Discrepancies in clavicle-to-carotid bifurcation length measurements for transcarotid artery revascularization using different imaging modalities.

OBJECTIVE: Transcarotid artery revascularization (TCAR) has emerged as an effective method for carotid artery stenting. However, anatomic eligibility for TCAR is most often limited by an inadequate clavicle-to-carotid bifurcation length of <5 cm. Preoperative clavicle-to-carotid bifurcation distances may be underestimated when using conventional straight-line measurements on computed tomographic angiography (CTA) imaging. We therefore compared clavicle-to-carotid bifurcation lengths as measured by straight-line CTA, center-line CTA, and intraoperative duplex ultrasound (US), to assess potential differences. METHODS: We conducted a single-center, retrospective review of consecutive TCAR procedures performed between 2016 and 2019 for atherosclerotic carotid disease. For each patient, we compared clavicle-to-carotid bifurcation lengths measured by straight-line CTA, center-line CTA using TeraRecon image reconstruction, and intraoperative duplex US with neck extension and rotation. We further assessed patient and imaging characteristics in individuals with a ≥0.5 cm difference among the measurement methods. In particular, common carotid artery (CCA) tortuosity, defined as the inability to visualize the entire CCA from clavicle to carotid bifurcation on both a single coronal and sagittal imaging cut, was examined as a contributing factor for these discrepancies. RESULTS: Of the 70 TCAR procedures identified, 46 had all three imaging modalities available for review. The median clavicle-to-carotid bifurcation length was found to be 6.4 cm (interquartile range [IQR], 5.4-6.7 cm) on straight-line CTA, 7.0 cm (IQR, 6.0-7.5 cm) on intraoperative duplex US, and 7.2 cm (IQR, 6.5-7.5 cm) on center-line CTA (P < .001). Patients with a ≥0.5 cm difference between their straight-line CTA and either their intraoperative duplex US or center-line CTA measurements were more likely to have tortuous CCAs (60.0% vs 19.1%; P = .01; 51.4% vs 0.0%; P = .01). There were no notable differences in age, gender, prior neck/cervical spine surgery, or neck immobility among these individuals. In patients with tortuous CCAs, duplex US and center-line CTA measurements added 1.0 cm (IQR, 0.6-1.5 cm) and 1.1 cm (IQR, 0.9-1.6 cm) more in length than straight-line CTA measurements, respectively. There was a strong linear correlation between the additional lengths provided by duplex US measurements and those provided by center-line CTA measurements for each individual within the tortuous CCA group (r = 0.83). CONCLUSIONS: The use of straight-line CTA during preoperative planning can underestimate the clavicle-to-carotid bifurcation lengths in patients undergoing carotid revascularization, particularly in those with tortuous CCAs. Both duplex US performed with extended-neck surgical positioning and center-line CTA provide similar and longer carotid length measurements, and should be utilized in patients with tortuous carotid vessels to better determine TCAR anatomic eligibility.

Racial Differences in Isolated Aortic, Concomitant Aortoiliac, and Isolated Iliac Aneurysms: This is a Retrospective Observational Study.

