Dynamics of B cell recovery following kidney/bone marrow transplant recipients.

Background: Previous studies identified B cell gene signatures and predominance of specific B cell subsets as a marker of operational tolerance following kidney transplantation. These findings suggested a role for B cells in the establishment or maintenance of tolerance. Here we analyzed B cell recovery in 4 subjects, 3 of whom achieved tolerance after combined kidney/bone marrow transplantation. Methods: Peripheral B cell subsets were examined longitudinally by flow cytometry. Immunoglobulin heavy chain repertoire analysis was performed using next generation sequencing. Lastly, the patients' serum reactivity to HLA was assessed by Luminex. Results: B cell counts recovered approximately 1 year posttransplant except for 1 subject who experienced delayed reconstitution. This subject resumed immunosuppression for acute rejection at 10 months posttransplant and underwent preemptive retransplantation at 3 years for chronic rejection. B cell recovery was accompanied by a high frequency of CD20+CD24highCD38high transitional B cells and a diversified clonal repertoire. However, all 4 subjects showed prevalence of CD20+CD27+ memory B cells around 6 months posttransplant when B cell counts were still low and the clonal B cell repertoire very limited. The predominance of memory B cells was also associated with high levels of somatically mutated IGHV sequences and transient serum reactivity to HLA. Conclusions: Our observations reveal the presence of memory B cells early posttransplant that likely escaped the preparative regimen at a time consistent with the establishment of tolerance. Further studies are warranted to characterize the functional properties of these persisting memory cells and evaluate their potential contribution to tolerance induction. Copyright (C) 2017 Wolters Kluwer Health, Inc. All rights reserved.

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