The price of freedom from GVHD

Researchers have solved the puzzle of how mesenchymal stromal stem cell (MSC) transfusions can dampen autoimmunity even though the cells themselves become undetectable soon after their administration. MSCs are bone marrow stem cells, but they do not need to engraft into the bone marrow to be effective. They are clearly effective at abrogating immune reactions including graft-vs.-host disease (GVHD) in some patients, but to date, clinicians have been unable to predict which ones. Researchers from King's College London investigated the molecular events following MSC transfusions in a mouse model of GVHD, and found that transfusions were only effective if the MSCs underwent apoptosis. In patients with GVHD, only those who had a cytotoxic response to MSC transfusions, killing the MSCs, benefited from treatment. However, the authors found that the "need for recipient cytotoxic cell activity could be replaced by the infusion of apoptotic MSCs generated ex vivo. . . . Therefore, we propose the innovative concept that patients should be stratified for MSC treatment according to their ability to kill MSCs or that all patients could be treated with ex vivo apoptotic MSCs." They published their findings in the Nov. 15, 2017, issue of Science Translational Medicine.

PD-1 for T1D

The T-cell checkpoint blocker was defective in mouse models of type 1 diabetes (T1D) as well as in patients with T1D, and restoring its function could reverse the disease, at least in its early stages, in mouse models. T1D is an autoimmune disease, but previous attempts at restoring immune tolerance to pancreatic beta cells have been unsuccessful, in part because they were not specific to the processes that drive T1D. Researchers from Boston Children's Hospital discovered that the autoreactive T cells that were the driving force behind T1D had dysfunctional checkpoint inhibition via the PD-1/PD-L1 axis in non-obese diabetic mice. They also showed that blood stem cells from T1D patients had the same defect in PD-1. Forced overexpression of PD-L1 on T cells from diabetic mice "inhibited the autoimmune response in vitro [and] reverted diabetes in newly hyperglycemic NOD mice in vivo. . . . Targeting a specific immune checkpoint defect in HSPCs thus may contribute to establishing a cure for T1D," the authors wrote. They published their results in the Nov. 15, 2017, issue of Science Translational Medicine.

TDP-43 takes the heat-shock protein

TDP-43 is a protein that plays a causal role in both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Scientists from the University of Pennsylvania have shown that TDP-43 led to neuronal damage by interfering with chromatin function under conditions of stress. The team screened for chromatin-related genes affected by TDP-43 in a fruit fly model, and showed that TDP-43 prevented chromatin changes that would have allowed for the expression of heat-shock protein. As a result, cells were vulnerable to damage and, ultimately, death. "These findings indicate that TDP-43-mediated neurodegeneration causes impaired chromatin dynamics that prevents appropriate expression of protective genes through compromised function of the chromatin remodeler CHD1/CHD2," the authors concluded. "Enhancing chromatin dynamics may be a treatment approach to amyotrophic lateral sclerosis (ALS)/frontotemporal dementia (FTD)." The paper was published in the Nov. 16, 2017, issue of Current Biology.

TRIMming protein opens new research avenues

Gene knockout technology is the rare example of a breakthrough that deserves its name, and gene editing technologies are further expanding the ability to alter protein levels. What has been missing from the toolbox, though, is a way to get rid of proteins without altering DNA or RNA. Researchers from the British Medical Research Council's Laboratory of Molecular Biology and the German Max Planck Institute for Biophysical Chemistry have developed such a method, which they have named Trim-Away. The method was based on a combination of an antibody to the protein in question and the protein TRIM21, which served as a target for ubiquitin tags that cells use to mark proteins for destruction. Combining the two "harnessed the cellular protein degradation machinery to remove unmodified native proteins within minutes of application. This rapidity minimizes the risk that phenotypes are compensated and that secondary, non-specific defects accumulate over time," the authors wrote, adding that "because Trim-Away utilizes antibodies, it can be applied to a wide range of target proteins using off-the-shelf reagents." The team published its method in the Nov. 16, 2017, issue of Cell.