OBJECTIVE: Our aim was to describe the racial and ethnic differences in presentation, baseline and operative characteristics, and outcomes after aortoiliac aneurysm repair. SUMMARY OF BACKGROUND DATA: Previous studies have demonstrated racial and ethnic differences in prevalence of abdominal aortic aneurysms and showed more complex iliac anatomy in Asian patients. METHODS: We identified all White, Black, Asian, and Hispanic patients undergoing aortoiliac aneurysm repair in the VQI from 2003 to 2019. We compared baseline comorbidities, operative characteristics, and perioperative outcomes by race and ethnicity. RESULTS: In our 60,435 patient cohort, Black patients, followed by Asian patients, were most likely to undergo repair for aortoiliac (W:23%, B:38%, A:31%, H:22%, P < 0.001) and isolated iliac aneurysms (W:1.0%, B:3.1%, A:1.5%, H:1.6%, P < 0.001), and White and Hispanic patients were most likely to undergo isolated aortic aneurysm repair (W:76%, B:59%, A:68%, H:76%, P < 0.001). Black patients were more likely to undergo symptomatic repair and underwent rupture repair at a smaller aortic diameter. The iliac aneurysm diameter was largest in Black and Asian patients. Asian patients were most likely to have aortic neck angulation above 60 degree, graft oversizing above 20%, and completion endoleaks. Also, Asian patients were more likely to have a hypogastric artery aneurysm and to undergo hypogastric coiling. CONCLUSION: Asian and Black patients were more likely to undergo repair for aortoiliac and isolated iliac aneurysms compared to White and Hispanic patients who were more likely to undergo repair for isolated aortic aneurysms. Moreover, there were significant racial differences in the demographics and anatomic characteristics that could be used to inform operative approach and device development.

Immunohistochemical analysis of Tn antigen expression in colorectal adenocarcinoma and precursor lesions.

BACKGROUND: The Tn antigen (CD175) is an O-glycan expressed in various types of human adenocarcinomas, including colorectal cancer (CRC), though prior studies have relied heavily upon poorly characterized in-house generated antibodies and lectins. In this study, we explored Tn expression in CRC using ReBaGs6, a well-characterized recombinant murine antibody with high specificity for clustered Tn antigen. METHODS: Using well-defined monoclonal antibodies, expression patterns of Tn and sialylated Tn (STn) antigens were characterized by immunostaining in CRC, in matched peritumoral [transitional margin (TM)] mucosa, and in normal colonic mucosa distant from the tumor, as well as in adenomas. Vicia villosa agglutinin lectin was used to detect terminal GalNAc expression. Histo-scoring (H scoring) of staining was carried out, and pairwise comparisons of staining levels between tissue types were performed using paired samples Wilcoxon rank sum tests, with statistical significance set at 0.05. RESULTS: While minimal intracellular Tn staining was seen in normal mucosa, significantly higher expression was observed in both TM mucosa (p < 0.001) and adenocarcinoma (p < 0.001). This pattern was reflected to a lesser degree by STn expression in these tissue types. Interestingly, TM mucosa demonstrates a Tn expression level even higher than that of the adenocarcinoma itself (p = 0.019). Colorectal adenomas demonstrated greater Tn and STn expression relative to normal mucosa (p < 0.001 and p = 0.012, respectively). CONCLUSIONS: In summary, CRC is characterized by alterations in Tn/STn antigen expression in neoplastic epithelium as well as peritumoral benign mucosa. Tn/STn antigens are seldom expressed in normal mucosa. This suggests that TM mucosa, in addition to CRC itself, represents a source of glycoproteins rich in Tn that may offer future biomarker targets.

SAR439859, a Novel Selective Estrogen Receptor Degrader (SERD), Demonstrates Effective and Broad Antitumor Activity in Wild-Type and Mutant ER-Positive Breast Cancer Models.

Primary treatment for estrogen receptor-positive (ER+) breast cancer is endocrine therapy. However, substantial evidence indicates a continued role for ER signaling in tumor progression. Selective estrogen receptor degraders (SERD), such as fulvestrant, induce effective ER signaling inhibition, although clinical studies with fulvestrant report insufficient blockade of ER signaling, possibly due to suboptimal pharmaceutical properties. Furthermore, activating mutations in the ER have emerged as a resistance mechanism to current endocrine therapies. New oral SERDs with improved drug properties are under clinical investigation, but the biological profile that could translate to improved therapeutic benefit remains unclear. Here, we describe the discovery of SAR439859, a novel, orally bioavailable SERD with potent antagonist and degradation activities against both wild-type and mutant Y537S ER. Driven by its fluoropropyl pyrrolidinyl side chain, SAR439859 has demonstrated broader and superior ER antagonist and degrader activities across a large panel of ER+ cells, compared with other SERDs characterized by a cinnamic acid side chain, including improved inhibition of ER signaling and tumor cell growth. Similarly, in vivo treatment with SAR439859 demonstrated significant tumor regression in ER+ breast cancer models, including MCF7-ESR1 wild-type and mutant-Y537S mouse tumors, and HCI013, a patient-derived tamoxifen-resistant xenograft tumor. These findings indicate that SAR439859 may provide therapeutic benefit to patients with ER+ breast cancer, including those who have resistance to endocrine therapy with both wild-type and mutant ER.

