Elsevier

Journal of Autoimmunity

Volume 31, Issue 4, December 2008, Pages 408-415
Journal of Autoimmunity

Presence of donor-derived thymic epithelial cells in [B6→MRL/lpr] mice after allogeneic intra-bone marrow–bone marrow transplantation (IBM–BMT)

https://doi.org/10.1016/j.jaut.2008.09.003Get rights and content

Abstract

We have previously shown that allogeneic intra-bone marrow–bone marrow transplantation (IBM–BMT) can be used to treat autoimmune diseases in MRL/lpr (H-2K) mice with replacing not only hematolymphoid cells but also stromal cells by normal C57BL/6 (B6: H-2b) mouse cells. In the present study, we examined for existence of donor-derived thymic epithelial cells (TECs) in the host thymus using green fluorescent protein (GFP)-B6 (H-2b) mice. In [GFP-B6→MRL/lpr] chimeric mice, splenocytes and thymocytes were completely replaced by donor-type cells, and levels of serum autoantibodies and proteinuria were significantly – reduced to those levels of normal donors. Interestingly, GFP-expressing TECs – not only medullary TECs, which express mouse thymus stromal (MTS)-10, but also cortical TECs, which express cytokeratin 18 – were found. Also, the number of autoimmune regulator (AIRE) expressing TECs, which regulates tissue-specific antigens to delete autoreactive cells, was reduced in the chimeric mice to that of the donor, whereas the number of forkhead box N1 (FOXN1) expressing TECs, which are crucial in the terminal differentiation of TECs, remained unchanged. These findings suggest that BMCs contain the precursors of functional TECs, and that they can differentiate into TECs, thereby correcting thymic function.

Introduction

The thymus is the organ in which T cells develop from their precursor cells [1], [2]. As these precursors develop into mature T cells, they migrate from the cortical area to the medullary area in the thymus, as they develop into mature T cells. The thymic epithelial cells (TECs) and dendritic cells (DCs) play important roles in this process. The cortical TECs (cTECs) induce major histocompatibility complex (MHC) restricted T cells by positive selection, and the medullary DCs (mDCs) delete self-antigen (Ag) reactive T cells by negative selection. Recent studies have identified functional molecules that are expressed in TECs. FOXN1 is a transcriptional factor for terminal differentiation of TECs during embryogenesis, and the lack of this gene results in the nu/nu phenotype [3], [4]. AIRE is the transcriptional activator for tissue-specific antigens, and is expressed in medullary TECs (mTECs) [5]. AIRE regulates the deletion of autoreactive T cells, and its deficiency leads to autoimmune diseases [6].

cTECs and mTECs had been thought to develop from different parts of the embryo. The cTECs were believed to be derived from the ectoderm of the third pharyngeal cleft, whereas the mTECs were believed to be derived from the endoderm of the third pharyngeal pouch [7], [8], [9]. However, recent reports indicate that both cTECs and mTECs are derived from a single germ layer of endoderm [10], [11], [12]. In addition, Rossi et al. showed that a single precursor expressing MTS24 from the fetal thymus can differentiate into both cTECs and mTECs [13]. These findings suggest the existence of a common precursor for cTECs and mTECs in the embryonic thymus. However, the precursors of TECs have not been well examined in adults.

Bone marrow transplantation (BMT) has been used as a potentially curative therapy for patients with a wide variety of diseases, including hematological disorders, congenital immunodeficiencies, metabolic disorders, autoimmune diseases, and solid tumors [14], [15], [16], [17], [18], [19]. To ensure fewer side effects, and/or better engraftment, a number of different approaches to BMT methods have been tried, among them being the transplantation of high doses of HSCs, and donor lymphocyte infusion (DLI) [20], [21]. However, in some cases, there remains the challenge of obtaining sufficient numbers of BMCs, preventing graft failure, or preventing the induction of the lethal GVHD. The development of a new cell-based method is therefore required.

We previously developed several bone marrow transplantation (BMT) methods [22], [23], [24], [25], [26], [27], including the intra-bone marrow (IBM)–BMT (IBM–BMT) method [28]: the direct injection of BMCs into the bone marrow cavity. This method facilitates the engraftment of not only donor-derived hemopoietic stem cells (HSCs) but also mesenchymal stem cells (MSCs). We have found that the IBM–BMT method can be used to treat autoimmune diseases in chimeric-resistant MRL/lpr mice by replacing normal HSCs and MSCs, although the conventional BMT method is ineffective in these mice.

BMCs are known to differentiate into several epithelial cells, such as those of the lung, liver, gastrointestinal tract, kidney, and skin after BMT [29], [30], [31], [32].

In the present study, we used the allogeneic IBM–BMT in MRL/lpr mice to examine the origin of TECs in the recipient thymus. Interestingly, donor-derived TECs were found in both the medullary and the cortical areas. In addition, the number of AIRE-expressing cells was found to be reduced in parallel with the treatment of the autoimmune diseases. These findings suggest that BMCs contain the precursors of functional TECs, and that they can differentiate into TECs, which result in the correction of thymic function.

Section snippets

Mice

Three- to four-month-old female MRL/MP-lpr/lpr mice (MRL/lpr) (H-2k) [33] were used as recipients, and 6- to 8-week-old female C57BL/6(B6) (H-2b) mice that expressed green fluorescent protein (GFP) were used as donors. Mice were obtained from SLC (Shizuoka, Japan) and maintained in our animal facilities under specific pathogen-free conditions.

IBM–BMT method

Three- to four-month-old MRL/lpr mice that were exhibiting the onset of autoimmune disease (proteinuria > 100 mg/dl and evident lymphadenopathy) were

Development of donor-derived hematolymphoid cells, and tolerance induction in [GFP-B6→MRL/lpr] chimeric mice after IBM–BMT

First, we performed allogeneic BMT in the autoimmune-prone MRL/lpr mice (H-2k) by IBM–BMT from GFP-bearing B6 mice (GFP-B6) (H-2b). Eight weeks after transplantation, all of the lymphocyte subsets (CD4+ T cells, CD8+ T cells, and B220+ B cells) in the spleen were GFP-positive, indicating that these cells had been replaced by donor-type cells in the [GFP-B6→MRL/lpr] chimeric mice (Fig. 1A). In addition, no abnormal CD3+B220+ lpr T cells were found. Thymocytes had also been replaced with

Discussion

In the present study, we examined the origins of TECs in chimeric mice [GFP-B6→MRL/lpr] using the IBM–BMT method. We confirmed that IBM–BMT can be used to treat autoimmune diseases in the MRL/lpr mice [27], [28]. Interestingly, not only the hematopoietic cells, but also some of both the medullary and the cortical TECs were donor-derived. The donor-type TECs expressed their functional molecules, FOXN1 and AIRE. In addition, the number of AIRE-expressing cells was significantly reduced in the

Acknowledgments

Supported by a grant from “Haiteku Research Center” of the Ministry of Education, a grant from the “Millennium” program of the Ministry of Education, Culture, Sports, Science and Technology, a grant from the “Science Frontier” program of the Ministry of Education, Culture, Sports, Science and Technology, a grant from the “The 21st Century Center of Excellence (COE)” program of the Ministry of Education, Culture, Sports, Science and Technology, a grant-in-aid for scientific research (B)

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  • Cited by (0)

    Drs T. Takaki and N. Hosaka contributed equally to this manuscript.

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