Chimerism and tolerance: past, present and future strategies to prolong renal allograft survival.

PURPOSE OF REVIEW: Immunological factors are a major cause of kidney allograft loss. Calcineurin inhibitors (CNIs) have improved short-term kidney allograft survival; however, they in turn contribute to long-term kidney allograft loss from chronic CNI nephrotoxicity. Tolerance induction in transplantation can avoid the long-term adverse effects of immunosuppressive medications. This review aims to critically discuss recent efforts in inducing transplantation tolerance. RECENT FINDINGS: Tolerance induction mediated by chimerism has shown some promise in minimizing or even complete withdrawal of immunosuppressive treatments in kidney allograft recipients. There has been a number of approaches as varied as the number of centres conducting these trials. However, they can be grouped into those mediated by transient microchimerism and those facilitated by more stable macro or full donor chimerism. The success rates in terms of long-term drug-free graft survival has been limited in microchimerism-mediated tolerance induction approaches. Mixed macrochimerism of less than 50% donor may be unstable with mostly the recipient's native immune system overpowering the donor chimeric status.Tolerance induction leading to chimerism has been limited to living donor kidney transplantation and additional long-term outcomes are required. Furthermore, immune monitoring after tolerance induction has faced a limitation in studying due to a lack of sufficient study participants and appropriate study controls. SUMMARY: Tolerance induction is one of several strategies used to prolong kidney allograft survival, but it has not been routinely utilized in clinical practice. However, future applications from the trials to clinical practice remain limited to living donor kidney transplantation. Once further data regarding tolerance inductions exist and practicality becomes widely accepted, tolerance induction may shift the paradigm in the field of kidney transplantation to achieve the best possible outcome of 'One Organ for Life'.

Pretransplant Desensitization with Costimulation Blockade and Proteasome Inhibitor Reduces DSA and Delays Antibody-Mediated Rejection in Highly Sensitized Nonhuman Primate Kidney Transplant Recipients.

BACKGROUND: Patients with broad HLA sensitization have poor access to donor organs, high mortality while waiting for kidney transplant, and inferior graft survival. Although desensitization strategies permit transplantation via lowering of donor-specific antibodies, the B cell-response axis from germinal center activation to plasma cell differentiation remains intact. METHODS: To investigate targeting the germinal center response and plasma cells as a desensitization strategy, we sensitized maximally MHC-mismatched rhesus pairs with two sequential skin transplants. We administered a proteasome inhibitor (carfilzomib) and costimulation blockade agent (belatacept) to six animals weekly for 1 month; four controls received no treatment. We analyzed blood, lymph node, bone marrow cells, and serum before desensitization, after desensitization, and after kidney transplantation. RESULTS: The group receiving carfilzomib and belatacept exhibited significantly reduced levels of donor-specific antibodies (P=0.05) and bone marrow plasma cells (P=0.02) compared with controls, with a trend toward reduced lymph node T follicular helper cells (P=0.06). Compared with controls, carfilzomib- and belatacept-treated animals had significantly prolonged graft survival (P=0.02), and renal biopsy at 1 month showed significantly reduced antibody-mediated rejection scores (P=0.02). However, four of five animals with long-term graft survival showed gradual rebound of donor-specific antibodies and antibody-mediated rejection. CONCLUSIONS: Desensitization using proteasome inhibition and costimulation blockade reduces bone marrow plasma cells, disorganizes germinal center responses, reduces donor-specific antibody levels, and prolongs allograft survival in highly sensitized nonhuman primates. Most animals experienced antibody-mediated rejection with humoral-response rebound, suggesting desensitization must be maintained after transplantation using ongoing suppression of the B cell response.

Resveratrol pretreatment enhanced homing of SDF-1α-preconditioned bone marrow-derived mesenchymal stem cells in a rat model of liver cirrhosis.

