On 28 February 2010, at the age of 76 years, Stefan Thierfelder passed away after a long debilitating disease. He was the head of the Institute of Immunology at the Helmholtz Zentrum München, and a scientist and pioneer in the field of SCT and Ab therapy.

The scientific journey of Stefan Thierfelder started in Paris at the Centre de Recherches sur les Maladies du Sang under the guidance of Jean Dausset, who is a Nobel laureate for his work on HLA. HLA–Ag disparity was one of the causes of transfusion reactions, and Stefan Thierfelder was appointed in 1965 to the Gesellschaft für Strahlenforschung (GSF, nowadays the Helmholtz Zentrum München) for the study of plt antibodies. However, in the context of radiation research, he devoted significantly more time to the investigation of SCT and the use of anti-lymphocyte antibodies for prevention of rejection and GVHD. As head of the Division of Immunology, he oversaw significant progress in immunogenetics with the definition of HLA-class II Ags in experimental SCT and in immune phenotyping of leukaemia. Depletion of T cells using specifically absorbed anti-thymocyte globulin and purging of an autologous marrow of residual leukaemia cells using antiglobulin against c-ALL Ag (CD10) were pioneered by him. He actively pursued translational programmes that were facilitated by the Haematologikum built on the Campus Großhadern of the University of Munich, located close to the University Hospital. This was not only the first BM transplant in a child with severe aplastic anaemia to be performed successfully, but also new methods such as T-cell depletion and Ab purging were introduced in the clinic. The same absorbed antiglobulins were helpful in differentiating ALL. Polyclonal antibodies were substituted by monoclonal antibodies. Recently, the first bispecific Ab licensed was developed by his collaborators. Symposiums for Immunobiology 1977 and 1980, as well as the Congress of the International Society for Experimental Hematology (ISEH) 1981 in Munich, reflected his international reputation.

Stefan Thierfelder was a well-educated companion for discussions not only in science but also in literature, arts, social and political issues. He was open minded and critical at the same time. As leader of a team he cultivated dialogue at any time and with everyone who was seriously interested. His originality and open mind combined with critical judgement provided a creative atmosphere supporting productivity and inspiring devotion from members of his group. We gratefully acknowledge his support and shall always remember him.