Immune Response in Moderate to Critical Breakthrough COVID-19 Infection After mRNA Vaccination.

SARS-CoV-2 variants of concern (VOCs) can trigger severe endemic waves and vaccine breakthrough infections (VBI). We analyzed the cellular and humoral immune response in 8 patients infected with the alpha variant, resulting in moderate to fatal COVID-19 disease manifestation, after double mRNA-based anti-SARS-CoV-2 vaccination. In contrast to the uninfected vaccinated control cohort, the diseased individuals had no detectable high-avidity spike (S)-reactive CD4+ and CD8+ T cells against the alpha variant and wild type (WT) at disease onset, whereas a robust CD4+ T-cell response against the N- and M-proteins was generated. Furthermore, a delayed alpha S-reactive high-avidity CD4+ T-cell response was mounted during disease progression. Compared to the vaccinated control donors, these patients also had lower neutralizing antibody titers against the alpha variant at disease onset. The delayed development of alpha S-specific cellular and humoral immunity upon VBI indicates reduced immunogenicity against the S-protein of the alpha VOC, while there was a higher and earlier N- and M-reactive T-cell response. Our findings do not undermine the current vaccination strategies but underline a potential need for the inclusion of VBI patients in alternative vaccination strategies and additional antigenic targets in next-generation SARS-CoV-2 vaccines.

The Serial Duplex Index Improves Differential Diagnosis of Acute Renal Transplant Dysfunction.

OBJECTIVES: Renal duplex sonography represents a standard noninvasive diagnostic procedure to demonstrate morphologic changes in acute kidney transplant dysfunction. We investigated whether a newly developed serial duplex index (SDI) can differentiate between acute cellular rejection and acute vascular rejection more effectively than the established Doppler parameters of the resistive index (RI) and pulsatility index (PI) in recently transplanted patients. METHODS: Serial duplex scans of patients with histologically proven acute tubular necrosis (n = 25), acute cellular rejection (n = 28), acute vascular rejection (n = 18), and normal graft function (n = 50, partially protocol biopsied) were retrospectively analyzed. For each patient, the RI, PI, and cortex-pelvis proportion (CPP) were included from the day of biopsy (t0) and 3 to 7 days before biopsy (t-1). The sequential CPP ratio (CPPt0 /CPPt-1 ), RI ratio (RIt0 /RIt-1 ), and PI ratio (PIt0 /Pit-1 ) were determined. The SDI was calculated as: RI ratio × PI ratio/CPP ratio. The diagnostic accuracy of the SDI was compared with that of the RI and PI ratios. RESULTS: Selected groups were statistically comparable in all routinely determined transplant parameters. The SDI was significantly different between patients with normal graft function, acute cellular rejection, and acute vascular rejection (P < .01, analysis of variance on ranks), whereas the RI and PI ratios were only significantly different between patients with normal graft function and acute vascular rejection (P < .05, analysis of variance on ranks). The indices' ranges were defined by the 95% confidence intervals between the allograft functions. CONCLUSIONS: The developed SDI was able to detect acute renal transplant rejection with greater sensitivity and specificity than the RI and PI ratios. Since the SDI distinguishes between acute tubular necrosis, acute cellular rejection, and acute vascular rejection, it might be a supportive tool to indicate renal biopsy.

Prognostic value and cost-effectiveness of different screening strategies for HLA antibodies prior to kidney transplantation.

HLA antibody screening is conducted routinely prior to kidney transplantation, but the comparative prognostic value and cost-effectiveness of different methods are unclear. Pre-transplant sera of 141 patients transplanted between 1998 and 2000 were screened by ELISA and Luminex assays, and antibody specificities of reactive sera determined using bead array techniques. ELISA screening detected donor-specific antibodies (DSA) in 19 patients, who had a higher incidence of impaired graft function (60% vs. 20%, p = 0.04) and antibody-mediated rejection (AMR) within 90 d after transplantation (AMR, 35% vs. 5%, p = 0.02). Luminex screening detected eight additional patients with DSA, among those one with AMR. Six of eight patients with Luminex-only-DSA reported no prior immunizing events. Death-censored graft survival was shorter only in patients with DSA and AMR (median, 1.7 yr instead of between 9.5 and 11.0 yr for patients without DSA or patients with DSA but no AMR, p < 0.001). Material costs per detected clinically relevant DSA were about 57% higher for Luminex screening, but this increase could be avoided by modifying the cut-off recommended by the manufacturer. Conclusively, specification of antibodies only in sera reactive in screening tests was cost-effective to prevent shortened graft survival. Preformed DSA were only harmful if AMR was diagnosed within 90 d after transplantation.