Stromal cell-derived factor-1α (SDF-1α) has been known to implicate in homing of MSCs, and resveratrol has been reported to have a positive influence on SDF-1 level in the site of injury. In this study, a combined strategy was applied to evaluate bone marrow-derived MSCs (BMSCs) homing to the rat model of liver cirrhosis induced by common bile duct ligation (CBDL): (1) pretreatment delivery of resveratrol into the cirrhotic liver, and (2) transplantation of ex vivo BMSC preconditioning with SDF-1α. BMSCs were preconditioned with 10 ng/µL SDF-1α for 1 h and then labeled with the CM-Dil. Cirrhosis was induced by CBDL. Animals received intraperitoneal injection of resveratrol for 7 days, started on day 28 of CBDL post-operative. On day 36 post-operative, 1 × 106 of SDF-1α-preconditioned BMSCs was injected via caudal vein. Animals were sacrificed at 72 h post-cell transplantation. Immunofluorescence and flow cytometry assessments showed that the BMSC+SDF+RV group had an increased rate of homing into the liver, but it had a decreased rate of homing into the lung and spleen, as compared with the other groups (P < 0.05). The BMSC+SDF+RV group showed high protein expression of SIRT1, but low protein expression of p53 in the liver (P < 0.05 vs other groups). CXCR4 and matrix metalloproteinase (MMP)-9 highly expressed in SDF-1α-preconditioned BMSCs in vitro, and that AKTs and CXCL12 expressed in injured liver undergoing resveratrol injection. Our findings suggest that reseveratrol pretreatment prior to SDF-1α preconditioning could be a promising strategy for designing cell-based therapies for liver cirrhosis.

Sources of Hematopoietic Stem and Progenitor Cells and Methods to Optimize Yields for Clinical Cell Therapy.

Bone marrow (BM) aspirates, mobilized peripheral blood, and umbilical cord blood (UCB) have developed as graft sources for hematopoietic stem and progenitor cells (HSPCs) for stem cell transplantation and other cellular therapeutics. Individualized techniques are necessary to enhance graft HSPC yields and cell quality from each graft source. BM aspirates yield adequate CD34+ cells but can result in relative delays in engraftment. Granulocyte colony-stimulating factor (G-CSF)-primed BM HSPCs may facilitate faster engraftment while minimizing graft-versus-host disease in certain patient subsets. The levels of circulating HSPCs are enhanced using mobilizing agents, such as G-CSF and/or plerixafor, which act via the stromal cell-derived factor 1/C-X-C chemokine receptor type 4 axis. Alternate niche pathway mediators, including very late antigen-4/vascular cell adhesion molecule-1, heparan sulfate proteoglycans, parathyroid hormone, and coagulation cascade intermediates, may offer promising alternatives for graft enhancement. UCB grafts have been expanded ex vivo with cytokines, notch-ligand, or mesenchymal stromal cells, and most studies demonstrated greater quantities of CD34+ cells ex vivo and improved short-term engraftment. No significant changes were observed in long-term repopulating potential or in patient survival. Early phase clinical trials using nicotinamide and StemReginin1 may offer improved short- and long-term repopulating ability. Breakthroughs in genome editing and stem cell reprogramming technologies may hasten the generation of pooled, third-party HSPC grafts. This review elucidates past, present, and potential future approaches to HSPC graft optimization.

Enhancing the efficacy of engraftment of cord blood for hematopoietic cell transplantation.

Clinical cord blood (CB) hematopoietic cell transplantation (HCT) has progressed well since the initial successful CB HCT that saved the life of a young boy with Fanconi anemia. The recipient is alive and well now 28 years out since that first transplant with CB cells from his HLA-matched sister. CB HCT has now been used to treat over 35,000 patients with various malignant and non-malignant disorders mainly using HLA-matched or partially HLA-disparate allogeneic CB cells. There are advantages and disadvantages to using CB for HCT compared to other sources of transplantable hematopoietic stem (HSC) and progenitor (HPC) cells. One disadvantage of the use of CB as a source of transplantable HSC and HPC is the limited number of these cells in a single CB collected, and slower time to neutrophil, platelet and immune cell recovery. This review describes current attempts to: increase the collection of HSC/HPC from CB, enhance the homing of the infused cells, ex-vivo expand numbers of collected HSC/HPC and increase production of the infused CB cells that reach the marrow. The ultimate goal is to manipulate efficiency and efficacy for safe and economical use of single unit CB HCT.

Cord-blood engraftment with ex vivo mesenchymal-cell coculture.

