Transplant drug could boost power of brain tumor treatments, study finds

Drs. Maria Castro and Pedro Lowenstein, both of the U-M Department of Neurosurgery, co-led the research. Credit: Image courtesy of University of Michigan Health System

Every day, organ transplant patients around the world take a drug called rapamycin to keep their immune systems from rejecting their new kidneys and hearts. New research suggests that the same drug could help brain tumor patients by boosting the effect of new immune-based therapies.

In experiments in animals, researchers from the University of Michigan Medical School showed that adding rapamycin to an immunotherapy approach strengthened the immune response against brain tumor cells.

What's more, the drug also increased the immune system's "memory" cells so that they could attack the tumor if it ever reared its head again. The mice and rats in the study that received rapamycin lived longer than those that didn't.

Now, the U-M team plans to add rapamycin to clinical gene therapy and immunotherapy trials to improve the treatment of brain tumors. They currently have a trial under way at the U-M Health System which tests a two-part gene therapy approach in patients with brain tumors called gliomas in an effort to get the immune system to attack the tumor. In future clinical trials, adding rapamycin could increase the therapeutic response.

The new findings, published online in the journal Molecular Cancer Therapeutics, show that combining rapamycin with a gene therapy approach enhanced the animals' ability to summon immune cells called CD8+ T cells to kill tumor cells directly. Due to this cytotoxic effect, the tumors shrank and the animals lived longer.

But the addition of rapamycin to immunotherapy even for a short while also allowed the rodents to develop tumor-specific memory CD8+ T cells that remember the specific "signature" of the glioma tumor cells and attacked them swiftly when a tumor was introduced into the brain again.

"We had some indication that rapamycin would enhance the cytotoxic T cell effect, from previous experiments in both animals and humans showing that the drug produced modest effects by itself," says Maria Castro, Ph.D., senior author of the new paper. Past clinical trials of rapamycin in brain tumors have failed.

"But in combination with immunotherapy, it became a dramatic effect, and enhanced the efficacy of memory T cells too. This highlights the versatility of the immunotherapy approach to glioma." Castro is the R.C. Schneider Collegiate Professor of neurosurgery and a professor of cell and developmental biology at U-M.

Rapamycin is an FDA-approved drug that produces few side effects in transplant patients and others who take it to modify their immune response. So in the future, Castro and her colleagues plan to propose new clinical trials that will add rapamycin to immune gene therapy trials like those already ongoing at UMHS.

She notes that other researchers currently studying immunotherapies for glioma and other brain tumors should also consider doing the same. "This could be a universal mechanism for enhancing efficacy of immunotherapies in glioma," she says.

Rapamycin inhibits a specific molecule in cells, called mTOR. As part of the research, Castro and her colleagues determined that brain tumor cells use the mTOR pathway to hamper the immune response of patients.

This allows the tumor to trick the immune system, so it can continue growing without alerting the body's T cells that a foreign entity is present. Inhibiting mTOR with rapamycin, then, uncloaks the cells and makes them vulnerable to attack.

Castro notes that if the drug proves useful in human patients, it could also be used for long-term prevention of recurrence in patients who have had the bulk of their tumor removed. "This tumor always comes back," she says.

Source: University of Michigan Health System

Understanding, improving body's fight against pathogens

Significant reductions in the number of plasma cells in the spleen and bone marrow were observed in the absence of DOK3. Each dot in the figure represents one plasma cell detected. Credit: Image courtesy of A*Star Agency for Science, Technology and Research

Scientists from A*STAR's Bioprocessing Technology Institute (BTI) have uncovered the crucial role of two signalling molecules, DOK3 and SHP1, in the development and production of plasma cells. These discoveries, published in two journals PNAS and Nature Communications, advance the understanding of plasma cells and the antibody response, and may lead to optimisation of vaccine development and improved treatment for patients with autoimmune diseases such as lupus and tumours such as multiple myeloma.

While they exist in small populations in humans, the large amounts of antibodies secreted by plasma cells make them key to the body's immune system and its ability to defend itself against pathogens, such as bacteria and viruses. Proper maintenance of a pool of plasma cells is also critical for the establishment of lifelong immunity elicited by vaccination.

Dysregulation of plasma cell production and maintenance could lead to autoimmune diseases and multiple myeloma. Autoimmune diseases occur when the immune system does not distinguish between healthy tissue and antigens, which are found in pathogens. This results in expansion of plasma cells which produce excessive amounts of antibodies leading to destruction of one's own healthy tissue. The discoveries by scientists in BTI's Immunology Group have improved understanding of the mechanism by which plasma cells are developed from a major class of white blood cells called B cells.

