Non-genetically engineered mammalian cells modified by sortase-mediated conjugation of an agent thereto are provided. Methods of conjugating agents to nongenetically engineered mammalian cells using sortase are provided. Methods of using the cells, e.g. a method of modulating an immune response of a subject to an entity of interest, a method of neutralizing a substance in the body of a subject, a method of treating a subject in need of treatment for deficiency of a protein, and a method of treating a subject in need of treatment for a disease, are provided.
