CD209⁺ monocyte-derived myeloid dendritic cells were increased in patients with leukemic cutaneous T-cell lymphoma undergoing extracorporeal photopheresis via the CELLEX^TM system

Background/Purpose: We previously reported that myeloid dendritic cells (mDC) were increased in patients with leukemic cutaneous T-cell lymphoma (L-CTCL) following extracorporeal photopheresis (ECP) using the Therakos UVAR XTS^™ system. We now assessed monocyte-derived mDCs (Mo-DCs) in L-CTCL patients treated with the CELLEX^TM photopheresis system. CD209, a transmembrane receptor, was used to define Mo-DCs. Methods: Peripheral blood samples from baseline pre-ECP and at Day 2, 1 month, 3 months, and 6 months post-ECP were analyzed by flow cytometry for Lin⁻HLA-DR⁺CD123⁺ plasmacytoid dendritic cells (pDCs), Lin⁻HLA-DR⁺CD11c⁺ mDCs, and CD209⁺ mDCs. The expression of CD209 mRNA was assessed by real-time PCR. Results: At baseline, 7 of 19 patients had lower than normal mDCs, and all patients had lower than normal CD209⁺ mDCs in peripheral blood mononuclear cells (0.005% in patients, n = 19, vs 0.50% in healthy donors, n = 7, P <.0001). The CD209⁺ mDC numbers only accounted for 3.28% out of total mDCs in patients compared with 66.51% in healthy donors. After treatment, the CD209⁺ mDC numbers showed increasing trends in patients. The average absolute numbers of CD209⁺ mDCs went up by 4.8-fold at 3 months (n = 10, P =.103) and by 6.4-fold at 6 months (n = 9, P =.100). CD209 mRNA expression went up in two patients responsive to therapy, parallel to CD209⁺ mDC numbers. L-CTCL patients achieved 70% overall clinical response rate (7/10) following ECP therapy with the CELLEX^TM system. Conclusions: Our results suggest that the CELLEX^TM photopheresis system is effective for treating L-CTCL patients like the UVAR XTS^™ system, and in vivo-generated Mo-DCs increase following ECP.