Persistence of gene expression profile in CD200 transgenic skin allografts is associated with graft survival on retransplantation to normal recipients

Molecular incompatibility between pig CD200 and human CD200 receptor in in vitro xenogeneic immune responses

Overexpression of human CD200 (hCD200) in porcine endothelial cells (PECs) has been reported to suppress xenogeneic immune responses of human macrophages against porcine endothelial cells. The current study aimed to address whether the above-mentioned beneficial effect of hCD200 is mediated by overcoming the molecular incompatibility between porcine CD200 (pCD200) and hCD200 receptor or simply by increasing the expression levels of CD200 without any molecular incompatibility across the two species. We overexpressed hCD200 or pCD200 using lentiviral vectors with V5 marker in porcine endothelial cells and compared their suppressive activity against U937-derived human macrophage-like cells (hMCs) and primary macrophages. In xenogeneic coculture of porcine endothelial cells and human macrophage-like cells or macrophages, hCD200-porcine endothelial cells suppressed phagocytosis and cytotoxicity of human macrophages to a greater extent than pCD200-porcine endothelial cells. Secretion of tumor necrosis factor-α, interleukin-1β, and monocyte chemoattractant protein-1 from human macrophages and expression of M1 phenotypes (inducible nitric oxide synthase, dectin-1, and CD86) were also suppressed by hCD200 to a greater extent than pCD200. Furthermore, in signal transduction downstream of CD200 receptor, hCD200 induced Dok2 phosphorylation and suppressed IκB phosphorylation to a greater extent than pCD200. The above data supported the possibility of a significant molecular incompatibility between pCD200 and human CD200 receptor, suggesting that the beneficial effects of hCD200 overexpression in porcine endothelial cells could be mediated by overcoming the molecular incompatibility across the species barrier rather than by simple overexpression effects of CD200.

Tissue-engineered vascular microphysiological platform to study immune modulation of xenograft rejection

Most of the vascular platforms currently being studied are lab-on-a-chip types that mimic capillary networks and are applied for vascular response analysis in vitro. However, these platforms have a limitation in clearly assessing the physiological phenomena of native blood vessels compared to in vivo evaluation. Here, we developed a simply fabricable tissue-engineered vascular microphysiological platform (TEVMP) with a three-dimensional (3D) vascular structure similar to an artery that can be applied for ex vivo and in vivo evaluation. Furthermore, we applied the TEVMP as ex vivo and in vivo screening systems to evaluate the effect of human CD200 (hCD200) overexpression in porcine endothelial cells (PECs) on vascular xenogeneic immune responses. These screening systems, in contrast to 2D in vitro and cellular xenotransplantation in vivo models, clearly demonstrated that hCD200 overexpression effectively suppressed vascular xenograft rejection. The TEVMP has a high potential as a platform to assess various vascular-related responses.

The CD200-CD200R cross-talk helps Leishmania donovani to down regulate macrophage and CD4+CD44+ T cells effector functions in an NFκB independent manner

The lacuna in the knowledge of immunobiology, especially in visceral infections that are fatal if left untreated, are a major hurdle in getting a vaccine candidate for leishmaniasis. Till date, only a few drugs are available to combat human leishmaniasis and a vaccine candidate either prophylactic or preventive is still awaited. Therefore, identification of host and parasitic factors involved in the regulation of specific immune mechanisms are essentially needed. In this study, we observed that CD200-CD200R immune inhibitory axis regulates host macrophages effectors properties and helps antigen experienced T cells (CD4⁺CD44⁺ T cells) to acquire anti-inflammatory cytokines (IL-4, IL-10, TGF-β, IL-27) producing abilities in an NFkB independent manner. After CD200 blocking the macrophages effectively inhibited proliferation of Leishmania amastigotes and also induced the production of IL-12, IFN-γ, TNF-α and nitric oxide (NOx). Further, the blocking of CD200 signaling also restored macrophages MHC-II expression and helped CD4⁺CD44⁺ T cells to produce pro-inflammatory cytokines like IL-2, IL-12 and IFN-γ. The finding of this study suggested the importance of immune inhibitory mechanisms in controlling Leishmania growth and survival and therefore, requires more studies to understand its role in vaccine induced immunity.

