Memory T follicular helper cells drive donor-specific antibodies independent of memory B cells and primary germinal center and alloantibody formation.

Human leukocyte antigen antibodies are important immunologic mediators of renal allograft loss and are difficult to control. The inability to permanently eliminate donor-specific antibodies (DSA) is partly due to an incomplete understanding of the cellular mechanisms driving alloantibody formation, recurrence, and maintenance. Memory T follicular helper (mTfh) cells rapidly interact with memory B cells upon antigen re-exposure for anamnestic humoral responses, but little is known about Tfh memory in transplantation. We hypothesized that alloreactive mTfh cells form after transplantation and play a critical role in DSA formation following alloantigen re-encounter. To test this hypothesis, we utilized murine skin allograft models to identify and characterize Tfh memory and interrogate its ability to mediate alloantibody responses. We identified alloreactive Tfh memory as a mediator of accelerated humoral alloresponses independent of memory B cells and primary germinal center, or DSA, formation. Furthermore, we demonstrate that mTfh-driven alloantibody formation is susceptible to CD28 costimulation blockade. These findings provide novel insight into a pathologic role for memory Tfh in alloantibody responses and strongly support shifting therapeutic focus from the singular targeting of B cell lineage cells and alloantibodies themselves to multimodal strategies that include inhibition of mTfh cells to treat DSA.

Implementation of an Online Intraoperative Assessment of Technical Performance for Surgical Trainees.

INTRODUCTION: Assessment of surgical resident technical performance is an integral component of any surgical training program. Timely assessment delivered in a structured format is a critical step to enhance technical skills, but residents often report that the quality and quantity of timely feedback received is lacking. Moreover, the absence of written feedback with specificity can allow residents to seemingly progress in their operative milestones as a junior resident, but struggle as they progress into their postgraduate year 3 and above. We therefore designed and implemented a web-based intraoperative assessment tool and corresponding summary "dashboard" to facilitate real-time assessment and documentation of technical performance. MATERIALS AND METHODS: A web form was designed leveraging a cloud computing platform and implementing a modified Ottawa Surgical Competency Operating Room Evaluation instrument; this included additional, procedure-specific criteria for select operations. A link to this was provided to residents via email and to all surgical faculty as a Quick Response code. Residents open and complete a portion of the form on a smartphone, then relinquish the device to an attending surgeon who then completes and submits the assessment. The data are then transferred to a secure web-based reporting interface; each resident (together with a faculty advisor) can then access and review all completed assessments. RESULTS: The Assessment form was activated in June 2021 and formally introduced to all residents in July 2021, with residents required to complete at least one assessment per month. Residents with less predictable access to operative procedures (night float or Intensive Care Unit) were exempted from the requirement on those months. To date a total of 559 assessments have been completed for operations performed by 56 trainees, supervised by 122 surgical faculty and senior trainees. The mean number of procedures assessed per resident was 10.0 and the mean number per assessor was 4.6. Resident initiation of Intraoperative Assessments has increased since the tool was introduced and scores for technical and nontechnical performance reliably differentiate residents by seniority. CONCLUSIONS: This novel system demonstrates that an online, resident-initiated technical assessment tool is feasible to implement and scale. This model's requirement that the attending enter performance ratings into the trainee's electronic device ensures that feedback is delivered directly to the trainee. Whether this aspect of our assessment ensures more direct and specific (and therefore potentially actionable) feedback is a focus for future study. Our use of commercial cloud computing services should permit cost-effective adoption of similar systems at other training programs.

Application of a digital PCR method for WT1 to myeloid neoplasms in CR and deep ELN WT1 molecular response (< 10 copies).

