Correlation of IFN_γ, CD107 and CD137 at the Single Cell Level Can Be Used To Monitor T Cell Responses in Patients after Immunotherapy.

As immunotherapies become increasingly important in the treatment of various cancers, monitoring the immune response to reflect the efficacy of the therapy also becomes increasingly important. Previously, tumor antigen-specific humoral responses in patients receiving vaccines for low-grade follicular lymphoma (FL) correlated with clinical outcomes, including tumor regression, molecular remission, progression free survival (PFS) and overall survival (OS). By contrast, T cell immune responses have been difficult to validate. T cell proliferation assays, mostly, measure CD4 T cell responses; whereas, CD8 T cells may be the important effectors generated by immunotherapies. However, assays designed to measure CD8 T cells, i.e. chromium release CTL assays, and IFN-γ ELISPOT and intracellular flow cytometry assays, are difficult to make reproducible. To address this issue, PBL were obtained from FL patients, cryopreserved, and thawed, then used to design a standardized method for detection of intracellular IFN-γ by flow cytometry. The combined stimulus of soluble anti-CD3 and anti-CD28 antibodies provides a robust stimulation, typically about 5% of normal PBL CD8+ T cells respond. By using a panel of irradiated B cell lymphoma cell lines as stimulators, we demonstrated that, on average, 1 – 2% of these T cells were capable of mounting a response in this assay. Surprisingly, CD8+ PBL T cells from several patients with FL were more responsive to combined anti-CD3 and anti-CD28 stimulation as well as to allo-stimulation, 15 – 22% and 2 – 6%, respectively. This response was accompanied by surface expression of CD107, a surrogate marker for CTL degranulation, in the same population of cells as demonstrated by multi-color flow cytometry. Both the IFN-γ and the CD107 responses were inhibited by an anti-class I antibody, W6/32, suggesting a class I restricted T cell receptor-mediated response. Furthermore, at later time points, these T cells also up-regulated CD137 on their surface. This activation molecule is upregulated on CD8 T cells in response to specific antigen recognition and provides an anti-apoptotic signal to the cells. In conclusion, immune competency of CD8 T cells isolated from FL patients can be assessed through allo-stimulation by a panel of B cell lymphoma cell lines. More importantly, correlation by flow cytometry of 3 independent indicators of response (IFN-γ, CD107 and CD137) within single populations of cells to both allo-stimulation and to the specific target, may lead to better understanding of the role of T cells in the immune response. Ultimately, these responses will need to be validated with patient outcomes in clinical trials of vaccines in lymphoma.