BACKGROUND: Poor engraftment due to low cell doses restricts the usefulness of umbilical-cord-blood transplantation. We hypothesized that engraftment would be improved by transplanting cord blood that was expanded ex vivo with mesenchymal stromal cells. METHODS: We studied engraftment results in 31 adults with hematologic cancers who received transplants of 2 cord-blood units, 1 of which contained cord blood that was expanded ex vivo in cocultures with allogeneic mesenchymal stromal cells. The results in these patients were compared with those in 80 historical controls who received 2 units of unmanipulated cord blood. RESULTS: Coculture with mesenchymal stromal cells led to an expansion of total nucleated cells by a median factor of 12.2 and of CD34+ cells by a median factor of 30.1. With transplantation of 1 unit each of expanded and unmanipulated cord blood, patients received a median of 8.34×10(7) total nucleated cells per kilogram of body weight and 1.81×10(6) CD34+ cells per kilogram--doses higher than in our previous transplantations of 2 units of unmanipulated cord blood. In patients in whom engraftment occurred, the median time to neutrophil engraftment was 15 days in the recipients of expanded cord blood, as compared with 24 days in controls who received unmanipulated cord blood only (P<0.001); the median time to platelet engraftment was 42 days and 49 days, respectively (P=0.03). On day 26, the cumulative incidence of neutrophil engraftment was 88% with expansion versus 53% without expansion (P<0.001); on day 60, the cumulative incidence of platelet engraftment was 71% and 31%, respectively (P<0.001). CONCLUSIONS: Transplantation of cord-blood cells expanded with mesenchymal stromal cells appeared to be safe and effective. Expanded cord blood in combination with unmanipulated cord blood significantly improved engraftment, as compared with unmanipulated cord blood only. (Funded by the National Cancer Institute and others; ClinicalTrials.gov number, NCT00498316.).

A future with less HLA: potential clinical applications of HLA-universal cells.

The high variability of the human leukocyte antigen (HLA) remains a major obstacle to the application of allogeneic products in cell-based therapies. We have developed a strategy to decrease the immunogenicity of cell and tissues to improve their survival after allogeneic transplantation in the absence of immunosuppression. Using RNA interference technology, the expression of HLA class I and II was stably downregulated. HLA-silenced cells demonstrated to prevent a de novo and escape a pre-formed alloimmune response in vitro and in vivo. Also, they demonstrated to be capable of engraft and survive after allogeneic transplantation independently of the donor's and recipient's genetic background. The generation of HLA-universal cells has may open new horizons in the field of regenerative medicine. Some of the potential clinical applications of HLA universal cells will be discussed in this review.

ABO desensitization affects cellular immunity and infection control after renal transplantation.

The impact of ABO desensitization on overall immunity, infectious control, and alloreactivity remains unknown. We compared 35 ABO-incompatible kidney transplant recipients (KTRs) to a control of 62 ABO compatible KTRs. Samples were collected before, at +1, +2, +3, +6, and +12 months post-transplantation. CMV-, BKV-specific, and alloreactive T cells were measured using an interferon-γ ELISPOT assay. The extent of immunosuppression was quantified by enumeration of lymphocyte subpopulations and cytokines. No differences were observed for 5-year allograft survival and function between both groups (P > 0.05). However, ABO-incompatible KTRs were more likely to develop CMV infection, BKV-associated nephropathy, and severe sepsis (P = 0.001). Interestingly, ABO-incompatible KTRs with poor HLA-match showed the highest rates of infections and inferior allograft function (P < 0.05). CD3+, CD4+ T-cell counts, interferon-γ and IL-10 levels were lower in ABO-incompatible KTRs early post-transplantation (P < 0.05). Likewise, ABO-incompatible KTRs showed impaired BKV- and CMV-specific T-cell immunity (P < 0.05). ABO-incompatible KTRs showed lower frequencies of alloreactive T cells (P < 0.05). Our data suggest T-cell depletion due to ABO desensitization, which may contribute to the increased risk of T-cell-dependent infections. Elimination of B cells serving as antigen-presenting cells, thereby causing impaired T-cell activation, plays a significant role in both impaired infection control and reduced alloreactive T-cell activation.

Primary vascularization of allografts governs their immunogenicity and susceptibility to tolerogenesis.

