Solid Organ Transplant Rejection Research Articles

Prescription Patterns of Mycophenolate Mofetil in a Group of Patients from Colombia

Background: Mycophenolate mofetil is used for the prevention of solid organ transplant rejection and for other indications, such as systemic lupus erythematosus (SLE). Objective: To determine the prescription patterns of mycophenolate mofetil in a group of Colombian patients. Methods: This was a cross-sectional study of patients receiving mycophenolate mofetil between 2021 and 2022. The data were obtained from a drug dispensing database. Sociodemographic, clinical (diagnostic), and pharmacological variables were identified. Results: A total of 979 patients who underwent treatment were identified; their mean age was 45.9 ± 17.1 years, and 87.4% were women. The main diagnosis associated with the use of mycophenolate mofetil was SLE (39.1%), followed by other rheumatic diseases (8.5%), nephrotic syndrome (7.5%), and solid organ transplantation (6.4%). The relationship between the mean dose and the defined daily dose was 0.75. Ten percent of patients received mycophenolate alone, whereas 32.9% received mycophenolate in combination therapy with conventional disease-modifying antirheumatic drugs and glucocorticoids. A total of 76.2% had polypharmacy (five or more drugs). Conclusions: Mycophenolate mofetil is used mainly in combination therapy for patients with SLE and other rheumatological diseases and for solid organ transplants at doses lower than those recommended.

Human OX40L-CAR-Tregs target activated antigen-presenting cells and control T cell alloreactivity.

Regulatory T cells (Tregs) make major contributions to immune homeostasis. Because Treg dysfunction can lead to both allo- and autoimmunity, there is interest in correcting these disorders through Treg adoptive transfer. Two of the central challenges in clinically deploying Treg cellular therapies are ensuring phenotypic stability and maximizing potency. Here, we describe an approach to address both issues through the creation of OX40 ligand (OX40L)-specific chimeric antigen receptor (CAR)-Tregs under the control of a synthetic forkhead box P3 (FOXP3) promoter. The creation of these CAR-Tregs enabled selective Treg stimulation by engagement of OX40L, a key activation antigen in alloimmunity, including both graft-versus-host disease and solid organ transplant rejection, and autoimmunity, including rheumatoid arthritis, systemic sclerosis, and systemic lupus erythematosus. We demonstrated that OX40L-CAR-Tregs were robustly activated in the presence of OX40L-expressing cells, leading to up-regulation of Treg suppressive proteins without induction of proinflammatory cytokine production. Compared with control Tregs, OX40L-CAR-Tregs more potently suppressed alloreactive T cell proliferation in vitro and were directly inhibitory toward activated monocyte-derived dendritic cells (DCs). We identified trogocytosis as one of the central mechanisms by which these CAR-Tregs effectively decrease extracellular display of OX40L, resulting in decreased DC stimulatory capacity. OX40L-CAR-Tregs demonstrated an enhanced ability to control xenogeneic graft-versus-host disease compared with control Tregs without abolishing the graft-versus-leukemia effect. These results suggest that OX40L-CAR-Tregs may have wide applicability as a potent cellular therapy to control both allo- and autoimmune diseases.

Successful use of therapeutic plasma exchange for the management of acute lung transplant rejection secondary to immune checkpoint inhibitor therapy

The use of immune checkpoint inhibitors (ICIs) in individuals with a history of solid organ transplantation is fraught with the emergence of solid organ transplantation rejection (SOTR). The current recommendations for the management of SOTRs secondary to ICI include the use of high-dose steroids along with the escalation of immunosuppressive therapy. Therapeutic Plasma Exchange (TPE) has been described to be effective in managing various immune-related toxicities, however, the data for using TPE in the setting of acute SOTRs induced by ICIs are limited. Herein, we describe the successful use of TPE in a patient with a history of bilateral lung transplantation who developed an episode of mixed acute cellular and antibody-mediated lung transplant rejection after a single dose of PD-1 inhibitor Pembrolizumab for the treatment of underlying melanoma.

Pharmacogenetic analysis of interleukin-10 variants and tacrolimus metabolism in kidney transplant patients from Pakistani population.

