Neutrophil derived CSF1 induces macrophage polarization and promotes transplantation tolerance

The colony‐stimulating factor 1 (CSF1) regulates the differentiation and function of tissue macrophages and determines the outcome of the immune response. The molecular mechanisms behind CSF1‐mediated macrophage development remain to be elucidated. Here we demonstrate that neutrophil‐derived CSF1 controls macrophage polarization and proliferation, which is necessary for the induction of tolerance. Inhibiting neutrophil production of CSF1 or preventing macrophage proliferation, using targeted nanoparticles loaded with the cell cycle inhibitor simvastatin, abrogates the induction of tolerance. These results provide new mechanistic insights into the developmental requirements of tolerogenic macrophages and identify CSF1 producing neutrophils as critical regulators of the immunological response.     

Heterogeneity of memory B cells

Potential solid organ transplant recipients broadly sensitized to HLA have long wait times, low transplant rates and poor outcomes. The new kidney allocation system has improved access to the most highly sensitized recipients; however, their long‐term outcomes are unknown. Emerging data suggest that memory B cell repertoire is broader than the plasma cell repertoire, therefore, despite refinements in anti‐HLA antibody detection technology, donor‐specific HLA‐ specific memory B cells may in fact be present in some, if not most, highly sensitized recipients with no detectable donor‐specific antibodies. In addition, new findings have underscored the heterogeneity in memory B cell generation, and in the signals that determine memory versus plasma cell fate during primary antigen encounter, as well as memory B cell differentiation upon antigen reencounter into plasma cells or reentry into germinal centers to subsequently emerge as higher affinity and class‐switched plasma cells. Thus, heterogeneity memory B cells generation may affect the efficacy of specific immunomodulation during the recall response. We propose that the ability to quantify donor‐specific B cell in transplant recipients is urgently required to provide insights into the mechanisms of sensitization and recall, and for the early detection of acute and chronic AMR.     

First live birth after uterus transplantation in the United States

Uterus transplantation has proven to be a successful treatment for women with absolute uterine infertility, caused either by the absence of a uterus or the presence of a nonfunctioning uterus. We report the first birth of a healthy child following uterus transplantation in the United States, from a recipient of a uterus allograft procured from an altruistic living donor. Two major modifications from the previously reported live births characterized this uterus transplant. First, the transplanted uterus relied upon and sustained the pregnancy while having only the utero‐ovarian vein as venous outflow. The implication is a significantly simplified living donor surgery that paves the way for minimally invasive laparoscopic or robot‐assisted techniques for the donor hysterectomy. Second, the time from transplantation to embryo transfer was significantly shortened from prior protocols, allowing for an overall shorter exposure to immunosuppression by the recipient and lowering the risk for potential adverse effects from these medications.     

Single nucleotide variant counts computed from RNA sequencing and cellular traffic into human kidney allografts

Advances in bioinformatics allow identification of single nucleotide polymorphisms (variants) from RNA sequence data. In an allograft biopsy, 2 genomes contribute to the RNA pool, 1 from the donor organ and the other from the infiltrating recipient's cells. We hypothesize that imbalances in genetic variants of RNA sequence data of kidney allograft biopsies provide an objective measure of cellular infiltration of the allograft. We performed mRNA sequencing of 40 kidney allograft biopsies, selected to represent a comprehensive range of diagnostic categories. We analyzed the sequencing reads of these biopsies and of 462 lymphoblastoid cell lines from the 1000 Genomes Project, for RNA variants. The ratio of heterozygous to nonreference genome homozygous variants (Het/Hom ratio) on all autosomes was determined for each sample, and the estimation of stromal and immune cells in malignant tumors using expression data (ESTIMATE) score was computed as a complementary estimate of the degree of cellular infiltration into biopsies. The Het/Hom ratios (P = .02) and the ESTIMATE scores (P < .001) were associated with the biopsy diagnosis. Both measures correlated significantly (r = .67, P < .0001), even though the Het/Hom ratio is based on mRNA sequence variation, while the ESTIMATE score uses mRNA expression. Het/Hom ratio and the ESTIMATE score may offer unbiased and quantitative parameters for characterizing cellular traffic into human kidney allografts.     

