Induction Therapy With Basiliximab in Heart-Transplanted Children Impairs Regulatory T-Cell Population (Treg)

Abstract

Introduction: Following transplantation, many transplant programs employ induction immunosuppression, a relatively intense prophylactic therapy used at the time of transplant to prevent early acute rejection. Of the induction drugs, the interleukin-2 receptor (CD25) antagonist basiliximab (BXM) is frequently used. The targets of BXM are activated effector T cells, that upregulate CD25 upon activation and undergo IL-2 mediated T-cell proliferation, compromising allograft survival [1]. However, regulatory T cells (Treg) also express high levels of CD25 constitutively, and they rely on CD25 not only for their own proliferation and survival but also for detection of excessive proliferation of effector cells [2][3]. Therefore, BXM may be able to prevent acute rejection by hindering IL-2 mediated T effector expansion, but it could also compromise the likelihood of tolerance by impairing Treg proliferation and function. Methods: We enrolled 6 children who received a heart transplant and were treated with an established immunosuppression regimen. Two of the children were treated with BXM (20 mg on Day 0 and +4 after transplant), and 4 children did not receive BXM as induction therapy. We performed an exhaustive immunologic analysis at different time points including Tregs to analyze the effect of BXM on immune cells. Results: We show that the use of BXM during the first 4 days post-transplant completely blocks CD25 on T cells including Tregs for at least 45 days. Moreover, Treg numbers and Foxp3 expression were decreased in BXM-treated patients compared to patients not treated with BXM. We confirm the direct effect of BXM on Tregs by treating in vitro PBMC from healthy donors with BXM (n = 6). Basiliximab produced a marked Treg deregulation inducing a decrease in Foxp3 expression, a reduction in IL-10 production and a diminution in Treg proliferation under α-CD3/α-CD28 activation. Treg cells were more sensitive to the inhibitory effect of BXM than total CD4+ or CD8+ T cells. Conclusion: The use of basiliximab induction in transplanted children could compromise Treg-mediated tolerance during the first months post-transplant, which is the period with highest incidence of acute rejection, and could contribute to deregulation of immune homeostasis. This impact of BXM must be considered when making clinical decisions regarding induction immunosuppression.FIGURE 1: Frequency of Foxp3+CD25+CD4+ Treg cells in heart transplated children receiving induction therapy with Basiliximab (+BXM, n=2), or patients not treated with basilimab (-BXM, n=4). Mean values ±SEM are showed.This work was supported by grants from Instituto de Salud Carlos III (ISCIII) co-financed by FEDER funds (PI15/00011; ICI14/00282).FIGURE 2: Changes (%) from pre-transplant values (BL=0) in absolute counts (cells per uL of blood) of Foxp3+CD4+ cells in heart transplanted children receiving induction therapy with basilimab (+BXM, n=2), or patients not treated with basiliximab (-BXM, n=4). Mean values ±SEM are showed.FIGURE 3: CFrequencies of CDA+Foxp3+ (Treg) cells, CD4+ and CD8+ T cells within untreated (clear box) or BXM treated (solid box) PBMC stimulated with anti-CD3/CD28 dynabeads for 72h. Average and error bars indicating the 90th and 10th percentiles of 6 experiments are represented. *=<0.05 when comparing BXM-treated and non treated conditions.