CD8A and cancer: New imaging tracers specifically targeting subsets of immune cells by the use of radiolabeled fragmented specific antibodies to CD8+ and CD4+ T cells (use of cys-diabody and minibody) and CD11b+ myeloid cells (use of variable domain of a camelid heavy-chain antibody) are successfully used in preclinical mouse models and currently being developed for advanced PET imaging in clinical monitoring applications to cancer immunotherapy [85–87].