Immune profile of pediatric renal transplant recipients following alemtuzumab induction

Abstract

The incidence of developing circulating anti-human leukocyte antigen antibodies and the kinetics of T cell depletion and recovery among pediatric renal transplant recipients who receive alemtuzumab induction therapy are unknown. In a collaborative endeavor to minimize maintenance immunosuppression in pediatric renal transplant recipients, we enrolled 35 participants from four centers and treated them with alemtuzumab induction therapy and a steroid-free, calcineurin-inhibitor-withdrawal maintenance regimen. At 3 months after transplant, there was greater depletion of CD4(+) than CD8(+) T cells within the total, naive, memory, and effector memory subsets, although depletion of the central memory subset was similar for CD4(+) and CD8(+) cells. Although CD8(+) T cells recovered faster than CD4(+) subsets overall, they failed to return to pretransplant levels by 24 months after transplant. There was no evidence for greater recovery of either CD4(+) or CD8(+) memory cells than naïve cells. Alemtuzumab relatively spared CD4(+)CD25(+)FoxP3(+) regulatory T cells, resulting in a rise in their numbers relative to total CD4(+) cells and a ratio that remained at least at pretransplant levels throughout the study period. Seven participants (20%) developed anti-human leukocyte antigen antibodies without adversely affecting allograft function or histology on 2-year biopsies. Long-term follow-up is underway to assess the potential benefits of this regimen in children.

Figures

Figure 1.

Depletion and recovery of T cell subsets after induction with alemtuzumab. Cells were available from 11 participants, except for TCM cells in which cells were available for five participants. (A) After alemtuzumab induction, there was profound depletion of both CD4+ and CD8+ T cells, but greater recovery of CD8+ than CD4+ T cells at 24 months compared with baseline (P=0.014). (B) For CD4+ T cells, there was no evidence that the recovery of memory cells was favored over naïve cells (P=0.740), whereas there was a nonsignificant trend toward greater recovery of the CD8+ memory subset (P=0.163). (C) Within the CD4+ memory subset, the recovery of TEM cells was almost twice that of TCM cells (P=0.027); within the CD8+ memory subset, recovery of both TEM and TCM was similar (P=0.556). Cell counts are expressed as 103 cells/µl.

Figure 2.

Depletion and recovery of CD4+25+FoxP3+ Tregs in comparison to total CD4+ and CD4+45RO+CCR7-62L- TEM cells. Cells were available from eight participants. (A and B) The initial depletion of Tregs was relatively less than that of total CD4+ T cells, resulting in a sharp increase in the percentage of Tregs within total CD4+ T cells that persisted for the first 12 months post-transplant. (C) Ratio of Tregs/TEM. Cell counts are expressed as 103 cells/µl.

Figure 3.

Development of circulating anti-HLA alloantibodies. (A) Anti-HLA alloantibodies were considered positive using a PRA >5% as threshold: the blue color represents anti-HLA class I positivity; the orange color anti-HLA class II positivity; the PRA values are shown in each positive cell; gray cells represent missing samples. (B) Cumulative hazard of development of any anti-HLA alloantibody type. (C) Cumulative hazards of anti-HLA class I versus class II alloantibody development. Asterisk indicates donor-specific alloantibodies.

Figure 4.

Longitudinal T cell profiles for available participants who developed cAb during the course of the study. Means (± SEM) of available participants who did not develop cAb are shown as controls (n=9; except for TCM, n=3). (A) CD4+ subsets, (B) CD8+ subsets. Cell counts are expressed as 103 cells/µl. AlloAb, alloantibodies.

Figure 5.

Longitudinal CD4+25+FoxP3+ Tregs profiles for available participants who developed cAb during the course of the study. Means (± SEM) of available participants who did not develop cAb are shown as controls (n=6). (A) Absolute Tregs counts, (B) ratio of Tregs/Total CD4+ cells, (C) ratio of Tregs/TEM cells. Cell counts are expressed as 103 cells/µl. AlloAb, alloantibodies.

Figure 6.

Therapeutic and sample collection protocols. Each subject received 0.3 mg/kg (to a maximum of 20 mg) of alemtuzumab. Tacrolimus was initiated at a dose of 0.05–0.1 mg/kg twice daily, with a target trough level of 5–10 ng/ml, and was switched to sirolimus between 2 and 3 months after transplant (10 mg/m2 of loading dose followed by 3 mg/m2 every 12 hours, adjusted to attain trough levels of 12–15 ng/ml during the first 6 months and 8–12 ng/ml thereafter). MMF was administered at doses of 1200 mg/m2 per day (max 2 g) twice or thrice daily until day 14 after transplant, 900 mg/m2 per day until tacrolimus was switched to sirolimus, and 600 mg/m2 per day for the remainder of the study. SRL, sirolimus.