Impact of Cryopreservation on Extracorporeal Photopheresis (ECP)-Treated Leukocyte Subsets

Extracorporeal photopheresis (ECP) is frequently utilized in the treatment of steroid-refractory acute and chronic graft-versus-host disease (GVHD). Although the mechanism of action is not fully understood, it has been postulated that its therapeutic effect is immunologic tolerance linked to the associated apoptosis of the treated cells. Despite significant advances in allogeneic hematopoietic stem cell transplantation (HSCT), prophylaxis and treatment of GVHD remain a challenge and major limitation associated with this therapy. Use of ECP is a valuable strategy; however, it is time, cost, resource intensive, and not readily accessible.

In an effort to expand access to this therapy, we are investigating the use of cryopreserved ECP-treated cells. This will provide the ability to administer a significant proportion of the treatment at a facility closer to the patient's residence, thereby decreasing the number of visits to the primary treatment center with the goal of improving and expanding access to this therapy. Here we report the effects of cryopreservation on ECP-treated leukocytes.

Mononuclear cells were pheresed from human patients, ECP-treated, and collected for viability and apoptotic analysis. Cells were then cryopreserved at -80°C or -150°C for 1 week, 1 month, and 3 months. Following thaw, repeat viability and apoptosis studies were performed on the leukocytes.

WBC viability for freshly ECP-treated leukocytes was 84.5% ± 3.5 at 1 week, 87.3% ± 5.2 at 1 month, and 79.1% ± 1.1 at 3 months post thaw. Similar results were seen for cells frozen in cryovials. Leukocytes frozen the day after ECP treatment had 1 week and 1 month WBC viabilities of 84.0 ± 4.1 and 83.1 ± 2.1, respectively. Apoptotic potential was well preserved at 3 months, with cryopreserved ECP-treated lymphocytes being 19.2%, 44.5%, 75.5%, and 94.0% apoptotic after thaw on days 0, 1, 2, and 3 in culture, respectively.

ECP-treated leukocytes cryopreserved at -80°C or -150°C for 3 months remain viable and as capable of apoptosis as freshly treated cells. Cryopreservation of an ECP-product warrants further in vivo investigation as a strategy to facilitate access to this needed therapy.