Assessment of lymphocyte-mediated cytotoxicity using flow cytometry

A novel approach to measuring cell-mediated lympholysis using quantitative flow and imaging cytometry

In this study, we established a novel isotope-free approach for the detection of cell-mediated lympholysis (CML) in MHC defined peripheral blood mononuclear cells (PBMCs) using multiparameter flow and imaging cytometry. CML is an established in vitro assay to detect the presence of cytotoxic effector T-lymphocytes precursors (CTLp). Current methods employed in the identification of CTLp in the context of transplantation are based upon the quantification of chromium ((51)Cr) released from target cells. In order to adapt the assay to flow cytometry, primary porcine PBMC targets were labeled with eFluor670 and incubated with major histocompatibility complex (MHC) mismatched effector cytotoxic lymphocytes (CTLs). With this method, we were able to detect target-specific lysis that was comparable to that observed with the (51)Cr-based assay. In addition, the use of quantitative cell imaging demonstrates the presence of accessory cells involved in the cytotoxic pathway. This innovative technique improves upon the standard (51)Cr release assay by eliminating the need for radioisotopes and provides enhanced characterization of the interactions between effector and target cells. This technique has wide applicability to numerous experimental and clinical models involved with effector-cell interactions.

New flow cytometric assays for monitoring cell-mediated cytotoxicity

The exact immunologic responses after vaccination that result in effective antitumor immunity have not yet been fully elucidated and the data from ex vivo T-cell assays have not yet defined adequate surrogate markers for clinical efficacy. A more detailed knowledge of the specific immune responses that correlate with positive clinical outcomes should help to develop better or novel strategies to effectively activate the immune system against tumors. Furthermore, clinically relevant material is often limited and, thus, precludes the ability to perform multiple assays. The two main assays currently used to monitor lymphocyte-mediated cytoxicity in cancer patients are the (51)Cr-release assay and IFN-gamma ELISpot assay. The former has a number of disadvantages, including low sensitivity, poor labeling and high spontaneous release of isotope from some tumor target cells. Additional problems with the (51)Cr-release assay include difficulty in obtaining autologous tumor targets, and biohazard and disposal problems for the isotope. The ELISpot assays do not directly measure cytotoxic activity and are, therefore, a surrogate marker of cyotoxic capacity of effector T cells. Furthermore, they do not assess cytotoxicity mediated by the production of the TNF family of death ligands by the cytotoxic cells. Therefore, assays that allow for the simultaneous measurement of several parameters may be more advantageous for clinical monitoring. In this respect, multifactor flow cytometry-based assays are a valid addition to the currently available immunologic monitoring assays. Use of these assays will enable detection and enumeration of tumor-specific cytotoxic T lymphocytes and their specific effector functions and any correlations with clinical responses. Comprehensive, multifactor analysis of effector cell responses after vaccination may help to detect factors that determine the success or failure of a vaccine and its immunological potency.

Elicitation of T cell responses to histologically unrelated tumors by immunization with the novel cancer-testis antigen, brother of the regulator of imprinted sites

Brother of the regulator of imprinted sites (BORIS) was previously described as a transcription factor for epigenetic reprogramming the expression of which is strictly confined to germ cells of adult testes but is aberrantly activated in the vast majority of neoplastic cells. Considering the critical role of BORIS in cancerogenesis and the fact that its expression pattern may preclude thymic tolerance, we generated DNA- and protein-based mouse BORIS antitumor vaccines using a non-DNA-binding version of the BORIS molecule. Clinical use of BORIS as a vaccine Ag would require that certain safety concerns be met. Specifically, administration of the functional BORIS protein would hypothetically pose a risk of BORIS accelerating the progression of cancer. To alleviate such safety concerns, we have developed vaccines based on the BORIS molecule lacking the DNA-binding zinc fingers domain. To enhance anti-BORIS cellular immune responses, we used a standard molecular adjuvant approach. It consisted of plasmids encoding murine IL-12 and IL-18 for a DNA-based vaccine and conventional Th1 type adjuvant, Quil A, for a protein-based vaccine. Both DNA- and protein-based vaccines induced Ag-specific CD4(+) T cell proliferation with Th1 and Th2 cytokine profiles, respectively. Protein-based, but not DNA-based, BORIS vaccine induced a significant level of Ab production in immunized animals. Importantly, potent anticancer CD8(+)-cytotoxic lymphocytes were generated after immunization with the DNA-based, but not protein-based, BORIS vaccine. These cytolytic responses were observed across a wide range of different mouse cancers including mammary adenocarcinoma, glioma, leukemia, and mastocytoma.