End stage renal disease (ESRD) occurs when the kidneys are unable to filter the waste products and excessive fluids from the blood that results into the accumulation of toxins and fluid in the body. Tacrolimus is commonly used immunosuppressant while sirolimus and cyclosporin are rarely used drugs to stop solid organ transplant rejection. The host's immunological response following transplantation produces interleukin-10 (IL-10), which influences the varied CYP3A-dependent drug disposition of tacrolimus. The aim of this study was to determine the genetic polymorphisms of IL-10 (rs1800871, rs1800872 and rs1800896) gene associated with tacrolimus metabolism in kidney transplant patients from Lahore Punjab, Pakistan. The study collected blood samples of 103 healthy individuals and 137 kidney transplant patients as control and treatment groups, respectively. We employed Tetra ARMS PCR for the genotype analysis of extracted DNA. The alleles were called on 2% agarose gel. Moreover, the study utilized SPSS software to analyze statistical significance of polymorphism. It was found that genotypic frequencies of IL-10 (rs1800871), IL-10 (rs1800872), and IL-10 (rs1800896) were (TT: 66.4%; TC: 31.4%; CC: 2.2%), (AA: 27.7%; AC: 54%; CC: 18.2%), (AA: 64.2%; GA: 17.5%; GG: 18.3%), respectively among kidney transplant patients. All parameters show significant association at different points after transplantation. Genetic analysis showed that TC and CC genotypes in rs1800871 (OR (95%CI) = 5.721 (3.231-10.131), P < 0.001; OR (95%CI) = 3.370 (0.642-17.672), P = 0.150), AC and CC genotypes in rs1800872 (OR (95%CI) = 1.294 (0.695-2.410), P = 0.415; OR (95%CI) = 1.453 (0.671-3.147), P = 0.342), GA and GG genotypes in rs1800896 (OR (95%CI) = 42.952 (17.566-105.021), P = 0.001; OR (95%CI) = 7.040 (2.563-19.333), P = 0.342) was associated with risk of renal rejection in kidney transplant patients. Besides, genetic models showed that TT in rs1800871, AA genotypes in rs1800872 and rs1800892 were associated with risk of renal rejection under dominant model when compared to controls (OR (95%CI) = 5.721 (3.231-10.131), P < 0.001; OR (95%CI) = 1.335 (0.735-9.290), P < 0.341; OR (95%CI) = 24.629 (10.599-57.230), P < 0.001), respectively. From the results, it is concluded that genetic polymorphism of IL-10 (rs1800871, rs1800872 and rs1800896) has a highly significant association with risk of renal rejection in Pakistani kidney transplant patients.

The evolution of cyclosporine treatments for treatment of ocular surface diseases.

Cyclosporine is a versatile immunomodulatory drug commonly employed in modern medicine. Although cyclosporine was initially used to prevent solid organ transplant rejection, its indications have extended to treat many inflammatory or autoimmune diseases. Cyclosporin is available for use in oral, intravenous, and topical forms, including eye drops to treat corneal and ocular surface conditions. It is naturally advantageous to administer cyclosporin directly into the eye, avoiding potential and dose limiting systemic adverse effects. However, the transition from systemic to topical administration has been a challenging one. This report reviews the evolution of ophthalmic cyclosporine treatment and explores its clinical impacts and future research directions. Latest advancements in formulations - from oil-based solutions to nanomicelle and gel systems and waterless formulations - have improved the therapeutic efficacy and tolerability of topically applied cyclosporine, demonstrating greater effectiveness in treating ocular surface parameters compared to oil-based solution. Cyclosporine continues to be a safe and effective immunomodulatory drug in the field of ophthalmology to treat various chronic inflammatory ocular surface diseases and dry eye. Currently, there are several commercially available topical preparations available for ophthalmic use each with unique formulation and clinical outcomes.

Management of paediatric monomorphic post-transplant lymphoproliferative disorders with low-intensity treatment: A multicentre international experience.

Monomorphic post-transplant lymphoproliferative disorder (mPTLD) is a major cause of morbidity/mortality following solid organ transplant (SOT), with infection, mPTLD progression and organ rejection presenting equal risks. Balancing these risks is challenging, and the intensity of therapy required by individual patients is not defined. Although an increasing body of evidence supports the use of a stepwise escalation of therapy through reduction in immunosuppression (RIS) to rituximab monotherapy and low-dose chemo-immunotherapy, many centres still use B-cell non-Hodgkin lymphoma (B-NHL) protocols, especially when managing Burkitt/Burkitt-like (BL) PTLD. This study sought to define outcomes for children managed in the UK or Spanish centres using low-intensity first-line treatments. Retrospective data were anonymously collected on patients younger than 18years of age, with post-SOT mPTLD diagnosed between 2000 and 2020. Only patients given low-intensity treatment at initial diagnosis were included. Fifty-six patients were identified. Age range was 0.9-18years (median 10.7). Most (62.5%) had early-onset PTLD. Haematopathological analysis showed 75% were diffuse large B-cell like, 14.3% were BL and nine of 33 (27%) harboured a MYC-rearrangement. Stage III-IV disease was present in 78.6%. All but one had RIS, 26 received rituximab monotherapy and 24 low-dose chemo-immunotherapy, mostly R-COP. Intensified B-NHL chemotherapy was required in 10/56 (17.9%). There were a total of 13 deaths in this cohort, three related to PTLD progression. The 1-year overall survival (OS), event-free survival (EFS) and progression-free survival (PFS) were 92.8%, 78.6% and 80.2%, respectively. R-COP provides an effective low-dose chemotherapy option. Escalation to more intensive therapies in the minority of inadequately controlled patients is an effective strategy.

