Background Interrogating immune cell composition andfunction in patients with cancer is critical for making disease prognoses,monitoring clinical efficacy of tumor immunotherapies, identifying novel therapeutic targets, and discovering pre-dictive biomarkers of disease. Both the adaptive and innate arms of the immune system play important roles in generating pro-or anti-tumor milieus. Effector cells such as NK cells and T cells can directly kill tumor cells via secretion or cell-surface expression of cytolytic proteins and modulate the immune response through costimulatory molecules.

Materials and Methods In multiple myeloma, malignant plasma cells accumulate in the bone marrow through clonal expansion, crowding out other cells and leading to anemia, renal insufficiency, immunosuppression, and increasing risk of multisystem organ damage if untreated. Cellular and antibody-mediated immunotherapeutic approaches, including CAR T cells and monoclonal antibodies targeting CD38, have been developed to treat multiple myeloma. Since NK cells can also indirectly impact CAR T cell or antibody-based immuno-therapies, characterizing these cells using optimized and reproducible assays is critical.

Results CyTOF®is a high-plex flow cytometry technology that uses metal-isotope-taggedantibodies to probe cellular phenotypes and functions. In contrast tofluorescence-based conventional and spectral flow cytometry, CyTOF experimental workflows are streamlined because 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 9 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.

Conclusions Here we demonstrate combining the Maxpar Direct Immune Profiling Assay with the NK Cell Expansion Panel (CD181, NKp30, NKp46, PD-1, NKG2A, ICOS, and TIGIT) or the T Cell Expansion Panel 3 (OX40, TIGIT, CD69, PD-1, Tim-3, ICOS, and 4-1BB) with the Basic Activation Expansion Panel (IL-2,TNFα, IFNγ, CD107a, perforin, granzyme B) to enable deep immunoprofiling of multiple myeloma PBMC.

A. Thomas-Claudepierre: A. Employment (full or part-time); Significant; Standard BioTools. D. Mahamed: A. Employment (full or part-time); Significant; Standard BioTools. M. Cohen: A. Employment (full or part-time); Significant; Standard BioTools. S. Li: A. Employment (full or part-time); Significant; Standard BioTools. L. Tracey: A. Employment (full or part-time); Significant; Standard BioTools. H. Yao: A. Employment (full or part-time); Significant; Standard BioTools. C. Loh: A. Employment (full or part-time); Significant; Standard BioTools. L. Fung: A. Employment (full or part-time); Significant; Standard BioTools.