We investigated the influence of allograft primary vascularization on alloimmunity, rejection, and tolerance in mice. First, we showed that fully allogeneic primarily vascularized and conventional skin transplants were rejected at the same pace. Remarkably, however, short-term treatment of mice with anti-CD40L Abs achieved long-term survival of vascularized skin and cardiac transplants but not conventional skin grafts. Nonvascularized skin transplants triggered vigorous direct and indirect proinflammatory type 1 T cell responses (IL-2 and IFN-γ), whereas primarily vascularized skin allografts failed to trigger a significant indirect alloresponse. A similar lack of indirect alloreactivity was also observed after placement of different vascularized organ transplants, including hearts and kidneys, whereas hearts placed under the skin (nonvascularized) triggered potent indirect alloresponses. Altogether, these results suggest that primary vascularization of allografts is associated with a lack of indirect T cell alloreactivity. Finally, we show that long-term survival of vascularized skin allografts induced by anti-CD40L Abs was associated with a combined lack of indirect alloresponse and a shift of the direct alloresponse toward a type 2 cytokine (IL-4, IL-10)-secretion pattern but no activation/expansion of Foxp3(+) regulatory T cells. Therefore, primary vascularization of allografts governs their immunogenicity and tolerogenicity.

Topical application of soluble CD83 induces IDO-mediated immune modulation, increases Foxp3+ T cells, and prolongs allogeneic corneal graft survival.

Modulation of immune responses is one of the main research aims in transplant immunology. In this study, we investigate the local immunomodulatory properties of soluble CD83 (sCD83) at the graft-host interface using the high-risk corneal transplantation model. In this model, which mimics the inflammatory status and the preexisting vascularization of high-risk patients undergoing corneal transplantation, allogeneic donor corneas are transplanted onto sCD83-treated recipient animals. This model allows the direct and precise application of the immune modulator at the transplantation side. Interestingly, sCD83 was able to prolong graft survival after systemic application as well as after topical application, which is therapeutically more relevant. The therapeutic effect was accompanied by an increase in the frequency of regulatory T cells and was mediated by the immune-regulatory enzyme IDO and TGF-ß. In vitro, sCD83 induced long-term IDO expression in both conventional and plasmacytoid dendritic cells via autocrine or paracrine production of TGF-ß, a cytokine previously shown to be an essential mediator of IDO-dependent, long-term tolerance. These findings open new treatment avenues for local immune modulation after organ and tissue transplantation.

Therapeutic plasma exchange rapidly improves cardiac allograft function in patients with presumed antibody-mediated rejection.

BACKGROUND: Allograft dysfunction due to presumed antibody-mediated rejection (pAMR) is one of the most serious complications of heart transplantation. Combination therapies of high-dose steroids, intravenous immune globulin, and/or therapeutic plasma exchange (TPE) are often used in this setting. METHODS: We performed a 9-year retrospective review of all episodes of pAMR treated with TPE at our institution. pAMR diagnosis was based on clinical and pathologic findings. Left ventricular ejection fraction (LVEF) was measured at baseline, prior to initiation of TPE, and during the course of treatment. RESULTS: There were 42 patients with 47 episodes of pAMR treated with TPE. The majority of episodes were treated with three TPE; however, eight required only two TPE and five episodes required >3 TPE. All episodes of pAMR had LVEF measured before and after the series of TPEs. The mean pre-TPE LVEF was 38% compared with a post-therapy mean LVEF of 50% (P < 0.0001). In 16 episodes of pAMR, for which LVEF was measured following each apheresis, there was significant improvement of allograft function after the first TPE (pre-TPE mean LVEF of 31% and post-first TPE mean LVEF of 37%; P = 0.02). Incremental and significant improvement in allograft function continued following each TPE. Changes in human leukocyte antigen-donor specific antibodies and fibrinogen did not correlate with ejection fraction response. CONCLUSIONS: The rapid improvement in allograft function in our patients is most likely due to TPE as other pharmacologic interventions have longer onset. TPE should be considered a first-line intervention in the setting of pAMR.

Adipose stromal/stem cells assist fat transplantation reducing necrosis and increasing graft performance.

