T Cells Vs. Tumor Cells: Arming/Deploying T Cells For A Successful Battle.

Modulating T cell immunity to treat human malignancies is showing increasing promise, but substantive obstacles remain. Reproducibly effective therapy will require many factors be in place, including an appropriate antigenic target, a high avidity and high magnitude T cell response, and the T cells having the ability to infiltrate and retain function in the tumor microenvironment. We have been systematically investigating strategies to address these issues. To identify targetable leukemia antigens, we compared gene expression profiles in purified leukemic stem cells with profiles in normal hematopoietic stem cells and other somatic cells, and identified two promising targets that are associated with the leukemic phenotype, WT1 and Cyclin A1, and to which CD8 T cells that lyse leukemic cells can be generated. Generating sufficient numbers of specific T cells with high avidity for the target in each patient is a substantive problem. We will discuss a just completed trial targeting WT1 in leukemia patients, which highlights the potential benefit of providing potent T cell responses to this pro-oncogenic protein. For this trial, we generated panels of WT1-specific CD8 T cells clones for each patient and then selected and expanded for adoptive therapy the highest avidity clone isolated. However, this approach is limited by the responses elicited for each patient, who often have compromised repertoires, and could be overcome by identifying the T cell receptor (TCR) gene from a defined high avidity leukemia-reactive T cell clone that can be introduced into large numbers of patient T cells to create a standardized reagent for treatment. However, ultimately the avidity of transduced T cells used for therapy is limited by the affinity of the introduced TCR, and high affinity TCRs for tumor antigens that are also normal self-antigens may not be readily identified in normal repertoires. Our lab has developed in collaboration with David Kranz9 lab methods to mutate/alter the CDR3 regions of the isolated antigen-specific TCR chains prior to introduction into recipient T cells to improve the affinity for the target antigen, as well as methods to interrogate the full repertoire of β-chain rearrangements capable of pairing with a defined TCR α-chain before negative selection. Strategies to evaluate the in vivo activity and safety of such TCRs in relevant mouse models will be described. Unfortunately, providing a high avidity T cell response does not necessarily result in tumor eradication. Major obstacles include the development of tolerance/anergy and/or exhaustion/dysfunction in tumor-reactive T cells, particularly within the tumor microenvironment. We have explored these issues in T cell therapy models in mice with leukemia or that “spontaneously” develop solid tumors as a consequence of regulated tissue-specific expression of an oncogene. These studies highlight the difficulties sustaining responses to tumor antigens that are self-proteins and the inhibitory pathways that are commonly operative within the tumor microenvironment, and have provided insights into how to potentially sustain activity by selecting or genetically modifying T cells to be resistant to obstacles that prevent tumor eradication. However, different tumor types can engage distinct pathways and have unique characteristics, and thus understanding the immunobiology of the tumor to be treated will likely be essential for designing effective therapies. Citation Format: Philip D. Greenberg, Sebastian Ochsenreither, Tom Schmitt, David Aggen, David Kranz, Matthias Wolfl, Jurgen Kuball, Ravi Majeti, Irv Weissman, Ingunn Stromnes, Andrea Schietinger, Gunnar Ragnarsson, Cassian Yee, Merav Bar, Aude Chapuis. T cells vs. tumor cells: Arming/deploying T cells for a successful battle. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr IA1.