Published in Frontiers in Immunology: Characterizing the Potency of a Novel Cell Therapy Using Single-Cell Functional Proteomics

T cell-based therapies have improved clinical outcomes for a number of different cancers including lymphoma, multiple myeloma, and acute lymphoblastic leukemia. Acute myeloid leukemia (AML), however, has proven difficult to treat, with some recent cell therapy trials resulting in insufficient responses and off-target effects. Strategies that take advantage of new T cell engineering techniques are currently being explored to offer improved AML treatment options.

One such strategy involves the use of bispecific T-cell engagers (BiTEs), molecules that have the ability to kill tumor cells in an antigen-dependent manner and recruit bystander T cells to tumor cells. BiTEs have a short half-life frequent infusions, but researchers have solved this problem by developing T cells that can secrete BiTES, called engager T cells (ENG-T cells). ENG-T cells can be further optimized for improved efficacy, persistence, and tolerability, but these modifications require additional characterization to understand how these cells are functioning. IsoPlexis’ single-cell solution for multiplexing extracellular proteins, Single-Cell Secretome, empowers researchers with insight into how individual engineered cells behave and drive immune responses against tumor cells.

Using Single-Cell Secretome to Characterize Engineered Cells

In a paper recently published in Frontiers of Immunology, researchers were able to characterize novel ENG-T cells by using ENG-T cells targeted to CD123, a tumor-associated antigen expressed by AML cells. Chronic exposure to an antigen (in this case, CD123) would reduce the activity of engineered T cells. To address this, the researchers modified the ENG-T cells to secrete IL-15, a cytokine that can improve the effector function of T cells. They then used Single-Cell Secretome to characterize how this modification affected cell function.

The researchers compared three groups of cells: ENG-T cells targeted to CD19 and expressing IL-15 (CD19.IL15), ENG-T cells targeted to CD123, and ENG-T cells targeted to CD123 and expressing IL-15 (CD123.IL15). The researchers measured the polyfunctionality, the ability of a cell to secrete two or more cytokines, of each group and found that the proportion of cells that were polyfunctional were lowest in the CD19IL.15 group, higher in the CD123 group, and highest in the CD123.IL15 group when stimulated with AML cells that express the CD123 antigen. Increased polyfunctionality of engineered T cells has previously been associated with improved efficacy and clinical outcomes.

To see how cytokine secretion profiles varied among the different cell types, the researchers compared the polyfunctional strength index (PSI) of the different types of ENG-T cells. PSI is calculated by multiplying the percentage of cells that are polyfunctional by the average signal intensity of the secreted proteins for each cell. The overall PSI of the three groups followed the same pattern as polyfunctionality, with the CD123.IL15 cells having the highest in response to CD123 antigen. When the PSI from just effector cytokines was compared, the CD123.IL15 cells again had the highest PSI, with CD19.IL15 cells, serving as the negative control, having the lowest. The CD123.IL15 cells also had the most unique combinations of cytokines being secreted from individual cells and exhibited a broader array of cells secreting effector cytokines. Additional in vivo studies showed that the addition of IL-15 secretion improved the persistence, expansion, and anti-AML activity of the CD123-ENG T cells.

The study underscores the utility of using IsoPlexis’ single-cell secretomic analysis to provide critical insights into function of engineered cell therapy products.

How Single-Cell Secretome Can Empower the Development of New Therapies

By using IsoPlexis’ single-cell functional analysis, researchers can gain key insights into cell function and activity throughout the development process. Metrics such as polyfunctionality and PSI, available only by analyzing cells at the single-cell level, have repeatedly been shown to be associated with better results and improved outcomes. By providing more information about cell products that bulk analyses may miss, single-cell functional proteomics allows researchers to more fully characterize the functions of cell therapy products.

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