Xenotransplanted Pig Sertoli Cells Inhibit Both the Alternative and Classical Pathways of Complement-Mediated Cell Lysis While Pig Islets Are Killed

Gene expression profiles of neonatal porcine Sertoli cells at baseline and after incubation in normal human serum as determined by RNA sequencing

Sertoli cells are unique cells that contribute to the formation of the blood-testis barrier, which is important in sustaining the environment to promote spermatogenesis and to protect immunogenic germ cells from autoimmune destruction. This is achieved through tight junctions and production of regulatory immune factors. These Sertoli cell attributes make them a relevant model for various studies involving male reproduction, autoimmune protection, and even transplantation. RNA sequencing analyses were performed on baseline neonatal porcine Sertoli cells (NPSC) and NPSC after incubation in normal human serum for 90 minutes. We previously analyzed this data for immune-related factors, such as complement components, and for differentially expressed genes related to immune function. Still, these data sets provide insight into understanding how Sertoli cells create an immunoregulatory environment, which has applications in reproduction, transplantation, and autoimmunity.

Grafted Sertoli Cells Exert Immunomodulatory Non-Immunosuppressive Effects in Preclinical Models of Infection and Cancer

The Sertoli cells (SeCs) of the seminiferous tubules secrete a multitude of immunoregulatory and trophic factors to provide immune protection and assist in the orderly development of germ cells. Grafts of naked or encapsulated SeCs have been proved to represent an interesting therapeutic option in a plethora of experimental models of diseases. However, whether SeCs have immunosuppressive or immunomodulatory effects, which is imperative for their clinical translatability, has not been demonstrated. We directly assessed the immunopotential of intraperitoneally grafted microencapsulated porcine SeCs (MC-SeCs) in murine models of fungal infection (Aspergillus fumigatus or Candida albicans) or cancer (Lewis lung carcinoma/LLC or B16 melanoma cells). We found that MC-SeCs (i) provide antifungal resistance with minimum inflammatory pathology through the activation of the tolerogenic aryl hydrocarbon receptor/indoleamine 2,3-dioxygenase pathway; (ii) do not affect tumor growth in vivo; and (iii) reduce the LLC cell metastatic cancer spread associated with restricted Vegfr2 expression in primary tumors. Our results point to the fine immunoregulation of SeCs in the relative absence of overt immunosuppression in both infection and cancer conditions, providing additional support for the potential therapeutic use of SeC grafts in human patients.

Complementing Testicular Immune Regulation: The Relationship between Sertoli Cells, Complement, and the Immune Response

Sertoli cells within the testis are instrumental in providing an environment for spermatogenesis and protecting the developing germ cells from detrimental immune responses which could affect fertility. Though these immune responses consist of many immune processes, this review focuses on the understudied complement system. Complement consists of 50+ proteins including regulatory proteins, immune receptors, and a cascade of proteolytic cleavages resulting in target cell destruction. In the testis, Sertoli cells protect the germ cells from autoimmune destruction by creating an immunoregulatory environment. Most studies on Sertoli cells and complement have been conducted in transplantation models, which are effective in studying immune regulation during robust rejection responses. In grafts, Sertoli cells survive activated complement, have decreased deposition of complement fragments, and express many complement inhibitors. Moreover, the grafts have delayed infiltration of immune cells and contain increased infiltration of immunosuppressive regulatory T cells as compared to rejecting grafts. Additionally, anti-sperm antibodies and lymphocyte infiltration have been detected in up to 50% and 30% of infertile testes, respectively. This review seeks to provide an updated overview of the complement system, describe its relationship with immune cells, and explain how Sertoli cells may regulate complement in immunoprotection. Identifying the mechanism Sertoli cells use to protect themselves and germ cells against complement and immune destruction is relevant for male reproduction, autoimmunity, and transplantation.

The Sertoli Cell Complement Signature: A Suspected Mechanism in Xenograft Survival

The complement system is an important component of transplant rejection. Sertoli cells, an immune regulatory testicular cell, survive long-term when transplanted across immunological barriers; thus, understanding the mechanisms behind this unique survival would be of great benefit to the transplantation field. This study focused on Sertoli cell inhibition of complement as relevant in xenotransplantation. Neonatal pig Sertoli cells (NPSCs) survived activated human complement in vitro while neonatal pig islet (NPI) aggregates and pig aortic endothelial cell (PAEC) survival were diminished to about 65% and 12%, respectively. PAECs cultured in NPSC-conditioned media and human complement demonstrated a 200% increase in survival suggesting that NPSCs secrete complement-inhibiting substances that confer protection. Bioinformatic and molecular analyses identified 21 complement inhibitors expressed by NPSCs with several significantly increased in NPSCs compared to NPIs or PAECs. Lastly, RNA sequencing revealed that NPSCs express 25 other complement factors including cascade components and receptors. Overall, this study identified the most comprehensive Sertoli cell complement signature to date and indicates that the expression of a variety of complement inhibitors ensures a proper regulation of complement through redundant inhibition points. Understanding the regulation of the complement system should be further investigated for extending xenograft viability.

