Quantitation of MHC tetramer-positive cells from whole blood: Evaluation of a single-platform, six-parameter flow cytometric method

Evaluation of a fit-for-purpose assay to monitor antigen-specific functional CD4+ T-cell subpopulations in rheumatoid arthritis using flow cytometry-based peptide-MHC class-II tetramer staining

Antigen-specific T cells can serve as a response biomarker in non-clinical or clinical immunotherapy studies in autoimmune disease. There are protocols with optimized multimer staining methods to detect peptide (p)MHCII+ CD4+ T cells, and some qualified and validated protocols for pMHCI+ CD8+ T cells. However, no protocol is fully or partially qualified to enumerate and characterize antigen-specific pMHCII+ CD4+ T cells from patient samples. Implementing such an assay requires a desired level of specificity and precision, in terms of assay repeatability and reproducibility. In transgenic type II collagen (CII)-immunized HLA-DR1/DR4 humanized mouse models of collagen-induced arthritis (CIA), CII259-273-specific T cells dominantly expand. Therefore antigen-specific T cells recognizing this epitope presented by rheumatoid arthritis (RA)-associated risk HLA-DR allomorphs are of interest to understand disease progression and responses to immunotherapy in RA patients. Using HLA-DRB1∗04:01 or ∗01:01-collagen type II (CII)259-273 tetramers, we evaluated parameters influencing precision and reproducibility of an optimized flow cytometry-based method for antigen-specific CD4+ T cells and eight specific subpopulations with and without tetramer positivity. We evaluated specificity, precision, and reproducibility for research environments and non-regulated laboratories. The assay has excellent overall precision with %CV<25% for intra-assay repeatability, inter-analyst precision, and inter-assay reproducibility. The precision of the assay correlated negatively with the cell viability after thawing, indicating that post-thaw viability is a critical parameter for reproducibility. This assay is suitable for longitudinal analysis of treatment response and disease activity outcome in RA patients, and adaptable for translational or immunotherapy clinical trial settings.

Generation of allo-restricted peptide-specific T cells using RNA-pulsed dendritic cells: A three phase experimental procedure

Designer T cells expressing transgenic T cell receptors (TCR) with anti-tumor specificity offer new treatment options for cancer patients. We developed a three phase procedure to identify T cells of high avidity based on the fact that T cells recognizing peptides presented by allogeneic MHC efficiently kill tumor cells. Autologous dendritic cells (DC) are co-transfected with ivt-RNA encoding an allogeneic MHC molecule and a selected antigen to allow them to express allogeneic MHC-peptide complexes that activate allo-restricted peptide-specific T cells. This approach provides great flexibility for obtaining high-avidity T cells as potential sources of TCR for adoptive T cell therapy.

Enumeration of WT1-specific CD8+ T cells for clinical application using an MHC Streptamer based no-wash single-platform flow-cytometric assay

The advent of novel strategies to generate leukemia-associated-antigen (LAA)-specific T cells for adoptive immunotherapies creates a demand for standardized good laboratory practice (GLP)-compliant enumeration assays to provide a secure clinical environment-whether it is to identify potential donors, define therapeutic doses for transplantation, or monitor clinical success. Here, we introduce a no-wash assay based on single-platform cell enumeration and Streptamer staining to determine the Wilms' tumor antigen 1 (WT1)-specific T cell immunity in clinical samples. We analyzed the performance of the WT1-specific MHC Streptamers in direct comparison to CMV- and EBV-specific MHC Streptamer staining by spiking antigen-specific T cells in PBMCs. The accuracy of the assay was high for all performed experiments with a mean recovery of 94% and a linear regression of 0.988. Differences were apparent regarding the limit of detection/quantification (LOD/LOQ). While results obtained for WT1 yielded an LOD/LOQ of 0.08 ± 0.04% and 0.11 ± 0.06% (1.33 ± 0.32 cells/µl and 1.9 ± 0.14 cells/µl), the overall LOD/LOQ was notably lower and accounted to 0.02 ± 0.02% and 0.05 ± 0.03% (0.60 ± 0.03 cells/µl and 1.27 ± 0.58 cells/µl). Subsequent screening of 22 healthy individuals revealed significantly higher values for WT1 (0.04 ± 0.02% and 1.5 ± 0.9 cells/µl) than for the irrelevant HIV pol (0.016 ± 0.01% and 0.5 ± 0.4 cells/µl). In contrast, no increased frequencies were observed for WT1-specific T cells compared to HIV-specific T cells using a classical wash-protocol. These findings strongly suggest the use of no-wash single-platform assays in combination with MHC Streptamer staining for the detection of low affinity LAA-specific T cells due to its high accuracy and sensitivity. © 2017 International Society for Advancement of Cytometry.

