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Professor Don Mason 1934 – 2021 

The BSI was saddened to learn about the recent death of our Honorary Member, Professor Don Mason. Don made significant contributions to cellular immunology and training the next generation of immunologists over decades. 


The immunology community lost a much valued friend and colleague on 13 January 2021 when Don Mason passed away peacefully surrounded by his family. An Honorary Life Member of the BSI, Don made influential fundamental contributions to cellular immunology and also trained several generations of successful immunologists across the world.

Don trained initially as a physicist, working for several years in the field of thermonuclear fusion before studying medicine and moving into immunology research in 1973 at the MRC Cellular Immunology Unit, in the Sir William Dunn School of Pathology, Oxford University. His research was highly innovative and often ahead of current paradigms. Together with Alan Williams and colleagues at the MRC Cellular Immunology Unit, Don focused on immunological studies using the rat as a model organism. He was among the first to identify the T-helper function of CD4+ T cells, initially in the mixed leukocyte reaction in vitro. Using panels of monoclonal antibodies generated at the Dunn School to key leukocyte surface molecules, he further analysed functions of lymphocytes. For example, using antibodies to restricted high molecular weight forms of CD45 (OX-22), he was able to show that CD4+ T cells that provided B cell help were distinct from those that mediated graft versus host disease, providing early evidence of the functional heterogeneity of T-helper cells.

Those studies also identified specialised suppressive T cells, now known as regulatory T cells, that control autoimmune and inflammatory responses. His work on the ability of thymocyte subpopulations to suppress autoimmune disease led him to conclude that the production of regulatory T cells was the third function of thymus. Although many immunologists at the time were sceptical of the concept of specialised T cells capable of policing the immune response, Don and a handful of immunologists continued to pursue this idea. Those studies established the foundations of the regulatory T cell field, now a major immunological paradigm that continues to define the field of immune regulation today.

Through his rigorous approach, Don also characterised many of the parameters regulating the development of experimental autoimmune encephalitis, a model of multiple sclerosis in rats, and potential therapeutic approaches. He extended these studies to other autoimmune diseases, thyroiditis and diabetes. Through his application of quantitative approaches, he published classical papers on antibody kinetics and a theoretical paper arguing that the specificity of the T cell receptor had to be broadly cross-reactive and not highly specific as was widely argued. This paper has been cited more than 700 times and remarkably after more than 20 years is still cited more than 30 times a year; a testament to the enduring quality of Don’s work that continues to influence immunologists today. 

Don was an inspiration and huge positive influence on his mentees. He led a small lab emphasising the joy of discovery accompanied by a robust and critical approach to data alongside a friendly and collegiate spirit. Many trainees became friends who Don kept in touch with, maintaining an interest in their career. His combination of high intellect combined with kindness and humility made him a highly regarded colleague in Oxford and beyond. He was generous with his time and aided and encouraged many researchers in other institutions by sharing reagents and discussing ideas freely.

Don’s strong scientific principles were matched by his concern for societal issues. He was a vegan, a Quaker and a committed pacifist. He adapted his lifestyle out of concern for the environment stating that humans will be the only species to threaten their own existence – sadly a prophecy with huge relevance today. He believed in the goodness of people. He corresponded with prisoners, showing kindness to those not as fortunate as himself and felt that everybody deserved a second chance. Most of all Don was a family man, immensely proud of his wife, children and grandchildren.

Fiona Powrie, Anne Cooke