AXL inhibition suppresses early allograft monocyte-to-macrophage differentiation and prolongs allograft survival.

Innate immune cells are important in the initiation and potentiation of alloimmunity in transplantation. Immediately upon organ anastomosis and reperfusion, recipient monocytes enter the graft from circulation and differentiate to inflammatory macrophages to promote allograft inflammation. However, factors that drive their differentiation to inflammatory macrophages are not understood. Here, we show that the receptor tyrosine kinase AXL was a key driver of early intragraft differentiation of recipient infiltrating monocytes to inflammatory macrophages in the presence of allogeneic stimulation and cell-to-cell contact. In this context, the differentiated inflammatory macrophages were capable of efficient alloantigen presentation and allostimulation of T cells of the indirect pathway. Consequently, early and transient AXL inhibition with the pharmacological inhibitor bemcentinib resulted in a profound reduction of initial allograft inflammation and a significant prolongation of allograft survival in a murine heart transplant model. Our results support further investigation of AXL inhibition as part of an induction regimen for transplantation.

Novel Approaches to Immunomodulation for Solid Organ Transplantation.

Despite significant advances in the field of transplantation in the past two decades, current clinically available therapeutic options for immunomodulation remain fairly limited. The advent of calcineurin inhibitor-based immunosuppression has led to significant success in improving short-term graft survival; however, improvements in long-term graft survival have stalled. Solid organ transplantation provides a unique opportunity for immunomodulation of both the donor organ prior to implantation and the recipient post transplantation. Furthermore, therapies beyond targeting the adaptive immune system have the potential to ameliorate ischemic injury to the allograft and halt its aging process, augment its repair, and promote recipient immune tolerance. Other recent advances include expanding the donor pool by reducing organ discard, and bioengineering and genetically modifying organs from other species to generate transplantable organs. Therapies discussed here will likely be most impactful if individualized on the basis of specific donor and recipient considerations.

Blocking CCL8-CCR8-Mediated Early Allograft Inflammation Improves Kidney Transplant Function.

BACKGROUND: In kidney transplantation, early allograft inflammation impairs long-term allograft function. However, precise mediators of early kidney allograft inflammation are unclear, making it challenging to design therapeutic interventions. METHODS: We used an allogeneic murine kidney transplant model in which CD45.2 BALB/c kidneys were transplanted to CD45.1 C57BL/6 recipients. RESULTS: Donor kidney resident macrophages within the allograft expanded rapidly in the first 3 days. During this period, they were also induced to express a high level of Ccl8, which, in turn, promoted recipient monocyte graft infiltration, their differentiation to resident macrophages, and subsequent expression of Ccl8. Enhanced graft infiltration of recipient CCR8+ T cells followed, including CD4, CD8, and γδ T cells. Consequently, blocking CCL8-CCR8 or depleting donor kidney resident macrophages significantly inhibits early allograft immune cell infiltration and promotes superior short-term allograft function. CONCLUSIONS: Targeting the CCL8-CCR8 axis is a promising measure to reduce early kidney allograft inflammation.

Apoptotic Donor Cells in Transplantation.

Despite significant advances in prevention and treatment of transplant rejection with immunosuppressive medications, we continue to face challenges of long-term graft survival, detrimental medication side effects to both the recipient and transplanted organ together with risks for opportunistic infections. Transplantation tolerance has so far only been achieved through hematopoietic chimerism, which carries with it a serious and life-threatening risk of graft versus host disease, along with variability in persistence of chimerism and uncertainty of sustained tolerance. More recently, numerous in vitro and in vivo studies have explored the therapeutic potential of silent clearance of apoptotic cells which have been well known to aid in maintaining peripheral tolerance to self. Apoptotic cells from a donor not only have the ability of down regulating the immune response, but also are a way of providing donor antigens to recipient antigen-presenting-cells that can then promote donor-specific peripheral tolerance. Herein, we review both laboratory and clinical evidence that support the utility of apoptotic cell-based therapies in prevention and treatment of graft versus host disease and transplant rejection along with induction of donor-specific tolerance in solid organ transplantation. We have highlighted the potential limitations and challenges of this apoptotic donor cell-based therapy together with ongoing advancements and attempts made to overcome them.