The development of standard samples with a defined number of antigen-specific T cells to harmonize T cell assays: a proof-of-principle study

The validation of assays that quantify antigen-specific T cell responses is critically dependent on cell samples that contain clearly defined measurable numbers of antigen-specific T cells. An important requirement is that such cell samples are handled and analyzed in a comparable fashion to peripheral blood mononuclear cells (PBMC). We performed a proof-of-principle study to show that retrovirally TCR-transduced T cells spiked at defined numbers in autologous PBMC can be used as standard samples for HLA/peptide multimer staining. NY-ESO-1157-165-specific, TCR-transduced CD8+ T cell batches were successfully generated from PBMC of several HLA-A*0201 healthy donors, purified by magnetic cell sorting on the basis of HLA tetramer (TM) staining and expanded with specific antigen in vitro. When subsequently spiked into autologous PBMC, the detection of these CD3+CD8+TM+ T cells was highly accurate with a mean accuracy of 91.6 %. The standard cells can be preserved for a substantial period of time in liquid nitrogen. Furthermore, TM staining of fresh and cryopreserved standard samples diluted at decreasing concentrations into autologous cryopreserved unspiked PBMC revealed that the spiked CD3+CD8+TM+ T cells could be accurately detected at all dilutions in a linear fashion with a goodness-of-fit of over 0.99 at a frequency of at least 0.02 % among the CD3+CD8+ T cell population. Notably, the CD3+CD8+TM+ cells of the standard samples were located exactly within the gates used to analyze patient samples and displayed a similar scatter pattern. The performance of the cryopreserved standard samples in the hands of 5 external investigators was good with an inter-laboratory variation of 32.9 % and the doubtless identification of one outlier.

Human antitumor CD8+ T cells producing Th1 polycytokines show superior antigen sensitivity and tumor recognition

Adoptive transfer of T cells expressing transgenic TCR with antitumor specificity provides a hopeful new therapy for patients with advanced cancer. To fulfill a large need for TCR with high affinity and specificity for various tumor entities, we sought to identify parameters for rapid selection of CTL clones with suitable characteristics. Twelve CTL clones displaying different Ag sensitivities for the same peptide-MHC epitope of the melanoma-associated Ag tyrosinase were analyzed in detail. Better MHC-multimer binding and slower multimer release are thought to reflect stronger TCR-peptide-MHC interactions; thus, these parameters would seem well suited to identify higher avidity CTL. However, large disparities were found comparing CTL multimer binding with peptide sensitivity. In contrast, CD8(+) CTL with superior Ag sensitivity mediated good tumor cytotoxicity and also secreted the triple combination of IFN-γ, IL-2, and TNF-α, representing a Th1 pattern often missing in lower avidity CTL. Furthermore, recipient lymphocytes were imbued with high Ag sensitivity, superior tumor recognition, as well as capacity for Th1 polycytokine secretion after transduction with the TCR of a high-avidity CTL. Thus, Th1 polycytokine secretion served as a suitable parameter to rapidly demark cytotoxic CD8(+) T cell clones for further TCR evaluation.

Dendritic cells pulsed with RNA encoding allogeneic MHC and antigen induce T cells with superior antitumor activity and higher TCR functional avidity

Adoptive transfer of T cells expressing transgenic T-cell receptors (TCRs) with antitumor function is a hopeful new therapy for patients with advanced tumors; however, there is a critical bottleneck in identifying high-affinity TCR specificities needed to treat different malignancies. We have developed a strategy using autologous dendritic cells cotransfected with RNA encoding an allogeneic major histocompatibility complex molecule and a tumor-associated antigen to obtain allo-restricted peptide-specific T cells having superior capacity to recognize tumor cells and higher functional avidity. This approach provides maximum flexibility because any major histocompatibility complex molecule and any tumor-associated antigen can be combined in the dendritic cells used for priming of autologous T cells. TCRs of allo-restricted T cells, when expressed as transgenes in activated peripheral blood lymphocytes, transferred superior function compared with self-restricted TCR. This approach allows high-avidity T cells and TCR specific for tumor-associated self-peptides to be easily obtained for direct adoptive T-cell therapy or for isolation of therapeutic transgenic TCR sequences.

