Immunophenotyping and efficacy of low dose ATG in non-sensitized kidney recipients undergoing early steroid withdrawal: a randomized pilot study

Abstract

Rabbit antithymocyte globulin (ATG) is commonly used as an induction therapy in renal transplant recipients, but the ideal dosage in tacrolimus-based early steroid withdrawal protocols has not been established. The purpose of this pilot study was to determine the immunophenotyping and efficacy of lower dose ATG in low immunological-risk kidney transplant recipients. In this prospective study, 45 patients were randomized (1∶1) to our standard dose ATG (total dose 3.75 mg/kg)(sATG) vs. lower dose 2.25 mg/kg (lowATG). All patients underwent early steroid withdrawal within 7 days. The primary end point was biopsy-proven acute rejection at 12 months. Prospective immunophenotyping of freshly isolated PBMCs was performed at baseline, 3, 6, 12 months post-transplant. The rate of acute rejection was 17% and 10% in the sATG and lowATG, respectively. Effector memory T cells, Tregs and recent thymic emigrants T cells had similar kinetics post-transplant in both groups. No statistically significant differences were found in graft survival, patient survival or infections between the two groups, though there was a non-significant increase in leukopenia (43%v s. 30%), CMV (8% vs. 0) and BK (4% vs. 0) infections in sATG group vs. lowATG. In sum, in low immunological risk kidney recipients undergoing steroid withdrawal, low dose ATG seems to be efficacious in preventing acute rejection and depleting T cells with potentially lower infectious complications. A larger study is warranted to confirm these findings.

Trial registration: ClinicalTrials.gov NCT00548405.

Figure 1. Flow diagram of patients screened and enrolled in the study.

Figure 2. Graft function after transplantation.

Serum creatinine was measured at 1, 6, 12 months post-transplantation, as a surrogate of graft function. Means±SD. At each time point, there was no statistically significant difference in serum creatinine between low-dose and high-dose arms by unpaired t-test analysis.

Figure 3. Flow cytometric analyses of peripheral T cells at different time points after transplantation.

A, Representative gating strategy of peripheral blood mononuclear cells with live gate, CD4 and CD8 subsets and effector memory T cells (CD45RO⁺CD62Llow). B, Percentage of total CD4 cells and total CD8 cells at 0, 3, 6 and 12 months after transplantation. C, Percentage of CD4⁺ and CD8⁺ effector memory cells after transplantation. Data are expressed as mean and standard deviation (n = 18-20 per group).

Figure 4. Flow cytometric analyses of Tregs and recent thymic emigrants (RTE) CD4 cells at different time points after transplantation.

Representative contour plots of Tregs (A) (CD25⁺Foxp3⁺ of CD4⁺ cells) and RTEs (D) (CD45RA⁺CD31⁺ of CD4⁺ cells) cells after gating on CD4⁺ T cells at different time points after transplantation. Percentage of Tregs (B) and ratio of Tregs related to baseline (C) at different points after transplantation. E, Percentage of RTEs at different points after transplantation. Data are expressed as mean and standard deviation (n = 18-20 per group).