Preservation of the Donor-Reactive T Cell Repertoire Following Extracorporeal Photopheresis

Abstract

Purpose Extracorporeal photopheresis (ECP) has been advocated as a therapy for chronic lung allograft dysfunction (CLAD), despite an absence of randomized controlled trials to support its use. ECP is postulated to alter the recipient lymphocyte population favoring regulatory over effector T cells, as well as altering cytokine profiles. We hypothesized that ECP would result in selective deletion of donor specific T cells, as identified by T-cell receptor (TCR) sequences. Methods For five subjects undergoing ECP, we performed TCR sequencing on peripheral blood collected peri-transplant, (0-14 weeks) pre-ECP, and (6-20 weeks) post-ECP. Donor-reactive recipient TCR sequences within the peri-transplant sample were identified by sequencing the cells which expanded during a mixed lymphocyte reaction against donor stimulated B cells. We compared the overlap with donor reactive sequences, Jaccard similarity (intersection over union) to the peri-transplant sample, Shannon alpha-diversity, and evenness between pre-and post-ECP samples using Pearson's correlation and paired Student's t-tests. Results The donor-reactive TCR proportions were correlated (r=0.91, p=0.03) but unchanged (p=0.51, Figure 1A) following ECP. TCR similarity to the peri-transplant sample (Figure 1B, p=0.12), alpha-diversity (p=0.37) and evenness (p=0.59) were also unchanged. Conclusion TCR sequencing demonstrated stability of donor-reactive T cell clones, which were readily identifiable in before and after ECP peripheral blood samples from this cohort. While these findings do not support the hypothesis that ECP results in deletion of donor-reactive T cell clones in patients with CLAD, more subtle effects might be apparent from larger cohorts.