Prolonged immunosuppression does not improve risk of sensitization or likelihood of retransplantation after kidney transplant graft failure.

The optimum approach towards immunosuppression withdrawal following kidney transplant failure is unclear. Prolonged weaning may be associated with reduced sensitization, less graft nephrectomy and greater likelihood of retransplantation, but conversely increased risk of infection, malignancy and death. We conducted a single-centre retrospective analysis of patients experiencing graft failure between 2007 and 2017, comparing rates of sensitization, retransplantation, nephrectomy, infection, malignancy and death between patients who had immunosuppression weaned over <90 vs. 90-180 vs. >180 days. Patient survival after immunosuppression withdrawal over <90 vs. 90-180 vs. >180 days was 73.3%, 72.1% and 80.4%, respectively (P = 0.35), with no differences in cPRA (80.06 vs. 81.21 vs. 85.42, P = 0.66) or retransplantation rate [24/31 (77.4%) vs. 21/35 (60.0%) vs. 22/36 (61.1%), P = 0.13]. There was significantly less nephrectomy after late immunosuppression cessation [10/42 (23.8%) vs. 7/42 (16.7%) vs. 3/43 (7.0%), P = 0.01] but no differences in infections or malignancy. On competing risk regression (death as competing risk) controlling for cofactors including age, nephrectomy and rejection, prolonged immunosuppression did not predict likelihood of retransplantation (SHR 1.000, P = 0.88). Prolonged immunosuppression withdrawal does not reduce sensitization or improve retransplantation rates but is associated with less nephrectomy. Immunosuppression withdrawal should be tailored to individual circumstances after graft failure.

Heterogeneity, functional specialization and differentiation of monocyte-derived dendritic cells.

Dendritic cells (DCs) are professional antigen-presenting cells that consist of functionally and phenotypically heterogeneous populations. Monocyte-derived DCs (moDCs) are a DC subset that have been attracting increasing interest owing to their potent influence on adaptive immune function and their rapid accumulation upon an inflammatory stimulus. Although early studies on moDCs mainly addressed infection, their emergence and function in other settings such as autoimmunity and allogeneic organ transplantation are now being increasingly appreciated. In this review, the relationship between murine monocyte subsets and the moDCs that arise from them is discussed. Their role in initiating and modulating innate and adaptive immune responses in various pathophysiological scenarios is also explored, including how they may separate their labour from conventional DCs. How these findings might relate to their human counterparts is also discussed. Overall, monocytes and moDCs exhibit complex and heterogeneous behaviours that are critical in responses against microbial invasion, autoimmunity and allograft rejection.

Monocyte-Derived Dendritic Cells Impair Early Graft Function Following Allogeneic Islet Transplantation.

Islet transplantation can cure type 1 diabetes but is limited by lack of donor organs and early graft dysfunction, such that many patients require multiple transplants to achieve insulin independence. Monocyte-derived dendritic cells (moDCs) arise during inflammation and allograft encounters where they can promote various innate and adaptive immune responses. To determine whether moDCs impair early graft function following allogeneic islet transplantation, we transplanted MHC-mismatched BALB/c (H-2d) islets into diabetic C57BL/6-CCR2.DTR recipients (H-2b) treated with either saline (control) or diphtheria toxin (DT) to deplete moDCs. Graft function was assessed by blood glucose (BG) measurement. DT treatment resulted in specific depletion of graft site moDCs posttransplant. Despite equivalent pretransplant BG levels [27.0 ± 1.3 vs. 29.6 ± 1.1 mM, not significant (ns)], DT recipients achieved lower posttransplant BG levels and better rates of normoglycemia than control recipients (11.0 ± 1.9 vs. 19.1 ± 1.4 mM, p = 0.004) at 1 day posttransplant in diabetic recipients. When a suboptimal donor dose of 200 islets was transplanted, DT-induced moDC depletion resulted in normoglycemia in 78% compared to 25% of control recipients (p = 0.03). As well as amelioration of graft dysfunction in the immediate peritransplant period, prolonged DT administration (15 days posttransplant) resulted in improved graft survival (21 vs. 11 days, p = 0.005). moDCs impair early graft function post-allogeneic islet transplantation. moDC depletion may allow for improved early graft function, permit transplantation with lower islet masses, and enhance graft survival.

Histological and Extended Clinical Outcomes After ABO-Incompatible Renal Transplantation Without Splenectomy or Rituximab.

