CD4+ memory T-cells are present within the microenvironment of most human non-small cell lung tumors and appear quiescent and non-responsive to the tumor. We question here how these cells are maintained within the tumor for prolonged periods, and how they may be activated in situ to kill tumors. The implantation of non-disrupted human lung tumor biopsy tissues into the subcutis of SCID mice, results in the establishment of xenografts with structurally and functionally intact tumor microenvironments. By monitoring changes in the histology, gene expression patterns, cell depletion analysis and the use of function blocking antibodies, it has been established that exogenous IL-12 mobilizes effector memory CD4+ T cells (TEM) to kill tumor cells in situ by indirect mechanisms that are dependent upon IFN-y. Using this human mouse chimeric model, we will first test the hypothesis that the sustained presence of the CD4+ TEM cells within human tumor microenvironments is dependent upon tumor-associated stromal fibroblasts and plasmacytoid dendritic cells that release Type I interferons and inhibit apoptosis of activated T cells.
In Aim 2, the ability of chemokines and their receptors to influence CD4+ TEM cells derived from the tumor microenvironment to home to and eradicate IL-12 treated tumor xenografts will be compared to central memory T cells (CD4+ TCM) derived from patients' tumor draining lymph nodes. In the final Aims, two specific issues regarding the IL-12 functional activation of memory T cells are addressed.
Aim 3 will establish in the tumor microenvironment whether one or more B7 family co-stimulatory (or negative regulatory) molecules expressed by dendritic cells, stromal cells or tumor cells regulate the anti-tumor response that is orchestrated by IL-12 activated TEM cells. In the final Aim, tumor-associated memory T cell responsiveness to T cell receptor stimuli, the intracellular events associated with this stimulation, and the ability of IL-12 to alter the responsiveness will be determined and compared to central memory and na?ve T cells. It is expected that the knowledge generated here with respect to the survival, migration and activation potential of tumor-associated memory T cells will lead to the design of improved immunotherapeutic approaches that can harness the anti-tumor activity of the memory T cells and enhance their activity by targeting and modulating other inflammatory leukocytes and stromal cells in the tumor microenvironment.
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