The determination of diagnostic, prognostic and predictive (therapeutic response) biomarkers is fundamental to personalized oncology treatments. In addition, intratumoral heterogeneity at the cellular level plays a critical role in disease progression and treatment efficiency. Therefore, the unambiguous identification of cell populations within heterogeneous samples such as blood, bone marrow or tumour biopsies requires the simultaneous quantitative determination of many biomarkers in individual cells. Traditionally, this type of studies has been conducted by flow cytometry, which is routinely limited to about 15 simultaneous marker measurements on each cell. However, the increasing need for multiparametric analysis, has pushed the development of alternative possibilities, like new spectral cytometers or the recently established mass cytometry (CyTOF®)[1]. Nonetheless, the possibilities for absolute quantitative analysis of molecular biomarkers using CyTOF have not been fully explored yet. Over the years, our group has developed quantitative strategies for single cell analysis of molecular biomarkers using quadrupole-based single-cell elemental analysis[2]. However, a significant limitation of conventional quadrupole or sector field ICP-MS instruments is their inability to simultaneously monitor multiple elements, hindering multiparametric single-cell analysis.

This work aims to develop quantitative strategies for the determination of molecular biomarkers in individual cells using mass cytometry. Such strategies are based, on one side, on the continuous introduction of inorganic calibrants, and, alternatively, on using element-specific microparticles in a strategy based on transient signal detection. Such experiments will be complemented and compared, when possible, with quantitative quadrupole-based SC-ICP-MS measurements using similar quantification methods. The chosen application for these experiments is the expression level of CD20, a surface transmembrane non-glycosilated protein marker expressed on developing B-cells, as well as many B-cell malignancies. Although CD20 is not expressed on precursor B cells, it appears early in the B cell maturation pathway, but is eventually lost from fully differentiated plasma cells. 

References
[1] D. Bandura; V. Baranov, O. Ornatsky et al. Analytical Chemistry, 2009, 81, 6813-6822
First name initials, Last name; J.S. Smith Journal title, year, volume, page numbers.
[2] M. Corte-Rodríguez, R. Álvarez-Fernández, P. García Cancela, M. Montes Bayón, J. Bettmer, Trends in Analytical Chemistry, 2020, 132, 116042