Pre-transplant donor-reactive IL-21 producing T cells as a tool to identify an increased risk for acute rejection

Immune landscape of the kidney allograft in response to rejection

Preventing kidney graft dysfunction and rejection is a critical step in addressing the nationwide organ shortage and improving patient outcomes. While kidney transplants (KT) are performed more frequently, the overall number of patients on the waitlist consistently exceeds organ availability. Despite improved short-term outcomes in KT, comparable progress in long-term allograft survival has not been achieved. Major cause of graft loss at 5 years post-KT is chronic allograft dysfunction (CAD) characterized by interstitial fibrosis and tubular atrophy (IFTA). Accordingly, proactive prevention of CAD requires a comprehensive understanding of the immune mechanisms associated with either further dysfunction or impaired repair. Allograft rejection is primed by innate immune cells and carried out by adaptive immune cells. The rejection process is primarily facilitated by antibody-mediated rejection (ABMR) and T cell-mediated rejection (TCMR). It is essential to better elucidate the actions of individual immune cell subclasses (e.g. B memory, Tregs, Macrophage type 1 and 2) throughout the rejection process, rather than limiting our understanding to broad classes of immune cells. Embracing multi-omic approaches may be the solution in acknowledging these intricacies and decoding these enigmatic pathways. A transition alongside advancing technology will better allow organ biology to find its place in this era of precision and personalized medicine.

Alloreactive T cells to Assess Acute Rejection Risk in Kidney Transplant Recipients

Memory T cells are important mediators of transplant rejection but are not routinely measured before or after kidney transplantation. The aims of this study were as follows: (1) validate whether pretransplant donor-reactive memory T cells are reliable predictors of acute rejection (AR) (2) determine whether donor-reactive memory T cells can distinguish AR from other causes of transplant dysfunction.

Methods

Samples from 103 consecutive kidney transplant recipients (2018-2019) were obtained pretransplantation and at time of for-cause biopsy sampling within 6 mo of transplantation. The number of donor-reactive interferon gamma (IFN-γ) and interleukin (IL)-21-producing memory T cells was analyzed by enzyme-linked immunosorbent spot (ELISPOT) assay.

Results

Of the 63 patients who underwent a biopsy, 25 had a biopsy-proven acute rejection (BPAR; 22 aTCMR and 3 aAMR), 19 had a presumed rejection, and 19 had no rejection. Receiver operating characteristic analysis showed that the pretransplant IFN-γ ELISPOT assay distinguished between patients who later developed BPAR and patients who remained rejection-free (area under the curve [AUC] 0.73; sensitivity 96% and specificity 41%). Both the IFN-γ and IL-21 assays were able to discriminate BPAR from other causes of transplant dysfunction (AUC 0.81; sensitivity 87% and specificity 76% and AUC 0.81; sensitivity 93% and specificity 68%, respectively).

Conclusions

This study validates that a high number of donor-reactive memory T cells before transplantation is associated with the development of AR after transplantation. Furthermore, it demonstrates that the IFN-γ and IL-21 ELISPOT assays are able to discriminate between patients with AR and patients without AR at the time of biopsy sampling.

Estimation of Sensitization Status in Renal Transplant Recipients by Assessing Indirect Pathway CD4+ T cell Response to Donor Cell-pulsed Dendritic Cell

BACKGROUND

. Generation of donor-specific human leukocyte antigen antibody (DSA) via indirect allorecognition is detrimental to long-term survival of transplant organs. The detection of such immune responses would make it possible to define patients with high risk of sensitization. In this study, we established a novel method for evaluating indirect allorecognition to assess sensitization in kidney transplant recipients.

METHODS

. Recipient CD14+ monocytes were mixed with donor peripheral blood mononuclear cells; cultured in the presence of IL-4, GM-CSF, IL-1β, and TNFα; and used as pulsed dendritic cells (DCs). Cell proliferation and cytokine production were evaluated by carboxyfluorescein diacetate succinimidyl ester-based T cell proliferation assay and Enzyme-Linked ImmunoSpot assay, respectively.

RESULTS

. CD4+ T cell proliferation was strongly observed in following coculture with allogeneic antigen-pulsed DC leading to interferon-γ and IL-21 production. About 1% of CD4+ T cells exhibited Tfh-like phenotype (PD-1highCXCR5+ICOS+CD40L+). Recipient DC pulsed with donor peripheral blood mononuclear cells was cocultured with recipient CD45RA+CD4+ and CD45RA-CD4+ (generally defined as naive and memory in humans, respectively) T cells. Irrespective of preformed or de novo DSA status, CD45RA+CD4+ T cells constantly produced IL-21. In contrast, IL-21-produced CD45RA-CD4+ T cells were significantly higher in preformed DSA-positive patients than those in negative patients (80.8 ± 51.2 versus 14.8 ± 20.4, P < 0.001). In de novo DSA-positive patients, IL-21-produced CD45RA-CD4+ T cells were significantly increased after transplantation compared with before transplantation (9.23 ± 9.08 versus 43.9 ± 29.1, P < 0.001).

