The Cross-Border Biotech Blog

Hedgehog Signaling Upholds Integrity of BBB

University of Montreal ♦ Published in Science, December 23, 2011

The blood-brain barrier (BBB) is a crucial boundary within the body that restricts the migration of blood-borne molecules and immune cells from circulation into the brain. Specialized endothelial cells tightly bound together with junctional proteins ensure that only certain small molecules are able to access the brain. Given that Hedgehog (Hh) signaling has been implicated in multiple sclerosis, a disease characterized by autoimmune destruction of myelin cells, researchers at the University of Montreal hypothesized that Hh signaling may have an influence on the formation of the BBB. They found that astrocytes in close proximity to endothelial cells in the BBB release Hh and that endothelial cells express Hh receptors, in keeping with the theory that Hh signaling is important for the integrity of the BBB. In order to demonstrate that Hh signaling also keeps leukocytes out of contact with the brain, researchers injected mice with cyclopamine, a small molecule inhibitor of the Hh pathway. Indeed, pharmacological inhibition of the Hh pathway led to acute disruption of the BBB and passage of leukocytes into the brain. Together these findings implicate the Hh pathway as being critical in the development and structural integrity of the BBB.

Super-Selective Oncolytic Virus

Ottawa Hospital Research Institute ♦ Published in Molecular Therapy (npg), December 20, 2011

More on oncolytic viruses this week but not with VSV this time, but rather the poxvirus JX-594. This particular virus, while having an excellent therapeutic index against multiple solid tumour types, is not that well understood. Researchers seeking to understand the mechanisms underlying its exquisite cancer cell selectivity identified multiple interactions. Three model systems were investigated, including primary normal and cancer cells, surgical explants, and mouse tumour models. It was found that selectivity of JX-594 was driven by multiple factors; the first time selectivity has been attributed to more than one specific mechanism. Among these factors were virus replication activation by the EGFR/Ras signaling pathway, cellular thymidine kinase levels (the virus is engineered to be responsive to TK so this was expected), and similar to VSV, hyporesponsiveness to type-I interferon. These finding will allow for the generation of more selective and potent oncolytic viruses.

Immunomodulators Enhance Polyfunctionality of T Cells Following Vaccination

McMaster Immunology Research Centre ♦ Published in Molecular Therapy (npg), December 20, 2011

Recombinant human adenovirus vaccines are capable of producing memory CD8+ T cell populations, however these populations lack polyfunctionality; in response to antigen stimulation they are not able to produce multiple different cytokines and chemokines. Researchers at McMaster have discovered that inhibiting mammalian target of rapamycin (mTOR) while stimulating OX40 alters not only the magnitude of T cell response, but also its phenotype and functionality. mTOR inhibition modulates differentiation of T cell pools while stimulation of OX40 enhances the process of costimulation. The addition of immunomodulators elicited greater immunity against multiple virus challenges in a mouse model, but was contingent upon sufficiently long transgene expression from the adenovirus under study.

Homeostasis in the Gut, Plasma Cells on Patrol

University of Toronto ♦  McGill University ♦ University of Bern ♦ Memorial University of Newfoundland

Published in Nature, December 11, 2011

The intestine is the largest mucosal surface in the body and is exposed to a diversity of microbes. This microbial life is healthy, although the immune system must still keep bacterial population sizes in check. One mechanism by which this is achieved is through the differentiation of B cells to plasma cells, which in turn secrete the immunoglobulin IgA. New findings indicate that plasma cells have additional roles that keep microbiota at bay. Researchers found that plasma cells secrete tumor-necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS), both of which exert antimicrobial activity. Microbial co-stimulation is pre-requisite for plasma cell multi-functionality. In order to investigate the effects that TNF-α and iNOS have on regulating flora in the gut, researchers used a double knockout mouse model. Removal of the two mediators led to a change in the composition of intestinal flora and a reduction in secretion of IgA from plasma cells.

