Extracorporeal photopheresis (ECP) is a well-known but lengthy cell therapy used for various conditions like cutaneous T-cell lymphoma and graft-versus-host disease. The number of mononuclear cells (MNCs) required for a clinical response to ECP is still uncertain. The purpose of this retrospective study was to determine the number of lymphocytes, monocytes and neutrophils in mononuclear cell products (MCP) by flow cytometry and the collection efficiency in the offline ECP setting.

We collected data from 10 different patients who underwent 162 ECP procedures using the Spectra Optia device for MNC collection. The white blood cell (WBC) count of MCP was measured using a hematology analyzer. MNCs were analyzed for CD45 and CD14 expression by flow cytometry to exactly determine the collected lymphocyte and monocyte fractions.

Collected MCP showed significant cell yields, with 55.3×10⁶/kg MNCs and 41.1×10⁶/kg lymphocytes. MCP were characterized by a high MNC percentage (81.3%) and a low percentage of neutrophils (18.7%). Mean collection efficiency for WBCs and for MNCs was 23.9% and 62.0%, respectively. The MNC fraction showed a moderate to high correlation between peripheral blood cell count of patients and MCP count.

This study is among the few reports that demonstrate the monocyte-to-lymphocyte relation in MCP for ECP as determined by flow cytometry. Compared to historical data from inline ECP, offline ECP processing of one total blood volume results in significantly higher cell yields. Hence, to reduce the burden on patients, we propose that the offline ECP processing time can be significantly shortened.

The authors declare no conflict of interest.