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Tumor-specific T cells are crucial for immunologic control of malignant disease. T cells can be induced in vivo by vaccination or adoptively transferred after activation ex vivo. We investigated the requirements for generating T cells with optimal antitumor effector functions in a murine lymphoma model. Using adoptive transfer, we show that in vivo efficacy of T cells cannot be predicted by tumor reactivity in vitro. A restricted T-cell receptor b chain repertoire of T-cell populations stimulated ex vivo against tumor cells was necessary but not sufficient for tumor protectivity. Tumor elimination furthermore required vaccination of donor mice, hence in vivo priming. The in vivo priming step may allow tumor-specific T cells to accumulate in vitro more rapidly and to survive for longer periods after withdrawal of the antigenic stimulus and adoptive transfer. A possible survival benefit of in vivo induced T cells may be ascribed to the responsiveness to homeostatic cytokines and to unique cytokine milieus encountered in vivo. Most importantly, monoclonal T cells cannot inhibit tumor growth. A prerequisite of tumor rejection was the expression of at least 2 T-cell receptor b chains by transferred T-cell populations. This finding has implications for designing adoptive transfer strategies for the clinic.

B cell-derived chronic lymphocytic leukemia (CLL) is an incurable disease that requires innovative therapeutic regimens. Experimental approaches of immunotherapy aiming at induction of systemic T-cell responses have been developed. Trioma cells provide a potent vaccine derived from malignant B cells that allows multiple antigens (Ags) from the parental tumor to be ingested by Ag-presenting cells. Like other strategies using modified whole tumor cells, this approach induces polyvalent responses. Using trioma cell-pulsed dendritic cells (DCs) for T-cell activation in vitro, we asked whether specific Ags overexpressed by CLL can be identified as target structures of such responses and what is the nature of these Ags. Expression levels of several genes in CLL samples were quantitated by reverse transcriptase-polymerase chain reaction. T lymphocytes were polyvalently stimulated by trioma-pulsed DCs and specificities were tested by determining cytokine secretion in the presence of target cells transfected with RNA coding for those Ags that were found to be overexpressed. We demonstrate that DCs pulsed with the modified tumor cells efficiently activate T lymphocytes against CLL and that overexpressed Ags related to leukemogenesis, such as BCL-2, MDM2, and ETV5, serve as targets for those T cells. Immune escape by Ag loss or mutation is less likely to occur if immunity is directed against altered self-proteins that are involved in malignant transformation. Therefore, vaccines based on modified tumor cells such as triomas hold promise for immunotherapy of CLL and other malignancies. Polyvalent vaccines originally designed as individualized therapeutics may be more broadly applicable, at least in patients showing similar Ag patterns.

No abstract

While Fibroblastic Reticulum Cells (FRC) of the lymph node (LN) are known to produce chemokines responsible for the migration of naïve T cells and DC, little is known about their interactions with these cells and their influence on DC and T cell activation. Therefore, we have evaluated the interaction between DC, FRC and T cells in an in vitro model. For the generation of FRC cells lymph nodes of BALB/c mice were isolated and cultured ex vivo. After co culture with FRC DCs were characterized by FACS analysis concerning their survival rate, maturation state and expression of cell surface molecules as well as for their production of soluble cytokines. The ability of DC to induce T cell proliferation was evaluated using the D011.10 TCR transgenic system and CFSE labeling. Our in vitro culture method leads to a highly homogeneous FRC population regarding expression of gp38, ER-TR 7, CD44 and V-CAM. Confocal microscopy analysis demonstrated that DC migrated to FRC where they made physical contact leading to stable associations in vitro as well as in vivo in the LN after DC were injected s.c.. Co incubation of DC with FRCs resulted in a complete down regulation of CD40 and partial decrease of co stimulatory molecules. Furthermore there was a strongly diminished ability of these DC to induce a peptide specific proliferation of naïve T cells although a clear CD25 up regulation could be detected. It remains to be investigated whether these CD25 positive T cells show a regulatory phenotype. Our results demonstrate that LN-FRC provide a milieu that may induce tolerogenic DCs which then drive naïve T cells to a rather regulatory phenotype.