Cyclosporine A Inhibits the T-bet-Dependent Antitumor Response of CD8(+) T Cells.

Transplant recipients face an increased risk of cancer compared with the healthy population. Although several studies have examined the direct effects of immunosuppressive drugs on cancer cells, little is known about the interactions between pharmacological immunosuppression and cancer immunosurveillance. We investigated the different effects of rapamycin (Rapa) versus cyclosporine A (CsA) on tumor-reactive CD8(+) T cells. After adoptive transfer of CD8(+) T cell receptor-transgenic OTI T cells, recipient mice received either skin grafts expressing ovalbumin (OVA) or OVA-expressing B16F10 melanoma cells. Animals were treated daily with Rapa or CsA. Skin graft rejection and tumor growth as well as molecular and cellular analyses of skin- and tumor-infiltrating lymphocytes were performed. Both Rapa and CsA were equally efficient in prolonging skin graft survival when applied at clinically relevant doses. In contrast to Rapa-treated animals, CsA led to accelerated tumor growth in the presence of adoptively transferred tumor-reactive CD8(+) OTI T cells. Further analyses showed that T-bet was downregulated by CsA (but not Rapa) in CD8(+) T cells and that cancer cytotoxicity was profoundly inhibited in the absence of T-bet. CsA reduces T-bet-dependent cancer immunosurveillance by CD8(+) T cells. This may contribute to the increased cancer risk in transplant recipients receiving calcineurin inhibitors.

Mesenchymal stem cells are short-lived and do not migrate beyond the lungs after intravenous infusion.

Mesenchymal stem cells (MSC) are under investigation as a therapy for a variety of disorders. Although animal models show long term regenerative and immunomodulatory effects of MSC, the fate of MSC after infusion remains to be elucidated. In the present study the localization and viability of MSC was examined by isolation and re-culture of intravenously infused MSC. C57BL/6 MSC (500,000) constitutively expressing DsRed-fluorescent protein and radioactively labeled with Cr-51 were infused via the tail vein in wild-type C57BL/6 mice. After 5 min, 1, 24, or 72 h, mice were sacrificed and blood, lungs, liver, spleen, kidneys, and bone marrow removed. One hour after MSC infusion the majority of Cr-51 was found in the lungs, whereas after 24 h Cr-51 was mainly found in the liver. Tissue cultures demonstrated that viable donor MSC were present in the lungs up to 24 h after infusion, after which they disappeared. No viable MSC were found in the other organs examined at any time. The induction of ischemia-reperfusion injury in the liver did not trigger the migration of viable MSC to the liver. These results demonstrate that MSC are short-lived after i.v. infusion and that viable MSC do not pass the lungs. Cell debris may be transported to the liver. Long term immunomodulatory and regenerative effects of infused MSC must therefore be mediated via other cell types.

Mesenchymal stem cells together with mycophenolate mofetil inhibit antigen presenting cell and T cell infiltration into allogeneic heart grafts.

Donor-derived mesenchymal stem cells (MSC) can induce long-term acceptance in a rat heart transplantation model when injected prior to transplantation in combination with mycophenolate mofetil (MMF). In contrast, MSC alone cause accelerated graft rejection. To better understand these conflicting data we studied the effects of MSC and MMF on lymphocyte populations in heart allografts and secondary lymphatic organs. Allogeneic MSC injected prior to transplantation are immunogenic in this model because activated CD4+ and CD8+ cells emerged earlier in secondary lymphatic organs of MSC- and MSC/MMF-treated animals, compared to animals not treated with MSC. Consequently T cells infiltrated the grafts of MSC-only treated animals promptly causing accelerated graft rejection. However, few T cells or antigen-presenting cells (APC) infiltrated the grafts of animals treated with MSC and MMF. Consistent with this finding, intercellular adhesion molecule 1 (ICAM-1) and E-selectin was down-regulated exclusively in MSC/MMF-treated grafts, indicating that MSC together with MMF interfere with endothelial activation. Additionally, the presence of interferon-gamma (IFN-γ) enhanced MSC capabilities to suppress T cell proliferation in vitro. Interestingly, MMF did not influence serum IFN-γ levels in vivo. Together, our data indicate that MSC pre-activate T cells, but co-treatment with MMF eliminates these T cells, decreases intragraft APC and T cell trafficking by inhibiting endothelial activation, and allows IFN-γ stimulation of suppressive MSC.

Inflammatory conditions affect gene expression and function of human adipose tissue-derived mesenchymal stem cells.