Mouse Sertoli Cells Inhibit Humoral-Based Immunity

Transplantation is used to treat many different diseases; however, without the use of immunosuppressants, which can be toxic to the patient, grafted tissue is rejected by the immune system. Humoral immune responses, particularly antibodies and complement, are significant components in rejection. Remarkably, Sertoli cells (SCs), immunoregulatory testicular cells, survive long-term after transplantation without immunosuppression. The objective of this study was to assess SC regulation of these humoral-based immune factors. Mouse SCs survived in vitro human complement (model of robust complement-mediated rejection) and survived in vivo as allografts with little-to-no antibody or complement fragment deposition. Microarray data and ELISA analyses identified at least 14 complement inhibitory proteins expressed by mouse SCs, which inhibit complement at multiple points. Interestingly, a mouse SC line (MSC-1), which was rejected by day 20 post transplantation, also survived in vitro human complement, showed limited deposition of antibodies and complement, and expressed complement inhibitors. Together this suggests that SC inhibition of complement-mediated killing is an important component of SC immune regulation. However, other mechanisms of SC immune modulation are also likely involved in SC graft survival. Identifying the mechanisms that SCs use to achieve extended survival as allografts could be utilized to improve graft survival.

Drug transport across the blood-testis barrier

The blood-testis barrier transfers nutrients to spermatogenic tubules to ensure the normal physiological function of the testes. It also restricts the "entry and exit" of biological macromolecules in the testicular lumen and provides a unique microenvironment for spermatogenesis. This makes the testes a safe place for some viruses and tumors, as immune factors cannot function and drugs fail to reach therapeutic concentrations in the testes. This review aimed to describe the factors regulating the structure and physiological function of the blood-testis barrier. By understanding therapeutic mechanisms of action, drugs can be developed to function in the testicles.

Sertoli Cell Immune Regulation: A Double-Edged Sword

The testis must create and maintain an immune privileged environment to protect maturing germ cells from autoimmune destruction. The establishment of this protective environment is due, at least in part, to Sertoli cells. Sertoli cells line the seminiferous tubules and form the blood-testis barrier (BTB), a barrier between advanced germ cells and the immune system. The BTB compartmentalizes the germ cells and facilitates the appropriate microenvironment necessary for spermatogenesis. Further, Sertoli cells modulate innate and adaptive immune processes through production of immunoregulatory compounds. Sertoli cells, when transplanted ectopically (outside the testis), can also protect transplanted tissue from the recipient’s immune system and reduce immune complications in autoimmune diseases primarily by immune regulation. These properties make Sertoli cells an attractive candidate for inflammatory disease treatments and cell-based therapies. Conversely, the same properties that protect the germ cells also allow the testis to act as a reservoir site for infections. Interestingly, Sertoli cells also have the ability to mount an antimicrobial response, if necessary, as in the case of infections. This review aims to explore how Sertoli cells act as a double-edged sword to both protect germ cells from an autoimmune response and activate innate and adaptive immune responses to fight off infections.

Xenogeneic Sertoli cells modulate immune response in an evolutionary distant mouse model through the production of interleukin-10 and PD-1 ligands expression

BACKGROUND

Immunomodulatory mechanisms of Sertoli cells (SCs) during phylogeny have not been described previously. This study attempted to reveal mechanisms of SC immune modulation in an evolutionary distant host.

METHODS

The interaction of the SC cell line derived from Xenopus tropicalis (XtSC) with murine immune cells was studied in vivo and in vitro. The changes in the cytokine production, the intracellular and surface molecules expression on murine immune cells were evaluated after co-culturing with XtSCs. Migration of XtSCs in mouse recipients after intravenous application and subsequent changes in spleen and the testicular immune environment were determined by flow cytometry.

