Autonomous and extrinsic regulation of thymopoiesis inhuman immune system (HIS) mice

Abstract

PortugalHuman Immune System (HIS) mice represent a novel biotechnology platform to dissect human haematopoiesis and immune responses. However, the limited human T-cell development that is observed in HIS mice restricts its utility for these applications. Here, we address whether reduced thymopoiesis in HIS mice reflects an autonomous defect in T-cell precursors and/or a defect in the murine thymic niche. Human thymocyte precursors seed the mouse thymus and their reciprocal interactions with murine thymic epithelial cells (TECs) led to both T-cell and TEC maturation. The human thymocyte subsets observed in HIS mice demonstrated survival, proliferative and phenotypic characteristics of their normal human counterparts, suggesting that the intrinsic developmental program of human thymocytes unfolds normally in this xenograft setting. We observed that exogenous administration of human IL-15/IL-15Ra agonistic complexes induced the survival, proliferation and absolute numbers of immature human thymocyte subsets, without any obvious effect on cell-surface phenotype or TCR Vb usage amongst the newly selected mature singlepositive (SP) thymocytes. Finally, when IL-15 was administered early after stem cell transplantation, we noted accelerated thymopoiesis resulting in the more rapid appearance of peripheral naïve T cells. Our results highlight the functional capacity of murine thymic stroma cells in promoting human thymopoiesis in HIS mice but suggest that the ''cross-talk'' between murine thymic stroma and human haematopoietic precursors may be suboptimal. As IL-15 immunotherapy promotes early thymopoiesis, this novel approach could be used to reduce the period of T-cell immunodeficiency in the post-transplant clinical setting. IntroductionSixty million years of evolution has generated important differences between the murine and human immune systems (HISs). As such, our knowledge of lymphocyte development, homeostasis and immune responses that is largely derived from mouse studies may not be directly applicable to man. The recent advances in the development of HIS mice provide a new model to experimentally dissect human lymphocyte biology that may eventually allow us to bridge the knowledge gap between murine and human in vivo studies of immune responses. T-cell development depends on instructive temporal-spatial signals provided by a resident cellular network known as thymic stroma [6,7]. TECs represent the main thymic stromal compartment in the pre-involution thymus and constitute a multifunctional platform that supports thymocyte commitment, survival, division, migration and selection. TECs are classically divided into two specialized functional subsets, cortical (cTECs) and medullary (mTECs). While cTECs are important at early stages of T-cell development and mediate positive selection, mTECs are critical at later stages governing negative selection and providing survival signals to mature single-positive (SP) thymocytes [6,8,9]. The generation of these two functionally competent TEC compartments is a prerequisite ...

Circulating IL-15 exists as heterodimeric complex with soluble IL-15Rα in human and mouse serum

“…45 In addition, soluble IL-15 heterodimers were reported to support survival and proliferation of immature human thymocyte subsets as well as to accelerate thymopoiesis. 46 Taken together, these findings suggest that increased IL-15 bioavailability results in strong systemic growth and mobilization signals for lymphocytes. Therefore, the ability of IL-15 to form stable soluble heterodimers with sIL-15R␣ that circulate in the bloodstream and are transported to sites away from the production makes IL-15 a hormone-like molecule, capable to act at distance, in addition to the membrane-bound heterodimeric cytokine with locally restricted functions during cell-to-cell interaction.…”

Human Hematopoietic Reconstitution and HLA-Restricted Responses in Nonpermissive Alymphoid Mice

“…Some groups reported that the introduction of HLA expression by the murine hosts greatly improved human responses in HIS mice (20)(21)(22)(23). Although murine MHC probably plays a major role in thymic selection of human T cells in the chimeras (20,24), none of the previous studies could exclude the generation of a mouserestricted human T cell response, precluding the use of these chimeras as preclinical models for vaccine design or immune responses to infections. Therefore, we generated murine hosts in which murine MHC molecules were replaced by HLA molecules to ensure strict education of the human thymocytes by HLA molecules.…”

“…Spleen cells from immunized mice were incubated for 10 min with Fc block, as described in the previous section. Cells were stained for 10 min at RT in FACS buffer with a mix of three HBV-specific pentamers, HLA-A2-env peptides (peptides 183-191 and 348-357) and HLA-A2-core peptide (peptides [18][19][20][21][22][23][24][25][26][27], all the three pentamers being conjugated with allophycocyanin (ProImmune, Oxford, U.K.). As controls, cells were incubated with hepatitis C virus (HCV)-specific pentamers HLA-A2 NS3 peptide (1073-1081).…”

Humanized mice: Current states and perspectives

“…In contrast, the thymus of HIS mice clearly harbors cortical regions, though incomplete [22], that contain chimera TECs and immature CD38 + human thymocytes. In addition, the HIS thymus has medullary regions that contain murine TECs that co-localize with human CD3 + T cells [19,40,41]. Several studies have shown that thymic development in HIS mice seems to recapitulate, at least phenotypically, the main steps of T cell development found in human thymuses.…”

“…Histological analyses of the chimera thymus have shown correct compartmentalization of both murine thymic epithelial cells (TECs) and human thymocytes; however, the latter are less represented than in human fetal thymus [40]. The rudimentary thymus of non-reconstituted hosts is characterized by a predominance of cortical-like TECs among stromal cells and by the absence of a medullary region.…”