My PhD work was informative but lacked the molecular insights needed to understand how to induce or break tolerance. At the time, in the late 1970s, organ transplants from genetically distinct cadaveric donors were becoming a more routine treatment for kidney failure. Patients were treated life-long with immunosuppressive drugs to prevent rejection, and using the drugs led to infections or cancer. This drew me to study organ transplant rejection and immune tolerance in my postdoc at the National Institutes of Health. During eight years there, I began understanding the yin-yang of tolerance, inducing and breaking it. This work set the stage for the rest of my 40+ year career as I bounced back and forth between research in autoimmune diabetes ( inducing it ) and cancer ( breaking it ) .
The first inflection point in the field was the advent of a new technological toolkit in the 1980s: the ability to make monoclonal antibodies to detect proteins controlling the immune system and genetic engineering, a technology that allowed the identification and manipulation of individual genes in the genome. These tools allowed us to better understand the key players — the cells, pathways, proteins and cytokines involved — and what determines whether an immune response is turned on or off. The second inflection point came with the knowledge that the immune system has sets of brakes and gas pedals designed to suppress and activate immune responses, respectively. We often imagine the immune system being composed of soldiers ready to look for and attack foreign threats. But, sometimes, these warriors make mistakes, attacking their own tissues and organs instead of foreign viruses, bacteria and other pathogens. In the 1990s, we realized that an entire arm of the immune system is designed to maintain tolerance, with some parts acting as policemen to prevent the warriors from inadvertently attacking their own tissue. For me, this epiphany manifested in a series of studies conducted in my lab. We were studying the molecules on the surface of T cells that were critical in boosting the immune response. There was good evidence that CD28 ( cluster of differentiation 28 ) , a protein expressed on all T cells, was critical to generating a productive immune response. So, we speculated that another molecule, cytotoxic T-lymphocyte associated protein 4 ( CTLA-4 ) , expressed on activated T cells and 50% identical to CD28, likely played a similar role. So, we made an anti-CTLA-4 monoclonal antibody to block its activity, assuming it would “ inhibit ” T cell activation. But much to my surprise, adding anti-CTLA-4 monoclonal antibodies to cultures didn ’ t prevent the immune response but enhanced it. This unexpected finding changed how we think about a class of molecules, including CTLA-4, expressed in the immune system that controls immune homeostasis. These checkpoints deter overzealous immune responses. This discovery established the checkpoint field and led to the development of checkpoint inhibitors that could block the off-signals and enhance tumor immunity. This discovery was an essential piece of the immune tolerance puzzle, resulting in the Nobel Prize-winning research by Drs. James Allison and Tasuku Honjo. Perhaps as importantly, the discovery of CD28 as an “ on ” signal and CTLA-4 as an “ off ” signal broke another dogma: that all T cells performed the same role in maintaining tolerance. It became clear in the early 2000s that Tregs, a specialized cell population, expressed a high level of CTLA-4 and functioned as a major controller of immunity, seeking and shutting down unwanted immune responses. This seminal discovery was made by Drs. Fred Ramsdell and Alexander Rudensky, co-founders of Sonoma Bio, along with Japanese scientist Dr. Shimon Sakaguchi. This research changed the course of my career and led to further research on the use of engineered Tregs as therapeutics pioneered in my lab and now at Sonoma Bio. Dr. Bluestone ’ s guiding philosophy of doing “ kick-ass science ” and collaborating with other scientists has pushed the boundaries of our understanding of immunology and immune tolerance and influenced the development of therapeutics for cancer and autoimmune diseases
Why are Tregs so critical, and what is their potential as therapeutics? The immune system is engaged in a delicate balancing act, committed to seeking and eliminating infectious pathogens and, at the same time, creating a tolerogenic environment to avoid inadvertent self-reactivity. One example of an immune system gone awry is the consequence of the SARs-CoV-2 infection. The immune system is poised to recognize and destroy the virus, but, often, immune cells start producing factors that cause severe lung inflammation, resulting in COVID-19. Most people die of the consequences of dysregulated immunity rather than the viral infection itself. This
Immune regulation graphic (Bucktrout, Bluestone and Ramsdell, 2018) Immune health is a delicate balance between tolerance and immunity
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