Taniguchi H, Abe M, Shirai T, Fukao K, Nakauchi H
Department of Immunology, Center for Tsukuba Advanced Research Alliance, Japan.
J Immunol. 1995 Dec 15;155(12):5631-6.
Although allogeneic bone marrow (BM) transplantation is an effective way to induce donor-specific tolerance, its clinical application is hampered because of the risk associated with vigorous myeloablative pretransplant conditioning. One approach to overcome this problem is to establish a lower chimeric state by mild myeloablation. It is not clear, however, whether there is a threshold in the extent of chimerism that is required for tolerance induction. In this study, we establish a mixed BM chimera system to examine the correlation between the reconstitution ratio of BM chimerism, donor-reactive T cell deletion, and skin graft acceptance using I-E alpha transgenic C57BL/6 mice as the BM and skin graft donors and Ly5 congenic C57BL/6 mice as the recipients. In this system, the class II MHC molecule I-E was the transplantation Ag, and the extent of I-E-reactive T cell deletion was determined by flow cytometry using a mAb specific for the V beta 11 TCR. The degree of BM chimerism was measured by examining the expression of donor-derived Ly5.2 and host-derived Ly5.1 on peripheral blood cells. Transplantation of I-E+ transgenic donor BM cells resulted in deletion of V beta 11+CD4+ T cells in recipient's PBL, and the extent of deletion was proportional to the degree of chimerism. When mice of different degrees of chimerism were tested for skin graft survival, we found that recipient mice with > 30% chimerism could accept skin grafts from I-E+ donor mice, whereas those with < 10% chimerism showed prolonged but not permanent graft survival. These findings revealed the sequence of events for induction of tolerance. First, the degree of BM chimerism determines the number of I-E+ cells in the thymus, which then elicits negative selection of I-E-reactive T cells in a form of clonal deletion. The extent of T cell deletion ultimately determines the mode of tolerance. These data provide experimental evidence for the potential use of partial chimerism by bone marrow transplantation for the induction of donor-specific tolerance in clinical settings.
尽管同种异体骨髓（BM）移植是诱导供体特异性耐受的有效方法，但其临床应用因与移植前强烈的清髓预处理相关的风险而受到阻碍。克服这一问题的一种方法是通过轻度清髓建立较低的嵌合状态。然而，尚不清楚嵌合程度是否存在诱导耐受所需的阈值。在本研究中，我们建立了一个混合BM嵌合体系统，以检查BM嵌合的重建比例、供体反应性T细胞缺失和皮肤移植接受之间的相关性，使用I-Eα转基因C57BL/6小鼠作为BM和皮肤移植供体，Ly5同基因C57BL/6小鼠作为受体。在这个系统中，II类MHC分子I-E是移植抗原，I-E反应性T细胞缺失的程度通过使用针对Vβ11 TCR的单克隆抗体的流式细胞术来确定。通过检测外周血细胞上供体来源的Ly5.2和宿主来源的Ly5.1的表达来测量BM嵌合程度。I-E+转基因供体BM细胞的移植导致受体PBL中Vβ11+CD4+ T细胞的缺失，缺失程度与嵌合程度成正比。当对不同嵌合程度的小鼠进行皮肤移植存活测试时，我们发现嵌合率>30%的受体小鼠可以接受来自I-E+供体小鼠的皮肤移植，而嵌合率<10%的小鼠移植存活时间延长但不是永久性的。这些发现揭示了诱导耐受的事件顺序。首先，BM嵌合程度决定了胸腺中I-E+细胞的数量，进而以克隆缺失的形式引发I-E反应性T细胞的阴性选择。T细胞缺失的程度最终决定了耐受模式。这些数据为骨髓移植部分嵌合在临床环境中诱导供体特异性耐受的潜在应用提供了实验证据。
