Clinical implications of basic science discoveries: janus resurrected--two faces of B cell and plasma cell biology

Dissecting the immune discrepancies in mouse liver allograft tolerance and heart/kidney allograft rejection

The liver is the most tolerogenic of transplanted organs. However, the mechanisms underlying liver transplant tolerance are not well understood. The comparison between liver transplantation tolerance and heart/kidney transplantation rejection will deepen our understanding of tolerance and rejection in solid organs. Here, we built a mouse model of liver, heart and kidney allograft and performed single-cell RNA sequencing of 66,393 cells to describe the cell composition and immune cell interactions at the early stage of tolerance or rejection. We also performed bulk RNA-seq of mouse liver allografts from Day 7 to Day 60 post-transplantation to map the dynamic transcriptional variation in spontaneous tolerance. The transcriptome of lymphocytes and myeloid cells were characterized and compared in three types of organ allografts. Cell-cell interaction networks reveal the coordinated function of Kupffer cells, macrophages and their associated metabolic processes, including insulin receptor signalling and oxidative phosphorylation in tolerance induction. Cd11b+ dendritic cells (DCs) in liver allografts were found to inhibit cytotoxic T cells by secreting anti-inflammatory cytokines such as Il10. In summary, we profiled single-cell transcriptome analysis of mouse solid organ allografts. We characterized the immune microenvironment of mouse organ allografts in the acute rejection state (heart, kidney) and tolerance state (liver).

Rational Design and Systemic Appraisal of an EGFR-Targeting Antibody-Drug Conjugate LR-DM1 for Pancreatic Cancer

By harnessing the payload DM1 and a monoclonal antibody LR004 through a noncleavable linker succinimidyl-4-(N-maleimidomethyl)-cyclohexane-1-carboxylate, we designed and evaluated an antibody-drug conjugate LR-DM1 with an appropriate drug-antibody ratio of 3.6. LR-DM1, which was targeted toward the epidermal growth factor receptor for pancreatic cancer, exhibited potent antiproliferation activity in vitro with a half-maximal inhibitory concentration value of 7.03 nM for Capan-2 cells. Particularly, it displayed prominent tumor growth inhibition in vivo under 20 mg/kg LR-DM1 dosage in a single administration or multiple administrations without apparent abnormality of pathological observation. Moreover, LR-DM1 possessed a relatively broad therapeutic index with a half-lethal dose above 300 mg/kg, which was over 15-fold higher than the highest administration dosage of 20 mg/kg. This initial study on LR-DM1 holds promise for further development of a new antibody drug conjugate that is transformative for treatment of patients concerned.

Immunological consequences of kidney cell death

Death of renal cells is central to the pathophysiology of acute tubular necrosis, autoimmunity, necrotizing glomerulonephritis, cystic kidney disease, urosepsis, delayed graft function and transplant rejection. By means of regulated necrosis, immunogenic damage-associated molecular patterns (DAMPs) and highly reactive organelles such as lysosomes, peroxisomes and mitochondria are released from the dying cells, thereby causing an overwhelming immunologic response. The rupture of the plasma membrane exhibits the "point of no return" for the immunogenicity of regulated cell death, explaining why apoptosis, a highly organized cell death subroutine with long-lasting plasma membrane integrity, elicits hardly any immune response. Ferroptosis, an iron-dependent necrotic type cell death, results in the release of DAMPs and large amounts of lipid peroxides. In contrast, anti-inflammatory cytokines are actively released from cells that die by necroptosis, limiting the DAMP-induced immune response to a surrounding microenvironment, whereas at the same time, inflammasome-associated caspases drive maturation of intracellularly expressed interleukin-1β (IL-1β). In a distinct setting, additionally interleukin-18 (IL-18) is expressed during pyroptosis, initiated by gasdermin-mediated plasma membrane rupture. As all of these pathways are druggable, we provide an overview of regulated necrosis in kidney diseases with a focus on immunogenicity and potential therapeutic interventions.