Multi-Center Analysis of Liver Transplantation for Combined Hepatocellular Carcinoma-Cholangiocarcinoma Liver Tumors.

BACKGROUND: Combined hepatocellular-cholangiocarcinoma liver tumors (cHCC-CCA) with pathologic differentiation of both hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma within the same tumor are not traditionally considered for liver transplantation due to perceived poor outcomes. Published results are from small cohorts and single centers. Through a multicenter collaboration, we performed the largest analysis to date of the utility of liver transplantation for cHCC-CCA. STUDY DESIGN: Liver transplant and resection outcomes for HCC (n = 2,998) and cHCC-CCA (n = 208) were compared in a 12-center retrospective review (2009 to 2017). Pathology defined tumor type. Tumor burden was based on radiologic Milan criteria at time of diagnosis and applied to cHCC-CCA for uniform analysis. Kaplan-Meier survival curves and log-rank test were used to determine overall survival and disease-free survival. Cox regression was used for multivariate survival analysis. RESULTS: Liver transplantation for cHCC-CCA (n = 67) and HCC (n = 1,814) within Milan had no significant difference in overall survival (5-year cHCC-CCA 70.1%, HCC 73.4%, p = 0.806), despite higher cHCC-CCA recurrence rates (23.1% vs 11.5% 5 years, p < 0.001). Irrespective of tumor burden, cHCC-CCA tumor patient undergoing liver transplant had significantly superior overall survival (p = 0.047) and disease-free survival (p < 0.001) than those having resection. For cHCC-CCA within Milan, liver transplant was associated with improved disease-free survival over resection (70.3% vs 33.6% 5 years, p < 0.001). CONCLUSIONS: Regardless of tumor burden, outcomes after liver transplantation are superior to resection for patients with cHCC-CCA. Within Milan criteria, liver transplant for cHCC-CCA and HCC result in similar overall survival, justifying consideration of transplantation due to the higher chance of cure with liver transplantation in this traditionally excluded population.

A fast, simple, and cost-effective method of expanding patient-derived xenograft mouse models of pancreatic ductal adenocarcinoma.

BACKGROUND: Patient-derived xenograft (PDX) mouse models of cancer have been recognized as better mouse models that recapitulate the characteristics of original malignancies including preserved tumor heterogeneity, lineage hierarchy, and tumor microenvironment. However, common challenges of PDX models are the significant time required for tumor expansion, reduced tumor take rates, and higher costs. Here, we describe a fast, simple, and cost-effective method of expanding PDX of pancreatic ductal adenocarcinoma (PDAC) in mice. METHODS: We used two established frozen PDAC PDX tissues (derived from two different patients) and implanted them subcutaneously into SCID mice. After tissues reached 10-20 mm in diameter, we performed survival surgery on each mouse to harvest 90-95% of subcutaneous PDX (incomplete resection), allowing the remaining 5-10% of PDX to continue growing in the same mouse. RESULTS: We expanded three consecutive passages (P1, P2, and P3) of PDX in the same mouse. Comparing the times required for in vivo expansion, P2 and P3 (expanded through incomplete resection) grew 26-60% faster than P1. Moreover, such expanded PDX tissues were successfully implanted orthotopically into mouse pancreases. Within 20 weeks using only 14 mice, we generated sufficient PDX tissue for future implantation of 200 mice. Our histology study confirmed that the morphologies of cancer cells and stromal structures were similar across all three passages of subcutaneous PDX and the orthotopic PDX and were reflective of the original patient tumors. CONCLUSIONS: Taking advantage of incomplete resection of tumors associated with high local recurrence, we established a fast method of PDAC PDX expansion in mice.

