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.

Figure 1.

Depletion and recovery of T cell subsets after induction with alemtuzumab. Cells were available from 11 participants, except for T_CM 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 T_EM cells was almost twice that of T_CM cells (P=0.027); within the CD8⁺ memory subset, recovery of both T_EM and T_CM 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^- T_EM 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/T_EM. 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 T_CM, 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/T_EM 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.