RESULTS

The in vitro co-culture model was established, allowing the study of XtSCs interaction with murine immune cells. Intracellular staining of interleukin (IL-)10 revealed a significant increase in its expression in macrophages and B cells co-cultured with XtSCs, compared to both unstimulated cells and xenogeneic control. On the contrary, a significant decrease in Th lymphocytes expressing interferon-gamma was observed. The expression of both PD-1 ligands (PD-L1 and PD-L2) was upregulated on the macrophage surfaces after co-culture with XtSCs, but not with the controls. XtSCs migrated specifically to testes when administered intravenously and modulated systemic and local testicular microenvironment; this was detected by the expression of molecules associated with suppressive phenotype by CD45⁺ cells in both spleen and testes.

CONCLUSION

We have demonstrated for the first time that SCs can migrate and modulate immune response in a phylogenetically distant host. It was further observed that SCs induce expression of molecules associated with immunosuppression, such as IL-10 and PD-1 ligands.

Neonatal Pig Sertoli Cells Survive Xenotransplantation by Creating an Immune Modulatory Environment Involving CD4 and CD8 Regulatory T Cells

The acute cell-mediated immune response presents a significant barrier to xenotransplantation. Immune-privileged Sertoli cells (SC) can prolong the survival of co-transplanted cells including xenogeneic islets, hepatocytes, and neurons by protecting them from immune rejection. Additionally, SC survive as allo- and xenografts without the use of any immunosuppressive drugs suggesting elucidating the survival mechanism(s) of SC could be used to improve survival of xenografts. In this study, the survival and immune response generated toward neonatal pig SC (NPSC) or neonatal pig islets (NPI), nonimmune-privileged controls, was compared after xenotransplantation into naïve Lewis rats without immune suppression. The NPSC survived throughout the study, while NPI were rejected within 9 days. Analysis of the grafts revealed that macrophages and T cells were the main immune cells infiltrating the NPSC and NPI grafts. Further characterization of the T cells within the grafts indicated that the NPSC grafts contained significantly more cluster of differentiation 4 (CD4) and cluster of differentiation 8 (CD8) regulatory T cells (Tregs) at early time points than the NPI grafts. Additionally, the presence of increased amounts of interleukin 10 (IL-10) and transforming growth factor (TGF) β and decreased levels of tumor necrosis factor (TNF) α and apoptosis in the NPSC grafts compared to NPI grafts suggests the presence of regulatory immune cells in the NPSC grafts. The NPSC expressed several immunoregulatory factors such as TGFβ, thrombospondin-1 (THBS1), indoleamine-pyrrole 2,3-dioxygenase, and galectin-1, which could promote the recruitment of these regulatory immune cells to the NPSC grafts. In contrast, NPI grafts had fewer Tregs and increased apoptosis and inflammation (increased TNFα, decreased IL-10 and TGFβ) suggestive of cytotoxic immune cells that contribute to their early rejection. Collectively, our data suggest that a regulatory graft environment with regulatory immune cells including CD4 and CD8 Tregs in NPSC grafts could be attributed to the prolonged survival of the NPSC xenografts.

Therapeutic application of Sertoli cells for treatment of various diseases

Sertoli cells (SCs) are immune privileged cells found in the testis that function to immunologically protect maturing germ cells from immune destruction. This immune protection is due to the blood-testis-barrier, which prevents infiltration of cytotoxic immune cells and antibodies, and SC production of immunomodulatory factors, that favor a tolerogenic environment. The ability of SCs to create an immune privileged environment has led to the exploration of their potential use in the treatment of various diseases. SCs have been utilized to create a tolerogenic ectopic microenvironment, to protect co-grafted cells, and to deliver therapeutic proteins through gene therapy. To date, numerous studies have reported the potential use of SCs for the treatment of diabetes, neurodegenerative disorders, and restoration of spermatogenesis. Additionally, SCs have been investigated as a delivery vehicle for therapeutic products to treat other diseases like Laron syndrome, muscular dystrophy, and infections. This review will provide an overview of these therapeutic applications.

The Good, the Bad and the Ugly of Testicular Immune Regulation: A Delicate Balance Between Immune Function and Immune Privilege

The testis is one of several immune privilege sites. These sites are necessary to decrease inflammation and immune responses that could be damaging to the host. For example, inflammation in the brain, eye or placenta could result in loss of cognitive function, vision or rejection of the semi-allogeneic fetus, respectively. In the testis, immune privilege is "good" as it is necessary for protection of the developing auto-immunogenic germ cells. However, there is also a downside or "bad" part of immune privilege, where pathogens and cancers can take advantage of this privilege and persist in the testis as a sanctuary site. Even worse, the "ugly" of privilege is how re-emerging viruses, such as Ebola and Zika viruses, can establish persistence in the testes and be sexually transmitted even months after they have been cleared from the bloodstream. In this review, we will discuss the delicate balance within the testis that provides immune privilege to protect the germ cells while still allowing for immune function to fight off pathogens and tumors.