Acute rejection in low-toxicity regimens: clinical impact and risk factors in the Symphony study.

The Symphony study assessed whether mycophenolate mofetil (MMF)-based regimens containing reduced doses of adjunct immunosuppressants could reduce toxicity while maintaining efficacy. Here, we examined the impact of acute rejection and associated risk factors. The incidence of biopsy-proven acute rejection in the low-dose tacrolimus group was approximately half that of the standard-dose cyclosporine and low-dose cyclosporine groups, and a third of that in the low-dose sirolimus group. The low-dose cyclosporine group had more severe rejection episodes (≥grade II) compared with other groups. Acute rejection was associated with a 10 mL/min glomerular filtration rate (GFR) reduction and a 5.3% absolute increase in graft loss at 12 months. Overall, the highest GFR was found in both rejecters and non-rejecters receiving low-dose tacrolimus, both in an intent-to-treat analysis and in patients successfully treated according to the protocol. In Cox regression models, human leukocyte antigen (HLA) mismatches and expanded criteria donors increased the acute rejection risk, while recipient age, living related donor, and MMF dose were associated with a reduced risk. Acute rejection was associated with worse outcome but did not entirely explain the differences among the treatment groups. The 2 g MMF plus low-dose tacrolimus combination appears to be the most efficient of all regimens examined regardless of acute rejection.

The pharmacodynamic effect of sirolimus: individual variation of cytokine mRNA expression profiles in human whole blood samples.

Sirolimus (SRL) has become an important alternative to calcineurin inhibitors due to its unique mechanism of action. Since rejection and poor graft outcome are still frequent problems despite therapeutic-range blood concentrations, pharmacodynamic measurements of its immunosuppressive effects would be of great clinical value to optimize treatment in individual patients. We performed a human whole blood assay using real time cytokine RT-PCR for the pharmacodynamic assessment of SRL. IL-2, IL-4 and IL-6 mRNA levels were quantitatively determined upon T-cell-specific stimulation in healthy individuals (n=11; in vitro) and in kidney-transplant patients (n=3; ex vivo). Furthermore, IL-2 protein secretion and T-cell proliferation was measured. After 24h incubation we observed a stronger suppression of IL-2 and IL-4 mRNA expression upon SRL addition (p<0.005; p<0.005) versus 4h (p<0.05; p<0.05). SRL effects displayed a remarkable interindividual variation, which proved to be independent of the concentration applied. Notably, 3/11 and 2/11 individuals had unaffected IL-2 and IL-4 mRNA expression after 4h incubation with SRL, respectively. In contrast, a general suppression of IL-2 protein secretion and T-cell proliferation was induced. Analysis of kidney-transplant patients verified interindividual variation and proved comparability of in vitro and ex vivo effects. We describe an individual degree of SRL-sensitivity that may correlate with clinical efficacy. Rather than analysis of one single peak, we suggest determination of two absolute cytokine mRNA peak levels for the pharmacodynamic assessment of SRL. However, prospective clinical studies are necessary to determine whether individual degrees of SRL-sensitivity correlate with clinical outcome.

Slowing the progression of chronic allograft nephropathy by conversion from cyclosporine to tacrolimus: a randomized controlled trial.