Bone marrow WT1 mRNA levels assessed by the ELN method are useful to establish prognostic correlations in myeloid malignancies treated with chemotherapy or hematopoietic stem cell transplantation (HCT). Those patients with WT1 levels below ten copies have a good outcome. However, some of these patients relapse. To further characterize this group of cases, we applied a new and sensitive digital (ddPCR) WT1 method. A consecutive series of 49 patients with treated myeloid malignancies and with an ELN WT1 quantitation of < 10 copies were included in the study. All cases (47 AML and 2 MDS) have received intensive chemotherapy or HCT. One to four micrograms of total RNA were retrotranscribed to obtain ≥ 10,000 ABL1 copies using the ELN protocol. Only those cases with a good quality cDNA were used in the ddPCR WT1 test. The ddPCR Gene Expression WT1 Assay of Bio-Rad© was used to perform the PCR amplification, and the microdroplets were quantified in the Bio-Rad's QX200 droplet reader. Eighteen patients showed a negative WT1 ddPCR assay (0 copies/µl), whereas 31 cases were positive (results ranged from 1 to 15.2 copies/µl). Survival analysis showed statistically significant differences in terms of OS between both groups, 83 ± 8% vs. 46 ± 9% (p = 0.024). A statistically significant correlation was also found between ddPCRWT1 results and CD123+ cell number detected by flow cytometry (p = 0.024). Larger series of patients tested with the current ddPCRWT1 method will solve whether it could be used to stratify patients with myeloid malignancies achieving deep WT1 molecular response (< 10 copies).

Selective CD28 Blockade Results in Superior Inhibition of Donor-Specific T Follicular Helper Cell and Antibody Responses Relative to CTLA4-Ig.

Donor-specific antibodies (DSAs) are a barrier to improved long-term outcomes after kidney transplantation. Costimulation blockade with CTLA4-Ig has shown promise as a potential therapeutic strategy to control DSAs. T follicular helper (Tfh) cells, a subset of CD4+ T cells required for optimal antibody production, are reliant on the CD28 costimulatory pathway. We have previously shown that selective CD28 blockade leads to superior allograft survival through improved control of CD8+ T cells relative to CTLA4-Ig, but the impact of CD28-specific blockade on CD4+ Tfh cells is unknown. Thus, we identified and characterized donor-reactive Tfh cells in a murine skin transplant model and then used this model to evaluate the impact of selective CD28 blockade with an anti-CD28 domain antibody (dAb) on the donor-specific Tfh cell-mediated immune response. We observed that the anti-CD28 dAb led to superior inhibition of donor-reactive CXCR5+ PD-1high Tfh cells, CD95+ GL7+ germinal center B cells and DSA formation compared with CTLA4-Ig. Interestingly, donor-reactive Tfh cells differentially upregulated CTLA4 expression, suggesting an important role for CTLA4 in mediating the superior inhibition observed with the anti-CD28 dAb. Therefore, selective CD28 blockade as a novel approach to control Tfh cell responses and prevent DSA after kidney transplantation warrants further study.

Microencapsulated adult porcine islets transplanted intraperitoneally in streptozotocin-diabetic non-human primates.

BACKGROUND: Xenogeneic donors would provide an unlimited source of islets for the treatment of type 1 diabetes (T1D). The goal of this study was to assess the function of microencapsulated adult porcine islets (APIs) transplanted ip in streptozotocin (STZ)-diabetic non-human primates (NHPs) given targeted immunosuppression. METHODS: APIs were encapsulated in: (a) single barium-gelled alginate capsules or (b) double alginate capsules with an inner, islet-containing compartment and a durable, biocompatible outer alginate layer. Immunosuppressed, streptozotocin-diabetic NHPs were transplanted ip with encapsulated APIs, and graft function was monitored by measuring blood glucose, %HbA1c, and porcine C-peptide. At graft failure, explanted capsules were assessed for biocompatibility and durability plus islet viability and functionality. Host immune responses were evaluated by phenotyping peritoneal cell populations, quantitation of peritoneal cytokines and chemokines, and measurement of anti-porcine IgG and IgM plus anti-Gal IgG. RESULTS: NHP recipients had reduced hyperglycemia, decreased exogenous insulin requirements, and lower percent hemoglobin A1c (%HbA1c) levels. Porcine C-peptide was detected in plasma of all recipients, but these levels diminished with time. However, relatively high levels of porcine C-peptide were detected locally in the peritoneal graft site of some recipients at sacrifice. IV glucose tolerance tests demonstrated metabolic function, but the grafts eventually failed in all diabetic NHPs regardless of the type of encapsulation or the host immunosuppression regimen. Explanted microcapsules were intact, "clean," and free-floating without evidence of fibrosis at graft failure, and some reversed diabetes when re-implanted ip in diabetic immunoincompetent mice. Histology of explanted capsules showed scant evidence of a host cellular response, and viable islets could be found. Flow cytometric analyses of peritoneal cells and peripheral blood showed similarly minimal evidence of a host immune response. Preformed anti-porcine IgG and IgM antibodies were present in recipient plasma, but these levels did not rise post-transplant. Peritoneal graft site cytokine or chemokine levels were equivalent to normal controls, with the exception of minimal elevation observed for IL-6 or IL-1ß, GRO-α, I-309, IP-10, and MCP-1. However, we found central necrosis in many of the encapsulated islets after graft failure, and explanted islets expressed endogenous markers of hypoxia (HIF-1α, osteopontin, and GLUT-1), suggesting a role for non-immunologic factors, likely hypoxia, in graft failure. CONCLUSIONS: With donor xenoislet microencapsulation and host immunosuppression, APIs corrected hyperglycemia after ip transplantation in STZ-diabetic NHPs in the short term. The islet xenografts lost efficacy gradually, but at graft failure, some viable islets remained, substantial porcine C-peptide was detected in the peritoneal graft site, and there was very little evidence of a host immune response. We postulate that chronic effects of non-immunologic factors, such as in vivo hypoxic and hyperglycemic conditions, damaged the encapsulated islet xenografts. To achieve long-term function, new approaches must be developed to prevent this damage, for example, by increasing the oxygen supply to microencapsulated islets in the ip space.