Impact of Blood Products Transfusion on Patients in the Immediate Post-Lung Transplant Period: A Cohort Study.

BACKGROUND Anemia is common in post-transplant patients. Blood product transfusion is associated with mortality and rejection in solid organ transplants. In lung transplant recipients, transfusion predisposes to primary graft dysfunction (PGD). The adverse effects and associated mortality of perioperative transfusions in lung transplant recipients have not been evaluated. This study examined the effects of perioperative blood transfusions in lung transplant recipients. MATERIAL AND METHODS We conducted a retrospective study of the effects of blood product transfusions in patients who received single- or double-lung transplantation at Houston Methodist Hospital between August 2017 and September 2019. Univariable and multiple logistic regression modeling were used to determine the characteristics associated with single events as well as a composite outcome within 30 days (including mortality, acute myocardial infarction, acute stroke, lower respiratory tract infection, urinary tract infection, surgical site infections, or PGD). RESULTS A total of 232 patients received lung transplants between December 2015 and September 2019 at our center. Univariable analysis revealed an increased risk of PGD (P<0.001), more mechanical ventilation days (P<0.001), more ICU days post-transplant (P<0.001), and greater need for ECMO support (P=0.001) in patients who received blood product transfusions. In univariate analysis, the composite outcome was also more common (P=0.01) in patients who received any transfusion perioperatively. A total of 7 patients died within 30 days from transplant, and they were all in the transfused group. CONCLUSIONS Among lung transplant recipients, PGD, ICU days, need for mechanical ventilation and ECMO support, and total composite events were significantly greater in patients who received blood transfusion perioperatively.

Antiviral activity of immunosuppressors alone and in combination against human adenovirus and cytomegalovirus

Human adenovirus (HAdV) and cytomegalovirus (HCMV) cause high morbidity and mortality in patients undergoing solid organ transplantation (SOT) and haematopoietic stem cell transplantation (HSCT). Immunosuppressors are used universally to prevent graft-vs-host disease in HSCT and graft rejection in SOT. The long-term use of these drugs is associated with a high risk of infection, but there is also evidence of their specific interference with viral infection. This study evaluated the antiviral activity of immunosuppressors commonly used in clinical practice in SOT and HSCT recipients in vitro to determine whether their use could be associated with reduced risk of HAdV and HCMV infection. Cyclophosphamide, tacrolimus, cyclosporine, mycophenolic acid, methotrexate, everolimus and sirolimus presented antiviral activity, with 50% inhibitory concentration (IC50) values at low micromolar and sub-micromolar concentrations. Mycophenolic acid and methotrexate showed the greatest antiviral effects against HAdV (IC50=0.05 µM and 0.3 µM, respectively) and HCMV (IC50=10.8 µM and 0.02 µM, respectively). The combination of tacrolimus and mycophenolic acid showed strong synergistic antiviral activity against both viruses, with combinatory indexes (CI50) of 0.02 and 0.25, respectively. Additionally, mycophenolic acid plus cyclosporine, and mycophenolic acid plus everolimus/sirolimus showed synergistic antiviral activity against HAdV (CI50=0.05 and 0.09, respectively), while methotrexate plus cyclosporine showed synergistic antiviral activity against HCMV (CI50=0.29). These results, showing antiviral activity in vitro against both HAdV and HCMV, at concentrations below the human Cmax values, may be relevant for the selection of specific immunosuppressant therapies in patients at risk of HAdV and HCMV infections.

Low-dose Interleukin-2 Therapy: Fine-tuning Treg in Solid Organ Transplantation?