IL-35 expression in hepatocellular carcinoma cells is associated with tumor progression

IL-35 has recently been demonstrated to play significant roles in the progression of various malignant tumors. We investigated the expression of IL-35 in hepatocellular carcinoma (HCC) and the regulatory mechanisms in HCC progression. Tissue microarray from 75 HCC patients revealed that IL-35 was primarily localized in the cytoplasm of cancer cells and peri-tumoral hepatocytes. Quantitative analysis showed that IL-35 expression was significantly lower in patients in the advanced stages than in the early stages. Significantly lower expression of IL-35 was also observed in HCC patients with higher histological grades, larger tumor size, positive microvascular invasion and lymph node/distant metastasis. IL-35 over-expression in HepG2 cells significantly upregulated HLA-ABC and CD95, reduced activities of MMP-2 and MMP-9, and decreased cell migration, invasion and colony formation capacities. Our data indicated that decreased expression of IL-35 in tumor tissues might contribute to the progression of HCC, and IL-35 may serve as a new therapeutic target for HCC.

Role of B cells in tolerance induction

PURPOSE OF REVIEW

B cells are known to play a central role in humoral immunity and to boost cellular immunity, however, in a variety of experimental models, B-cell subsets ameliorate inflammation and autoimmune disease, indicating that they can also play a regulatory role. Here, we highlight the advances in regulatory B-cell (Breg) biology of the past year with an emphasis on findings pertinent to transplantation. Several recent observations highlight the relevance to clinical transplantation. Data from at least three independent groups demonstrated that spontaneously tolerant renal transplant recipients exhibit a peripheral blood B-cell signature although the significance of these data remains unclear. Moreover, new data suggest that regulatory B cells may serve as a biomarker for long-term allograft outcomes. Finally, recent evidence suggesting that plasma cells may be an essential component of Bregs raises new concerns about targeting antibody producing cells.

RECENT FINDINGS

We describe new information on Breg mechanisms of action to suppress the alloresponse, signals to expand Bregs in vitro, and more functional evidence of Breg involvement in operationally tolerant kidney patients and in maintaining stable allograft function.

SUMMARY

Although lymphocyte depletion remains central to tolerance induction therapy, the sparing or expansion of regulatory B cells may be an additional strategy to preempt graft rejection.

B cells and progressive multifocal leukoencephalopathy: search for the missing link

Progressive multifocal leukoencephalopathy (PML) is a deadly demyelinating disease due to JC virus (JCV) replication in the brain. PML classically occurs in patients with severe immunodepression, and cases have recently been linked to therapeutic monoclonal antibodies such as natalizumab and also rituximab, which depletes B cells. B cells appear to play a complex role in the pathogenesis of PML. They may act as a viral reservoir and as a vector for viral dissemination in the central nervous system. Anti-JCV antibody responses appear to have a limited effect on JCV replication in the brain. However, accumulating evidence suggests that B cells may considerably influence T cell responses through their cytokine secretion. This immunomodulatory function of B cells may play an important role in the control of JCV infection and in the pathogenesis of PML, including rituximab-induced PML.

Monitoring B cell subsets and alloreactivity in kidney transplantation

B cells are the precursors of antibody producing plasma cells that can give rise to the formation of donor-specific antibodies. However, recent data suggest that besides their role in antibody production, B cells participate in antibody-independent responses, potentially leading to allograft rejection or allograft tolerance. The presence of CD20(+) B cells in kidney graft biopsies has been shown during severe acute rejection episodes and during chronic rejection. Furthermore, operationally tolerant kidney transplant recipients showed a clear B cell dominated fingerprint of tolerance. Several techniques exist to study B cells on different levels. Numerous classification schemes allow for the distinction of many different B cell subsets using flow cytometry. Regardless, data on B cell subsets during stable graft function, rejection or tolerance remain scarce. To obtain a complete picture of the role of B cells during transplantation, antigen specific B cell assays may be required. Therefore, techniques have now been developed that allow for studying the specificity and frequency of HLA specific B cells. Here, we present an overview of the existent assays, panels and techniques intended to characterize peripheral B cells, and the currently available HLA specific B cell functional assays that may allow for monitoring the humoral alloimmune response in transplant recipients.