VSV 2.0: IL-15 Engineered

McMaster University ♦ Published in Cancer Gene Therapy (npg), December 9, 2011

A popular approach to the development of oncolytic viruses for cancer therapy has been the use of the single-stranded RNA virus known vesicular stomatitis virus (VSV). This particular virus has a hypersensitivity to the protein type I interferon (IFN). Upon exposure to a virus the body releases IFN in attempt to prevent infection. The beauty of VSV is that while normal healthy cells are highly sensitive to IFN, tumour cells remain hyporesponsive. Systemic administration of VSV has little to no effect on normal cells as the virus cannot replicate within them. However, because they fail to respond to IFN, cancer cells remain susceptible to VSV infection, VSV replication, and eventually cell lysis. While VSV alone has been shown to be effective in preclinical models, long-term survival is not greatly increased.

Researchers at McMaster’s Centre for Gene Therapeutics have upped the anti with the development of a genetically engineered VSV that expresses an interleukin-15 (IL-15) transgene. IL-15 is a cytokine that has a critical role in adaptive immune responses to pathogenic entities. The group showed that injections of the IL-15 VSV in a mouse model of colon cancer led to strong localized expression of the cytokine in vivo. The new IL-15-rich microenvironment surrounding tumours increased the adaptive immune response targeted at tumour cells by recruiting and activating natural killer cells and T-cells. This novel virus has the two-fold effect of not only lysing cells, but enhancing anti-tumoral T-cell response. Mice receiving injections exhibited better survival overall.

hiPSC-derived HSCs Engraft Mouse Model

McMaster Stem Cell and Cancer Research Institute ♦ Published in Stem Cells, November 30, 2011

There are several sources currently being used to isolate hematopoietic stem cells (HSCs) for transplantation in humans. Included in these are the bone marrow, peripheral blood, and umbilical cord blood. However, HSCs derived from human embryonic stem cells (hESCs) have, as of yet, failed to be a viable source for transplantation. Although hESCs are capable of hematopoietic differentiation in the petri dish, their HSC progeny are unable to engraft human-mouse xenograft models. This investigation shows that human induced pluripotent stem cells (hiPSCs), which are also capable of hematopoietic differentiation in vitro, produce HSCs that can successfully engraft following transplantation into the mouse model; similar to HSCs from adult sources. This is an advance in terms of studying hematopoietic transplantation in humans from pluripotent sources. Despite the ability of hiPSC-derived HSCs to engraft they were unable to reconstitute hematopoiesis. However, they could establish colonies after being removed from the bone marrow compartment suggesting that a molecular mechanism blocks their capacity to differentiate in vivo. Investigators believe that misexpression of various microRNAs may explain why hiPSCs are unable to reconstitute hematopoiesis.

Breast Cancer Stem Cells, From Where Do They Originate?

British Columbia Cancer Agency ♦ University of Melbourne ♦ University of British Columbia

Published in Stem Cells, November 30, 2011

There has been a lot of talk recently about aldehyde dehydrogenase (ALDH) because it seems to be expressed across such a diversity of different stem cell types. We know that it is expressed by hematopoietic progenitors, mesenchymal progenitors, neural progenitors, and endothelial progenitors. Researchers investigating the expression of ALDH in a number of functionally defined mammary cell types have come across an interesting finding. They found that ALDH expression is actually lower in mammary stem/progenitor cells, that have bilineage differentiation potential, than it is in cells committed to particular lineages. Progenitor cells of the luminal lineage, for example, express relatively high levels of ALDH. It seems that a molecular switch upregulates ALDH, particularly the ALDH1A3 isoform, during the process of lineage commitment. The finding that ALDH is upregulated during differentiation challenges the notion that breast cancer stem cells arise from mammary stem cells. Recent reports have associated ALDH activity with breast cancer stem cells, but if ALDH expression is turned on during differentiation then breast cancer stem cells may in fact be the less primitive luminal progenitor. Further investigation of the temporal and spatial expression of ALDH in the breast should help explain this quandary.