Microfluidic device may in time replace BM biopsy for MM diagnosis and assessment

Inter-disciplinary subjects are often at the forefront of new developments in Medicine, as researchers look for better means to improve diagnostics and monitor treatment progression. A prime example recently in MM is the development of a microfluidic device, through a collaboration between two researchers: Mohammed A. Qasaimeh working across three departments – the Division of Engineering, New York University, Abu Dhabi, the Mechanical and Aerospace Engineering Department, New York University, USA and the Department of Mechanical Engineering, Massachusetts Institute of Technology (MIT), Cambridge, USA, along with Yichao C. Wu, also from MIT, along with a team of researchers.

Their study, published in Scientific Reports in April 2017, describes the microfluidic cell capture of plasma cells from a small blood sample using an antibody against CD138, an antigen highly expressed on plasma cells.

Key highlights:

• The device has one inlet and a waste outlet, and is the size of a glass slide (25 mm x 75 mm)
• The herringbone geometry of the channels enables better capture by creating microvortices and circulating fluid flow in the transverse direction
• Capture occurs via a fixed biotinylated anti-CD138 (immobilized on a neutravidin coated surface)
• Cells are then visualized post-capture with the addition of fluorescently labelled anti-CD138 which binds to the cell surface (green)
• Addition of a fluorescently labelled anti-kappa or anti-lambda immunoglobulin light chain antibody (red) binds intracellularly following permeabilization and can provide clonal information 
• Optimization to allow for a high capture efficiency while retaining high blood flow was carried out, along with studies to assess optimal antibody concentration
• Analysis of 1 ml of whole blood can be carried out in less than an hour
• Optimal coating with anti-CD138 was achieved at a concentration of 20 µg/ml; the flow rate was maintained at 20 µl/ml for cell capture
• EDTA anti-coagulant added to whole blood was found to best aid efficient cell capture, when compared to heparin or pre-processing of samples with Ficoll
• Significant differences were observed between healthy controls and MM patients in terms of the number of CPCs captured, indicating that this in itself is a reliable measure
• Extremely low (<10 CPCs/ml) were detected in healthy samples and the number of CPCs captured correlated with serum paraprotein levels
• The kappa: lambda ratio also correlated with serum paraprotein levels, but further investigation is required to understand this fully
• A good correlation was observed between cell capture number and flow cytometry data, indicating reliability this approach

Conclusion:

This microfluidic device could change the way in which MM patients are diagnosed, replacing the highly invasive and painful procedure of bone marrow biopsy that can only be carried out in certain hospitals by well-trained experts, with a high-throughput technology requiring only a few milliliters of blood. This can work as a standalone technology to measure both cell number, as an indicator of MM, along with clonal information about the cancer type (kappa or lambda). This would decrease hospital costs and enable more frequent monitoring of patients from initial diagnosis, throughout their treatment journey. In addition, the ability to stain captured cells with an array of antibodies paves the way for tests that could further define the nature of an individual’s disease, and help expand our knowledge of MM biology in general.

Abstract

The necessity for bone marrow aspiration and the lack of highly sensitive assays to detect residual disease present challenges for effective management of multiple myeloma (MM), a plasma cell cancer. We show that a microfluidic cell capture based on CD138 antigen, which is highly expressed on plasma cells, permits quantitation of rare circulating plasma cells (CPCs) in blood and subsequent fluorescence-based assays. The microfluidic device is based on a herringbone channel design, and exhibits an estimated cell capture efficiency of ~40-70%, permitting detection of <10 CPCs/mL using 1-mL sample volumes, which is difficult using existing techniques. In bone marrow samples, the microfluidic-based plasma cell counts exhibited excellent correlation with flow cytometry analysis. In peripheral blood samples, the device detected a baseline of 2-5 CD138⁺ cells/mL in healthy donor blood, with significantly higher numbers in blood samples of MM patients in remission (20-24 CD138⁺ cells/mL), and yet higher numbers in MM patients exhibiting disease (45-184 CD138⁺ cells/mL). Analysis of CPCs isolated using the device was consistent with serum immunoglobulin assays that are commonly used in MM diagnostics. These results indicate the potential of CD138-based microfluidic CPC capture as a useful 'liquid biopsy' that may complement or partially replace bone marrow aspiration.