Intracellular Cytokine Responses Allow Early Detection Of Patients At Risk Of Polyomavirus-Associated Graft Nephropathy

Polyomavirus-associated graft nephropathy (PAN) has emerged as a significant risk factor for kidney graft loss. We analyzed intracellular cytokine responses, CD4+ T-cell helper function and T-cell dependent and independent B-cell responses for possible protective vs. permissive immunological effects on BK-virus replication up to 2 years posttransplant. 105 renal transplant recipients were included in a prospective single-center study and were randomized to receive CsA/MMF (n=31), Tacr/ MMF (n=32) or Tacr/MMF with conversion to everolimus (Erl; n=32), respectively. 10 patients were not randomized (NR group) due to contraindications to MMF therapy. Immunological tests were performed pre- and post-transplant (3 months, 1 and 2 years) and BK virus screening was performed by rt-PCR testing in serum and urine specimens obtained on days 0, 14, 30, 60, 90, 120, 180, 270, 360 and 720. 7/105 (6.7 %) patients developed biopsy-proven PAN (CsA/MMF: n=1, Tacr/MMF: n=3, Tacr/Erl: n=2, NR: n=1), and 4 of these lost their grafts (Tacr/MMF: n=1, Tacr/ERL: n=2, NR: n=1). 21/105 (20.0 %) patients had documented BK viremia. BK viremia preceded PAN in all cases and was significantly associated with Tacr/MMF immunosuppression (Tacr/ MMF 11/32 (34.4 %), CsA/MMF 4/31 (12.9 %), Tacr/Erl 5/32 (15.6 %); p=0.034; NR 1/10 (10.0 %)). Intracellular CD4 cell IL-2, IL-4 and IFN-γ responses as well as B cell responses did not differ significantly between patients with BK viremia and those without. However, patients with BK viremia showed significantly diminished IL-2 production of CD8+ T-cells at 3 months (14.2±1.8 % vs. 20.4±1.5 %, p=0.011) and 1 year post-transplant (14.1±2.1 % vs. 20.5±1.4 %, p=0.014) compared with non-viremic patients. CD4 helper function was significantly elevated in BK viremic patients at 3 months post-transplant (129±17 % vs. 76±9 %, p=0.006). Compared with BK viremic patients not proceeding to PAN, patients developing PAN showed significantly lower CD4 cell IL-4 responses 1 and 2 years post-transplant (1 year: 0.8±0.2 % vs. 1.5±0.1 %, p=0.007; 2 years: 0.9±0.1 % vs. 1.7±0.1 %, p=0.001) and a diminished IFN-γ response 1 year post-transplant (12.0±2.3 % vs. 21.0±1.3 %, p=0.011). Our data demonstrate that patients on a Tacr/MMF-based immunosuppression were at increased risk of developing BK viremia. Low CD8 cell IL-2 responses at 3 months post-transplant may predict the risk of developing BK viremia, and compromised Th1 and Th2 (CD4 cell IFN-γ and IL-4, respectively) responses may predict the risk of proceeding from BK viremia to PAN. Compromised CD4 helper function and B cell responses were not associated with the development of BK viremia.