BACKGROUND: Chronic allograft nephropathy (CAN) is a multifactorial process with immunologic and nonimmunologic factors. Because tacrolimus (Tac) has been ascribed a beneficial effect on some of these factors when compared to cyclosporine A (CyA), a randomized controlled trial was conducted to investigate whether conversion from CyA to Tac can ameliorate the progression of renal dysfunction in kidney transplant recipients (KTR) with CAN. METHODS: Of the 46 patients with biopsy-proven CAN enrolled, 24 were converted from CyA to Tac, whereas 22 patients were maintained on CyA. Serum creatinine (SCrea), lipid profiles and an antihypertensive score (AHS) were determined after 3, 6 and 12 months. AHS is based on the total number and dosages of antihypertensive medications used. SCrea and AHS were additionally evaluated at 36 months. RESULTS: SCrea was decreased in the Tac group (Tac(baseline): 297 +/- 67 micromol/L; Tac(6): 261+/- 70 micromol/L, P < 0.001; Tac(12): 254 +/- 55 micromol/L, P < 0.001; Tac(36): 255 +/- 78 micromol/L, P = 0.235), whereas a significant increase of SCrea was detected in the CyA group (CyA(baseline): 279 +/- 77 micromol/L, CyA(12): 333 +/- 98 micromol/L, P < 0.001; CyA(36): 317 +/- 89 micromol/L, P < 0.001). Compared to CyA therapy, SCrea in the Tac group declined after 12 and 36 months (P = 0.011 and 0.048, respectively) as well as AHS (Tac(12): 59 +/- 13, CyA(12): 83 +/- 14, P < 0.001; Tac(36): 60 +/- 12, CyA(36): 84 +/- 14, P < 0.001). LDL cholesterol was lower in the Tac group after 12 months (Tac(12): 2.5 +/- 0.5 mmol/L, CyA(12): 3.5 +/- 0.6 mmol/L, P < 0.001). CONCLUSION: Conversion from CyA to Tac in KTR with CAN improves allograft function, lowers blood pressure, and reduces LDL cholesterol. This superior profile may translate into improved long-term graft survival.

Cells differentiated from mouse embryonic stem cells via embryoid bodies express renal marker molecules.

Differentiation of mouse embryonic stem (ES) cells via embryoid bodies (EB) is established as a suitable model to study cellular processes of development in vitro. ES cells are known to be pluripotent because of their capability to differentiate into cell types of all three germ layers including germ cells. Here, we show that ES cells differentiate into renal cell types in vitro. We found that genes were expressed during EB cultivation, which have been previously described to be involved in renal development. Marker molecules characteristic for terminally differentiated renal cell types were found to be expressed predominantly during late stages of EB cultivation, while marker molecules involved in the initiation of nephrogenesis were already expressed during early steps of EB development. On the cellular level--using immunostaining--we detected cells expressing podocin, nephrin and wt-1, characteristic for differentiated podocytes and other cells, which expressed Tamm-Horsfall protein, a marker for distal tubule epithelial cells of kidney tissue. Furthermore, the proximal tubule marker molecules renal-specific oxido reductase, kidney androgen-related protein and 25-hydroxyvitamin D3alpha-hydroxylase were found to be expressed in EBs. In particular, we could demonstrate that cells expressing podocyte marker molecules assemble to distinct ring-like structures within the EBs. Because the differentiation efficiency into these cell types is still relatively low, application of fibroblast growth factor (FGF)-2 in combination with leukaemia inhibitory factor was tested for induction, but did not enhance ES cell-derived renal differentiation in vitro.

Time course and frequency of Epstein-Barr virus reactivation after kidney transplantation: linkage to renal allograft rejection.

The onset and frequency of Epstein-Barr virus (EBV) reactivation after kidney transplantation are unknown. By use of quantitative real-time polymerase chain reaction measurements, evidence of early EBV reactivation, occurring within the first week after the initiation of immunosuppressive therapy (median, 3 days), was observed in 13 of 23 patients, of whom 10 subsequently developed rejection episodes after 2-45 days (median, 5 days). By contrast, rejection was only diagnosed in 1 of 10 patients who did not show signs of viral reactivation. We suggest that EBV reactivation may induce a T cell response that, through the phenomenon of allo-cross-reactivity, could play a critical role in graft rejection.

Cooperative influence of the interleukin-6 promoter polymorphisms -597, -572 and -174 on long-term kidney allograft survival.