Role of Human CD200 Overexpression in Pig-to-Human Xenogeneic Immune Response Compared With Human CD47 Overexpression

BACKGROUND

Macrophages play important roles in xenograft rejection. Here, we investigated whether overexpression of human CD200 or CD47 in porcine endothelial cells (PEC) can suppress macrophages activation in xenogeneic immune responses.

METHODS

PECs and human macrophages were incubated together, harvested, and analyzed for in vitro macrophage phagocytic and cytotoxicity activity, and cytokine release. Next, PECs were injected into renal subcapsular space of humanized mice. On day 10 posttransplantation, we analyzed xenograft survival and perigraft inflammatory cell infiltrations in PEC-to-humanized mouse transplantation.

RESULTS

PECs highly expressing human CD200, CD47, or both CD47/CD200 were established by lentiviral vector transduction. Both CD200 and CD47 suppressed in vitro macrophage phagocytic and cytotoxic activity against PECs; decreased TNF-α, IL-1β, and IL-6 secretion; and increased IL-10 secretion. However, simultaneous overexpression of CD200 and CD47 did not show additive effects. Next, PECs were transplanted into NOD-scid IL-2Rg null mice, and human monocytes and lymphocytes were adoptively transferred 1 day after xenotransplantation. PEC xenograft cell death and apoptosis were decreased in the CD200-PEC and CD47/CD200-PEC groups. Perigraft infiltration of human T cells was suppressed by CD47; CD200 suppressed infiltration of human macrophages to a greater extent than CD47; and the CD47/CD200-PEC group exhibited the lowest level of leukocyte infiltration. In summary, overexpression of CD200 in PECs suppressed xenogeneic activation of human macrophages and improved survival of PEC xenografts in humanized mice; however, coexpression of CD200 and CD47 did not show additive effects.

CONCLUSIONS

Therefore, overexpression of human CD200 in donor pigs could constitute a promising strategy for overcoming xenograft rejection.

Comparative Analysis of Immune Checkpoint Molecules and Their Potential Role in the Transmissible Tasmanian Devil Facial Tumor Disease

Immune checkpoint molecules function as a system of checks and balances that enhance or inhibit immune responses to infectious agents, foreign tissues, and cancerous cells. Immunotherapies that target immune checkpoint molecules, particularly the inhibitory molecules programmed cell death 1 and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), have revolutionized human oncology in recent years, yet little is known about these key immune signaling molecules in species other than primates and rodents. The Tasmanian devil facial tumor disease is caused by transmissible cancers that have resulted in a massive decline in the wild Tasmanian devil population. We have recently demonstrated that the inhibitory checkpoint molecule PD-L1 is upregulated on Tasmanian devil (Sarcophilus harrisii) facial tumor cells in response to the interferon-gamma cytokine. As this could play a role in immune evasion by tumor cells, we performed a thorough comparative analysis of checkpoint molecule protein sequences among Tasmanian devils and eight other species. We report that many of the key signaling motifs and ligand-binding sites in the checkpoint molecules are highly conserved across the estimated 162 million years of evolution since the last common ancestor of placental and non-placental mammals. Specifically, we discovered that the CTLA-4 (MYPPPY) ligand-binding motif and the CTLA-4 (GVYVKM) inhibitory domain are completely conserved across all nine species used in our comparative analysis, suggesting that the function of CTLA-4 is likely conserved in these species. We also found that cysteine residues for intra- and intermolecular disulfide bonds were also highly conserved. For instance, all 20 cysteine residues involved in disulfide bonds in the human 4-1BB molecule were also present in devil 4-1BB. Although many key sequences were conserved, we have also identified immunoreceptor tyrosine-based inhibitory motifs (ITIMs) and immunoreceptor tyrosine-based switch motifs (ITSMs) in genes and protein domains that have not been previously reported in any species. This checkpoint molecule analysis and review of salient features for each of the molecules presented here can serve as road map for the development of a Tasmanian devil facial tumor disease immunotherapy. Finally, the strategies can be used as a guide for veterinarians, ecologists, and other researchers willing to venture into the nascent field of wild immunology.