Combined Deletion of Vhl and Kif3a Accelerates Renal Cyst Formation

A subset of familial and sporadic clear cell renal cell carcinomas (ccRCCs) is believed to develop from cystic precursor lesions. Loss of function of the von Hippel-Lindau tumor suppressor gene (VHL) predisposes renal epithelial cells to loss of the primary cilium in response to specific signals. Because the primary cilium suppresses renal cyst formation, loss of the cilium may be an initiating event in the formation of ccRCC. To test this hypothesis, we analyzed the consequences of inducible renal epithelium–specific deletion of Vhl together with ablation of the primary cilium via deletion of the kinesin family member 3A (Kif3a) gene. We developed a microcomputed tomography–based imaging approach to allow quantitative longitudinal monitoring of cystic burden, revealing that combined loss of Vhl and Kif3a shortened the latency of cyst initiation, increased the number of cysts per kidney, and increased the total cystic burden. In contrast with findings in other cystic models, cysts in Kif3a mutant mice did not display accumulation of hypoxia-inducible factor 1-α (HIF1α), and deletion of both Hif1a and Kif3a did not affect cyst development or progression. Vhl/Kif3a double mutation also increased the frequency of cysts that displayed multilayered epithelial growth, which correlated with an increased frequency of misoriented cystic epithelial cell divisions. These results argue against the involvement of HIF1α in promoting renal cyst growth and suggest that the formation of simple and atypical renal cysts that resemble ccRCC precursor lesions is greatly accelerated by the combined loss of Vhl and the primary cilium.     

Comparing Humoral and Cellular Immune Response Against HBV Vaccine in Kidney Transplant Patients

Host protection upon vaccination usually results from the complex interplay of humoral and cellular components of the immune system. Exploring hepatitis B surface antigen (HBsAg)‐specific T cell responses and their correlation with humoral responses under immunosuppression, we analyzed 51 renal transplant recipients, differing in HBV vaccine–specific antibody titers (non [NRs]‐, low [LRs]‐, and high responders [HRs]) and in 22 healthy controls (HCs) in a cross‐sectional study. HBsAg‐specific T cells were analyzed by flow cytometry according to expression of activation markers CD40L and/or CD69, and the cytokines IFNγ, IL‐2, TNFα, and IL‐17. No significant differences in responder rate and magnitude of HBsAg‐specific T cell responses were found between HCs and HRs. Interestingly, HBsAg‐specific Th‐cells were also observed in 50% of humoral NRs. Frequencies of HBsAg‐specific CD40L+ Th‐cells were significantly higher in HRs compared to LRs (p = 0.009) and in LRs in comparison to NRs (p = 0.043). All but NRs showed a predominance of multi‐potent HBsAg‐specific TNFα+IL‐2+ Th‐cells. As expected, HBsAg‐specific CD8⁺ T cells were rarely found. In conclusion, mounting of hepatitis B vaccine‐specific T cell responses is possible in kidney transplant recipients despite immunosuppression. Detection of HBV‐specific Th‐cells in a significant proportion of humoral NRs contributes to the current discussion on conferring immune protection by cellular memory in such patients.     