Regulatory T cells (Treg), a subset of CD4 + T cells, are potent regulators of immune reactions, which have been shown to be a promising therapeutic alternative to toxic immunosuppressive drugs. Data support the utility of Treg in managing immunopathologies, including solid organ transplant rejection, graft-versus-host disease, and autoimmune disorders. Notably, reports suggest that interleukin-2 (IL-2) is critical to survival of Treg, which constitutively express high levels of CD25, that is, the IL-2 receptor α-chain, and are exquisitely sensitive to IL-2, even at very low concentrations in contrast to effector T cells, which only upregulate IL-2 receptor α-chain on activation. This has led to the notion of using low doses of exogenous IL-2 therapeutically to modulate the immune system, specifically Treg numbers and function. Here, we summarize developments of clinical experience with low-dose IL-2 (LD-IL-2) as a therapeutic agent. So far, no clinical data are available to support the therapeutic use of LD-IL-2 therapy in the solid organ transplant setting. For the latter, fine-tuning by biotechnological approaches may be needed because of the narrow therapeutic window and off-target effects of LD-IL-2 therapy and so to realize the therapeutic potential of this molecule.

A New Hypothesis Describing the Pathogenesis of Oral Mucosal Injury Associated with the Mammalian Target of Rapamycin (mTOR) Inhibitors.

It has been 24 years since rapamycin (sirolimus) was approved to mitigate solid organ transplant rejection and 16 years since mTOR (mammalian/mechanistic target of rapamycin) inhibitors reached patients as a cancer therapy. While the clinical benefits of mTOR inhibitors (mTORi) are robust, so too are their toxicities. Among the most common issues is the development of ulcers of the oral mucosa (mTOR-inhibitor associated stomatitis; mIAS). These lesions are distinct from those of other anti-cancer agents, occur with regularity, and impact patient outcomes. mIAS' pathogenesis has been the subject of speculation, and its similar presentation to recurrent aphthous stomatitis (RAS) has led to the hypothesis that it might serve as a surrogate to better understand RAS. Based on a review of the literature, the current manuscript provides a hypothesis regarding the mechanisms by which mTORis uniquely initiate mucosal injury and an explanation for the observation that steroids (also an immunosuppressive) are effective in its treatment through a non-immunologic mechanism. Unexplained unique features of mIAS are discussed in this review in the context of future investigation.

Development and Validation of a Liquid Chromatography Mass Spectrometry Method to Measure Highly Concentrated Tacrolimus and Cyclosporine Specimens Prepared from Commercial Pharmaceutical Products to Assess Administration Through Feeding Tubes

Abstract Background Tacrolimus and cyclosporine are common immunosuppressive drugs used in the prevention and treatment of solid-organ transplant rejection (e.g., kidney, liver, heart). Other indications include several autoimmune diseases such as Crohn’s disease, autoimmune hepatitis, and rheumatoid arthritis. To prevent toxicity while achieving therapeutic efficacy, tacrolimus and cyclosporine in whole blood specimens are commonly measured in medical centers so that their dosages can be precisely adjusted. Different from adult patients, pediatric patients often require smaller doses and the use of feeding tubes for drug administration. In order to assess nonspecific adsorption by feeding tubes, we modified our in-house clinical method to measure highly concentrated tacrolimus and cyclosporine specimens prepared from clinical pharmaceutical products. Method: Highly concentrated tacrolimus and cyclosporine specimens were serially diluted with dimethyl sulfoxide (2,000 times for tacrolimus and 20,000 times for cyclosporine) before measurements by our clinical method using liquid chromatography mass spectrometry. The method for highly concentrated tacrolimus and cyclosporine was validated, with analytical measurement range determined with in-house prepared concentrated specimens at varying concentrations, precision (repeatability and reproducibility) assessed by multiple measurements of concentrated specimens at three different concentrations, accuracy assessed by recovery studies, and matrix effect assessed by post-column infusion and by matrix dilution with dimethyl sulfoxide. Results The method was linear from 10 ug/mL to 80 ug/mL for tacrolimus, and 1 mg/mL to 8 mg/mL for cyclosporine with r2 &amp;gt; 0.99. Repeatability and reproducibility were &amp;lt;10% CV. Minimal matrix effect was observed. Recovery studies using commercial calibrators to measure specimens prepared from reference materials and dimethyl sulfoxide identified no significant bias for tacrolimus but an average positive bias of 20% for cyclosporine, and a correction factor was used to finalize cyclosporine results for specimens prepared from clinical pharmaceutical products. The positive bias was eliminated when calibrators were prepared in dimethyl sulfoxide. Conclusion s: We have developed and validated a LC-MS/MS method for the measurement of highly concentrated tacrolimus and cyclosporine in specimens prepared from clinical pharmaceutical products. We hypothesize that one or more components in the commercial calibrators have contributed to the positive bias of cyclosporine in those specimens. Our method can be used to support studies that assess nonspecific adsorption by feeding tubes.

