Cellular immune profile of kidney transplant patients developing anti-HLA antibodies during childhood

Adaptive immune cell responses as therapeutic targets in antibody-mediated organ rejection

Humoral alloimmunity of organ transplant recipient to donor can lead to antibody-mediated rejection (ABMR), causing thousands of organ transplants to fail each year worldwide. However, the mechanisms of adaptive immune cell responses at the basis of humoral alloimmunity have not been entirely understood. In this review, we discuss how recent investigations have uncovered the key contributions of T follicular helper (T_FH) and B cells and their coordinated actions in driving donor-specific antibody generation and immune progression towards ABMR. We show how recognition of the role of T_FH-B cell interactions may allow the elaboration of improved clinical strategies for immune monitoring and the identification of novel therapeutic targets to tackle ABMR that will ultimately improve organ transplant survival.

Efficacy and Safety of Bone Marrow-Derived Mesenchymal Stem Cells for Chronic Antibody-Mediated Rejection After Kidney Transplantation- A Single-Arm, Two-Dosing-Regimen, Phase I/II Study

Objective

To investigate the efficacy and safety of bone marrow-derived mesenchymal stem cells (BM-MSCs) on chronic active antibody-mediated rejection (cABMR) in the kidney allograft.

Methods

Kidney recipients with biopsy-proven cABMR were treated with allogeneic third-party BM-MSCs in this open-label, single-arm, single-center, two-dosing-regimen phase I/II clinical trial. In Regimen 1 (n=8), BM-MSCs were administered intravenously at a dose of 1.0×10⁶ cells/kg monthly for four consecutive months, while in Regimen 2 (n=15), the BM-MSCs dose was 1.0×10⁶ cells/kg weekly during four consecutive weeks. The primary endpoints were the absolute change of estimated glomerular filtration rate (eGFR) from baseline (delta eGFR) and the incidence of adverse events associated with BM-MSCs administration 24 months after the treatment. Contemporaneous cABMR patients who did not receive BM-MSCs were retrospectively analyzed as the control group (n =30).

Results

Twenty-three recipients with cABMR received BM-MSCs. The median delta eGFR of the total BM-MSCs treated patients was -4.3 ml/min per 1.73m² (interquartile range, IQR -11.2 to 1.2) 2 years after BM-MSCs treatment (P=0.0233). The median delta maximum donor-specific antibody (maxDSA) was -4310 (IQR -9187 to 1129) at 2 years (P=0.0040). The median delta eGFR of the control group was -12.7 ml/min per 1.73 m² (IQR -22.2 to -3.5) 2 years after the diagnosis, which was greater than that of the BM-MSCs treated group (P=0.0342). The incidence of hepatic enzyme elevation, BK polyomaviruses (BKV) infection, cytomegalovirus (CMV) infection was 17.4%, 17.4%, 8.7%, respectively. There was no fever, anaphylaxis, phlebitis or venous thrombosis, cardiovascular complications, or malignancy after BM-MSCs administration. Flow cytometry analysis showed a significant decreasing trend of CD27^-IgD^- double negative B cells subsets and trend towards the increase of CD3⁺CD4⁺PD-1⁺/lymphocyte population after MSCs therapy. Multiplex analysis found TNF-α, CXCL10, CCL4, CCL11 and RANTES decreased after MSCs treatment.

Conclusion

Kidney allograft recipients with cABMR are tolerable to BM-MSCs. Immunosuppressive drugs combined with intravenous BM-MSCs can delay the deterioration of allograft function, probably by decreasing DSA level and reducing DSA-induced injury. The underlying mechanism may involve immunomodulatory effect of MSCs on peripheral B and T cells subsets.

Characterization of follicular T helper cells and donor-specific T helper cells in renal transplant patients with de novo donor-specific HLA-antibodies

T follicular helper (T_FH) cells are a heterogeneous subset of immunocompetent T helper (T_H) cells capable of augmenting B cell responses in lymphoid tissues. In transplantation, exposure to allogeneic tissue activates T_FH cells increasing the risk of the emergence of de novo donor-specific HLA-antibodies (dnDSA). These can cause antibody-mediated rejection (AMR) and allograft loss. Follicular regulatory T (T_FR) cells counteract T_FH cell activity. Here, we investigated the implications of T_FH and T_FR cells on dnDSA formation after renal transplantation (RTX). Considering T_FH cells to be CXCR5⁺ and IL-21⁺, we found by flow cytometry that patients with dnDSA produced IL-21 more abundantly compared to healthy volunteers. In in vitro alloreactivity assays, patients with dnDSA featured an enhanced alloreactive T_H cell pool in response to donor-specific HLA antigens. Besides, longitudinal investigations suggested enhanced alloreactivity shortly after transplantation increasing the risk of dnDSA development. Taken together, in spite of continuous immunosuppression we report a strong IL-21 response in T_FH cells and an expanded reservoir of donor-specific memory T_H cells in patients with dnDSA. This warrants further investigations if aberrant T_FH cell activation may precede the formation of dnDSA promoting AMR.

Waning of vaccine-induced immunity to measles in kidney transplanted children

Vaccine-preventable diseases are a significant cause of morbidity and mortality in solid organ transplant recipients who undergo immunosuppression after transplantation. Data on immune responses and long-term maintenance after vaccinations in such population are still limited.We cross-sectionally evaluated the maintenance of immune response to measles vaccine in kidney transplanted children on immunosuppressive therapy. Measles-specific enzyme-linked immunosorbent assay and B-cell enzyme-linked immunosorbent spot were performed in 74 kidney transplant patients (Tps) and in 23 healthy controls (HCs) previously vaccinated and tested for humoral protection against measles. The quality of measles antibody response was measured by avidity test. B-cell phenotype, investigated via flow cytometry, was further correlated to the ability of Tps to maintain protective humoral responses to measles over time.We observed the loss of vaccine-induced immunity against measles in 19% of Tps. Nonseroprotected children showed signs of impaired B-cell distribution as well as immune senescence and lower antibody avidity. We further reported as time elapsed between vaccination and transplantation, as well as the vaccine administration during dialysis are clinical factors affecting the maintenance of the immune memory response against measles.Tps present both quantitative and qualitative alterations in the maintenance of protective immunity to measles vaccine. Prospective studies are needed to optimize the vaccination schedules in kidney transplant recipients in order to increase the immunization coverage over time in this population.