Development of biomaterials that exert control over the function of cells of the immune system could lead to new immunotherapies for treatment of diseases as diverse as cancer, persistent viral infections, and autoimmunity. Biomaterials can also be envisioned that serve as model scaffolds for studying the function of immune cells in a three-dimensional biomimetic environment, where particular aspects of cell function can be probed by systematic variation of physical parameters. We are currently developing materials for these two immunological applications, first for basic studies of lymphocyte function in a lymphoid tissue-mimicking synthetic structure, and second as engineered vaccines. To create an in vitro 3D model of the T zone of the lymph node, we have developed a novel approach based on colloidal crystal templating to create hydrogel structures presenting ECM-derived adhesion peptides. This 3D biomimetic matrix can be used to identify the influence of environmental factors on lymphocyte activation. For engineered vaccines, we are studying antigen-delivery particles designed to activate dendritic cells (DCs) in vivo. Biodegradable hydrogel particles with diameters ranging from < 100 nm to similar to1 mum have been prepared with pH-sensitive co-monomers to allow these antigen-encapsulating particles to respond to the reduced pH within endosomes of DCs.