BACKGROUND: Excellent short-term results have been reported in ABO-incompatible (ABOi) renal transplant recipients managed solely with antibody removal and conventional immunosuppression. However, long-term clinical outcomes with this regimen and predictive information from protocol biopsies are lacking. METHODS: We compared outcome data in ABOi and ABO-compatible (ABOc) recipients receiving this regimen approximately 4 years posttransplant, and histology from biopsies approximately 12 months posttransplant. RESULTS: Patient and graft survivals among 54 ABOi recipients were 98.1% and 90.7%, respectively, at 4 years. Graft function was similar between ABOi (creatinine, 140.3 µmol/L) and ABOc recipients (creatinine, 140.2 µmol/L) (P = 0.99), with no significant change over the study period in either group (Δcreatinine, -0.83 vs 6.6 µmol/L) (P = 0.59). There was no transplant glomerulopathy in biopsies from either group. Interstitial fibrosis (IF) and tubular atrophy (TA) was present in 7 (28%) of 25 ABOi compared with 7 (20.6%) of 34 ABOc (P = 0.52). Progression of IF/TA from implantation was noted in 6 (24%) of 25 ABOi and 6 (17.6%) of 34 ABOc, respectively. C4d staining without antibody-mediated rejection was present in 13 (52%) 25 early posttransplant biopsies from ABOi recipients by immunohistochemistry, but in only 4 (16%) of 25 at 12 months. CONCLUSIONS: ABO-incompatible renal transplant performed with antibody removal and conventional immunosuppression continues to provide excellent patient and graft survival, and stable renal function over 4 years. Coupled with absent transplant glomerulopathy and low rates of progressive IF/TA on earlier biopsies, this suggests that ABOi with conventional immunosuppression and antibody removal, without rituximab or splenectomy, can achieve long-term outcomes comparable to ABO-compatible transplantation.

Innate Allorecognition Results in Rapid Accumulation of Monocyte-Derived Dendritic Cells.

Although the mechanisms governing the innate recognition of pathogen-associated molecular patterns have been well defined, how allogeneic cellular stimuli evoke innate responses remains less so. In this article, we report that upon i.v. transfer (to avoid major iatrogenic interference), allogeneic but not syngeneic leukocytes could induce a rapid (after 1 d) accumulation of host monocyte-derived dendritic cells (moDCs) without any increase in conventional DCs. This occurred in various donor-host strain combinations, did not require MHC mismatch, and could be induced by various donor cell types including B cells, T cells, or NK cells. Using RAG(-/-)γc(-/-) and scid γc(-/-)mice with different MHC, we found that the presence of either donor or host lymphoid cells was required. Alloinduced moDC accumulation was significantly reduced when splenocytes from mice deficient in NK cells by genetic ablation were used as donors. A major component of this moDC accumulation appears to be recruitment. Our findings provide new insights into how the innate and adaptive immune system may interact during allogeneic encounters and thus transplant rejection.

Plasmacytoid dendritic cells are short-lived: reappraising the influence of migration, genetic factors and activation on estimation of lifespan.

Plasmacytoid dendritic cells (pDCs) play an important role in immunity to certain pathogens and immunopathology in some autoimmune diseases. They are thought to have a longer lifespan than conventional DCs (cDCs), largely based on a slower rate of BrdU labeling by splenic pDCs. Here we demonstrated that pDC expansion and therefore BrdU labeling by pDCs occurs in bone marrow (BM). The rate of labeling was similar between BM pDCs and spleen cDCs. Therefore, slower BrdU labeling of spleen pDCs likely reflects the "migration time" (∼2 days) for BrdU labeled pDCs to traffic to the spleen, not necessarily reflecting longer life span. Tracking the decay of differentiated DCs showed that splenic pDCs and cDCs decayed at a similar rate. We suggest that spleen pDCs have a shorter in vivo lifespan than estimated utilizing some of the previous approaches. Nevertheless, pDC lifespan varies between mouse strains. pDCs from lupus-prone NZB mice survived longer than C57BL/6 pDCs. We also demonstrated that activation either positively or negatively impacted on the survival of pDCs via different cell-death mechanisms. Thus, pDCs are also short-lived. However, the pDC lifespan is regulated by genetic and environmental factors that may have pathological consequence.

Monocyte-Derived Dendritic Cells Promote Th Polarization, whereas Conventional Dendritic Cells Promote Th Proliferation.

Monocyte-derived dendritic cells (moDCs) dramatically increase in numbers upon infection and inflammation; accordingly, we found that this also occurs during allogeneic responses. Despite their prominence, how emergent moDCs and resident conventional DCs (cDCs) divide their labor as APCs remain undefined. Hence, we compared both direct and indirect presentation by murine moDCs versus cDCs. We found that, despite having equivalent MHC class II expression and in vitro survival, moDCs were 20-fold less efficient than cDCs at inducing CD4(+) T cell proliferation through both direct and indirect Ag presentation. Despite this, moDCs were more potent at inducing Th1 and Th17 differentiation (e.g., 8-fold higher IFN-γ and 2-fold higher IL-17A in T cell cocultures), whereas cDCs induced 10-fold higher IL-2 production. Intriguingly, moDCs potently reduced the ability of cDCs to stimulate T cell proliferation in vitro and in vivo, partially through NO production. We surmise that such division of labor between moDCs and cDCs has implications for their respective roles in the immune response.