Professor Kai-Michael Toellner studied biology at the University of Hohenheim, Germany, where he had his first contact with immunology in the laboratory of Clinical Chemistry and Laboratory Medicine, Katharinenhospital Stuttgart, working on new flow cytometry techniques to measure lymphocytes in cerebrospinal fluid. From there he moved to the Forschungszentrum Borstel, Germany, for a PhD project on the regulation of germinal centre reactions by T lymphocytes and cytokines under the mentorship of Professor Johannes Gerdes. In 1994, Kai Toellner started as a postdoctoral research fellow at the Department of Immunology, University of Birmingham, initially under the mentorship of Professor Ian MacLennan and later with his own research team.

His main interests are cellular interactions and differentiation processes that happen in lymphoid tissues during cellular responses to vaccines or pathogens. During these processes lymphocytes differentiate to become high affinity effector cells that will produce pathogen-specific neutralising antibody and form immunological memory that can protect us over a long time. Processes studied are the role of cytokines produced by T lymphocytes and stroma onto the selection and differentiation of B lymphocytes, the role of antibody and B cell receptor signals on the selection of B cells in germinal centres, and which signals regulate output of effector B cells from the germinal centre, i.e. cytokines, chemokines, and accessory cells regulating differentiation of high affinity plasma cells and memory B cells.

He has active collaborations with several labs in the UK, Germany, Italy, and Australia.