Biomarkers for Clinical Response of Extracorporeal Photopheresis

Introduction: Post-transplant morbidity and mortality are majorly determined by GvL effect counter-balanced by GvHD. Treatment with systemic steroids represents the first-line therapy for GvHD, but is associated with increased incidence of infection and relapse. ECP can reduce the extent of GvHD while preserving anti-virus/-tumor activity. However, ECP, a time-consuming and relatively expensive therapy, requires specialized equipment and staff expertise as well as the mechanism of action remains unclear. Therefore, this study was performed to address these unsolved questions.

Materials and Methods: 16 patients with acute GvHD (aGvHD) of the gut °II-IV suffering from severe diarrhea were treated by ECP in addition to triple-drug immunosuppressive therapy. Furthermore, 11 patients with chronic GvHD (cGvHD) of the skin or lung despite triple-drug received ECP treatment. Patients were evaluated according to their individual response and clinical condition. Phenotypical analysis of different cellular subsets of patients and healthy donors was performed by multicolor flow cytometry. Functional properties of virus-specific CD8⁺ T and NK cells were evaluated by INF-γ-ELISPOT and ⁵¹Cr-release assay.

Results: 27 patients were treated by ECP in this study. However, 2 aGvHD and 2 cGvHD patients had to be withdrawn from ECP treatment after a few ECP cycles due to pancytopenia or poor clinical condition. For patients with aGvHD 8 up to 25 ECP cycles were needed for response. All patients achieving a complete response (CR) were still alive 1 year after initiating ECP therapy. Overall response, i.e. CR or partial response (PR) according to NIH criteria, was obtained in 11 of 16 patients with aGvHD (79%). Out of 9 cGvHD patients 7 (77.8%) reached PR, and 2 (22.2%) remained stable under ECP treatment. After 1 year, overall survival (OS) was 60% for aGvHD patients responding to ECP, while only 25% for non-responders. OS for cGvHD patients was 91%.During intensive ECP treatment for patients with aGvHD of the gut, the average stool volume and frequency decreased and consistency changed from loose to formed stool. Steroids could be tapered down to a mean of 22% of the initial dosage. cGvHD patients were stabilized under ECP treatment and steroid dosage could be reduced to a mean of 38%. Clinically responding patients showed increased numbers of regulatory cells including MDSCs, Foxp3⁺CD8⁺ and Foxp3⁺CD25⁺CD4⁺ Tregs, as well as CD4^-CD8^-CD3⁺ T, Vδ2⁺ T cells, and regulatory B lymphocytes. Furthermore, loss of CD62L expression on effector cells like CD4⁺ T_E, CD8⁺ T_E, NK and NKT cells was observed under ECP treatment. Interestingly, ECP treatment did not dramatically influence the frequency of CD4⁺CD8⁺CD3⁺ T, γδ T cells and NKT cells which possess anti-virus/-tumor function. ELISPOT and ⁵¹Cr-release assays revealed stable anti-viral activity of CD8⁺ T cells as well as functional cytotoxicity of NK cells. Moreover, CD8⁺ T, CD8⁺ T_EM, CD62L⁺CD4⁺ T_EMRA, CD56⁺CD3^- NK and CD56^brightCD16^- NK cells could serve as reliable biomarkers for prediction of response to ECP.

Conclusion: ECP treatment might stabilize or even improve clinical situation of patients suffering from GvHD. In clinically responding patients an immunomodulation was observed in terms of increasing numbers of regulatory cells with loss of migratory capacity of effector cells while anti-virus/-leukemia T cell function was preserved.