There is emerging interest in the application of mesenchymal stem cells (MSC) for the prevention and treatment of autoimmune diseases, graft-versus-host disease and allograft rejection. It is, however, unknown how inflammatory conditions affect phenotype and function of MSC. Adipose tissue-derived mesenchymal stem cells (ASC) were cultured with alloactivated peripheral blood mononuclear cells (PBMC) (mixed lymphocyte reaction: MLR), with proinflammatory cytokines [interferon (IFN)-γ, tumour necrosis factor (TNF)-α and interleukin (IL)-6] or under control conditions, and their full genome expression and function examined. Proinflammatory cytokines mainly increased indoleamine-2,3-dioxygenase expression, whereas ASC cultured with MLR showed increased expression of COX-2, involved in prostaglandin E(2) production. Both conditions had a stimulatory, but differential, effect on the expression of proinflammatory cytokines and chemokines, while the expression of fibrotic factors was decreased only in response to proinflammatory cytokines. Functional analysis demonstrated that inflammatory conditions affected morphology and proliferation of ASC, while their differentiation capacity and production of trophic factors was unaffected. The immunosuppressive capacity of ASC was enhanced strongly under inflammatory conditions. In conclusion, ASC showed enhanced immunosuppressive capacity under inflammatory conditions, while their differentiation capacity was preserved. Therefore, in vitro preconditioning provides ASC with improved properties for immediate clinical immune therapy.

Antigen-specific recognition is critical for the function of regulatory CD8(+)CD28(-) T cells.

The immunomodulatory properties of CD8 T cells with regulatory phenotype have become evident. It remains unclear whether the immunomodulatory function of CD8(+)CD28(-) T cells requires antigen-specific TCR interaction with major histocompatibility complex class I (MHC I). We have isolated naïve CD8(+)CD28(-) T suppressor cells (Tsup) from H2-Kk Des-TCR mice that express a transgenic, MHC class I-restricted, clonotypic TCR against an allogeneic MHC class I molecule (H2-Kb) plus self-peptide. These cells were compared to B10.BR wild type (w/t) CD8(+)CD28(-) T cells and to naïve CD4(+)CD25(+) regulatory T cells (Treg) of the same strains. Des CD8 effector T cells proliferated more readily when stimulated by H2-Kb splenocytes than w/t controls, whereas Des CD4 T cells showed the same alloresponse as w/t cells. Activation and proliferation of B10.BR CD4 T cells stimulated by H2-Kb APC were suppressed more effectively by Des CD8(+)CD28(-) T cells than by w/t CD8(+)CD28(-) T cells. On the contrary, Des CD4(+)CD25(+) T cells inhibited T cell proliferation less effectively than w/t CD4(+)CD25(+) T cells. In conclusion, we demonstrate that the function of naive Tsup is strongly enhanced by antigen recognition. Therefore we expect that Tsup are possible candidates for antigen-specific immunosuppressive therapy.

Mesenchymal stem cells require a sufficient, ongoing immune response to exert their immunosuppressive function.

Mesenchymal stem cells (MSC) have emerged to be one of the most promising candidates for cellular immunotherapy in solid organ transplantation because the reduction of conventional immunosuppression is highly desirable. However, little is known about the details of MSC-mediated immunomodulation and their clinical relevance. To address conflicting studies about the ability of MSC to suppress or augment T-cell proliferation, we introduce a transplantation-related rat model that allows studying the influence of MSC on alloproliferation. Hearts transplanted in a fully allogeneic transplantation model (LEW to ACI) were rejected earlier when recipients were pretreated with donor MSC, indicating activation of T cells in vivo. In additional co-culture experiments, T cells were differently affected by allogeneic MSC depending on the extent of previous activation: When conditions were rendered proinflammatory by adding high concanavalin A (ConA) concentrations or proinflammatory cytokines (interferon-gamma, interleukin-2, or tumor necrosis factor-alpha), MSC inhibited proliferation. Application of low doses of ConA or anti-inflammatory cytokines like IL-10 abrogated the suppressive effect of MSC. For application of MSC in solid organ transplantation, it will be important to further describe this switch effect of MSC function.

Mesenchymal stem cells can induce long-term acceptance of solid organ allografts in synergy with low-dose mycophenolate.

The induction of tolerance towards allogeneic solid organ grafts is one of the major goals in transplantation medicine. Mesenchymal stem cells (MSC) inhibit the immune response in vitro, and thus are promising candidate cells to promote acceptance of transplanted organs in vivo. Such novel approaches of tolerance induction are needed since, to date, graft acceptance can only be maintained through life-long treatment with unspecific immunosuppressants that are associated with toxic injury, opportunistic infections and malignancies. We demonstrate that donor-derived MSC induce long-term allograft acceptance in a rat heart transplantation model, when concurrently applied with a short course of low-dose mycophenolate. This tolerogenic effect of MSC is at least partially mediated by the expression of indoleamine 2,3-dioxygenase (IDO), demonstrated by the fact that blocking of IDO with 1-methyl tryptophan (1-MT) abrogates graft acceptance. Moreover we hypothesize that MSC interact with dendritic cells (DC) in vivo, because allogeneic MSC are rejected in the long-term but DC acquire a tolerogenic phenotype after applying MSC. In summary, we demonstrate that MSC constitute a promising tool for induction of non-responsiveness in solid organ transplantation that warrants further investigation in clinical trials.