Blockade of Common Gamma Chain Cytokine Signaling with REGN7257, an Interleukin 2 Receptor Gamma (IL2RG) Monoclonal Antibody, in Combination with Costimulatory Blockers Delayed Skin Graft Rejection in Mice

There is a current medical need to identify innovative maintenance therapies to prevent allograft rejection in solid organ transplantation. During transplant rejection, recipient immune cells identify a grafted organ as foreign and attack it: CD4 + T cells orchestrate transplant rejection by recruiting a range of effector cells responsible for the damage of rejection including CD8 + T cells, NK cells, B cells and macrophages. These pathogenic immune cell responses can be driven by cytokines of the common gamma chain (γ c) cytokine family (IL2, IL4, IL7, IL9, IL15, and IL21). γ c cytokines signal through their corresponding receptors, expressed primarily on immune cells, that share a common coreceptor, interleukin 2 receptor subunit gamma (IL2RG) that is required for signaling. To understand the role of γ c cytokines in driving transplant rejection, we generated REGN7257, a fully human IL2RG monoclonal antibody that inhibits γ c cytokine-induced signaling, and we tested its ability to suppress allogeneic immune cell responses in a mouse model of skin graft rejection when delivered as a monotherapy and in combination with mycophenolate mofetil (MMF) or T cell costimulatory pathway blockers. In this model, recipient B6/129 (mixed background) Il2rg hu/hu mice were transplanted with tail skin from BALB/cJ donor mice. Graft survival was analyzed using a log rank Mantel-Cox test to detect statistically significant differences across groups (*=p&amp;lt;0.033; **= p&amp;lt;0.002; ***=p&amp;lt;0.0002; ****=p&amp;lt;0.0001). In a mouse model of skin graft rejection, γ c cytokine signaling blockade with REGN7257 given as maintenance immunosuppression effectively improved overall graft survival (Median Survival Time [MST] IL2RG=13) compared to mice that received a control antibody (MST CTRL=9 [****vs IL2RG Ab]), and with similar efficacy to that observed with the calcineurin inhibitor tacrolimus (MST TAC=12.5 [**vs control, n.s. vs IL2RG Ab]). In treatment combination experiments, while monotherapy treatment with the antiproliferative agent MMF was not as efficient as REGN7257 at delaying skin graft rejection (MST MMF=10 [*vs control] and MST IL2RG=12 [*vs MMF]), simultaneous blockade of cell proliferation and γ c cytokine signaling conferred an advantage over monotherapies (MST MMF+IL2RG=15.5 [****vs control, **vs IL2RG Ab]). Similarly, induction therapy consisting of γ c cytokine signaling blockade followed by maintenance immunosuppression using the CTLA4-Ig fusion protein abatacept, significantly improved overall skin graft survival (MST IL2RG+CTLA4=19.5 [****vs control]) compared to REGN7257 induction only (MST IL2RG=11 [****vs control and combo]) or abatacept maintenance only (MST CTLA4=10 [*vs control, ****vs combo]). Finally, maintenance immunosuppression combining blocking of γc cytokine signaling together with blocking of both CD28 and CD40L costimulatory signals prolonged skin graft survival better than any combination therapies of only 2 pathway blockers (MST TRIPLE=26 [**vs control] and MST DOUBLE=16-21 [n.s.-** vs triple]). Overall, our study showed that γ c cytokine blockade could potentially be an alternative to calcineurin inhibitor-based regimens to prevent rejection by specifically targeting immune cells. Our data also highlighted the inherent complexity of effector mechanisms and pathways involved in allograft rejection and showed that prolonged allograft survival requires simultaneous blockade of multiple T cell activating signals, including inhibition of cytokine signaling and costimulatory signals. These data provide evidence of γ c cytokines as key drivers of allogeneic immune cell responses during acute transplant rejection, offering a potentially novel strategy for the management of transplant patients.