O-glycan recognition and function in mice and human cancers.

Protein glycosylation represents a nearly ubiquitous post-translational modification, and altered glycosylation can result in clinically significant pathological consequences. Here we focus on O-glycosylation in tumor cells of mice and humans. O-glycans are those linked to serine and threonine (Ser/Thr) residues via N-acetylgalactosamine (GalNAc), which are oligosaccharides that occur widely in glycoproteins, such as those expressed on the surfaces and in secretions of all cell types. The structure and expression of O-glycans are dependent on the cell type and disease state of the cells. There is a great interest in O-glycosylation of tumor cells, as they typically express many altered types of O-glycans compared with untransformed cells. Such altered expression of glycans, quantitatively and/or qualitatively on different glycoproteins, is used as circulating tumor biomarkers, such as CA19-9 and CA-125. Other tumor-associated carbohydrate antigens (TACAs), such as the Tn antigen and sialyl-Tn antigen (STn), are truncated O-glycans commonly expressed by carcinomas on multiple glycoproteins; they contribute to tumor development and serve as potential biomarkers for tumor presence and stage, both in immunohistochemistry and in serum diagnostics. Here we discuss O-glycosylation in murine and human cells with a focus on colorectal, breast, and pancreatic cancers, centering on the structure, function and recognition of O-glycans. There are enormous opportunities to exploit our knowledge of O-glycosylation in tumor cells to develop new diagnostics and therapeutics.

Validation of a predictive modeling approach to demonstrate the relative efficacy of three different schedules of the AKT inhibitor AZD5363.

PURPOSE: Intermittent dosing of inhibitors of the PI3K/AKT/mTOR network offers the potential to maximize the therapeutic margin. Here, we validate a predictive modeling approach to establish the relative efficacy of continuous and two intermittent dosing schedules of the AKT inhibitor AZD5363. METHODS: A mathematical model of pharmacokinetics, pharmacodynamics and anti-tumor effect was constructed based upon experimental data from dosing regimens that give constant and transient inhibition of the AKT pathway. RESULTS: Continuous and intermittent dosing of AZD5363 inhibited growth of BT474c xenografts and caused dose- and time-dependent inhibition of AKT substrate phosphorylation. Both dosing schedules inhibited proliferation, but a higher intermittent dose also induced apoptosis. The mathematical model described this pharmacodynamic and efficacy data well, for both monotherapy and combination dosing with docetaxel, and predicted that equivalent efficacy could be achieved at 1.3- and 1.7× continuous dose when AZD5363 was dosed intermittently for 4 and 2 days per week, respectively. These predictions were confirmed in two independent xenograft models. Moreover, the model also correctly predicted the relative efficacy of three different sequences of intermittent dosing of AZD5363 with docetaxel. CONCLUSIONS: Equivalent anti-tumor activity to continuous dosing can be achieved at modestly increased intermittent doses of AZD5363. These intermittent dosing regimens may potentially overcome tolerability issues seen with continuous dosing and enable greater flexibility of dosing schedule in combination with other agents, including chemotherapy.

Probing ADAMTS13 substrate specificity using phage display.

