Extracorporeal photopheresis as an immunomodulatory agent: Haematocrit-dependent effects on natural killer cells

Apoptosis induction by extracorporeal photopheresis is enhanced by increasing the 8-methoxypsoralen concentration and by replacing plasma with saline

BACKGROUND

Extracorporeal photopheresis (ECP), an apheresis-based therapy for various immunological diseases, works mainly by inducing apoptosis in lymphocytes. Several factors influence the efficacy of ECP with the photosensitizer 8-methoxypsoralen (8-MOP) and ultraviolet light A (UVA). This study aimed to optimize treatment by varying the 8-MOP starting concentration and the cell suspension medium.

MATERIALS AND METHODS

All patients (n = 13) included in this study received photopheresis as medically indicated. Cells collected with a Spectra Optia apheresis system were suspended in plasma or physiological saline (NaCl) and incubated with 200 ng/ml versus 340 ng/ml photosensitizer before UVA irradiation (Macogenic G2 or UVA PIT system). Lymphocyte apoptosis and caspase activity were analyzed by flow cytometry and fluorimetry, and residual 8-methoxypsoralen concentrations by liquid chromatography-mass spectrometry.

RESULTS

Raising the 8-MOP starting concentration significantly increased lymphocyte apoptosis, with values of 22% versus 35% (plasma) and 28%-46% (NaCl) at 24 h post-ECP and 37% versus 86% (plasma) and 74% versus 97% (NaCl) at 48 h for 200 ng/ml versus 340 ng/ml. Pre-transfusion residual 8-MOP levels were 168 ng/ml (plasma) and 162 ng/ml (NaCl) versus 290 ng/ml (plasma) and 266 ng/ml (NaCl) for the lower versus higher dose, respectively.

DISCUSSION

Hence, 8-MOP concentration influences the efficacy of photopheresis as lymphocyte apoptosis rates were significantly higher with the higher starting concentration and with NaCl versus plasma. This indicates that increased 8-MOP starting doses and saline as additional suspension medium could help in improving ECP's efficacy.

Extracorporeal Photopheresis for Bronchiolitis Obliterans Syndrome After Lung Transplantation

BACKGROUND

Lung transplantation is a therapeutic option for select patients with end-stage lung disease. However, successful lung transplantation is hampered by chronic lung allograft dysfunction, in particular bronchiolitis obliterans syndrome (BOS). Although there is no approved or standard treatment for BOS, which may have several distinct phenotypes, extracorporeal photopheresis (ECP) has shown promising results in patients who develop BOS refractory to azithromycin treatment.

METHODS

We reviewed all relevant clinical data indexed on PubMed from 1987 to 2017 to evaluate the role of ECP in patients with BOS.

RESULTS

Seven small studies investigated the immunomodulatory effects of ECP in patients after solid organ transplant, and 12 studies reported clinical data specific to ECP therapy for BOS. Studies indicate that ECP triggers an apoptotic cellular cascade that exerts various immunomodulatory effects mediated via increases in anti-inflammatory cytokines, a decrease in proinflammatory cytokines, and an increase in tolerogenic regulatory T cells. Clinical evidence derived from relatively small single-center studies suggests that ECP therapy is associated with improvement or stabilization in lung function and sustainable, statistically significant, decreases in the rate of lung function decline in patients with BOS. Additionally, when adverse event data were reported, ECP was generally well tolerated. None of the comparative studies were randomized.

CONCLUSIONS

Immunomodulation mediated via ECP is a rational therapeutic option that may improve clinical outcomes in patients with BOS, particularly in the context of in-depth patient phenotyping as part of a stratified approach to treatment; good quality randomized controlled trials are needed to confirm observational findings.