Recently, we demonstrated an association of the IL-6 promoter polymorphism at position -174 (G-->C) with kidney allograft survival whereby carriers of the -174GG genotype were identified as having superior graft survival. As two additional polymorphisms were discovered in the neighborhood at positions -572 (G-->C) and -597 (G-->A), respectively, and as functional studies revealed a cooperative impact of all three on the IL-6 gene transcription, we investigated whether there is a combined effect on kidney transplant outcome. We determined IL-6 promoter haplotypes -597 (G-->C)/-572 (G-->A)/-174 (G-->C)(-597/-572/-174haplotype) using a PCR system with sequence-specific primers in 158 patients after primary cadaveric kidney transplantation. We here show that the -597 and -174 polymorphism are in tight-linkage disequilibrium and that homozygous carriers of the GGG-597/-572/-174 haplotype (GGG/GGG genotype) have superior 3-year graft survival rates compared with the 8.0-fold increased risk of premature graft loss in all other patients. Interestingly, patients carrying the GGG/GCG genotype had the lowest allograft survival rate. Thus determination of the combined -597/-572/-174 genotype allows for further differentiation of -174GG patients into subgroups and consequently for a more accurate identification of patients at risk. Our results indicate that the three polymorphisms act in a cooperative fashion and we provide evidence for an exceptional clinical impact of the IL-6-597/-572/-174 genotype on the success of kidney transplantation.

Sensitivity of whole-blood T lymphocytes in individual patients to tacrolimus (FK 506): impact of interleukin-2 mRNA expression as surrogate measure of immunosuppressive effect.

BACKGROUND: To optimize immunosuppressive treatment in individual transplant patients, functional measurements of the effects of tacrolimus (FK 506) are of clinical importance. Previous investigations have demonstrated the occurrence of tacrolimus-resistant production of interleukin-2 (IL-2) in vitro, which may explain in part why rejection episodes are still a frequent problem despite attainment of therapeutic blood concentrations and HLA matching. However, an adequate surrogate marker to define the tacrolimus response in individual patients has not been established. METHODS: We investigated the immunosuppressive effects of tacrolimus on anti-CD3/anti-CD28 T-cell costimulation in a human whole-blood assay, analyzing T-cell proliferation, activation marker expression (CD25, CD69), IL-2 protein expression, and cytokine mRNA expression in vitro (n = 11 healthy individuals). We also quantified IL-2 mRNA expression in patients undergoing tacrolimus (n = 4) or cyclosporin A (CsA; n = 4) monotherapy before ex vivo living-donor kidney transplantation. RESULTS: T-cell proliferation; CD25, CD69, and IL-2 concentrations; and IL-4 mRNA were significantly decreased in vitro. In contrast, cytokine mRNA profiles revealed variable tacrolimus sensitivity. Whole-blood samples from 3 of 11 healthy individuals demonstrated marked suppression of IL-2 mRNA expression (>50%) when tacrolimus was administered in vitro. When CsA was added to whole-blood cultures, the influence on IL-2 mRNA expression was comparable to that of tacrolimus in 9 of 11 individuals. Two individuals responded conversely, indicating that differences in the in vitro response to tacrolimus and CsA among individuals may be attributable to potential heterogeneity in the involvement of the CD28 pathway. Kinetic profiles of IL-2 mRNA expression also revealed individually distinct degrees of calcineurin inhibitor sensitivity in patients undergoing tacrolimus or CsA monotherapy before living-donor kidney transplantation. CONCLUSIONS: Our results suggest an individual degree of calcineurin inhibitor sensitivity of activated whole-blood lymphocytes based on IL-2 mRNA expression. Our approach is potentially valuable for identifying transplant patients in whom IL-2 mRNA expression is unaffected or even enhanced after initiation of immunosuppressive therapy. Such individuals may be less sensitive to the immunosuppressive agent and therefore at increased risk of transplant rejection. Prospective studies are necessary to determine the correlation of IL-2 mRNA expression with the clinical risk of transplant rejection.

Molecular parameters for precise diagnosis of asymptomatic Epstein-Barr virus reactivation in healthy carriers.

Asymptomatic Epstein-Barr virus (EBV) reactivations periodically occur in oral mucosa-associated lymphoid tissues. Until now, EBV reactivation has been diagnosed by serologic profiles that suggest virus replication. Serologic responses, however, are delayed and do not necessarily indicate ongoing replicative activity. The aim of the present study was to establish in healthy carriers parameters for a molecular diagnosis of reactivated EBV infection. Recent studies emphasized the association of an increase in peripheral-B-cell viral load with replicative activity at remote sites. Therefore, real-time PCR was used to quantitate EBV genomes in the peripheral blood mononuclear cells (PBMC) (viral load) and plasma samples (viremia) of 22 healthy EBV-seropositive blood donors over a period of 15 months. Furthermore, transcription of the immediate-early gene encoding BZLF1 was investigated in the PBMC of all volunteers. Serology suggested reactivation in nine donors, of whom all but one showed at least once a significant increase in viral load. Another five individuals also exhibited significant changes in viral load but no serologic response. Of the 13 volunteers with significant increases in viral load, 6 had a period of viremia accompanying the rise in viral load. A stable viral load without viremia and negative serology was seen in eight adults. BZLF1 mRNA was undetectable throughout. We conclude that for healthy subjects serology underestimates the frequency of asymptomatic EBV reactivations. Prospective examination of peripheral viral load and viremia is suitable for the exact diagnosis of EBV reactivation, which might be of advantage for immunocompromised patients in whom EBV reactivations are considerably harmful.