Von Willebrand factor (VWF) is a large, multimeric protein that regulates hemostasis by tethering platelets to the subendothelial matrix at sites of vascular damage. The procoagulant activity of plasma VWF correlates with the length of VWF multimers, which is proteolytically controlled by the metalloprotease ADAMTS13. To probe ADAMTS13 substrate specificity, we created phage display libraries containing randomly mutated residues of a minimal ADAMTS13 substrate fragment of VWF, termed VWF73. The libraries were screened for phage particles displaying VWF73 mutant peptides that were resistant to proteolysis by ADAMTS13. These peptides exhibited the greatest mutation frequency near the ADAMTS13 scissile residues. Kinetic assays using mutant and wild-type substrates demonstrated excellent agreement between rates of cleavage for mutant phage particles and the corresponding mutant peptides. Cleavage resistance of selected mutations was tested in vivo using hydrodynamic injection of corresponding full-length expression plasmids into VWF-deficient mice. These studies confirmed the resistance to cleavage resulting from select amino acid substitutions and uncovered evidence of alternate cleavage sites and recognition by other proteases in the circulation of ADAMTS13 deficient mice. Taken together, these studies demonstrate the key role of specific amino acids residues including P3-P2' and P11', for substrate specificity and emphasize the importance in flowing blood of other ADAMTS13-VWF exosite interactions outside of VWF73.

Targeting Wnt-driven cancer through the inhibition of Porcupine by LGK974.

Wnt signaling is one of the key oncogenic pathways in multiple cancers, and targeting this pathway is an attractive therapeutic approach. However, therapeutic success has been limited because of the lack of therapeutic agents for targets in the Wnt pathway and the lack of a defined patient population that would be sensitive to a Wnt inhibitor. We developed a screen for small molecules that block Wnt secretion. This effort led to the discovery of LGK974, a potent and specific small-molecule Porcupine (PORCN) inhibitor. PORCN is a membrane-bound O-acyltransferase that is required for and dedicated to palmitoylation of Wnt ligands, a necessary step in the processing of Wnt ligand secretion. We show that LGK974 potently inhibits Wnt signaling in vitro and in vivo, including reduction of the Wnt-dependent LRP6 phosphorylation and the expression of Wnt target genes, such as AXIN2. LGK974 is potent and efficacious in multiple tumor models at well-tolerated doses in vivo, including murine and rat mechanistic breast cancer models driven by MMTV-Wnt1 and a human head and neck squamous cell carcinoma model (HN30). We also show that head and neck cancer cell lines with loss-of-function mutations in the Notch signaling pathway have a high response rate to LGK974. Together, these findings provide both a strategy and tools for targeting Wnt-driven cancers through the inhibition of PORCN.

Monoclonal antibody lead characterization: in vitro and in vivo methods.

This chapter describes in vitro and in vivo methods to characterize a lead monoclonal antibody candidate in the drug discovery setting. Approaches to characterize monoclonal antibody specificity, heavy and light chain composition, and antibody mode of action including the ability to mediate secretion of effector molecules, inhibit cell proliferation, induce apoptosis, or elicit antibody effector function are described. ELISA and flow cytometry based methods, as well as in vitro assays to assess for cell proliferation, ADCC, and CDC are detailed.In addition, both subcutaneous and orthotopic in vivo tumor xenograft models to assess antibody efficacy are described. The xenograft tumor model is a valuable tool for assessing the therapeutic activity of a monoclonal antibody drug candidate. Xenograft models are generated by the implantation of tumor cells or tumor fragments of human origin into immune-compromised mice or rats. This allows for fast and efficient in vivo evaluation of an antibody drug candidate in human cancer models. Here, we describe the procedures for generating preclinical animal tumor models frequently employed in the preclinical drug discovery setting.

Prolonged diabetes reversal after intraportal xenotransplantation of wild-type porcine islets in immunosuppressed nonhuman primates.

Cell-based diabetes therapy requires an abundant cell source. Here, we report reversal of diabetes for more than 100 d in cynomolgus macaques after intraportal transplantation of cultured islets from genetically unmodified pigs without Gal-specific antibody manipulation. Immunotherapy with CD25-specific and CD154-specific monoclonal antibodies, FTY720 (or tacrolimus), everolimus and leflunomide suppressed indirect activation of T cells, elicitation of non-Gal pig-specific IgG antibody, intragraft expression of proinflammatory cytokines and invasion of infiltrating mononuclear cells into islets.

Heart transplantation in baboons using alpha1,3-galactosyltransferase gene-knockout pigs as donors: initial experience.

