Oxidative stress-induced IL-15 trans-presentation in keratinocytes contributes to CD8+ T cells activation via JAK-STAT pathway in vitiligo.

Oxidative stress and effector memory CD8+ T cells have been greatly implicated in vitiligo pathogenesis. However, the crosstalk between these two crucial pathogenic factors has been merely investigated. IL-15 has been regarded as an important cytokine exerting its facilitative effect on memory CD8+ T cells function in various autoimmune diseases. In the present study, we initially discovered that the IL-15 expression was significantly increased in vitiligo epidermis and highly associated with epidermal H2O2 content. In addition, epidermal IL-15 expression was mainly derived from keratinocytes. Then, we showed that oxidative stress promoted IL-15 and IL-15Rα expression as well as IL-15 trans-presentation by activating NF-κB signaling in keratinocytes. What's more, the trans-presented IL-15, rather than the secreted one, was accounted for the potentiation of CD8+ TEMs activation. We further investigated the mechanism underlying trans-presented IL-15 in potentiating CD8+ TEMs activation and found that the blockage of IL-15-JAK-STAT signaling could be a potent therapeutic approach. Taken together, our results demonstrate that oxidative stress-induced IL-15 trans-presentation in keratinocytes contributes to the activation of CD8+ TEMs, providing a novel mechanism by which oxidative stress initiates autoimmunity in vitiligo.

Autonomous and extrinsic regulation of thymopoiesis in human immune system (HIS) mice.

Human 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-15Rα agonistic complexes induced the survival, proliferation and absolute numbers of immature human thymocyte subsets, without any obvious effect on cell-surface phenotype or TCR Vß usage amongst the newly selected mature single-positive (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.

IL-15 transpresentation promotes both human T-cell reconstitution and T-cell-dependent antibody responses in vivo.

Cytokine immunotherapies targeting T lymphocytes are attractive clinical interventions against viruses and tumors. In the mouse, the homeostasis of memory α/ß CD8(+) T cells and natural killer (NK) cells is significantly improved with increased IL-15 bioavailability. In contrast, the role of "transpresented" IL-15 on human T-cell development and homeostasis in vivo is unknown. We found that both CD8 and CD4 T cells in human immune system (HIS) mice are highly sensitive to transpresented IL-15 in vivo, with both naïve (CD62L(+)CD45RA(+)) and memory phenotype (CD62L(-)CD45RO(+)) subsets being significantly increased following IL-15 "boosting." The unexpected global improvement in human T-cell homeostasis involved enhanced proliferation and survival of both naïve and memory phenotype peripheral T cells, which potentiated B-cell responses by increasing the frequency of antigen-specific responses following immunization. Transpresented IL-15 did not modify T-cell activation patterns or alter the global T-cell receptor (TCR) repertoire diversity. Our results indicate an unexpected effect of IL-15 on human T cells in vivo, in particular on CD4(+) T cells. As IL-15 promotes human peripheral T-cell homeostasis and increases the frequency of neutralizing antibody responses in HIS mice, IL-15 immunotherapy could be envisaged as a unique approach to improve vaccine responses in the clinical setting.

Interleukin-15 receptor blockade in non-human primate kidney transplantation.

BACKGROUND: Interleukin (IL)-15 is a chemotactic factor to T cells. It induces proliferation and promotes survival of activated T cells. IL-15 receptor blockade in mouse cardiac and islet allotransplant models has led to long-term engraftment and a regulatory T-cell environment. This study investigated the efficacy of IL-15 receptor blockade using Mut-IL-15/Fc in an outbred non-human primate model of renal allotransplantation. METHODS: Male cynomolgus macaque donor-recipient pairs were selected based on ABO typing, major histocompatibility complex class I typing, and carboxy-fluorescein diacetate succinimidyl ester-based mixed lymphocyte responses. Once animals were assigned to one of six treatment groups, they underwent renal transplantation and bilateral native nephrectomy. Serum creatinine level was monitored twice weekly and as indicated, and protocol biopsies were performed. Rejection was defined as a increase in serum creatinine to 1.5 mg/dL or higher and was confirmed histologically. Complete blood counts and flow cytometric analyses were performed periodically posttransplant; pharmacokinetic parameters of Mut-IL-15/Fc were assessed. RESULTS: Compared with control animals, Mut-IL-15/Fc-treated animals did not demonstrate increased graft survival despite adequate serum levels of Mut-IL-15/Fc. Flow cytometric analysis of white blood cell subgroups demonstrated a decrease in CD8 T-cell and natural killer cell numbers, although this did not reach statistical significance. Interestingly, two animals receiving Mut-IL-15/Fc developed infectious complications, but no infection was seen in control animals. Renal pathology varied widely. CONCLUSIONS: Peritransplant IL-15 receptor blockade does not prolong allograft survival in non-human primate renal transplantation; however, it reduces the number of CD8 T cells and natural killer cells in the peripheral blood.

CD8(+) T cells resistant to costimulatory blockade are controlled by an antagonist interleukin-15/Fc protein.

BACKGROUND: Although permanent engraftment is often achieved with new therapeutics, chronic rejection and graft failure still occur. As the importance of CD8(+) T cells in rejection processes has been underlined in various transplant models, and as interleukin (IL)-15 is involved in the activation of CD8(+) T cells, we hypothesize that CD8(+) T cell "escape" from costimulation blockade might be a IL-15/IL-15R dependent process. METHODS: In a murine islet allograft model employing a fully major histocompatibility complex-mismatched strain combination of Balb/c donors to CD4 C57BL/6 recipients, a monotherapy with the IL-15 antagonist, IL-15 mutant/Fcgamma2a, or the costimulatory blockade molecule, CTLA4/Fc, was used. In addition to monitoring graft survival, infiltration of alloreactive immune cells was analyzed by histology and immunohistochemistry, and alloimmune response of proliferative CD8(+) T cells was measured in vivo. RESULTS: Sixty percent of the recipients treated with CTLA4/Fc acutely rejected their islet allograft, comparable to untreated control animals (50% survival). In contrast, the IL-15 antagonist proved to be highly effective, with 100% of recipients accepting their allograft. Immunohistology study demonstrated a remarkable decrease of CD8(+) T-cell intragraft infiltration in IL-15 mutant/Fcgamma2a treated animals with well-preserved islet architecture and a reduced frequency of proliferating alloreactive CD8(+) T cells in comparison with that of untreated and CTLA4/Fc treated groups. CONCLUSIONS: In this study, we determined the efficacy and potential therapeutic benefit of the IL-15 antagonist on CD4-independent CD8(+) T-cell responses to alloantigens. Targeting the IL-15/IL-15R pathway represents a potent strategy to prevent rejection driven by CD8(+) T cells resistant to costimulation blockade.