Individual variability in cyclosporin A sensitivity: the assessment of functional measures on CD28-mediated costimulation of human whole blood T lymphocytes.

The quantitative analysis of cyclosporin A (CsA) effects might be helpful for optimizing immunosuppressive treatment after allogeneic organ transplantation in individual patients, as rejection can occur despite the existence of CsA blood levels within therapeutic ranges. Previous investigations found that costimulation of the CD28 pathway generally mediates CsA-resistant proliferation of T cell receptor (TCR)-activated T lymphocytes. However, here we describe considerable interindividual variation regarding the immunosuppressive effects of CsA (1000 microg/L) on anti-CD3/CD28 T cell costimulation in a human whole blood assay. In the in vitro study, we found a significant reduction of T cell proliferation, activation marker expression (CD25, CD69) on the T cell surface, and interleukin-2 (IL-2) protein expression in whole blood samples of all healthy subjects (n = 11). However, the investigation of cytokine mRNA profiles revealed variable results of in vitro CsA sensitivity. Whole blood samples of 3 of 11 healthy individuals demonstrated a marked suppression of IL-2 mRNA expression (>50%) and a partial inhibition of IL-4, interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) mRNA expression on addition of CsA. In contrast, the remaining 8 healthy individuals had cytokine mRNA expression levels that were unaffected or even increased when CsA was administered in vitro. In patients undergoing CsA monotherapy (ex vivo study, n = 9), we found a significant suppression of IL-2 mRNA levels in 4 of 9 patients ex vivo. Thus, we cannot confirm a universal CsA resistance of T cells on anti-CD3/CD28 costimulation. Instead, our results suggest an individual degree of CsA sensitivity that might be more consistent with clinical experience. Prospective studies are necessary to determine if individual degrees of CsA sensitivity correlate with clinical events and are associated with a low or high risk of transplant rejection.

[CO2 angiography of transplanted kidneys]. / CO2-Angiographie von Transplantatnierenarterien.

PURPOSE: To compare image quality and diagnostic accuracy of carbon dioxide (CO2) and iodinated contrast medium as a contast medium in renal transplant artery angiography. MATERIAL AND METHODS: In this prospective, non-randomized, intra-individual study, we examined 17 patients. Digital subtraction angiography (DSA) was performed first with CO2 to find the optimal projection. Then at least one confirming run was performed with CM ("gold standard"). The quality of the angiographic studies with CO2 and CM and their diagnostic accuracy were compared. Blood creatinine levels were monitored during three days after angiography. RESULTS: Three of four renal transplant artery stenoses were diagnosed correctly with CO2. The false-negative CO2 angiography was due to poor contrast. There were no false-positive results with CO2. Regardless the inferior image quality of CO2 angiography, its positive predictive value was 100%. Renal function was not compromised. CONCLUSION: The primary use of CO2 as a contrast medium for the angiographic evaluation of renal transplant arteries is feasible and practical. It reduces the amount of CM needed. However, in order to confirm the diagnosis, at least one additional series with CM should be performed.

The kidney as a second site of human C-reactive protein formation in vivo.