Anti-CD200R2, anti-IL-9, anti-IL-35, or anti-TGF-β abolishes increased graft survival and Treg induction induced in cromolyn-treated CD200R1KO.CD200tg mice

BACKGROUND

Rejection is associated with early degranulation (≥80%) of graft-infiltrating CD200R1 receptor-positive mast cells (MCs). Survival is increased, and MC degranulation is decreased, in CD200 mice but not in CD200R1KO mice. CD200 engagement of CD200R2 (not present on MCs) alters dendritic cell differentiation and enhances induction of Foxp3 regulatory T cells (Tregs). We investigated whether attenuation of MC degranulation by sodium cromoglycate allowed CD200 to increase survival in CD200R1KO mice.

METHODS

C57BL/6 control, CD200R1KO, CD200, or CD200R1KO.CD200 mice received BALB/c grafts with or without treatment with cromoglycate. Survival was monitored daily from day 10, with mixed lymphocyte culture responses measured on day 14 or 21 and graft immunohistology performed on day 14.

RESULTS

Decreased MC degranulation and increased graft Foxp3 Treg infiltration/survival occurred in CD200 mice and in CD200-treated control mice or CD200R1KO.CD200 mice receiving cromoglycate. Neutralizing anti-CD200 or anti-CD200R1/R2 monoclonal antibody caused graft rejection, as did anti-interleukin (IL)-9, anti-IL-35, or anti-transforming growth factor-β antibodies, with the latter also decreasing graft-infiltrating Tregs.

CONCLUSION

These data imply a coordinated effect of MCs and Tregs on increased graft survival induced by CD200, with a critical role for IL-9, IL-35, and transforming growth factor-β in the development/function of Tregs.

Fundamental immunology of skin transplantation and key strategies for tolerance induction

Transplantation of allogeneic or xenogeneic skin grafts can evoke strong immune responses that lead to acute rejection of the graft tissues. In this process, donor-derived dendritic cells play crucial roles in the triggering of such immune responses. Both the innate and acquired host immune systems participate in graft rejection. At present, the rejection of skin grafts cannot be well-controlled by ordinary systemic immunosuppression therapy. Although several strategies for the long-term survival of allogeneic or xenogeneic skin grafts have been demonstrated in animal models, the induction of long-term tolerance to skin grafts is still a great challenge in clinical settings. In this article, we review the progress in the understanding of immune responses to skin grafts and discuss the possible methods that can decrease the immunogenicity of graft tissues and improve the survival of skin grafts, especially those included in preoperative pre-treatments.

CD200:CD200R-Mediated Regulation of Immunity

The type 1 membrane glycoprotein CD200, widely expressed on multiple cells/tissues, uses a structurally similar receptor (CD200R1), whose expression is more restricted to cells of the myeloid and lymphoid lineages, to transmit signals affecting responses in multiple physiological systems. Thus CD200 expression is reported to exert effects on cancer growth, autoimmune and allergic disorders, infection, transplantation, bone development and homeostasis, and reproductive biology. It was initially thought, based on the idea that CD200R1 was mostly expressed on cells of myeloid origin, that CD200:CD200R1 interactions were primarily dedicated to controlling myeloid cell function. However additional members of the CD200R family have now also been identified, although their function(s) remain unclear, and CD200R1 itself is now known to be expressed by subsets of T cells and other cells. Together these observations add layers of complexity to our understanding of CD200-related regulation. In common with a number of physiological systems, the mechanism(s) of CD200-induced signaling seem to fit within a similar framework of opposing actions of kinases and phosphatases. This paper highlights the advances in our knowledge of immunoregulation achieved following CD200:CD200R interaction and the potential clinical applicability of that information.