B-309 Development and Validation of a LC-MS/MS Method for Highly Concentrated Tacrolimus and Cyclosporine Specimens Prepared from Clinical Pharmaceutical Products to Assess Adsorption By Feeding Tubes

Abstract Background Tacrolimus and cyclosporine are common immunosuppressive drugs used in the prevention and treatment of solid-organ transplant rejection (e.g., kidney, liver, heart). Other indications include several autoimmune diseases such as Crohn’s disease, autoimmune hepatitis, and rheumatoid arthritis. To prevent toxicity while achieving therapeutic efficacy, tacrolimus and cyclosporine in whole blood specimens are commonly measured in medical centers so that their dosages can be precisely adjusted. Different from adult patients, pediatric patients often require smaller doses and the use of feeding tubes for drug administration. In order to assess nonspecific adsorption by feeding tubes, we modified our in-house clinical method to measure highly concentrated tacrolimus and cyclosporine specimens prepared from clinical pharmaceutical products. Methods Highly concentrated tacrolimus and cyclosporine specimens were serially diluted with dimethyl sulfoxide (2000 times for tacrolimus and 20 000 times for cyclosporine) before measurements by our clinical method using liquid chromatography mass spectrometry. The method for highly concentrated tacrolimus and cyclosporine was validated, with analytical measurement range determined with in-house prepared concentrated specimens at varying concentrations, precision (repeatability and reproducibility) assessed by multiple measurements of concentrated specimens at three different concentrations, accuracy assessed by recovery studies, and matrix effect assessed by post-column infusion and by matrix dilution with dimethyl sulfoxide. Results The method was linear from 10 ug/mL to 80 ug/mL for tacrolimus, and 1 mg/mL to 8 mg/mL for cyclosporine with r2 &amp;gt; 0.99. Repeatability and reproducibility were &amp;lt;10% CV. Minimal matrix effect was observed. Recovery studies using commercial calibrators to measure specimens prepared from reference materials and dimethyl sulfoxide identified no significant bias for tacrolimus but an average positive bias of 20% for cyclosporine, and a correction factor was used to finalize cyclosporine results for specimens prepared from clinical pharmaceutical products. The positive bias was eliminated when calibrators were prepared in dimethyl sulfoxide. Conclusion We have developed and validated a LC-MS/MS method for the measurement of highly concentrated tacrolimus and cyclosporine in specimens prepared from clinical pharmaceutical products. We hypothesize that one or more components in the commercial calibrators have contributed to the positive bias of cyclosporine in those specimens. Our method can be used to support studies that assess nonspecific adsorption by feeding tubes.

Cardiac Allograft Rejection: Strategies for Success in the Face of Immune Challenges.

Heart transplantation for patients with end-stage heart failure refractory to medical therapy has remained definitive treatment with significant advances in posttransplant care. Despite improvement in postoperative morbidity and mortality, acute cellular rejection (ACR) and antibody-mediated rejection (AMR) remain substantial challenges that can lead to allograft failure and patient mortality. Immunosuppressive agents have been the mainstay of both prevention and treatment for ACR and AMR; however, many challenges exist with traditional therapies. There are a multitude of molecular pathways involved in mediating the humoral and cellular response to rejection, offering various targets for treatment. This review summarizes therapies used in the management of ACR and AMR as extrapolated from use in induction therapy and treatment of other solid-organ transplant rejection. Future studies focused on cardiac transplant recipients are needed to expand therapeutic options.

Co-expression of HLA-E and HLA-G on genetically modified porcine endothelial cells attenuates human NK cell-mediated degranulation.

Natural killer (NK) cells play an important role in immune rejection in solid organ transplantation. To mitigate human NK cell activation in xenotransplantation, introducing inhibitory ligands on xenografts via genetic engineering of pigs may protect the graft from human NK cell-mediated cytotoxicity and ultimately improve xenograft survival. In this study, non-classical HLA class I molecules HLA-E and HLA-G were introduced in an immortalized porcine liver endothelial cell line with disruption of five genes (GGTA1, CMAH, β4galNT2, SLA-I α chain, and β-2 microglobulin) encoding three major carbohydrate xenoantigens (αGal, Neu5Gc, and Sda) and swine leukocyte antigen class I (SLA-I) molecules. Expression of HLA-E and/or HLA-G on pig cells were confirmed by flow cytometry. Endogenous HLA-G molecules as well as exogenous HLA-G VL9 peptide could dramatically enhance HLA-E expression on transfected pig cells. We found that co-expression of HLA-E and HLA-G on porcine cells led to a significant reduction in human NK cell activation compared to the cells expressing HLA-E or HLA-G alone and the parental cell line. NK cell activation was assessed by analysis of CD107a expression in CD3-CD56+ population gated from human peripheral blood mononuclear cells. CD107a is a sensitive marker of NK cell activation and correlates with NK cell degranulation and cytotoxicity. HLA-E and/or HLA-G on pig cells did not show reactivity to human sera IgG and IgM antibodies. This in vitro study demonstrated that co-expression of HLA-E and HLA-G on genetically modified porcine endothelial cells provided a superior inhibition in human xenoreactive NK cells, which may guide further genetic engineering of pigs to prevent human NK cell mediated rejection.

