Early Post-Transplant Peripheral B-Cell Profiles in Kidney Transplant Recipients: Clinical Associations and...

Background: The clinical relevance of circulating B-cell subpopulations during the early period after kidney transplantation remains incompletely understood. Methods: In this prospective single-center study, frequencies and absolute numbers of peripheral B-cell subpopulations were longitudinally assessed by flow cytometry in 71 kidney transplant recipients before transplantation (T0) and at 3 (T3), 6 (T6) and 12 months (T12) post-transplant. Associations with graft function, rejection episodes and clinical variables were explored. Results: During the first post-transplant year, relative frequencies of total and naïve B cells declined, whereas absolute counts showed modest increases. Memory B-cells expanded over time, driven by both class-switched (CSBC) and class-non-switched (CNSBC) subsets. Transitional regulatory B cells (tBregs) and plasmablasts decreased significantly, while memory regulatory B cells (mBregs) remained stable. Pre-transplant B-cell profiles did not differ between recipients experienced rejection and those with stable graft function. At T12, rejection was associated with a shift toward a memory-dominant peripheral profile, characterized by reduced naïve representation. tBregs showed modest positive associations with graft function during follow-up. Hierarchical clustering identified naïve- and memory-dominant phenotypes representing distinct post-transplant immune compositions. Conclusions: Early post-transplant peripheral B-cell landscapes are dynamic and heterogeneous. Peripheral B-cell phenotyping shows limited value as a standalone clinical monitoring tool.