Extracorporeal photopheresis attenuates murine GVHD via bone marrow-derived IL-10 and preserves responses to dendritic cell vaccination

Extracorporeal photopheresis (ECP) is emerging as a therapy for graft-versus-host-disease (GVHD), but the full mechanism of action and the impact on immunity have not been fully established. After murine minor histocompatibility antigen-mismatched bone marrow transplant (alloBMT), co-infusion of ECP-treated splenocytes with T cell-replete bone marrow attenuated GVHD irrespective of the donor strain of the ECP-treated splenocytes, and was associated with increased numbers of regulatory T cells. Co-culture of myeloid dendritic cells (mDC) with ECPtreated splenocytes resulted in increased interleukin (IL)-10 production after sub-maximal stimulation with lipopolysaccharide. Furthermore, male mDCs exposed to ECP-treated splenocytes were less potent at inducing CD8+ HY-responses when used as a vaccine in vivo. The efficacy of ECP-treated splenocytes was enhanced when administered just prior to delayed donor lymphocyte infusion (DLI) following T cell depleted alloBMT, allowing for the administration of sufficient numbers of T cells to respond to mDC vaccination in the absence of a thymus. Finally, the therapeutic effect of ECP-treated splenocytes were lost in recipients of IL-10 deficient bone marrow. We demonstrate that ECP-treated splenocytes attenuate GVHD irrespective of the source of ECP-treated cells via a mechanism that likely involves modulation of DCs, and requires IL-10 produced by bone marrow-derived cells. Importantly, attenuation of GVHD by ECP-treated splenocytes permits DLI-dependent responses to DC vaccines following alloBMT. Corresponding Author: Christian M. Capitini, MD, National Cancer Institute/NIH, Building 10, MSC 1104, 10 Center Drive, Bethesda, MD 20892, capitinic@mail.nih. gov, ph: 301-451-7033, fax: 301-451-7052. *C.M. C. and J.P.E.D. contributed equally to this work. Disclaimer The content of this publication does not necessarily reflect the views of policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government. Authorship Contribution: C.M. C. and J.P.E.D. designed and performed research, collected, analyzed, and interpreted data, performed statistical analysis, and drafted the manuscript; S.M. L. , S.H and N.M. N. performed research, collected, analyzed, and interpreted data, and performed statistical analysis; and T.J.F. designed and supervised research, analyzed and interpreted data, and revised the manuscript. Conflict-of-interest disclosure: The authors declare no competing financial interests. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access