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Abstract: PO2391

B-Cell Maturation Phenotypes and Time Post-Transplant

Session Information

Category: Transplantation

  • 1901 Transplantation: Basic

Authors

  • Gama, Alcino, CHU de Quebec-Universite Laval, Quebec, Quebec, Canada
  • Desy, Olivier, CHU de Quebec-Universite Laval, Quebec, Quebec, Canada
  • Beland, Stephanie, CHU de Quebec-Universite Laval, Quebec, Quebec, Canada
  • Bouchard-Boivin, François, CHU de Quebec-Universite Laval, Quebec, Quebec, Canada
  • De Serres, Sacha A., CHU de Quebec-Universite Laval, Quebec, Quebec, Canada
Background

Over the past decade, B cell participation in allograft response has been progressively elucidated. Beside the occurrence of DSA (donor-specific alloantibodies), different patterns of B cell phenotypes are also being related to graft outcome. Loss of naive B cells and appearance of memory B cells have been linked to chronic rejection and ultimately to graft loss. Here we show the impact of time post-transplant on phenotypic B cell changes, particularly regarding different distributions of naive B cells.

Methods

Single-center, observational cohort of 82 kidney transplant recipients (KTr), adults and clinically stable. Blood samples were collected between January 2015 and November 2018. Peripheral blood mononuclear cells (PBMCs) were isolated and analyzed on flow cytometry. B cells (CD19+) were stained for CD38 and IgD and classified according to Bm classification (IgD vs CD38).

Results

The median time post-transplant was 2.9 [0.9-9.89] years and the mean age was 54±13 years. 63% of the patients were males and mean eGFR was 49±17mL/min. B cells absolute counts were lower in later phases post-transplant (R -0.4, p<0.01). Among all B cell subtypes, Bm2 compartment (comprised mainly by naive B cells) had the most significant reduction in both absolute counts (R -0.62, p<0.01) and relative percentage (R -0.58, p<0.01) over time. On the opposite, mature B cells (both Bm5 and early Bm5 compartments) absolute counts did not differ over time (R -0.04 and 0.11 respectively, p>0.05) whereas the percentages of them were positively correlated with time post-transplant (R 0.40 and 0.56 respectively, p<0.01). Linear regression model showed that the absolute reduction in Bm2 cell compartment (i.e. naive B cells) was independent of age, sex, graft function and immunosuppression scheme.

Conclusion

Patients with longer time post-transplant have fewer circulating peripheral B cells. Phenotypic analysis of B cell subsets reveals that this reduction is due to an absolute decrease in naive B cells counts. Mature B cell absolute numbers, on the other hand, did not change significantly. Either exhaustion due to long-term immunosuppression or immunologic accommodation due to chronic alloantigen exposure could explain these observations.