T follicular helper cells in the generation of alloantibody and graft rejection.

PURPOSE OF REVIEW: T follicular helper (Tfh) cells are an increasingly relevant CD4 T cell subset responsible for the provision of help to B cells for the generation of an effective humoral immune response. Here we review recent studies that have provided critical insights into the mechanisms of Tfh cell differentiation and function, and introduce newly identified roles for Tfh cells in human disease. RECENT FINDINGS: Novel molecular regulators of the Tfh cell differentiation program along with new found roles for the costimulatory and coinhibitory inducible T cell costimulator (ICOS), programmed death 1, and cytotoxic T lymphocyte antigen 4 pathways on Tfh cell function have been appreciated. Although circulating Tfh and Tfh-like subset signatures have been linked to numerous immune conditions, extrapolation of these findings to organ transplantation is just beginning. SUMMARY: The combination of recent progress with regard to Tfh cell biology at the basic science and clinical levels is guiding the elucidation of the role of Tfh cells in the alloimmune response. Application of this knowledge toward the development of novel therapeutic strategies for use in transplantation is imminent.

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.

Belatacept and sirolimus prolong nonhuman primate islet allograft survival: adverse consequences of concomitant alefacept therapy.

Calcineurin inhibitors (CNI) and steroids are known to promote insulin resistance, and their avoidance after islet transplantation is preferred from a metabolic standpoint. Belatacept, a B7-specific mediator of costimulation blockade (CoB), is clinically indicated as a CNI alternative in renal transplantation, and we have endeavored to develop a clinically translatable, belatacept-based regimen that could obviate the need for both CNIs and steroids. Based on the known synergy between CoB and mTOR inhibition, we studied rhesus monkeys undergoing MHC-mismatched islet allotransplants treated with belatacept and the mTOR inhibitor, sirolimus. To extend prior work on CoB-resistant rejection, some animals also received CD2 blockade with alefacept (LFA3-Ig). Nine rhesus macaques were rendered diabetic with streptozotocin and underwent islet allotransplantation. All received belatacept and sirolimus; six also received alefacept. Belatacept and sirolimus significantly prolonged rejection-free graft survival (median 225 days compared to 8 days in controls receiving basiliximab and sirolimus; p = 0.022). The addition of alefacept provided no additional survival benefit, but was associated with Cytomegalovirus reactivation in four of six animals. No recipients produced donor-specific alloantibodies. The combination of belatacept and sirolimus successfully prevents islet allograft survival in rhesus monkeys, but induction with alefacept provides no survival benefit and increases the risk of viral reactivation.

Costimulatory Blockade and Solid Organ Transplantation: The Past, Present, and Future.