Single cell transcriptomics of mouse kidney transplants reveals a myeloid cell pathway for transplant rejection.

Myeloid cells are increasingly recognized as major players in transplant rejection. Here, we used a murine kidney transplantation model and single cell transcriptomics to dissect the contribution of myeloid cell subsets and their potential signaling pathways to kidney transplant rejection. Using a variety of bioinformatic techniques, including machine learning, we demonstrate that kidney allograft-infiltrating myeloid cells followed a trajectory of differentiation from monocytes to proinflammatory macrophages, and they exhibited distinct interactions with kidney allograft parenchymal cells. While this process correlated with a unique pattern of myeloid cell transcripts, a top gene identified was Axl, a member of the receptor tyrosine kinase family Tyro3/Axl/Mertk (TAM). Using kidney transplant recipients with Axl gene deficiency, we further demonstrate that Axl augmented intragraft differentiation of proinflammatory macrophages, likely via its effect on the transcription factor Cebpb. This, in turn, promoted intragraft recruitment, differentiation, and proliferation of donor-specific T cells, and it enhanced early allograft inflammation evidenced by histology. We conclude that myeloid cell Axl expression identified by single cell transcriptomics of kidney allografts in our study plays a major role in promoting intragraft myeloid cell and T cell differentiation, and it presents a potentially novel therapeutic target for controlling kidney allograft rejection and improving kidney allograft survival.

Proteinuric Kidney Diseases: A Podocyte's Slit Diaphragm and Cytoskeleton Approach.

Proteinuric kidney diseases are a group of disorders with diverse pathological mechanisms associated with significant losses of protein in the urine. The glomerular filtration barrier (GFB), comprised of the three important layers, the fenestrated glomerular endothelium, the glomerular basement membrane (GBM), and the podocyte, dictates that disruption of any one of these structures should lead to proteinuric disease. Podocytes, in particular, have long been considered as the final gatekeeper of the GFB. This specialized visceral epithelial cell contains a complex framework of cytoskeletons forming foot processes and mediate important cell signaling to maintain podocyte health. In this review, we will focus on slit diaphragm proteins such as nephrin, podocin, TRPC6/5, as well as cytoskeletal proteins Rho/small GTPases and synaptopodin and their respective roles in participating in the pathogenesis of proteinuric kidney diseases. Furthermore, we will summarize the potential therapeutic options targeting the podocyte to treat this group of kidney diseases.

Role of androgen receptor in prostatic neoplasia versus hyperplasia.

INTRODUCTION: Androgens play a fundamental role in the growth, differentiation, and maintenance of prostate tissue. The objective of the study was to evaluate and compare the androgen receptor (AR) expression in benign prostatic hyperplasia (BPH), prostatic intraepithelial neoplasia (PIN), and prostatic adenocarcinoma. A relationship between the Gleason score and AR expression was also determined in cases of prostatic adenocarcinoma. MATERIALS AND METHODS: A total of 25 cases were collected which included 10 cases of prostatic adenocarcinoma, 10 cases of BPH, and five cases of PIN. Histopathological evaluation was done to determine the type of lesion including Gleason scoring. Immunohistochemistry (IHC) was performed for AR using monoclonal anti-AR antibody. RESULTS: Specific AR immunostaining was present in all 25 cases in varying intensity. The staining was more intense in cases of adenocarcinoma and PIN as compared BPH. There was no significant statistical difference in the intensity of staining of AR. The Gleason score was inversely related to the intensity of AR staining in adenocarcinoma. There was no significant statistical association between the AR expression and tumor, necrosis, metastasis (TNM) stage. DISCUSSION: AR nuclear expression is present in benign and malignant prostatic epithelium. In this study, cases of prostate cancer demonstrated a higher staining intensity for AR when compared with BPH. The intensity of AR staining in prostate cancer significantly reduces as the Gleason grade of the tumor increases. The staining intensity for AR was heterogeneous specifically in cases of prostate cancer. Our results indicate that AR maybe considered as a prognostic marker in prostate cancer.