Basics of standardization and calibration in cytometry--a review

Standardization, calibration, and controls (negative and positive controls) are essential for quality assurance. Cytometers are capable of reliable and repeatable cellular analyses. However, a prerequisite is instrument calibration and standardized preanalytics. Calibration is often done by beads. Beads are available for different quality control applications, e.g. calibration of size and measuring scale, compensation, absolute cell counting, and laser alignment. Results can be standardized by converting MFI values into MESF or ABC values. Standardized data allow comparison of experiments over a long period of time and between different instruments and laboratories. Alterations in the sensitivity of the cytometer can be detected by routinely performing quality control. The process of quality assurance quantifies and helps manage the variance from the desired value. Results can thus be compared objectively with those of other laboratories. Standardization is the basis of cytometry and a prerequisite for obtaining reliable data.

Functional inactivation of EBV-specific T-lymphocytes in nasopharyngeal carcinoma: implications for tumor immunotherapy

Nasopharyngeal carcinoma (NPC) is an Epstein-Barr virus (EBV) associated malignancy with high prevalence in Southern Chinese. In order to assess whether defects of EBV-specific immunity may contribute to the tumor, the phenotype and function of circulating T-cells and tumor infiltrating lymphocytes (TILs) were investigated in untreated NPC patients. Circulating naïve CD3⁺CD45RA⁺ and CD4⁺CD25⁻ cells were decreased, while activated CD4⁺CD25⁺ T-cells and CD3⁻CD16⁺ NK-cells were increased in patients compared to healthy donors. The frequency of T-cells recognizing seven HLA-A2 restricted epitopes in LMP1 and LMP2 was lower in the patients and remained low after stimulation with autologous EBV-carrying cells. TILs expanded in low doses of IL-2 exhibited an increase of CD3⁺CD4⁺, CD3⁺CD45RO⁺ and CD4⁺CD25⁺ cells and 2 to 5 fold higher frequency of LMP1 and LMP2 tetramer positive cells compared to peripheral blood. EBV-specific cytotoxicity could be reactivated from the blood of most patients, whereas the TILs lacked cytotoxic activity and failed to produce IFNγ upon specific stimulation. Thus, EBV-specific rejection responses appear to be functionally inactivated at the tumor site in NPC.

Severe interference between retinal angiography and automated four-color flow cytometry analysis of blood mononuclear cells

BACKGROUND

Retinal angiography has become a widely used diagnostic tool. It requires the intravenous administration of the fluorescent dyes fluorescein and indocyanin green. We recently received blood taken 8 h after retinal angiography, without our knowing it. We describe the failure of an automated flow cytometry system in the enumeration of lymphocyte subpopulations in this sample.

METHODS

Cell enumeration was achieved by the use of the lyse-no wash MultiTEST procedure (Becton-Dickinson) together with the FACSCalibur cytometer. Absolute cell counts were obtained using TruCount beads. Data were analyzed automatically by the MultiSET and manually with the CellQuest softwares.

RESULTS

The dot plots obtained with this sample looked quite abnormal. All monuclear cells stained brightly in the FITC channel irrespective of anti-CD3-FITC conjugate binding. This resulted in a major undercompensation for the increased spillover of the fluorescein emission into the PE-channel. PE-labeled cell and TruCount bead events coalesced. The MultiSET software failed to draw proper gatings and proved useless. Alternative manual gatings could partially rescue the analysis.

CONCLUSIONS

Clinicians and cytometrists should be aware that, because of dye entry or binding, blood mononuclear cells collected shortly after retinal angiography are not suitable even for common cytometry applications.

Dextramers: New generation of fluorescent MHC class I/peptide multimers for visualization of antigen-specific CD8+ T cells

Direct identification as well as isolation of antigen-specific T cells became possible since the development of "tetramers" based on avidin-fluorochrome conjugates associated with mono-biotinylated class I MHC-peptide monomeric complexes. In principle, a series of distinct class I MHC-peptide tetramers, each labelled with a different fluorochrome, would allow to simultaneously enumerate as many unique antigen-specific CD8(+) T cells. Practically, however, only phycoerythrin and allophycocyanin conjugated tetramers have been generally available, imposing serious constraints for multiple labeling. To overcome this limitation, we have developed dextramers which are multimers based on a dextran backbone bearing multiple fluorescein and streptavidin moieties. Here we demonstrate the functionality and optimization of these new probes on human CD8(+) T cell clones with four independent antigen specificities. Their applications to the analysis of relatively low frequency antigen-specific T cells in peripheral blood, as well as their use in fluorescence microscopy, are demonstrated. The data show that dextramers produce a stronger signal than their fluoresceinated tetramer counterparts. Thus, these could become the reagents of choice as the antigen-specific T cell labeling transitions from basic research to clinical application.

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