Hearts from alpha1,3-galactosyltransferase knockout pigs (GalT-KO, n = 8) were transplanted heterotopically into baboons using an anti-CD154 monoclonal antibody-based regimen. The elimination of the galactose-alpha1,3-galactose epitope prevented hyperacute rejection and extended survival of pig hearts in baboons for 2-6 months (median, 78 d); the predominant lesion associated with graft failure was a thrombotic microangiopathy, with resulting ischemic injury. There were no infectious complications directly related to the immunosuppressive regimen. The transplantation of hearts from GalT-KO pigs increased graft survival over previous studies.

T cells from presensitized donors fail to cause graft-versus-host disease in a pig-to-mouse xenotransplantation model.

BACKGROUND: The ability of T cells from pigs, the most suitable donors for clinical xenotransplantation, to induce graft-versus-host disease (GVHD) and to facilitate hematopoietic cell engraftment in highly disparate xenogeneic recipients remains unclear. In this article, the authors address these questions in a presensitized pig-to-mouse transplantation model using porcine cytokine-transgenic mice. METHODS: Swine donors were presensitized by mouse skin grafting and boosted by the injection of mouse cells after the skin graft was rejected. Porcine peripheral blood mononuclear cells (PBMC) and splenocytes were collected at various times after mouse skin grafting, and their potential to induce GVHD and to facilitate donor hematopoietic cell engraftment in conditioned murine recipients was evaluated. RESULTS: Presensitization of donor pigs resulted in marked enhancement of anti-mouse responses, as reflected in augmented anti-mouse mixed lymphocyte responses, cell-mediated cytotoxicity, and antibody production. However, injection of high numbers of PBMC and splenocytes (>1 x 10(8)) with bone marrow cells from the presensitized pigs failed to induce detectable GVHD or long-term chimerism in mice that were treated with depleting anti-T-cell and natural killer cell antibodies, cobra venom factor, medronate-liposomes, and 4 Gy of whole-body and 7 Gy of thymic irradiation. Histologic analysis revealed no mononuclear cell infiltration or GVHD-associated lesions in the liver, intestine, lungs, or skin of the mouse recipients. Furthermore, the recipient mice had no detectable T cells or anti-pig immunoglobulin G antibodies in the blood by 6 weeks after injection of porcine cells. CONCLUSION: These results demonstrate that porcine T-cell function is severely impaired in the xenogeneic murine microenvironment.

Thrombotic microangiopathy and graft arteriopathy in pig hearts following transplantation into baboons.

BACKGROUND: Acute humoral xenograft rejection (AHXR) is an immunologic barrier in pig-to-baboon organ transplantation (Tx). We report microvascular thrombosis and myocardial necrosis in a series of cardiac xenografts. METHODS: Ten baboons underwent heterotopic heart Tx from pigs transgenic for human decay-accelerating factor. Recipients were treated with soluble Gal glycoconjugates and multiple immunosuppressive agents. Grafts were removed when palpable contractions stopped. Stained tissue sections from harvested grafts were analyzed by light and fluorescence microscopy. RESULTS: Xenograft survival ranged from 4 to 139 (mean 37, median 27) days. Some histology was typical for AHXR (n = 4; median survival 22 days). Hemorrhage and edema were only focal in the longer-surviving grafts (n = 4, median survival 54 days). All grafts had multiple platelet-rich fibrin thrombi occluding myocardial vessels. Ischemic damage was manifested by contraction band necrosis in four grafts, myocytolysis in eight, coagulative necrosis in nine, and patchy myocyte dropout in all grafts. A notable paucity of interstitial mononuclear cells was observed in all grafts. Marked intimal thickening resembling that of allograft vasculopathy was observed in one graft. Immunofluorescence showed immunoglobulin (Ig)G and/or IgM deposition in five grafts. Multivessel C4d deposition appeared in seven grafts. Significant C3 deposition was absent. CONCLUSIONS: Cardiac xenograft survival in the pig-to-baboon model can be significantly prolonged by vigorous immunosuppressive treatment of recipient animals. Additional efforts to block humoral activation of graft endothelial cells and/or to overcome species-specific molecular coagulation pathway incompatibilities may prevent the development of microvascular thrombosis and myocardial infarction. Cardiac xenograft vasculopathy (chronic rejection) can occur with prolonged graft survival.

alpha1,3-Galactosyltransferase gene-knockout miniature swine produce natural cytotoxic anti-Gal antibodies.