C-reactive protein (CRP) is the main acute phase reactant in humans. Its production is presumably restricted to the liver but extrahepatic expression by inflamed tissue has not been studied in detail. By real-time PCR and immunohistochemistry we here show that renal cortical tubular epithelial cells (TEC) express CRP mRNA and protein within 6 h after stimulation with conditioned medium (CM) or IL-6, but not IL-1alpha or TNF-alpha. Western blot analysis with monoclonal anti-CRP antibody that recognizes native CRP revealed protein secretion into supernatants of CM-stimulated TEC cultures. While hepatoma-derived Hep3B cells could be induced similarly, peripheral blood mononuclear cells could not. CRP mRNA transcripts were observed in nephrectomized renal allografts with severe acute rejection but not with chronic allograft nephropathy (CAN). Of 19 needle biopsies of acutely rejecting kidney transplants, 15 demonstrated CRP mRNA production with the relative expression levels increasing with the severity of rejection. On the other hand, none of 7 graft biopsies with acute tubular necrosis (ATN) or CAN showed CRP mRNA expression. By using monoclonal anti-CRP antibody, cortical tubules as well as glomerular cells were shown to locally express CRP in rejecting, but not in ATN kidneys. We conclude that inflamed kidneys represent a so far unknown site of CRP formation in vivo. These data shed new light on the acute phase reaction not merely representing a systemic inflammatory pathway but probably being part of the local immune response.

Delayed cytokine mRNA expression kinetics after T-lymphocyte costimulation: a quantitative measure of the efficacy of cyclosporin A-based immunosuppression.

BACKGROUND: Because cyclosporin A (CsA) and glucocorticoids inhibit the production of interleukin-2 (IL-2) and other cytokines, quantitative analysis of cytokine mRNA might constitute a pharmacodynamic measure for immunosuppressive drug effects. We investigated whether immunosuppressive drugs influence cytokine mRNA expression kinetics during T-cell costimulation. METHODS: We used a human whole blood assay to determine basal (unstimulated) IL-2, IL-4, and tumor necrosis factor-alpha (TNF-alpha) mRNA concentrations and expression kinetics after anti-CD3/anti-CD28 monoclonal antibody costimulation in kidney transplant recipients undergoing CsA-based immunosuppressive triple therapy and in healthy controls (ex vivo study I). The effect of CsA on IL-2 mRNA expression kinetics was also determined ex vivo in patients undergoing CsA monotherapy (ex vivo study II) and after in vitro addition of CsA. RESULTS: In ex vivo study I, basal TNF-alpha mRNA but not IL-2 and IL-4 mRNA was decreased in kidney transplant patients. We observed shifts in peak IL-2 and IL-4 (from 8 to 24 h) and TNF-alpha (from 4 to 8 h of costimulation) mRNA expression in kidney transplant patients after T-cell costimulation. In patients undergoing CsA monotherapy (ex vivo study II), the inhibitory effect of CsA was detectable as an individually delayed increase in IL-2 mRNA during costimulation. In vitro addition of CsA also induced a dose-independent displacement of IL-2 mRNA expression kinetics (i.e., a delay). CONCLUSIONS: A delayed increase in cytokine mRNA expression during T-cell costimulation may represent a sensitive effect of immunosuppression. The single analysis of one absolute or peak mRNA value could be misleading. For prospective studies involving measurement of cytokine mRNA, we therefore suggest the parameter "area of cytokine mRNA expression over time", which should include absolute cytokine mRNA values at two different time points of mRNA kinetics.

The interleukin-6 -174promoter polymorphism is associated with long-term kidney allograft survival.

BACKGROUND: Th1-dependent effector mechanisms may be responsible for allograft rejection. Recently, interleukin-6 (IL-6) has been shown to antagonize CD4+ T cells to effector Th2 cells and, in the process, differentiate them into Th1 cells. METHODS: To assess the role of IL-6 in long-term allograft survival, 158 patients after first cadaveric kidney transplantation were analyzed for the biallelic -174G-->C promoter polymorphism of the IL-6 gene. RESULTS: Carriers of the -174C-allele (genotype GC/CC) had an inferior three-year graft survival (71/104 = 68.3%; P = 0.0059) with a 3.7-fold increased relative risk of graft loss compared to carriers of the -174GG-genotype (48/54 = 88.9%). The -174GC/CC-genotype retained its negative impact on graft survival when other established prognostic factors and further cytokine polymorphisms (-308TNF-alpha, TGF-beta1 codon 10 & 25, -592/-819/-1082IL-10 and +874IFN-gamma) were considered simultaneously. CONCLUSIONS: Since the clinical impact on transplant outcome seems as important as matching for histocompatibility antigens, genotyping of the IL-6 -174polymorphism may offer a new method for identifying patients at increased risk of allograft loss.