There is an unmet clinical need for immunotherapeutic strategies which specifically target the active immune cells participating in the process of rejection after solid organ transplantation. The monocyte-macrophage cell lineage is increasingly recognized as a major player in acute and chronic allograft immunopathology. The dominant presence of cells of this lineage in rejecting allograft tissue is associated with worse graft function and survival. Monocytes and macrophages contribute to alloimmunity via diverse pathways: antigen processing and presentation, co-stimulation, pro-inflammatory cytokine production and tissue repair. Cross talk with other recipient immune competent cells and donor endothelial cells leads to amplification of inflammation and a cytolytic response in the graft. Surprisingly little is known about therapeutic manipulation of the function of cells of the monocyte-macrophage lineage in transplantation by immunosuppressive agents. Although not primarily designed to target monocyte-macrophage lineage cells, multiple categories of currently prescribed immunosuppressive drugs, such as mycophenolate mofetil, mTOR inhibitors and calcineurin inhibitors, do have limited inhibitory effects. These effects include diminishing the degree of cytokine production, blocking co-stimulation and inhibiting the migration of monocytes to the site of rejection. Outside the field of transplantation, some clinical studies have shown that the monoclonal antibodies canakinumab, tocilizumab and infliximab are effective in inhibiting monocyte functions. Indirect effects have also been shown for simvastatin, a lipid lowering drug, and BET (Bromodomain and Extra-Terminal motif) inhibitors that reduce the cytokine production by monocytes-macrophages in patients with diabetes mellitus and rheumatoid arthritis. To date, detailed knowledge concerning the origin, the developmental requirements and functions of diverse specialized monocyte-macrophage subsets justifies research for therapeutic manipulation. Here, we will discuss the effects of currently prescribed immunosuppressive drugs on monocytes/macrophages features and the future challenges.

PURPOSE: Immunotherapies have shown limited responses in patients with advanced pancreatic cancer. Recently, we reported that dendritic cell (DC)–based immunotherapy induced T-cell responses against pancreatic cancer antigens. The primary objective of this study was to determine the efficacy of DC-based immunotherapy to prevent recurrence of disease. METHODS: This was a single-center, open-label, single-arm, combined phase I/II trial. The primary end point was the 2-year recurrence-free survival (RFS) rate. A 2-year RFS rate of ≥60% was defined as a clinically meaningful improvement. We included patients with pancreatic cancer after resection and completion of standard-of-care (SOC) treatment without recurrent disease on cross-sectional imaging. Patients were treated with autologous DCs pulsed with an allogeneic mesothelioma tumor cell lysate, comprising antigens also expressed in pancreatic ductal adenocarcinoma. RESULTS: Thirty-eight patients were included in the analysis of the primary end point (47% male, 53% female). The median age was 62 years (IQR, 55-68). Twenty-eight patients (74%) received five DC vaccinations and completed the study protocol. Three patients (8%) received four vaccinations, and seven patients (16%) received three vaccinations. After a median follow-up of 25.5 months, 26 patients (68%) had not developed recurrence of disease. The estimated 2-year RFS was 64%. Vaccination led to the enrichment of circulating activated CD4+ T cells and the detection of treatment-induced immune responses in vitro. T-cell receptor-sequencing analyses of a resected solitary lung metastasis showed influx of vaccine-specific T cells. CONCLUSION: This study reached its primary end point of a 2-year RFS rate of ≥60% following pancreatectomy after SOC treatment and adjuvant DC-based immunotherapy in patients with pancreatic cancer. These results warrant a future randomized trial.

We hypothesize that T cells such as interleukin (IL)-21⁺B cell lymphoma 6 (BCL6)⁺ T follicular helper cells can regulate B cell-mediated immunity within the allograft during acute T cell-mediated rejection; this process may feed chronic allograft rejection in the long term. To investigate this mechanism, we determined the presence and activation status of organized T and B cells in so-called ectopic lymphoid structures (ELSs) in different types of acute renal allograft rejection. Biopsies showing the following primary diagnosis were included: acute/active antibody-mediated rejection, C4d⁺ (a/aABMR), acute T cell-mediated rejection grade I (aTCMRI) and acute T cell-mediated rejection grade II (aTCMRII). Paraffin sections were stained for T cells (CD3 and CD4), B cells (CD20), follicular dendritic cells (FDCs, CD23), activated B cells (CD79A), immunoglobulin (Ig)D, cell proliferation (Ki67) and double immunofluorescent stainings for IL-21 and BCL6 were performed. Infiltrates of T cells were detected in all biopsies. In aTCMRI, B cells formed aggregates surrounded by T cells. In these aggregates, FDCs, IgD and Ki67 were detected, suggesting the presence of ELSs. In contrast, a/aABMR and aTCMRII showed diffuse infiltrates of T and B cells but no FDCs and IgD. IL-21 was present in all biopsies. However, co-localization with BCL6 was observed mainly in aTCMRI biopsies. In conclusion, ELSs with an activated phenotype are found predominantly in aTCMRI where T cells co-localize with B cells. These findings suggest a direct pathway of B cell alloactivation at the graft site during T cell mediated rejection.

Background: During acute heart transplant rejection, infiltration of lymphocytes and monocytes is followed by endothelial injury and eventually myocardial fibrosis. To date, no information is available on monocyte-macrophage related cellular shifts and their polarization status during rejection. Here, we aimed to define and correlate monocyte-macrophage endomyocardial tissue profiles obtained at rejection and time-points prior to rejection, with corresponding serial blood samples in 25 heart transplant recipients experiencing acute cellular rejection. Additionally, 33 healthy individuals served as control. Material and Methods: Using histology, immunohistochemistry, confocal laser scan microscopy and digital imaging expression of CD14, CD16, CD56, CD68, CD80 and CD163 was explored to define monocyte and macrophage tissue profiles during rejection. Fibrosis was investigated using Sirius Red stainings of rejection, non-rejection and one-year biopsies. Expression of co-stimulatory and migration-related molecules on circulating monocytes, and production potential for pro- and anti-inflammatory cytokines were studied using flowcytometry. Results: At tissue level, striking CD16+ monocyte infiltration was observed during rejection (p<0.001). Significantly more CD68+CD163+ M2 macrophages were documented during rejection compared to barely present CD68+CD80+ M1 macrophages. Rejection was associated with severe fibrosis in 1-year biopsies (p<0.001). Irrespective of rejection status, decreased frequencies of circulating CD16+ monocytes were found in patients compared to healthy individuals. Rejection was reflected by significantly increased CD54 and HLA-DR expression on CD16+ monocytes with retained cytokine production potential. Conclusions: CD16+ monocytes and M2- macrophages hallmark the correlates of heart transplant acute cellular rejection on tissue level, and seem to be associated with fibrosis on the long-term.