Functional Analysis of Immunocompromised Patients’ Leucocytes by Single-cell Mass Cytometry

Abstract

Immunodeficiencies make up a large group of diseases characterized by heterogeneous clinical manifestations, including life-threatening infections, autoimmunity, chronic inflammation, allergy and malignant diseases. They are classically divided in primary (PID) and secondary (SID) immunodeficiencies and they can be caused by monogenic defects or be secondary to exogenous factors, malignant or non-malignant diseases. In the last 20 years, accelerating progress has been made in identifying new forms of PIDs thanks to the advances of molecular and genetic characterizations. These disorders are either diagnosed early in life or even later, in adults. It is estimated that 1-2% of the population might be affected with any type of the whole PID spectrum. Immune cell characterization, particularly by flow cytometry techniques, has extensively showed its importance in the clinical management of patients presenting immune deficiencies with quantitative cell defects, as well as in the understanding of the immune system. It has already improved the classification of immunological diseases, as well as contributed to improve treatment efficacy and follow-up. Recently, mass cytometry techniques have been used for diagnostic purposes, significantly increasing the breadth and depth of the functional and phenotypic characterization of a patient’s immune cells, in comparison to traditional flow cytometry techniques. These advancements are driven by the great increase in measurable parameters provided by mass cytometry, which allows for all major known immune cell populations and subpopulations to be characterized with a single analysis. The major contribution of this research resides in directly testing the functional activity and response of a patient's immune cells to different stimuli. The highly multiparametric nature of mass cytometry allows for both a broad and in depth characterization of the functional immune response using only a minimal volume of a patient's blood (1 mL) with results available within one day, thus drastically improving time to diagnosis. In addition to having a proportional and phenotypic characterization of a patient's immune cells, identifying the functionally abnormal cell population(s) will provide the clinicians with an even better understanding of their patient's immunological defect. Interpretation of the mass cytometry results along with the patient's clinical data will allow for the identification of signatures associated with specific immunological defects, new classes of immunodeficiencies and therapies that are best adapted to a specific class of an immunological disorder, hence improving the diagnosis and the benefits for immunocompromised patients