Abstract 6671: Simplifying high-parameter phenotypic and functional characterization of cancer immune cells
Authors: Mahamed Deeqa , Cohen Michael , Li Stephen , Tracey Lauren , Yao Huihui , Loh Christina , Fung Leslie 
Published: April 2023

Abstract
Interrogating immune cell composition and function in patients with cancer is critical for making disease prognoses, monitoring clinical efficacy of tumor immunotherapies, identifying novel therapeutic targets, and discovering predictive biomarkers of disease. Both the adaptive and innate arms of the immune system play important roles in generating pro- or anti-tumor milieus. In particular, natural killer (NK) cells are gaining increasing attention as potential cell-based therapies in immuno-oncology, including in adoptive transfer of chimeric antigen receptor (CAR) and iPSC-derived NK cells or off-the-shelf NK cell lines to target multiple myeloma. Since NK cells can also indirectly impact CAR T cell or antibody-based immunotherapies, characterizing these cells using optimized and reproducible assays is critical. CyTOF® is a high-plex flow cytometry technology that exploits metal-isotope-tagged antibodies to probe cellular phenotypes and functions. In contrast to fluorescence-based conventional and spectral flow cytometry, CyTOF experimental workflows are streamlined as autofluorescence is not an issue and signal spillover is minimal, allowing rapid design and application of 40-plus-marker panels. To expand on the increasing clinical and preclinical utility of the 30-marker Maxpar® Direct™ Immune Profiling Assay™ (Maxpar Direct Assay), we developed nine add-on Expansion Panels for deeper phenotyping of specific cell types and activation states, including panels designed to characterize ex vivo and activated myeloid cells, T cells, and NK cells. Peripheral blood mononuclear cells from healthy donors and donors with multiple myeloma were stimulated in vitro, then stained in the 30-antibody Maxpar Direct Assay tube with the NK Cell Expansion Panel (CD181, NKp30, NKp46, PD-1, NKG2A, ICOS, and TIGIT) or the T Cell Panel 3 (OX40, TIGIT, CD69, PD-1, Tim-3, ICOS, and 4-1BB) as drop-in antibodies. Surface staining was followed by intracellular staining with the Basic Activation Expansion Panel antibodies (IL-2, TNFα, IFNγ, perforin, granzyme B) after cell fixation and permeabilization. Anti-CD107a was added during stimulation to measure degranulation. Samples were acquired on a CyTOF XT™ instrument in automated batch acquisition mode. Automated analysis was performed with Maxpar Pathsetter™ software to enumerate immune cell types and quantify marker expression. In addition to the 37 populations identified by Pathsetter with the base Maxpar Direct Assay, the new Expansion Panels allowed deeper profiling of NK and T cells, while the Basic Activation Panel revealed their cytokine responsiveness and cytotoxic potential. Thus, the optimized single-tube Maxpar Direct Assay is a powerful tool that can be further expanded and customized with predefined panels or antibodies to comprehensively study immune cells in health and disease.
For Research Use Only. Not for use in diagnostic procedures.
Citation Format: Deeqa Mahamed, Michael Cohen, Stephen Li, Lauren Tracey, Huihui Yao, Christina Loh, Leslie Fung. Simplifying high-parameter phenotypic and functional characterization of cancer immune cells. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6671.