Investigating the Role of Dendritic Cells in Extracorporeal Photopheresis Using an In Vitro Model.
Udo Holtick, MD1,*,
Scott R. Marshall, MD1,*,
Muzlifah Haniffa, MD2,*,
Catharien M. Hilkens, PhD2,*,
Xiao N. Wang, MD,PhD1,* and
Anne M. Dickinson, PhD1,*
(Intr. by Stephen J. Proctor) 1 Haematological Sciences, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom and 2 Immunotherapy Group, Rheumatology, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
Graft versus Host disease (GvHD) is the major limitation tosuccessful allogeneic hematopoietic stem cell transplantationand contributes significantly to transplant related mortalityand morbidity. Steroid refractory or steroid depending GvHDin particular is linked to poor survival or life quality. Conventionalimmunosuppression has very limited success in these conditionsand increases susceptability for infection and relapse.
Extracorporeal Photopheresis (ECP) is a promising therapy foracute and chronic GvHD not responding to conventional immunosuppressivetherapy. ECP treatment seems not to result in a pan-immunosuppressionbut has quite selective effects on the pathogenic process inGvHD.
The mechanisms of action of ECP in GvHD known so far includelymphocyte apoptosis, cytokine modulation and increased regulatoryT cell numbers. It has been suggested that monocytes and dendriticcells (DC) were more resistant to ECP induced apoptosis, sothat they might either be directly modulated by ECP or modulatedby encounter with apoptotic cells and this way aquiring immunomodulatingproperties. Here we tested the first hypothesis analysing directeffects of ECP on monocyte derived dendritic cells in vitro.
Direct in vitro PUVA treatment leads to activation of monocytederived immature DCs (upregulation of CD83, CD86, HLA-DR, reducedendocytosis capacity, increased migratory capacity), whereasmature DCs are not affected. However, immature and mature DCsundergo apoptosis later on within 24h-72h. Prestimualtion witheither antigen (KLH), IL-12 or co-culture with CD40L expressingcells could not prevent apoptosis. Further DC stimulation throughCD40L is abrogated 24h after treatment. DC cytokine analysis(IL-12, TNF) is pending. After in vitro PUVA primary dermalDCs and Langerhans Cells migrated from skin biopsies undergoapoptosis similarly to monocyte derived DCs.
Going along with the early activation, the stimulatory capacityof in vitro PUVA treated immature DCs is enhanced in an MLRon naive T cells. IL-10 levels are decreased as compared tountreated or UVA treated cells. Secondary stimulation througheither CD3/CD28 beads or mature DCs leads to reduced proliferationof naive T cells that were primarily stimulated with in vitroPUVA treated as compared to untreated immature DCs. Cytokineanalysis after secondary stimulation is pending.
We conclude that in our model in vitro PUVA modulates the characterespecially of immature dendritic cells. However, immunostimulatingand immunosuppressive characteristics could be described dependingon the assay. Cytokine results after second stimulation (Th1/Th2)are pending. Apoptosis is a major finding and occurs both inmonocytes and DCs after 2472h. Our findings indicatethat there might be direct ECP effects on monocytes and DCsgoing beyond the process of merely depleting antigen presentingcells. Further relevance is currently being investigated.
* Corresponding author
Disclosure: No relevant conflicts of interest to declare.