Use of preventive extracorporeal photopheresis before myeloablative conditioning for allogeneic stem cell transplantation in paediatric patients

Background: Extracorporeal photopheresis (ECP) is currently used to treat acute and chronic graft-versus disease not-responsive to conventional therapy. ECP is believed to have an immunomodulatory effect and may do so by modulating DC function and induction of regulatory T cells (Treg). A significant delay in the time to onset of acute graft-versus-host disease (GVHD) has recently been reported for adult patients receiving preventive ECP, performed prior to myeloablative conditioning regimen. The use of preventive ECP in pediatrics has so far not been addressed. Objective: To evaluate the efficacy and safety of preventive of ECP performed before a myeloablative conditioning regimen in pediatrics. Methods: Eleven pediatric patients receiving an allogeneic hematopoietic stem cell transplant were treated with conventional myeloablative conditioning (n=8) or in addition with prophylactic ECP performed on two successive days before starting myeloablation (n=3) and followed up until d100. The control group (n=8) included five transplants from matched unrelated donors and three from sibling donors, while the treatment group (n=3) included two transplants from matched unrelated donors and one from sibling donor. Regulatory T cell frequency was estimated by FACS analysis before conditioning and, for ECP treated patients, before performing ECP, too. Results: Preventive ECP significantly reduced the incidence of acute GVHD grade II-IV. While all patients in the control group developed acute GVHD grade II-IV, only two out of three treated patients experienced acute GvHD grade II-IV (p=0.04338). No adverse effects were observed following preventive ECP. The relative size of Treg was increased after the second day of ECP in one sample with low size before treatment, while in two samples with higher basic frequency, Treg did not further increase. Conclusion: Extracorporeal photopheresis incorporated in the myeloablative conditioning regimen was not associated with major adverse effects. A statistically significant reduction of the incidence of acute GVHD was observed. Albeit definitive conclusions cannot be drawn owing to the low size of the cohort, the preliminary results encourage to investigate the usefulness of preventive ECP as a remedy to reduce the incidence and/or severity of acute GvHD.