Unshelterin' telomeres fights glioblastoma

Removing the protective cap from telomeres by interfering with the protein shelterin reduced the stem cell-like properties of glioblastoma cells, even if it did not alter the length of the telomeres. Telomeres are the ends of DNA and function as a way for cells to keep track of how many divisions they have undergone, since they become a bit shorter with every cell division. Researchers from the Spanish National Center of Oncology Research showed that knocking out the shelterin protein TRF1 in a mouse model of glioblastoma inhibited the start and progression of glioblastoma multiforme. Chemical inhibitors of GBM1 were able to cause telomere damage and reduce proliferation in human cell cultures and xenograft models. "These results have a potential impact in cancer treatment as current therapies are unable to kill glioma stem cells and patients die owing to the recurrence of the tumors," the authors wrote. Their work appeared in the Nov. 13, 2017, issue of Cancer Cell.

Tumor organoids predict drug response

Primary liver cancer (PLC) is an aggressive cancer with a high fatality rate. Due to rising obesity rates, its incidence is also increasing. Researchers from The Wellcome Trust/CRUK Gurdon Institute at the British University of Cambridge have developed organoids for each of the three subtypes of PLC, which can be a hepatocellular carcinoma, cholangiocarcinoma, or mixed. The team had recently reported making a liver organoid. In their new work, they used essentially the same approach to make organoids from primary liver tumor cells. The organoids remained similar in their mutational profiles to their parental cells over extended culturing periods, and could be used to uncover drug sensitivities. The team also used them to identify new biomarkers of poor prognosis. The authors concluded, "With a short timescale from establishment to drug testing, this novel in vitro primary liver cancer system thus makes hitherto inaccessible possibilities for predicting patient-specific drug responses and creating personalized à la carte therapies into a reality." They reported their methods in the Nov. 13, 2017, online issue of Nature Medicine.

Gut microbes worth their salt

High salt intake affected the gut microbiome composition of mice, and supplementing the animals with certain bacterial species that were depleted by a high-salt diet reduced inflammation and prevented salt intake from aggravating high blood pressure and the mouse equivalent of multiple sclerosis. A high-salt diet contributes to hypertension, which is a major risk factor for cardiovascular disease. A team from the German Max-Delbrück Center for Molecular Medicine and the Massachusetts Institute of Technology investigated whether salt's effect on blood pressure was mediated by immune mechanisms in addition to effects on the kidney and the vasculature. They showed that activation of the immune system by the gut microbiome also played a role by activating pro-inflammatory TH17 cells. A commentary accompanying the paper cautioned that "one might predict – because of other variable factors – that the effects [of the gut microbiome on hypertension] will be modest and restricted to a subset of individuals. Nonetheless, even modest effects are more than worthy of further study, because of the profound potential for global health benefits." Paper and commentary were published in the Nov. 16, 2017, issue of Nature.

Nonviral CRISPR

As the genome editing method CRISPR/Cas9 continues to be developed apace, researchers from the Massachusetts Institute of Technology have developed a method to deliver CRISPR/Cas9 to cells in vivo without the use of viral vectors. One of the challenges of RNA-based therapeutics is that RNAs are normally rapidly degraded in the body. RNA-based therapeutics have been successful in part because their developers have found ways to make RNA resistant to degradation. In their work, the team identified parts of the guide RNA that targets CRISPR that could be modified to make it more resistant to degradation without interfering with its activity. "Using lipid nanoparticle formulations of these enhanced sgRNAs (e-sgRNA) and mRNA encoding Cas9, we show that a single intravenous injection into mice induces >80 percent editing of Pcsk9 in the liver," the authors wrote. Serum Pcsk9 is reduced to undetectable levels, and cholesterol levels are significantly lowered about 35 percent to 40 percent in animals. That strategy may enable nonviral, Cas9-based genome editing in the liver in clinical settings." The team reported its method in the Nov. 13, 2017, issue of Nature Biotechnology.

Biased compound may lead to safer pain relief

Despite being at the center of a massive public health crisis, opioid painkillers continue to be the most effective analgesics available. Researchers from The Scripps Research Institute have developed opioid agonists that could lead to safer painkillers. Mu opioid receptors can activate downstream signaling via two separate pathways, one linked to beta-arrestin signaling and one that activates G protein-coupled receptors (GPCRs). The team showed that respiratory suppression, a side effect of opioid receptor activation that is responsible for many fatal overdoses, was linked specifically to activation of the beta-arrestin pathways. "We find that beta-arrestin-biased compounds, such as fentanyl, are more likely to induce respiratory suppression at weak analgesic doses, while G protein signaling bias broadens the therapeutic window, allowing for antinociception in the absence of respiratory suppression," the authors wrote. Their work appeared in the Nov. 16, 2017, issue of Cell.