Belatacept is the first costimulatory blockade agent clinically approved for transplant immunosuppression. Although more than 10 years of study have demonstrated that belatacept offers superior long-term renal allograft and patient survival compared to conventional calcineurin inhibitor (CNI)-based immunosuppression regimens, the clinical adoption of belatacept has continued to lag because of concerns of an early risk of acute cellular rejection (ACR) and various logistical barriers to its administration. In this review, the history of the clinical development of belatacept is examined, along with the findings of the seminal BENEFIT and BENEFIT-EXT trials culminating in the clinical approval of belatacept. Recent efforts to incorporate belatacept into novel CNI-free immunosuppression regimens are reviewed, as well as the experience of the Emory Transplant Center in using a tapered course of low-dose tacrolimus in belatacept-treated renal allograft patients to garner the long-term outcome benefits of belatacept without the short-term increased risks of ACR. Potential avenues to increase the clinical adoption of belatacept in the future are explored, including surmounting the logistical barriers of belatacept administration through subcutaneous administration or more infrequent belatacept dosing. In addition, belatacept conversion strategies and potential expanded clinical indications of belatacept are discussed for pediatric transplant recipients, extrarenal transplant recipients, treatment of antibody-mediated rejection (AMR), and in patients with failed renal allografts. Finally, we discuss the novel immunosuppressive drugs currently in the development pipeline that may aid in the expansion of costimulation blockade utilization.

Three-year Outcomes After Conversion From Monthly to Every 2-month Belatacept Maintenance Therapy in Kidney Transplant Recipients: Results From a Randomized Controlled Trial.

Maintenance immunosuppression with belatacept following kidney transplantation results in improved long-term graft function as compared with calcineurin inhibitors. However, broad application of belatacept has been limited, in part related to logistical barriers surrounding a monthly (q1m) infusion requirement. Methods: To determine whether every 2-mo (q2m) belatacept is noninferior to standard q1m maintenance, we conducted a prospective, single-center randomized trial in low-immunologic-risk, stable renal transplant recipients. Here, post hoc analysis of 3-y outcomes, including renal function and adverse events, are reported. Results: One hundred sixty-three patients received treatment in the q1m control group (n = 82) or q2m study group (n = 81). Renal allograft function as measured by baseline-adjusted estimated glomerular filtration rate was not significantly different between groups (time-averaged mean difference of 0.2 mL/min/1.73 m2; 95% confidence interval: -2.5, 2.9). There were no statistically significant differences in time to death or graft loss, freedom from rejection, or freedom from donor-specific antibodies (DSAs). During the extended 12- to 36-mo follow-up, 3 deaths, 1 graft loss occurred in the q1m group, compared with 2 deaths, and 2 graft losses in the q2m group. In the q1m group, 1 patient developed DSAs and acute rejection. In the q2m group, 3 patients developed DSAs and 2 associated with acute rejection. Conclusions: Based on the similar renal function and survival at 36 mo compared with q1m, q2m belatacept is a potentially viable maintenance immunosuppressive strategy in low immunologic risk kidney transplant recipients that may facilitate increased clinical utilization of costimulation blockade-based immunosuppression.

A novel monoclonal antibody to CD40 prolongs islet allograft survival.

The importance of CD40/CD154 costimulatory pathway blockade in immunosuppression strategies is well-documented. Efforts are currently focused on monoclonal antibodies specific for CD40 because of thromboembolic complications associated with monoclonal antibodies directed towards CD154. Here we present the rational development and characterization of a novel antagonistic monoclonal antibody to CD40. Rhesus macaques were treated with the recombinant anti-CD40 mAb, 2C10, or vehicle before immunization with keyhole limpet hemocyanin (KLH). Treatment with 2C10 successfully inhibited T cell-dependent antibody responses to KLH without significant peripheral B cell depletion. Subsequently, MHC-mismatched macaques underwent intraportal allogeneic islet transplantation and received basiliximab and sirolimus with or without 2C10. Islet graft survival was significantly prolonged in recipients receiving 2C10 (graft survival time 304, 296, 265, 163 days) compared to recipients receiving basiliximab and sirolimus alone (graft survival time 8, 8, 10 days). The survival advantage conferred by treatment with 2C10 provides further evidence for the importance of blockade of the CD40/CD154 pathway in preventing alloimmune responses. 2C10 is a particularly attractive candidate for translation given its favorable clinical profile.

