Most immunotherapies are based on two main strategies, active and passive. Active immunotherapy relies on the activation of the patient’s immune system, as is the case in traditional vaccine development. Vaccines are currently used for disease infection, but in the case of cancer, vaccines in development are being designed to specifically attack tumor cells already growing within a patient’s body. Passive immunotherapy, on the other hand, bypasses the patient’s innate immune system and relies on in vitro stimulated immune cells or immune components to carry the burden as effectors. Ex vivo expansion of lymphocytes or antibody production are utilized, and the products are administered to the patient in order to directly take effect. The goal of immunotherapy is to harness the powers of the immune system to either attack foreign antigens, as is the case for tumor immunotherapy, or inhibit the response to a foreign antigen, which would be beneficial in an organ transplant setting. Techniques such as vaccination, adoptive transfer of T cells, and administration of monoclonal antibodies and other immune-mediating small molecules have all been used in an attempt to control immune responses to known antigens. In each of these cases, the molecular and cellular events responsible for an immune response have not been completely defined, and only recently have correlative studies been used to help understand the mechanisms and extent of immune activation following each technique. Real-time monitoring of immune responses to immunotherapy would be incredibly beneficial but has proven to be quite difficult. Until recently, none of the cellular activities could be monitored in vivo and serial studies within individuals were not possible [33, 55, 95]. Advances within the field of molecular imaging have pushed past some of these boundaries and the use of novel nanoparticles has created multiple modalities with which a basic scientist can now attempt to monitor the efficacy of an experimental immunotherapy. The future holds the promise of
not only monitoring the trafficking of immune cells throughout the body but also quantifying the molecular activity and viability of the cells involved in the immune response [50, 51].In this chapter, we will review the role nanoparticles play in aiding the study of cellular and molecular function following immunotherapy. Each of the main imaging modalities currently being used for cellular and molecular imaging will be discussed with a heavy emphasis on magnetic resonance imaging (MRI) as this is our lab’s main area of interest. The practice of immunotherapy is currently far from being optimized, and hopefully with the aid of novel nanoparticles and breakthrough imaging techniques the field will be advanced to the point of standard of care for a variety of ailments.