Dendritic cells, which were codiscovered by Dr. Steinman with Zanvil A. Cohn at Rockefeller, are pivotal to the adaptive and innate branches of the immune system. Dr. Steinman's research focuses on the mechanisms employed by dendritic cells to regulate lymphocyte function in tolerance and resistance, as well as the use of dendritic cells to understand the development of immune-based diseases and the design of new therapies and vaccines.

Lymphocytes are the principal mediators of immune function, but by themselves they do not control immunity. A system of dendritic cells is needed to capture, process and present antigens and to provide additional controls on the development of antigen specific resistance and tolerance. Consequently, dendritic cells (DCs) are providing an important means to monitor and manipulate immune function in several diseases.

One set of DC functions involves the capture of protein antigens, which are then converted to peptides within either the endocytic system or the cytoplasm. The peptides bind to newly synthesized products of the major histocompatibility complex (MHC) — a region of the genome important for immunity and autoimmunity — and then exit to the cell surface for presentation to T cells. Dendritic cells express a number of distinct receptors for antigen uptake. One of these receptors is the multilectin DEC-205. Following DEC-205 mediated uptake, antigens are efficiently processed onto both MHC class I and II molecules.

Also under study is a new family of C-type lectins, called SIGNs, that recognize clinically important infectious agents. For example, DC-SIGN has an endocytic function but also binds and transmits HIV-1 from DCs to T lymphocytes. Dr. Steinman's lab is investigating the uptake and processing of dying cells, particularly tumor cells, with the goal of improving DC based immunotherapy for cancer.

A second set of DC functions relates to their role as key accessories in the control of tolerance and resistance. While DCs provide important innate and adaptive resistance mechanisms to infections, in the absence of infection they also present self-antigens and harmless proteins from the environment, thereby actively silencing or tolerizing the immune system and defining the immunological "self." Dr. Steinman's group is currently investigating active suppressor or regulatory T cell mechanisms that allow DCs to induce tolerance.

But during infection, DCs undergo an intricate differentiation process termed maturation. DCs express additional receptors that allow them to respond to microbial components and other environmental cues to become catalysts, or adjuvants, for the initiation of immunity. Dr. Steinman's lab is linking the maturation of dendritic cells in situ with the uptake and processing of antigens, using new methods to selectively target the antigens to DCs. This work results in antigen presentation on both MHC class I and II products, leading to the formation of functioning CD8+ killer and CD4+ helper T lymphocytes. The lab is currently targeting microbial, self and tumor antigens to DCs in different maturational states in the context of different diseases, including HIV-1 and autoimmune diabetes.

Dendritic cells represent a new class of immune cells having important and unique accessories in the onset of several immune responses, including graft rejection, resistance to tumors, autoimmune disease, and infections. Dr. Steinman's work has led to a new understanding of the control of tolerance and resistance and opened a new field of study within immunology: the role of DCs in immune regulation, their potential for immunization enhancement, and the treatment of autoimmune disorders.

Dr. Steinman received his undergraduate degree from McGill University in 1963 and his M.D. from Harvard Medical School in 1968. After an internship and residency at Massachusetts General Hospital, he joined Rockefeller in 1970 as a postdoc in the Laboratory of Cellular Physiology and Immunology. He was appointed assistant professor in 1972, associate professor in 1976 and professor in 1988. In 1995 he was named the Henry G. Kunkel Professor, and in 1998 he was appointed director of the Christopher H. Browne Center for Immunology and Immune Diseases.

Dr. Steinman was the recipient of the Albert Lasker Award for Basic Medical Research in 2007. He received the New York City Mayor's Award for Excellence in Science and Technology in 2004 and the Gairdner Foundation International Award in 2003. He is a member of the National Academy of Sciences and the Institute of Medicine.