthesis of co-stimulatory factor proteins CD86, CD83, CD80 and CD40 and secretion of inflammatory cytokines. The results of human umbilical cord blood monocyte-derived DC - GAD35 autoantigen incubation experiments showed that inoculation of immature DCs (iDCs), with CTB-GAD35 protein dramatically suppressed levels of CD86, CD83, CD80 and CD40 co-stimulatory factor protein biosynthesis in comparison with GAD35 alone inoculated iDCs. Surprisingly, incubation of iDCs in the presence of the CTB-autoantigen and the strong immunostimulatory molecules PMA and Ionomycin revealed that CTB-GAD35 was capable of arresting PMA + Ionomycin induced DC maturation. Consistant with this finding, CTB-GAD35 mediated suppression of DC maturation was accompanied by a dramatic decrease in the secretion of the pro-inflammatory cytokines IL-12/23p40 and IL-6 and a significant increase in secretion of the immunosuppressive cytokine IL-10. Taken together, our experimental data suggest that linkage of the weak adjuvant CTB to the dominant type 1 diabetes autoantigen GAD strongly inhibits DC maturation through the down regulation of major co-stimulatory factors and inflammatory cytokine biosynthesis. These results emphasize the possibility that CTB-autoantigen fusion proteins enhance DC priming of naïve Th0 cell development in the direction of immunosuppressive T lymphocytes. The immunological phenomena observed here establish a basis for improvement of adjuvant augmented multi-component subunit vaccine strategies capable of complete suppression of organ-specific autoimmune diseases in vivo.

Onset of juvenile Type 1 diabetes (T1D) occurs when autoreactive lymphocytes progressively destroy the insulin-producing beta-cells in the pancreatic Islets of Langerhans. The increasing lack of insulin and subsequent onset of hyperglycemia results in increased damage to nerves, blood vessels, and tissues leading to the development of a host of severe disease symptoms resulting in premature morbidity and mortality. To enhance restoration of normoglycemia and immunological homeostasis generated by lymphocytes that mediate the suppression of autoimmunity, the non-toxic B chain of the plant AB enterotoxin ricin (RTB), a castor bean lectin binding a variety of epidermal cell receptors, was genetically linked to the coding region of the proinsulin gene (INS) and expressed as a fusion protein (INS–RTB) in transformed potato plants. This study is the first documented example of a plant enterotoxin B subunit linked to an autoantigen and expressed in transgenic plants for enhanced immunological suppression of T1D autoimmunity.