Significance of intragraft CD138+ lymphocytes and p-S6RP in pediatric kidney transplant biopsies

Abstract

Background: We have previously shown that intragraft CD20+ B cells are associated with acute cellular rejection (ACR) and allograft loss. Phosphorylation of S6 ribosomal protein, a downstream target of the PI3K/Akt/mTOR pathway, promotes growth and proliferation of cells and could identify metabolically active cells such as alloantibody secreting plasma cells. Because CD20+ lymphocytes can differentiate into CD138+ plasma cells, we aimed to identify functionally active plasma cells by using intragraft CD138 quantification and p-S6RP staining and correlate these results with allograft rejection, function, and survival.

Methods: We examined 46 renal transplant biopsies from 32 pediatric patients who were biopsied for clinical suspicion of rejection. Immunohistochemical staining for C4d, CD20, CD138, and p-S6RP was performed. Patient creatinine clearance and graft status was followed up postbiopsy.

Results: Patients with greater than or equal to six CD138+ cells/high power field (hpf) had worse graft survival with a hazard ratio of 3.4 (95% CI 1.3-9.2) 2 years postbiopsy compared with those with 0 to 5 cells/hpf (P=0.016). CD138+ cells were stained for p-S6RP, indicating functionally active plasma cells. They were associated with ACR (P=0.004) and deteriorating graft function (R=0.22, P=0.001). Intragraft CD20+ and CD138+ cells found together in ACR were associated with poorer graft survival than either marker alone, hazard ratio 1.5 (95% CI 1.1-2.2, P=0.01).

Conclusions: A threshold of greater than or equal to six CD138+ metabolically active plasma cells per hpf, coexisting with CD20+ B cells, was associated with poor allograft function and survival. This may represent an additional antibody-mediated process present in the setting of ACR and could play an important role in characterization and treatment of transplant rejection.

Figure 1

Kaplan-Meier graft survival grouped by CD138+ counts post-biopsy. Patients included (n=32).

Figure 2

Relationship between intragraft CD138+ counts and CrCl (ml/min/1.73m²).

Figure 3

ROC curve for intragraft CD138+ plasma cells associated with ACR

Figure 4

A) Biopsy with CD138+ plasma cells associated with ACR. Arrows highlight clusters of CD138 positive plasma cells (CD138 immunoperoxidase stain; original magnification 400×). B) Biopsy with ACR and positive S-6RP staining in interstitial plasma cells. Arrow highlights plasma cell with eccentric nucleus and perinuclear halo (s6RP immunoperoxidase stain; original magnification 400×).

Figure 4

A) Biopsy with CD138+ plasma cells associated with ACR. Arrows highlight clusters of CD138 positive plasma cells (CD138 immunoperoxidase stain; original magnification 400×). B) Biopsy with ACR and positive S-6RP staining in interstitial plasma cells. Arrow highlights plasma cell with eccentric nucleus and perinuclear halo (s6RP immunoperoxidase stain; original magnification 400×).

Figure 5

Kaplan-Meier graft survival grouped by no intragraft biomarkers, either CD20 or CD138, and both CD20 & CD138. Patients included (n=32).