Date: August 2019
Author: David Draper, PhD | Associate Director, Scientific Development
In this Tech Spotlight, we demonstrate the latter capability by presenting data generated using the new Expanded CompT™ panel, a 16-color panel that takes flow analysis of T cell activation and differentiation to a level above any other panel in the Labcorp service portfolio.
Flow cytometry using large antibody panels has the advantage of examining a greater number of cell subsets. This capability is particularly important when a comprehensive data set is required, but limited tumor material is available for analysis. Moreover, panels with a large number of antibodies can also be used to enable deep immunophenotypic insight into a few subsets, or an even deeper analysis into a single subset. In this Tech Spotlight, we demonstrate the latter capability by presenting data generated using the new Expanded CompT™ panel, a 16-color panel that takes flow analysis of T cell activation and differentiation to a level above any other panel in the Covance service portfolio.
The Expanded CompT™ panel builds upon the CompT™ panel, our most popular standard panel to examine CD4+ and CD8+ T cells. This improved panel adds effector and memory T cell markers, plus four additional markers for analysis of T cell activation and exhaustion. Table 1 describes the components of the Expanded CompT™ panel, and using untreated murine MC38 colon adenocarcinomas, Figure 1 illustrates its gating and analysis strategy.
Table 1: Expanded CompT™ Panel Antibodies and Description of Their Utility
|CD45||Pan immune cell marker|
|CD3||Pan-T cell marker|
|CD4||CD4+ T cell marker|
|CD8||CD8+ T cell marker|
|FoxP3||Regulatory T cell marker|
|CD25||Regulatory T cell marker/IL-2 receptor|
|CD62L||Naïve T cell/Memory marker|
|CD69||T cell activation marker|
|PD-1||T cell activation/Exhaustion marker|
|LAG-3||T cell activation/Exhaustion marker|
|TIM-3||T cell exhaustion marker|
|ICOS||T cell activation marker|
|Granzyme B||Anti-tumor cytotoxicity marker|
|Viability Dye||Dead cell exclusion|
|The Expanded CompT™ can be customized to include NK/NKT cell markers (CD49b/CD335) to enable granzyme B and activation marker expression in these subsets.|
Expanded CompT™ Panel Gating Strategy
As with all Covance T cell panels, analysis begins with dead cell exclusion and subsequent CD45+ immune cell delineation to gate on CD3+ T cells (not shown). Figure 1A displays the downstream endpoints of CD4+ and CD8+ T cell analysis that are shared between the CompT™ and Expanded CompT™ panels. These include CD69 and PD-1, which become upregulated upon T cell activation. Their expression has been correlated with the exhausted T cell phenotype. Another shared endpoint is CD8+ T cell proliferation, provided by using Ki-67 expression as a surrogate marker. Finally, CD4+ T cells are examined to quantify helper T cells and regulatory T cells (Tregs). Figure 1B and 1C illustrate the added endpoints used to expand upon the CompT™ panel, which are further described below.
Effector/Memory T Cell Analysis
Analysis of effector and memory CD8+ T cell differentiation is shown in Figure 1B. Conversion of T cells to a memory phenotype is important for the development of lasting immunological response to rechallenge in the context of both infection and cancer pathogenesis. CD44 and CD62L analysis enables the delineation of T cells into four differentiation states. These include naïve or inactivated T cells, activated effector T cells (Teff), effector memory (Tem) and central memory (Tcm) subsets. Tem and Tcm subsets can circulate but have tendencies to reside in non-lymphoid and lymphoid tissues, respectively. Recent reports have demonstrated that both of these subsets have distinct roles in the anti-tumor response. A third resident memory (Trm) population has more recently been described as playing an important role in controlling tumor growth in a variety of models and can be delineated using CD103, among other markers. The Expanded CompT™ panel can be customized to include analysis of Trm cells.
T Cell Activation, Exhaustion, and Granzyme B Analysis
The Expanded CompT™ panel includes ICOS, LAG-3, TIM-3, and granzyme B analysis, which are four intensively investigated biomarkers for T cell functionality (Figure 1C). The analysis of these targets alone and in combination can provide insight into the anti-tumor potential of CD8+ T cells. Evidence supports a co-stimulatory and anti-tumor role for ICOS receptor signaling, thus making ICOS an attractive therapeutic target. Granzyme B is often used as a biomarker for cytolytic activity and can correlate with CD8+ T cell anti-tumor responses. Conversely, PD-1, LAG-3 and TIM-3 are inhibitory receptors and while the expression of these three receptors has been linked to T cell exhaustion, a growing body of data suggests heterogeneity among sub-populations exists within the exhausted PD-1 expressing CD8+ T cells. This heterogeneity correlates with the expression pattern of these inhibitory receptors. This profile can help define different sub-populations that have distinct potential to be re-invigorated to proliferate and/or lyse tumor cells. Figure 2 illustrates how the Expanded CompT™ panel can quantify cells with double and triple positive expression for inhibitory receptors and provide insight into the heterogeneous PD-1 expressing T cell subset and its functionality. Numerous other T cell activation and inhibitory receptors have been described and implicated in influencing tumor immune responses; these include TIGIT, OX-40, CD137, CTLA-4, and others. Covance has experience analyzing many of these markers in ex vivo tumor analysis. With minimal developmental efforts, the Expanded CompT™ can be customized to meet your unique pre-clinical needs.
Customization – NK/NKT Cell Analysis and Further Options
Covance can configure custom panels with up to 18 colors, which creates options for the MI-Expanded CompT™ panel. In addition to substituting or adding different T cell activation/exhaustion markers as described in the previous section, NK/NKT cell analysis is a potentially valuable endpoint. This is enabled by the addition of CD49b/CD335 markers to the panel (Figure 3).
Fig. 3: Expanded CompT™ panel customization to enables analysis NK and NKT cell subsets in naïve MC38 tumor-derived cells. CD3 expression was used to delineate CD49b/CD335+ NK cells and NKT cells. Granzyme B expression levels in these subsets was quantified by downstream analysis.
NK and NKT cells are an important source of IFNγ, have indirect effects on enhancing CD8+ T cell anti-tumor responses, and can directly lyse tumor cells by releasing cytolytic granules such as granzyme B.[7,8] Other options include IFNγ, TNFα, or other cytokine analyses for a more in depth profile of PD1+ and PD1– CD8+ T cells. Or add CD103 analysis to examine resident memory T cells for a deeper memory T cell profile in the tumor. Covance’s team has extensive experience developing custom flow cytometry services. To learn more about how the Expanded CompT™ panel can be incorporated into it into your preclinical research, contact the scientists at Labcorp.
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7Zhu, Yanting, Bo Huang, and Jue Shi. “Fas ligand and lytic granule differentially control cytotoxic dynamics of natural killer cell against cancer target.” Oncotarget 7.30 (2016): 47163.