Over the past two decades, immune cell therapy has emerged as a potent treatment for multiple cancers, first through groundbreaking leukemia therapy, and more recently, by tackling solid tumors. Developing successful therapeutic strategies using live cells could benefit from the ability to rapidly determine their in vivo biodistribution and persistence. Assaying cell biodistribution is unconventional compared to traditional small molecule drug pharmacokinetic readouts used in the pharmaceutical pipeline, yet this information is critical towards understanding putative therapeutic outcomes and modes of action. Towards this goal, efforts are underway to visualize and quantify immune cell therapy in vivo using advanced magnetic resonance imaging (MRI) techniques. Cell labeling probes based on perfluorocarbon nanoemulsions, paired with fluorine-19 MRI detection, enables background-free quantification of cell localization and survival. Here, we highlight recent preclinical and clinical uses of perfluorocarbon probes and 19F MRI for adoptive cell transfer (ACT) studies employing experimental T lymphocytes, NK, PBMC, and dendritic cell therapies. We assess the forward looking potential of this emerging imaging technology to aid discovery and preclinical phases, as well as clinical trials. The limitations and barriers towards widespread adoption of this technology, as well as alternative imaging strategies, are discussed.

IntroductionThe ability of neoplastic cells to evade the immune system remains a formidable barrier limiting the success of immunotherapy. Tumor cells can employ various mechanisms to escape detection by immune cells. These can include down-regulation of major histocompatibility complex (MHC) class I expression, 1-4 production of immunosuppressive cytokines such as transforming growth factor-␤, 1,5 up-regulation of Fas ligand, 6 and deregulation of zeta chain on T cells. 7 In both mouse and human, natural killer (NK) cells are composed of different subsets, which are characterized by the expression of inhibitory and/or activating receptors specific for MHC class I determinants. [8][9][10][11] In mice, these receptors belong to the family of Ly49 receptors, which are lectinlike molecules. 12 The human counterpart, killer immunoglobulin-like receptors, belongs to the immunoglobulin superfamily. 11 A small percentage of T cells in mice also express Ly49 receptors. 13 It has been shown that binding of the inhibitory receptors by the appropriate class I molecules results in generation of negative signals leading to inactivation of NK cell functions. [13][14][15] This inhibitory signal has been shown to dominate over activating stimuli. 15 Furthermore, the rapid rejection of tumors lacking the expression of MHC class I by NK cells demonstrates the pivotal role MHC plays in regulating NK function. [16][17][18] In spite of these studies demonstrating the functions of the inhibitory receptors in vitro, the in vivo functions of these receptors on either NK or T cells remain to be elucidated.One potential means for tumor escape may be by expressing MHC class I determinants at a level that allows sufficient binding of the Ly49 inhibitory receptors and thus escape from NKmediated killing. In To examine the effects of blockade of the inhibitory receptors on antitumor activity, we have used a C1498 mouse leukemia model and F(abЈ) 2 fragments of 5E6 monoclonal antibody (mAb), 21 which binds to Ly49C and I receptors, for in vitro as well as in vivo studies. The use of F(abЈ) 2 fragments allowed us to examine the responses that are due to blocking the Ly49 receptors without For personal use only. on May 12, 2018. by guest www.bloodjournal.org From depletion of the subset in vivo. The results from these studies demonstrate that blockade of Ly49 inhibitory receptors augments NK cell-mediated antitumor effects and that strategies to block NK inhibitory receptor interactions may be of potential use in cancer therapy. Materials and methods MiceC57BL/6 (B6, H2 b ) mice were obtained from the Animal Production Area (National Cancer Institute at Frederick [NCI-Frederick], MD), and B6 severe combined immunodeficient scid/scid (SCID) mice were generously provided by Dr Robert H. Wiltrout (NCI-Frederick). All mice were kept in a specific pathogen-free condition and used at 8 to 12 weeks of age. Antibodies and generation of F(ab) 2 fragmentsAntimouse Fc␥R (2.4G2, rat immunoglobulin [Ig]-G2a), fluorescein isothiocyanate (FITC)-conjugated anti...

Interleukin-7 (IL-7) is required for the development and survival of T cells and plays a critical role in modulating T-cell homeostasis. This review will address current understanding of IL-7 biology, review recent clinical experiences and discuss potential future clinical applications of IL-7, or IL-7 blockade, in the setting of disease.