*Purpose: Recipients with sensitization to HLA defined by a high percentage of Panel Reactive Antibodies (PRA) or Donor-specific anti-HLA antibodies (DSA) are at higher immunologic risk for poor graft outcomes. Little is known about the prevalence and impact of circulating HLA-specific B cells (HSB) frequencies and their phenotype on graft outcomes. Utilizing a novel multiplex bead-based assay to identify and phenotype HSB, we studied the circulating HSB in kidney transplant recipients and correlated with rejection.

*Methods: PBMC taken at serial time-points from kidney transplant recipients (n=24; 14 with no rejection, 10 with rejection) were incubated with single antigen HLA-coated multiplexed beads (One Lambda) for HLA Class I and II. Using multi-parameter flow cytometry, HLA-specific B cells (HSB) were identified by the formation of HLA Bead-B-cell Rosettes (BBR) (Blue dots, Fig. A; Orange regions represent individual bead specificities). IgD/CD27 double negative HSB cells (DNB) were enumerated by plotting BBR population on IgD vs CD27 plot (Blue dots in lower left corner of dot-plot, Fig. B; Orange dots represent B cells).

*Results: DNB frequencies at 0 and 3 months post-transplant were higher (at 0 months: 0.3112 ± 0.04904 % vs 0.09946 ± 0.04111%, p=0.0032, Fig. C; at 3 months: 0.2703 ± 0.09659% vs 0.05444 ± 0.03046%, p=0.0234, Fig. D) in recipients who went on to have rejection within 1 yr post-transplant compared to those that didn’t.

*Conclusions: Pre-transplant and 3-months post-transplant HLA class II-specific IgD/CD27 Double Negative B cell frequencies assessed by a novel multiplex bead-based assay predicts rejection in kidney transplant recipients within 1 yr. These data suggest that circulating B cells specific for donor HLA antigens and their phenotype as assessed by this novel assay serve as potential biomarkers for risk stratification of kidney transplant recipients.

« Back to 2022 American Transplant Congress