CTLA4Ig prevents alloantibody formation following nonhuman primate islet transplantation using the CD40-specific antibody 3A8.

Islet transplantation to treat type 1 diabetes has been limited in part by toxicities of current immunosuppression and recipient humoral sensitization. Blockade of the CD28/CD80/86 and CD40/CD154 pathways has shown promise to remedy both these limitations, but translation has been hampered by difficulties in translating CD154-directed therapies. Prior CD40-directed regimens have led to prolonged islet survival, but fail to prevent humoral allosensitization. We therefore evaluated the addition of CTLA4Ig to a CD40 blockade-based regimen in nonhuman primate (NHP) alloislet transplantation. Diabetic rhesus macaques were transplanted allogeneic islets using the CD40-specific antibody 3A8, basiliximab induction, and sirolimus with or without CTLA4Ig maintenance therapy. Allograft survival was determined by fasting blood glucose levels and flow cytometric techniques were used to test for donor-specific antibody (DSA) formation. CTLA4Ig plus 3A8, basiliximab and sirolimus was well tolerated and induced long-term islet allograft survival. The addition of CTLA4Ig prevented DSA formation, but did not facilitate withdrawal of the 3A8-based regimen. Thus, CTLA4Ig combines with a CD40-specific regimen to prevent DSA formation in NHPs, and offers a potentially translatable calcineurin inhibitor-free protocol inclusive of a single investigational agent for use in clinical islet transplantation without relying upon CD154 blockade.

Alternative immunomodulatory strategies for xenotransplantation: CD40/154 pathway-sparing regimens promote xenograft survival.

Immunosuppressive therapies that block the CD40/CD154 costimulatory pathway have proven to be uniquely effective in preclinical xenotransplant models. Given the challenges facing clinical translation of CD40/CD154 pathway blockade, we examined the efficacy and tolerability of CD40/CD154 pathway-sparing immunomodulatory strategies in a pig-to-nonhuman primate islet xenotransplant model. Rhesus macaques were rendered diabetic with streptozocin and given an intraportal infusion of ≈ 50 000 islet equivalents/kg wild-type neonatal porcine islets. Base immunosuppression for all recipients included maintenance therapy with belatacept and mycophenolate mofetil plus induction with basiliximab and LFA-1 blockade. Cohort 1 recipients (n = 3) were treated with the base regimen alone; cohort 2 recipients (n = 5) were additionally treated with tacrolimus induction and cohort 3 recipients (n = 5) were treated with alefacept in place of basiliximab, and more intense LFA-1 blockade. Three of five recipients in both cohorts 2 and 3 achieved sustained insulin-independent normoglycemia (median rejection-free survivals 60 and 111 days, respectively), compared to zero of three recipients in cohort 1. These data show that CD40/CD154 pathway-sparing regimens can promote xenoislet survival. Further optimization of these strategies is warranted to aid the clinical translation of islet xenotransplantation.

Nondepleting anti-CD40-based therapy prolongs allograft survival in nonhuman primates.

Costimulation blockade of the CD40/CD154 pathway has been effective at preventing allograft rejection in numerous transplantation models. This strategy has largely depended on mAbs directed against CD154, limiting the potential for translation due to its association with thromboembolic events. Though targeting CD40 as an alternative to CD154 has been successful at preventing allograft rejection in preclinical models, there have been no reports on the effects of CD40-specific agents in human transplant recipients. This delay in clinical translation may in part be explained by the presence of cellular depletion with many CD40-specific mAbs. As such, the optimal biologic properties of CD40-directed immunotherapy remain to be determined. In this report, we have characterized 3A8, a human CD40-specific mAb and evaluated its efficacy in a rhesus macaque model of islet cell transplantation. Despite partially agonistic properties and the inability to block CD40 binding of soluble CD154 (sCD154) in vitro, 3A8-based therapy markedly prolonged islet allograft survival without depleting B cells. Our results indicate that the allograft-protective effects of CD40-directed costimulation blockade do not require sCD154 blockade, complete antagonism or cellular depletion, and serve to support and guide the continued development of CD40-specific agents for clinical translation.

Methotrexate consolidation treatment according to pharmacogenetics of MTHFR ameliorates event-free survival in childhood acute lymphoblastic leukaemia.