Autologous fat transfer (AFT) is a procedure for adipose tissue (AT) repair after trauma, burns, post-tumor resections and lipodystrophies still negatively impacted by the lack of graft persistence. The reasons behind this poor outcome are unclear and seem to involve damages in either harvested/transplanted mature adipocytes or on their mesenchymal progenitors, namely adipose stromal/stem cells (ASC), and due to post-transplant AT apoptosis and involution. A rabbit subcutaneous AT regeneration model was here developed to first evaluate graft quality at different times after implant focusing on related parameters, such as necrosis and vasculogenesis. Standard AFT was compared with a strategy where purified autologous ASC, combined with hyaluronic acid (HA), assisted AFT. Five million of autologous ex vivo isolated CD29+, CD90+, CD49e+ ASC, loaded into HA, enriched 1 ml of AT generating an early significant protective effect in reducing AFT necrosis and increasing vasculogenesis with a preservation of transplanted AT architecture. This beneficial impact of ASC assisted AFT was then confirmed at three months with a robust lipopreservation and no signs of cellular transformation. By a novel ASC assisted AFT approach we ensure a reduction in early cell death favoring an enduring graft performance possibly for a more stable benefit in patients.

New ways to separate graft-versus-host disease and graft-versus-tumour effects after allogeneic haematopoietic stem cell transplantation.

A major challenge to transplant immunologists and physicians remains the separation of harmful graft-versus-host disease (GvHD) and beneficial graft-versus-tumour (GvT) effects after allogeneic haematopoietic stem cell transplantation. Recent advances in our understanding of the allogeneic immune response provide potential new opportunities to achieve this goal. Three potential new approaches that capitalize on this new knowledge are considered in depth; the manipulation of organ-specific cytokines and other pro-inflammatory signals, the selective manipulation of donor effector T cell migration, and the development of cell-mediated immunosuppressive strategies using donor-derived regulatory T cells. These new approaches could provide strategies for local control of allogeneic immune responses, a new paradigm to separate GvHD and GvT effects. Although these strategies are currently in their infancy and have challenges to successful translation to clinical practice, all have exciting potential for the future.

Chemoselection of allogeneic HSC after murine neonatal transplantation without myeloablation or post-transplant immunosuppression.

The feasibility of allogeneic transplantation, without myeloablation or post-transplant immunosuppression, was tested using in vivo chemoselection of allogeneic hematopoietic stem cells (HSCs) after transduction with a novel tricistronic lentiviral vector (MGMT(P140K)-2A-GFP-IRES-TK (MAGIT)). This vector contains P140K-O(6)-methylguanine-methyltransferase (MGMT(P140K)), HSV-thymidine kinase (TK(HSV)), and enhanced green fluorescent protein (eGFP) enabling (i) in vivo chemoselection of HSC by conferring resistance to benzylguanine (BG), an inhibitor of endogenous MGMT, and to chloroethylating agents such as 1,3-bis(2-chloroethyl)nitrosourea (BCNU) and, (ii) depletion of proliferating cells such as malignant clones or transduced donor T cells mediating graft versus host disease (GVHD), by expression of the suicide gene TK(HSV) and Ganciclovir (GCV) administration. Non-myeloablative transplantation of transduced, syngeneic, lineage-depleted (Lin(-)) BM in neonates resulted in 0.67% GFP(+) mononuclear cells in peripheral blood. BG/BCNU chemoselection, 4 and 8 weeks post-transplant, produced 50-fold donor cell enrichment. Transplantation and chemoselection of major histocompatibility complex (MHC)-mismatched MAGIT-transduced Lin(-) BM also produced similar expansion for >40 weeks. The efficacy of this allotransplant approach was validated in Hbb(th3) heterozygous mice by correction of ß-thalassemia intermedia, without toxicity or GVHD. Negative selection, by administration of GCV resulted in donor cell depletion without graft ablation, as re-expansion of donor cells was achieved with BG/BCNU treatment. These studies show promise for developing non-ablative allotransplant approaches using in vivo positive/negative selection.

Therapeutic apheresis in kidney transplantation: a review of renal transplant immunobiology and current interventions with apheresis medicine.

Transplantation is the treatment of choice for end stage renal disease. Kidney transplants convey both a significant survival advantage to the individual recipient as well as cost savings to the medical system. Circulating alloantibodies directed against donor human leukocyte antigens and blood group antigens are fairly common among potential recipients. They are known to injure allografts, shorten allograft survival, and limit access to kidney transplantation. Hence, screening for pretransplant alloantibodies using complement dependent cytotoxic cross-matching and more sensitive techniques such as the solid phase assays, have become routine in an attempt to avoid incompatible donor-recipient pairs and risk stratify those with donor specific antibodies (DSA). By removing harmful antibodies, therapeutic apheresis (TA) has become a critical tool for improving access to transplantation in cases where the immunologic risk had previously been considered unacceptable. It has also allowed us to transplant across the barrier of ABO blood group incompatibility and expand the pool of donors with reasonable success. Furthermore, it is an important tool in the treatment of antibody-mediated rejection. Advanced apheresis technologies, such as immunoadsorption, and the use of TA in combination with innovative paired-donor exchange programs, offer the potential to further improve access and outcomes, minimizing the short comings of one single form of therapy alone.