LIS1, a glyco-humanized swine polyclonal anti-lymphocyte globulin, as a novel induction treatment in solid organ transplantation.

Anti-thymocyte or anti-lymphocyte globulins (ATGs/ALGs) are immunosuppressive drugs used in induction therapies to prevent acute rejection in solid organ transplantation. Because animal-derived, ATGs/ALGs contain highly immunogenic carbohydrate xenoantigens eliciting antibodies that are associated with subclinical inflammatory events, possibly impacting long-term graft survival. Their strong and long-lasting lymphodepleting activity also increases the risk for infections. We investigated here the in vitro and in vivo activity of LIS1, a glyco-humanized ALG (GH-ALG) produced in pigs knocked out for the two major xeno-antigens αGal and Neu5Gc. It differs from other ATGs/ALGs by its mechanism of action excluding antibody-dependent cell-mediated cytotoxicity and being restricted to complement-mediated cytotoxicity, phagocyte-mediated cytotoxicity, apoptosis and antigen masking, resulting in profound inhibition of T-cell alloreactivity in mixed leucocyte reactions. Preclinical evaluation in non-human primates showed that GH-ALG dramatically reduced CD4+ (p=0.0005,***), CD8+ effector T cells (p=0.0002,***) or myeloid cells (p=0.0007,***) but not T-reg (p=0.65, ns) or B cells (p=0.65, ns). Compared with rabbit ATG, GH-ALG induced transient depletion (less than one week) of target T cells in the peripheral blood (<100 lymphocytes/L) but was equivalent in preventing allograft rejection in a skin allograft model. The novel therapeutic modality of GH-ALG might present advantages in induction treatment during organ transplantation by shortening the T-cell depletion period while maintaining adequate immunosuppression and reducing immunogenicity.

Methods to Study TLRs in Transplantation.

Toll-like receptors (TLRs) are key regulators of immune responses, including alloimmune responses. In this chapter, we present protocols to study whether and/or how TLRs can contribute to solid-organ transplant rejection. We describe methods to reduce heterogeneity in microbiome variations between animals before beginning experiments to limit confounding factors, protocols using TLR agonists to prevent anti-CD154/donor splenocyte transfer-mediated tolerance, and recipes to heat-kill microbes or use hosts genetically deficient in TLR-dependent pathways to distinguish between TLR-dependent and live bacteria-dependent effects.

Exploring the Impact of Humoral Immunogenicity with Tabelecleucel for the Treatment of EBV+ PTLD Following HCT and SOT

Background: Tabelecleucel is a non-genetically modified, allogeneic Epstein-Barr virus (EBV)-T-cell immunotherapy which targets and eliminates EBV-expressing cells in an HLA-restricted manner to treat patients (pts) with EBV+ post-transplant lymphoproliferative disease (PTLD) following hematopoietic stem cell transplantation (HCT) or solid organ transplantation (SOT). The theoretical risk of invoking a humoral or cell-mediated immune response against tabelecleucel is limited to the partially mismatched HLA allele. Tabelecleucel has proven to be safe and effective, with no confirmed evidence for clinical manifestation of immunogenicity in association with tabelecleucel. However, the theoretical consequences of eliciting an immune reaction against the mismatched HLA range from transient appearance of anti-HLA antibodies without any manifestation of clinically significant effects to the development of severe life-threatening conditions, which may include the potential for organ rejection. Therefore, evaluating the potential risk of immunogenicity against an allogeneic cell therapy like tabelecleucel is an important step in assessing the safety profile of the therapeutic agent. In this study we will assess the potential impact of humoral immunogenicity against tabelecleucel in pts with EBV+ PTLD after failure of rituximab or rituximab and chemotherapy enrolled in the ALLELE (NCT03394365) clinical study. Methods: Humoral immunogenicity was assessed through two methods of anti-HLA antibody detection that evaluated a total of 28 pts on study. The primary approach evaluated 9 pts by a pan anti-HLA detection method that provides a positive or negative result. In this approach evaluable pts must have a negative result in pre-treatment measurement and have at least one post-treatment measurement. Results are coupled with the pt's clinical safety profile to assess treatment related immunogenicity. The secondary approach evaluated 24 pts in a single-antigen bead method that provides not just a positive or negative result but also defines the specificity and strength of the positive result. Cross referencing the allele specificity of the Class I or Class II anti-HLA antibodies with the HLA type of the pt, the transplant and the infusion product aids in elucidating the source of the anti-HLA antibodies in these pts. Results: Two of the nine pts tested using the pan anti-HLA antibody detection approach had detection of anti-HLA antibodies in their pre-treatment sample. The remaining 7 evaluable pts had a median of 1 post-treatment measurement (min, max: 1, 3) and the median time post-treatment evaluated was 113 days (min, max: 40, 179). Six out of the 7 evaluable pts did not develop any anti-HLA antibodies post-treatment. One pt in the SOT cohort did develop anti-HLA antibodies 40 days after initial dosing on cycle 2 day 1. No treatment-emergent serious adverse events were reported for this pt, and only one adverse event of grade 1 fever was assessed as possibly related per investigator. The pt received additional doses of tabelecleucel yet did not manifest any subsequent events of fever or any signs of organ rejection. The second, single-antigen bead-based approach evaluated 24 pts. Four had anti-HLA antibodies present prior to tabelecleucel infusion. None of the pts evaluated had any incidence of de novo anti-HLA antibodies emerging post-treatment. For the 4 pts with pre-existing anti-HLA antibodies, evaluation of their safety profile and comparison to the total HLA immune profile of the pt is currently underway and will be reported at the time of presentation. Conclusions: To date, there has been no confirmed evidence for clinical manifestation of immunogenicity in association with tabelecleucel. Only 1 pt (tested using the pan anti-HLA method) out of 28 pts (tested using either method) had de novo emergence of anti-HLA antibodies post-infusion. This pt did not experience any severe events potentially reflecting immunogenicity such as hypersensitivity or SOT rejection. Taken together, these results reaffirm the low potential risk of developing humoral immunogenicity following tabelecleucel administration in HCT or SOT recipients with EBV+ PTLD after failure of rituximab or rituximab and chemotherapy.

