In vivo augmentation of tumor-specific CTL responses by class I/peptide antigen complexes on microspheres (large multivalent immunogen)

Tumor membrane Ag immobilized on cell size microspheres (large multivalent immunogen (LMI)) was previously shown to augment tumor-specific CTL activity and reduce tumor growth, and a clinical trial examining this approach is in progress. In the current study, LMI treatment has been examined using adoptive transfer of TCR-transgenic CD8 T cells to visualize Ag-specific cells during the response. OT-I T cells specific for H-2K^b/OVA_257-264 were transferred into mice that were then challenged with LMI made by immobilizing H-2K^b/OVA_257-264 on microspheres (K^b/OVA_257-264-LMI) alone, or along with i.p. challenge with OVA-expressing E.G7 tumor. K^b/OVA_A257-264-LMI caused significant reduction of tumor growth when administered to E.G7bearing mice. When administered alone, the K^b/OVA_257-264-LMI caused only weak clonal expansion of OT-I cells in the spleen and lymph nodes, although most of the OT-I cells up-regulated expression of CD44 and VLA-4. In contrast, K^b/OVA_257-264-LMI administration to E.G7-bearing mice stimulated no detectable expansion of OT-I cells in the spleen and lymph nodes but caused a rapid increase in the number of OT-I cells in the peritoneal cavity, the site of the growing tumor. These results demonstrate the potential for using class I/tumor peptide complexes for immunotherapy. In addition, they suggest a model for the mechanism of CTL augmentation in which recognition of the LMI Ag results in altered trafficking of the tumor-specific CD8 T cells so that they reach the site of a growing tumor more rapidly and in greater numbers, where they may further expand and acquire effector function.