CONCLUSIONS

. Assessment of indirect pathway CD4+ T cell response could provide new insights into the underlying mechanism of de novo DSA production, leading to the development of effective strategies against antibody-mediated rejection.

miR-155 Derived from Bone Marrow Mesenchymal Stem Cell-Secreted Exosomes Reduces Kidney Rejection in Rat Allogeneic Transplantation Model via SDF-1/CXCR4

Aberrantly expressed miR-155 is associated with renal rejection after allogeneic transplantation. This study mainly explored the mechanism of miR-155 derived from bone marrow mesenchymal stem cell-secreted exosomes (BMSC-exo) in renal rejection after allogeneic transplantation. Thirty Fischer rats and 40 Lewis rats were used as donors and recipients, respectively. The Lewis rats were randomized into 4 groups (10 rats per group): Control group, miR-155 group, positive control group and CXCR4 agonist group. The following indicators were monitored in BMSC-exo: miR-155 expression, serum creatinine level, renal histopathological changes, CADI score, number of cells that were positive for TGF-β, Smad3 and α-SMA, as well as the protein levels of Smad3, TGF-β, CXCR4 and SDF-1. miR-155 expression in BMSC-exo was significantly higher than that in HKb-20 cells. On the 7th day after surgery, the serum creatinine levels of rats in the miR-155 group and positive control group reduced significantly, while decreasing slowly in the control group and CXCR4 agonist group. The CADI scores of rats in the miR-155 group and positive control group were significantly higher than those in the control group and CXCR4 agonist group (P < 0.05). No significant difference was found either between the miR-155 group and positive control group, or between the control group and CXCR4 agonist group (P > 0.05). Rats in the control group and CXCR4 agonist group had more cells that were positive for TGF-β, Smad3 and α-SMA, while those in the miR-155 group and positive control group showed less. The Smad3, TGF-β, CXCR4 and SDF-1 proteins were weakly expressed in the miR-155 group and positive control group, but strongly expressed in the control group and CXCR4 agonist group. No significant difference in the protein levels was found either between the miR-155 group and positive control group, or between the control group and CXCR4 agonist group (P > 0.05). miR-155 derived from BMSC-exo is protective against allogeneic kidney transplantation. Specifically, BMSC-exo-derived miR-155 blocked the activity of SDF-1/CXCR4 and TGF-β/Smad3 pathways, thereby downregulating the expression of α-SMA. As a result, it ameliorated renal fibrosis and alleviated renal dysfunction, ultimately leading to the prevention and reduction of renal rejection following allograft transplantation.

High Tacrolimus Intrapatient Variability and Subtherapeutic Immunosuppression are Associated With Adverse Kidney Transplant Outcomes

BACKGROUND

Kidney transplant recipients with high intrapatient variability (IPV) in tacrolimus (Tac) exposure experience more rejection and reduced graft survival. To understand the underlying pathophysiology of this association, the authors investigated whether patients with high tacrolimus IPV have a more activated immune system than patients with low IPV. In addition, exposure to tacrolimus and mycophenolic acid (MPA) was studied in relation to rejection and graft survival.

METHODS

At the time of patient inclusion (5-7 years post-transplantation), the frequency of donor-reactive cells was determined by enzyme-linked immunosorbent assay, and the development of donor-specific anti-Human Leukocyte Antigen antibodies (DSA) was measured by Luminex Single Antigen assay. Tacrolimus IPV was retrospectively calculated between 6 and 12 months and the exposure to tacrolimus and MPA was determined between 1 and 5 years post-transplantation.

RESULTS

A total of 371 kidney transplant recipients were included in this study, of whom 56 developed a rejection episode after 12 months and 60 experienced graft failure after 5-7 years. No correlations were found between tacrolimus IPV or immunosuppression exposure and the number of donor-reactive cells after 5 years of transplantation. DSA were detected more often in patients with low exposure to both tacrolimus and MMF [4/21 (19%) versus 17/350 (4.9%), P = 0.04]. In this cohort, neither tacrolimus IPV nor low overall immunosuppression exposure was associated with a higher incidence of rejection. However, regression analysis showed that a higher tacrolimus IPV was associated with an increased incidence of graft failure (odds ratio = 1.03, P = 0.02).

CONCLUSIONS

This study verifies the relationship between high tacrolimus IPV and impaired kidney allograft survival in long-term follow-up. DSA was also found to be more prevalent in patients with subtherapeutic concentrations of tacrolimus and MPA. An increased prevalence of donor-specific alloreactivity is yet to be demonstrated in patients with high IPV.

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.