Recent advances in treatment for childhood acute lymphoblastic leukaemia (ALL) have significantly increased outcome. High-dose methotrexate (MTX) is the most commonly used regimen during the consolidation period, but the optimal dose remains to be defined. We investigated the usefulness of the MTHFR genotype to increase the MTX dosage in the consolidation phase in 141 childhood ALL patients enrolled in the ALL/SHOP-2005 protocol. We also investigated the pharmacogenetic role of polymorphisms in genes involved in MTX metabolism on therapy-related toxicity and survival. Patients with a favourable MTHFR genotype (normal enzymatic activity) treated with MTX doses of 5 g m⁻² had a significantly lower risk of suffering an event than patients with an unfavourable MTHFR genotype (reduced enzymatic activity) that were treated with the classical MTX dose of 3 g m⁻² (P=0.012). Our results indicate that analysis of the MTHFR genotype is a useful tool to optimise MTX therapy in childhood patients with ALL.

Islet xenotransplantation using gal-deficient neonatal donors improves engraftment and function.

Significant deficiencies in understanding of xenospecific immunity have impeded the success of preclinical trials in xenoislet transplantation. Although galactose-α1,3-galactose, the gal epitope, has emerged as the principal target of rejection in pig-to-primate models of solid organ transplant, the importance of gal-specific immunity in islet xenotransplant models has yet to be clearly demonstrated. Here, we directly compare the immunogenicity, survival and function of neonatal porcine islets (NPIs) from gal-expressing wild-type (WT) or gal-deficient galactosyl transferase knockout (GTKO) donors. Paired diabetic rhesus macaques were transplanted with either WT (n = 5) or GTKO (n = 5) NPIs. Recipient blood glucose, transaminase and serum xenoantibody levels were used to monitor response to transplant. Four of five GTKO versus one of five WT recipients achieved insulin-independent normoglycemia; transplantation of WT islets resulted in significantly greater transaminitis. The WT NPIs were more susceptible to antibody and complement binding and destruction in vitro. Our results confirm that gal is an important variable in xenoislet transplantation. The GTKO NPI recipients have improved rates of normoglycemia, likely due to decreased susceptibility of xenografts to innate immunity mediated by complement and preformed xenoantibody. Therefore, the use of GTKO donors is an important step toward improved consistency and interpretability of results in future xenoislet studies.

CD40-specific costimulation blockade enhances neonatal porcine islet survival in nonhuman primates.

The widespread clinical implementation of alloislet transplantation as therapy for type 1 diabetes has been hindered by the lack of suitable islet donors. Pig-to-human islet xenotransplantation is one strategy with potential to alleviate this shortage. Long-term survival of porcine islets has been achieved using CD154-specific antibodies to interrupt the CD40/CD154 costimulation pathway; however, CD154-specific antibodies seem unlikely candidates for clinical translation. An alternative strategy for CD40/CD154 pathway interruption is use of CD40-specific antibodies. Herein, we evaluate the ability of a chimeric CD40-specific monoclonal antibody (Chi220) to protect islet xenografts. Neonatal porcine islets (~50,000 IEQ/kg) were transplanted intraportally into pancreatectomized diabetic macaques. Immunosuppression consisted of induction therapy with Chi220 and the IL-2 receptor-specific antibody basiliximab, and maintenance therapy with sirolimus and the B7-specific fusion protein belatacept. Chi220 effectively promoted xenoislet engraftment and survival, with five of six treated recipients achieving insulin-independent normoglycemia (median rejection-free survival 59 days; mean 90.8 days, maximum 203 days). No thromboembolic phenomena were observed. CD40 represents a promising alternative to CD154 as a therapeutic target, and the efficacy of CD40-specific antibodies in islet xenotransplantation warrants further investigation.

CXCL13 Is an Indicator of Germinal Center Activity and Alloantibody Formation Following Transplantation.