Pathogen Stimulation History Impacts Donor‐Specific CD8+ T Cell Susceptibility to Costimulation/Integrin Blockade–Based Therapy

Recent studies have shown that the quantity of donor‐reactive memory T cells is an important factor in determining the relative heterologous immunity barrier posed during transplantation. Here, we hypothesized that the quality of T cell memory also potently influences the response to costimulation blockade‐based immunosuppression. Using a murine skin graft model of CD8⁺ memory T cell–mediated costimulation blockade resistance, we elicited donor‐reactive memory T cells using three distinct types of pathogen infections. Strikingly, we observed differential efficacy of a costimulation and integrin blockade regimen based on the type of pathogen used to elicit the donor‐reactive memory T cell response. Intriguingly, the most immunosuppression‐sensitive memory T cell populations were composed primarily of central memory cells that possessed greater recall potential, exhibited a less differentiated phenotype, and contained more multi‐cytokine producers. These data, therefore, demonstrate that the memory T cell barrier is dependent on the specific type of pathogen infection via which the donor‐reactive memory T cells are elicited, and suggest that the immune stimulation history of a given transplant patient may profoundly influence the relative barrier posed by heterologous immunity during transplantation.     

Interferon Gamma ELISPOT Testing as a Risk‐Stratifying Biomarker for Kidney Transplant Injury: Results From the CTOT‐01 Multicenter Study

Previous studies suggest that quantifying donor‐reactive memory T cells prior to kidney transplantation by interferon gamma enzyme‐linked immunosorbent spot assay (IFNγELISPOT) can assist in assessing risk of posttransplant allograft injury. Herein, we report an analysis of IFNγELISPOT results from the multicenter, Clinical Trials in Organ Transplantation‐01 observational study of primary kidney transplant recipients treated with heterogeneous immunosuppression. Within the subset of 176 subjects with available IFNγELISPOT results, pretransplant IFNγELISPOT positivity surprisingly did not correlate with either the incidence of acute rejection (AR) or estimated glomerular filtration rate (eGFR) at 6‐ or 12‐month. These unanticipated results prompted us to examine potential effect modifiers, including the use of T cell‐depleting, rabbit anti‐thymocyte globulin (ATG). Within the no‐ATG subset, IFNγELISPOT^neg subjects had higher 6‐ and 12‐month eGFRs than IFNγELISPOT^pos subjects, independent of biopsy‐proven AR, peak PRA, human leukocyte antigen mismatches, African‐American race, donor source, and recipient age or gender. In contrast, IFNγELISPOT status did not correlate with posttransplant eGFR in subjects given ATG. Our data confirm an association between pretransplant IFNγELISPOT positivity and lower posttransplant eGFR, but only in patients who do not receive ATG induction. Controlled studies are needed to test the hypothesis that ATG induction is preferentially beneficial to transplant candidates with high frequencies of donor‐reactive memory T cells.     

De Novo Donor‐Specific HLA Antibodies Are Associated With Rapid Loss of Graft Function Following Islet Transplantation in Type 1 Diabetes

Outcomes after islet transplantation continue to improve but etiology of graft failure remains unclear. De novo donor‐specific human leukocyte antigen (HLA) antibodies (DSA) posttransplant are increasingly recognized as a negative prognostic marker. Specific temporal associations between DSA and graft function remain undefined particularly in programs undertaking multiple sequential transplants. Impact of de novo DSA on graft function over 12 months following first islet transplant was determined prospectively in consecutive recipients taking tacrolimus/mycophenolate immunosuppression at a single center. Mixed‐meal tolerance test was undertaken in parallel with HLA antibody assessment pretransplant and 1–3 months posttransplant. Sixteen participants received a total of 26 islet transplants. Five (19%) grafts were associated with de novo DSA. Five (31%) recipients were affected: three post–first transplant; two post–second transplant. DSA developed within 4 weeks of all sensitizing grafts and were associated with decreased stimulated C‐peptide (median [interquartile range]) at 3 months posttransplant (DSA negative: 613(300–1090); DSA positive 106(34–235) pmol/L [p = 0.004]). De novo DSA directed against most recent islet transplant were absolutely associated with loss of graft function despite maintained immunosuppression at 12 months in the absence of a rescue nonsensitizing transplant. Alemtuzumab induction immunosuppression was associated with reduced incidence of de novo DSA formation (p = 0.03).