Mononuclear cell recruitment during extracorporeal photopheresis: Partial results of a phase 1/2 randomized clinical trial in multiple sclerosis.

Background: Despite the routine clinical use of extracorporeal photopheresis (ECP) for the last decades, there has been no sufficient investigation on the intra-apheresis dynamics of mononuclear cells (MNCs).
Objective: This research aims to verify the "intra-apheresis recruitment" (IAR) of MNCs, which may be particularly useful in cases with low preapheresis MNC counts.
Methods: Prospective data of ECP procedures for patients with multiple sclerosis (MS) in the context of the PHOMS study (NCT05168384) were analyzed. ECPs were performed with the use of the Therakos® CellEx® Photopheresis System, and the recruitment factor (RF), collection efficiency 1 (CE ₁ ), and fold enrichment (FE) for MNCs, lymphocytes, monocytes, and neutrophils were calculated at various intervals per the approved protocol.
Results: A total of 252 ECP procedures were performed on nine patients with MS, and data from 45 ECPs were analyzed for this study. IAR (RF ≥ 1) of MNCs, lymphocytes, and monocytes was observed in the 93.3 %, 95.5 %, and 88.8 % of the ECP procedures, respectively. CE ₁ exceeded 100 % for these populations in 13.3 %, 11.1 %, and 24.4 % of ECPs, while FE ≥ 1 for MNCs and lymphocytes was found in all ECPs, and in 97.8 % of ECPs for monocytes. Additionally, RF correlated positively with CE ₁ for MNCs (r = 0.40, p = 0.006) and lymphocytes (r = 0.43, p = 0.003), as well as with FE for monocytes (r = 0.39, p = 0.01) and lymphocytes (r = 0.48, p = 0.001), further improving collection quality.
Conclusions: Administering photopheresis with suboptimal MNC counts was plausible and did not worsen the anticipated cytopenias. Moreover, our findings revealed sustained IAR of MNCs in patients with MS who underwent ECP.
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