Label-free quantitative lymphocyte activation profiling using microfluidic impedance cytometry

ABSTRACT

Circulating lymphocytes are integral components of our adaptive immunity with emerging clinical applications in immune status monitoring in infectious diseases and cell-mediated cancer immunotherapies. Herein we present a novel impedance-based microfluidic assay for label-free lymphocyte activation profiling based on native or antigen-specific T-lymphocyte biophysical responses. Single cell impedance profiling of T-lymphocytes first revealed distinct biophysical differences in cell size and membrane electrical impedance of healthy, activated (CD3/CD28) and dead lymphocyte populations. Impedance characterization of peripheral blood mononuclear cells (PBMCs) stimulated with mitogen phytohemagglutinin (PHA) or Tuberculin Purified Protein Derivative antigen (PPD) after 24 hours also showed an increase in lymphocyte cell size (∼8 to 10 µm) which corresponded to activated lymphocytes (CD69+CD137+). We next developed a spiral inertial microfluidics cell sorter integrated with coplanar electrodes for direct impedance quantification of activated lymphocytes. By removing non-activated smaller lymphocytes (< 8 µm) and employing hydrodynamic-based single stream particle focusing, we demonstrated significant enrichment of activated lymphocytes (∼11.7-fold) to electrically detect low levels of lymphocyte activation (< 5%). Finally, the developed biochip is coupled with magnetic activated cell sorting (MACS) to quantify CD4+ T-lymphocytes response in PBMCs stimulated with PPD. A differential impedance cell count ratio (stimulated/unstimulated) was defined to distinguish activated T-lymphocytes, which showed better sensitivity as compared to immunophenotyping by flow cytometry. Taken together, the integrated impedance biosensor can be further developed as a rapid multiplexed screening assay to detect antigen-specific T-lymphocyte responses to characterize host immunity and diagnosis of infectious diseases (e.g tuberculosis, dengue and COVID-19).