Sertoli Cells Engineered to Express Insulin to Lower Blood Glucose in Diabetic Mice

Long-term survival of allo- and xenotransplanted immune-privileged Sertoli cells (SCs) is well documented suggesting that SCs can be used to deliver foreign proteins for cell-based gene therapy. The aim of this study was to use a lentivirus carrying proinsulin cDNA to achieve stable expression and lowering of blood glucose levels (BGLs). A SC line transduced with the lentivirus (MSC-LV-mI) maintained stable insulin expression in vitro. These MSC-LV-mI cells were transplanted and grafts were analyzed for cell survival, continued proinsulin mRNA, and insulin protein expression. All grafts contained MSC-LV-mI cells that expressed proinsulin mRNA and insulin protein. Transplantation of MSC-LV-mI cells into diabetic mice significantly lowered BGLs for 4 days after transplantation. Interestingly, in three transplanted SCID mice and one transplanted BALB/c mouse, the BGLs again significantly lowered by day 50 and 70, respectively. This is the first time SC transduced with a lentiviral vector was able to stably express insulin and lower BGLs. In conclusion, a SC line can be modified to stably express therapeutic proteins (e.g., insulin), thus taking us one step further in the use of SCs as an immune-privileged vehicle for cell-based gene therapy.

GM1 Induced the inflammatory response related to the Raf-1/MEK1/2/ERK1/2 pathway in co-culture of pig mesenchymal stem cells with RAW264.7

Pig-human xenotransplantation can trigger cell-mediated immune responses. We explored the role of gangliosides in inflammation related to immune rejection in xenotransplantation. Co-culture of xenogeneic cells (pig-MSCs and RAW264.7) was used to emulate xenotransplantation conditions. MTT assay results indicated that cell viability was significantly decreased in pADMSCs co-cultured with RAW264.7 cells. GM1 and GM3 were highly expressed in pADMSCs co-cultured with RAW264.7 cells. pADMSCs co-cultured with RAW264.7 cells strongly expressed pro-inflammatory proteins such as COX-2, iNOS, p50, p65, pIκBα, and TNF-α. GM1-knockdown pADMSCs co-cultured with RAW 264.7 cells did not show significantly altered cell viability, but pro-inflammatory proteins were markedly inhibited. Co-culture of pADMSCs with RAW264.7 cells induced significant phosphorylation (p) of JNK1/2 and pERK1/2. However, pERK1/2 and pJNK1/2 were decreased and MEK1/2 and Raf1 were suppressed in GM1-knockdown pADMSCs co-cultured with RAW264.7 cells. Thus, the Raf-1/MEK1/2/ERK1/2 and JNK1/2 pathways were significantly upregulated in response to increases of GM1 in co-cultured xenogeneic cells. However, the inflammatory response was suppressed in co-culture of GM1-knockdown pADMSCs with RAW264.7 cells via down-regulation of the Raf-1/MEK1/2/ERK1/2 and JNK1/2 pathways. Therefore, the ganglioside GM1 appears to play a major role in the inflammatory response in xenotransplantation via the Raf-1/MEK1/2/ERK1/2 and JNK1/2 pathways.

Signaling pathways regulating blood-tissue barriers - Lesson from the testis

Signaling pathways that regulate blood-tissue barriers are important for studying the biology of various blood-tissue barriers. This information, if deciphered and better understood, will provide better therapeutic management of diseases particularly in organs that are sealed by the corresponding blood-tissue barriers from systemic circulation, such as the brain and the testis. These barriers block the access of antibiotics and/or chemotherapeutical agents across the corresponding barriers. Studies in the last decade using the blood-testis barrier (BTB) in rats have demonstrated the presence of several signaling pathways that are crucial to modulate BTB function. Herein, we critically evaluate these findings and provide hypothetical models regarding the underlying mechanisms by which these signaling molecules/pathways modulate BTB dynamics. This information should be carefully evaluated to examine their applicability in other tissue barriers which shall benefit future functional studies in the field. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.