Donor-specific antibodies (DSA) are a recognized cause of allograft injury, yet biomarkers that indicate their development posttransplant or guide management are not available. CXCL13 (chemokine [C-X-C motif] ligand 1) is a chemoattractant produced within secondary lymphoid organs necessary for germinal center (GC) and alloantibody formation. Perturbations in serum CXCL13 levels have been associated with humoral immune activity. Therefore, CXCL13 may correlate with the formation of HLA antibodies following transplantation. METHODS: A murine skin graft model was utilized to define the production and kinetics of CXCL13 in response to alloantigen. Human Tfh:B-cell in vitro cocultures were performed to evaluate CXCL13 production by human lymphocytes, and serum from healthy controls and human transplant recipients with and without de novo DSA was tested for CXCL13. RESULTS: CXCL13 was detectable in the blood of allografted mice and correlated with Tfh and GC B-cell responses. Greater CXCL13 expression was observed in the draining lymph nodes of allografted mice as compared with naïve or syngeneic graft recipients, and serum levels preceded the detection of DSA posttransplant. Similarly, productive human Tfh:B-cell interactions that led to plasmablast differentiation and IgG formation also exhibited CXCL13 expression. CXCL13 levels in human transplant recipients with de novo DSA were greater than in healthy controls and stable transplant patients and also correlated with the development of alloantibodies in a small cohort of serially monitored recipients. CONCLUSIONS: CXCL13 indicates GC alloreactivity and alloantibody formation and correlated with DSA formation in kidney transplant recipients, thereby introducing CXCL13 as a potential biomarker for HLA antibodies.

[Neurological complications in haematopoietic stem cell transplant patients]. / Complicaciones neurológicas en pacientes sometidos a trasplante de progenitores hematopoyéticos.

INTRODUCTION: Neurological complications are some of the most important complications that can occur in a patient undergoing haematopoietic stem cell transplantation (HSCT), not only because of the high mortality rate, but also because of the sequelae that appear in survivors. The causes of such complications are manifold and very often coexist in the same patient: toxicity of the conditioning regimen, graft-versus-host disease and its treatment, infections and their treatment, platelets and coagulation disorders, liver failure or arterial hypertension with low platelet count. AIMS: The aim of the present study is to provide a clinical description and to describe the risk factors for complications involving the central nervous system that may occur during the course of HSCT, in order to assist in the early detection of these disorders that may have a negative influence on the morbidity and mortality of these patients. DEVELOPMENT: The following types of neurological complications are described: central nervous system infections, vascular complications, pharmacological toxicity, metabolic complications, immune-mediated disorders and post-HSCT carcinogenesis, and effects of graft-versus-host disease and thrombotic microangiopathy on the nervous system. CONCLUSIONS: The patient undergoing HSCT is at particular risk for the development of neurological complications. Early diagnosis and treatment are needed to try to reduce the high morbidity and mortality in these patients.

TITLE: Complicaciones neurológicas en pacientes sometidos a trasplante de progenitores hematopoyéticos.Introducción. Las complicaciones neurológicas son algunas de las más importantes que se pueden presentar en un paciente sometido a un trasplante de progenitores hematopoyéticos (TPH), no sólo porque conllevan una mortalidad elevada, sino también por las secuelas que aparecen en los supervivientes. Las causas de dichas complicaciones son múltiples y, muy frecuentemente, coexisten en el mismo paciente: toxicidad del régimen de acondicionamiento, enfermedad del injerto contra el hospedador y su tratamiento, infecciones y su tratamiento, plaquetopenia y trastornos de la coagulación, fallo hepático o hipertensión arterial con plaquetopenia. Objetivos. El objetivo del presente estudio es el de aportar una descripción clínica y de los factores de riesgo de las complicaciones sobre el sistema nervioso central que pueden presentarse en el curso de un TPH, para ayudar en la detección precoz de estos trastornos que pueden influir negativamente en la morbimortalidad de estos pacientes. Desarrollo. Se describen los siguientes tipos de complicaciones neurológicas: infecciones sobre el sistema nervioso central, complicaciones vasculares, toxicidad farmacológica, complicaciones metabólicas, trastornos inmunomediados y carcinogenia pos-TPH, y efectos de la enfermedad del injerto contra el hospedador y de la microangiopatía trombótica sobre el sistema nervioso. Conclusiones. El paciente sometido a TPH es de especial riesgo para el desarrollo de complicaciones neurológicas. Se precisan un diagnóstico y un tratamiento precoces para intentar disminuir la elevada morbimortalidad de estos pacientes.