For the first time, the molecule DOK3 was found to play an important role in formation of plasma cells. While calcium signalling typically controls a wide range of cellular processes that allow cells to adapt to changing environments, it was found to inhibit the expression of the membrane proteins essential for plasma cell formation. These membrane proteins include PDL1 and PDL2, and represent some of the key targets for the development of immunotherapy by pharmaceutical companies. DOK3 was able to promote the production of plasma cells by reducing the effects of calcium signalling on these membrane proteins. The absence of DOK3 would thus result in defective plasma cell formation.

In another study, BTI scientists discovered the importance of SHP1 signalling to the long term survival of plasma cells. While the molecule SHP1 has a proven role in prevention of autoimmune diseases, it was found that the absence of SHP1 would result in the failure of plasma cells to migrate from the spleen where they are generated to the bone marrow, a survival niche where they are able to survive for much longer periods. This could result in a reduction of the body's immune response and thus, an increased susceptibility to infections and diseases. The scientists in this study also successfully rectified the defective immune response caused by an absence of SHP1 by applying antibody injections, which might advance the development of therapeutics. On the other hand, targeting SHP1 might be a strategy to treat multiple myeloma where the accumulation of cancerous plasma cells in the bone marrow survival niches is undesirable.

Findings hold potential for improved treatment

The discovery of these new targets for modulating the antibody response allows the development of novel therapeutic strategies for patients with autoimmune diseases and cancer.Understanding the mechanism that governs plasma cell differentiation is also critical for the optimal design of vaccines and adjuvants, which are added to vaccines to boost the body's immune response.

Prof Lam Kong Peng, Executive Director of BTI, said, "These findings allow better understanding of plasma cells and their role in the immune system. The identification of these targets not only paves the way for development of therapeutics for those with autoimmune diseases and multiple myeloma, but also impacts the development of immunological agents for combating infections."

Source: A*Star Agency for Science, Technology and Research

How llamas' unusual antibodies might help in the fight against HIV/AIDS

Llamas contribute to the fight against AIDS. Credit: Nika Stropakke, CC-BY

Most vaccines work by inducing an immune response characterized by neutralizing antibodies against the respective pathogen. An effective HIV vaccine has remained elusive so far, but researchers have continued to make progress, often employing innovative methods. A study published on December 18th in PLOS Pathogens reports that a combination of antibodies from llamas can neutralize (destroy) a wide range of circulating HIV viruses.

After initial disappointment that HIV vaccine candidates were unable to elicit neutralizing antibodies, researchers found that some HIV-infected individuals did produce such antibodies. The current challenge is therefore to find safe and effective vaccine formulations (as opposed to HIV infection) that trigger the development of neutralizing antibodies that can recognize and prevent infection with all or most circulating HIV subtypes.

Many known neutralizing antibodies are directed against a specific part of the virus that binds to the CD4 receptor on the human target cells, and structural biology studies indicated that the site is a narrow groove. Antibodies in most mammals are relatively large proteins made up of two copies of two different individual parts (or chains), and bulkiness might be one reason why neutralizing antibodies are rare. Llamas are a notable exception: besides the common four-chain antibodies they also produce smaller ones made up of only two of the four chains. Robin Weiss, an HIV expert, and Theo Verrips, a llama antibody expert, therefore started working with this unconventional research animal.

Laura McCoy (working with Weiss at University College London, UK) led an international group of researchers to test immunization protocols and the resulting immune response in llamas. Having previously identified one particular HIV neutralizing llama antibody, for this study the researchers immunized two additional llamas and identified a total of three new neutralizing antibodies. The four HIV neutralizing llama antibodies target different parts of the CD4-binding site of the virus, and the researchers could show that when used in combination, rather than interfering with each other, they are more potent and can neutralize all of the 60 different HIV strains tested.

To understand how the llama immunization--which included two sets of four sequential vaccine injections per animal--worked, the researchers sequenced many copies of antibody-coding genes from blood cells collected after the first set of immunizations and after a further four rounds of vaccination. They also looked at the "naïve" antibody repertoire from seven llamas that had not been vaccinated. The results suggest that the neutralizing antibodies were not part of the pre-immunization repertoire, nor were they detectable after the first vaccination round. Rather, they were generated as immune cells repeatedly encountered the vaccine and responded by maturing specific antibodies that can recognize it.

While it is encouraging that broadly neutralizing antibodies were found in all of the immunized llamas, they are present only at low concentrations in the blood, and so fail to meet the goal for a protective HIV vaccine. Nonetheless, the researchers conclude that the llama model has allowed them to examine the generation of four broadly neutralizing antibodies induced by vaccination, which has not been possible in any other species.

Source: PLOS.