Infections following rejection therapies in kidney and liver transplant recipients.

Infections are known complications of solid-organ transplant. Treatment for rejection may increase risk of infection. We aimed to study frequency of infection and identify the risk factors for infections in solid organ transplant (SOT) (liver and kidney) recipients treated for rejection. This is a retrospective chart review of all liver and kidney transplant recipients treated for rejection at our institution from 2014 to 2020. We collected information on episodes of acute rejection in the first year of transplant and infections within 6 months following rejection treatment. We identified 257 transplant patients treated for rejection. One hundred twelve (43.6%) developed infections, with a total of 226 infections. Urinary tracts infections were the most common, 72 (31.9%), followed by cytomegalovirus viremia in 37 (16.4%), bacteremia in 24 (10.6%), and BK virus in 14 (6.2%). Female sex (p = .047), elevated neutrophil count at rejection (p = .002), and increased number of rejection episodes (p = .022) were predictors of infection in kidney and simultaneous liver-kidney recipients. No specific type of induction or rejection therapy was identified as a risk factor for infection, likely due to the prophylaxis protocols at our institution. Infection post rejection treatment was associated with higher graft loss (p = .021) and mortality (p = .031) in kidney transplant recipients. Infections are common complications after treatment of SOT rejection. Female gender, higher neutrophil at time of rejection, and increased numbers of rejection episodes were predictors of infections after rejection in simultaneous liver-kidney and kidney transplant patients. Infections were predictors of graft loss at 6 months and mortality at any point in follow-up in kidney transplant patients.

Estimation of Antibody-Verified Eplet Mismatch Load, 2-Field HLA Resolution vs Imputation in a Large Cohort of European Donors

The assessment of class II eplet mismatch load is useful to determine the risk of chronic rejection in solid organ transplantation. However, high-resolution (2-field) HLA typing is mandatory to accurately define eplet mismatches. The imputation of the most frequent allele has been used in retrospective studies. Here, we sought to investigate the concordant of antibody-verified (AbV) eplet load in different class II alelles between real 2-field HLA typing and HLA imputed by most frequent allele in a large White cohort. The allelic frequency of the different HLA class II loci was calculated using a database of high-resolution typing of 23,628 voluntary Spanish bone marrow donors obtained from the Spanish Registry of Bone Marrow Donors, managed by the Josep Carreras Foundation. The AbV eplet count in the different class II alleles was performed using the HLA-Matchmaker v3.1 algorithm. The probability of imputing the correct allele compared to the most frequent for DRB1 and DQB1 loci was 69.3% and 53.0%, respectively. However, studying the less frequent alleles, the same AbV eplet load was observed in 82.22% and 76.15%, respectively. Our data show that despite the potential error in the imputation of class II HLA typing, the number of AbV eplets is not significantly over- or underestimated in our population. Until high-resolution typing is widely established for solid organ transplantation, retrospective studies of AbV eplet mismatch load with imputed high-resolution types provide an acceptable outcome in White people.