An in vivo model of double-unit cord blood transplantation that correlates with clinical engraftment.

Double-unit cord blood transplantation (DCBT) appears to enhance engraftment despite sustained hematopoiesis usually being derived from a single unit. To investigate DCBT biology, in vitro and murine models were established using cells from 39 patient grafts. Mononuclear cells (MNCs) and CD34(+) cells from each unit alone and in DCB combination were assessed for colony-forming cell and cobblestone area-forming cell potential, and multilineage engraftment in NOD/SCID/IL2R-γ(null) mice. In DCB assays, the contribution of each unit was measured by quantitative short tandem repeat region analysis. There was no correlation between colony-forming cell (n = 10) or cobblestone area-forming cell (n = 9) numbers and clinical engraftment, and both units contributed to DCB cocultures. In MNC transplantations in NOD/SCID/IL2R-γ(null) mice, each unit engrafted alone, but MNC DCBT demonstrated single-unit dominance that correlated with clinical engraftment in 18 of 21 cases (86%, P < .001). In contrast, unit dominance and clinical correlation were lost with CD34(+) DCBT (n = 11). However, add-back of CD34(-) to CD34(+) cells (n = 20) restored single-unit dominance with the dominant unit correlating not with clinical engraftment but also with the origin of the CD34(-) cells in all experiments. Thus, unit dominance is an in vivo phenomenon probably associated with a graft-versus-graft immune interaction mediated by CD34(-) cells.

CTLA4-Ig prevents alloantibody production and BMT rejection in response to platelet transfusions in mice.

BACKGROUND: Platelet (PLT) transfusions can induce humoral and cellular alloimmunity. HLA antibodies can render patients refractory to subsequent transfusion, and both alloantibodies and cellular alloimmunity can contribute to subsequent bone marrow transplant (BMT) rejection. Currently, there are no approved therapeutic interventions to prevent alloimmunization to PLT transfusions other than leukoreduction. Targeted blockade of T-cell costimulation has shown great promise in inhibiting alloimmunity in the setting of transplantation, but has not been explored in the context of PLT transfusion. STUDY DESIGN AND METHODS: We tested the hypothesis that the costimulatory blockade reagent CTLA4-Ig would prevent alloreactivity against major and minor alloantigens on transfused PLTs. BALB/c (H-2(d)) mice and C57BL/6 (H-2(b)) mice were used as PLT donors and transfusion recipients, respectively. Alloantibodies were measured by indirect immunofluorescence using BALB/c PLTs and splenocytes as targets. BMTs were carried out under reduced-intensity conditioning using BALB.B (H-2(b) ) donors and C57BL/6 (H-2(b)) recipients to model HLA-identical transplants. Experimental groups were given CTLA4-Ig (before or after PLT transfusion) with control groups receiving isotype-matched antibody. RESULTS: CTLA4-Ig abrogated both humoral alloimmunization (H-2(d) antibodies) and transfusion-induced BMT rejection. Whereas a single dose of CTLA4-Ig at time of transfusion prevented alloimmunization to subsequent PLT transfusions, administration of CTLA4-Ig after initial PLT transfusion was ineffective. Delaying treatment until after PLT transfusion failed to prevent BMT rejection. CONCLUSIONS: These findings demonstrate a novel strategy using an FDA-approved drug that has the potential to prevent the clinical sequelae of alloimmunization to PLT transfusions.

Cardiac antibody-mediated rejection.

Many factors limit short- and long-term survival after pediatric heart transplantation. Historically, attention had been directed toward T-cell responses and acute cellular rejection. Presence of pretransplant antibodies against HLA is associated with increased donor wait times and poor post-transplant outcomes. Therapies aimed to mitigate circulating antibodies include plasmapheresis, protein A immunoadsorption columns, intravenous immune globulin, rituximab, and bortezomib. The negative effects of B cells, HLA antibodies, and AMR and potential interventions are the focus of this review article.