BACKGROUND: The expression of galactose alpha 1,3 galactose (Gal) in pigs has proved a barrier to xenotransplantation. Miniature swine lacking Gal (Gal pigs) have been produced by nuclear transfer/embryo transfer. METHODS: The tissues of five Gal pigs of SLA dd haplotype (SLA) were tested for the presence of Gal epitopes by staining with the Griffonia simplicifolia IB4 lectin. Their sera were tested by flow cytometry for binding of IgM and IgG to peripheral blood mononuclear cells (PBMC) from wild-type (Gal) SLA-matched pigs; serum cytotoxicity was also assessed. The cellular responses of PBMC from Gal swine toward Gal SLA-matched PBMC were tested by mixed leukocyte reaction and cell-mediated lympholysis assays. RESULTS: None of the tissues tested showed Gal expression. Sera from all five Gal pigs manifested IgM binding to Gal pig PBMC, and sera from three showed IgG binding. In all five cases, cytotoxicity to Gal cells could be demonstrated, which was lost after treatment of the sera with dithiothreitol, indicating IgM antibody-mediated cytotoxicity. PBMC from Gal swine had no proliferative or cytolytic T-cell response toward Gal SLA-matched PBMC. CONCLUSIONS: Gal pigs do not express Gal epitopes and develop anti-Gal antibodies that are cytotoxic to Gal pig cells. The absence of an in vitro cellular immune response between Gal and Gal pigs is related to their identical SLA haplotype and indicates the absence of immunogenicity of Gal in T-cell responses. The model of Gal organ transplantation into a Gal SLA-matched recipient would be a valuable large animal model in the study of accommodation or B-cell tolerance.

Suppression of natural and elicited antibodies in pig-to-baboon heart transplantation using a human anti-human CD154 mAb-based regimen.

Natural and elicited antipig antibodies (Abs) lead to acute humoral xenograft rejection (AHXR). Ten baboons underwent heterotopic heart transplantation (Tx) from human decay-accelerating factor (hDAF) pigs. Depletion of anti-Galalpha1, 3Gal (Gal) Abs was achieved by the infusion of a Gal glycoconjugate from day-1. Immunosuppression included induction of antithymocyte globulin, thymic irradiation, and cobra venom factor, and maintenance with a human antihuman CD154 mAb, mycophenolate mofetil, and methylprednisolone; heparin and prophylactic ganciclovir were also administered. Pig heart survival ranged from 4 to 139 (mean 37, median 27) days, with three functioning for >50 days. Graft failure (n = 8) was from classical AHXR [4], thrombotic microangiopathy [3], or intragraft thrombosis [1], with death (n = 2) from pneumonia [1], or possible drug toxicity (with features of thrombotic microangiopathy) [1]. Anti-Gal Abs (in microg/mL) were depleted by Gal glycoconjugate before graft implantation from means of 41.3 to 6.3 (IgM) and 12.4-4.6 (IgG), respectively, and at graft excision were 6.3 and 1.7 microg/mL, respectively. No elicited Abs developed, and no cellular infiltration was seen. The treatment regimen was effective in maintaining low anti-Gal Ab levels and in delaying or preventing AHXR. The combination of costimulatory blockade and heparin with Tx of a Gal-negative pig organ may prolong graft survival further.

Pathology of xenograft rejection: a commentary.

Trends in solid organ xenograft pathology are presented, with the focus on pig-to-nonhuman primate models. A simplified classification of rejection is followed, including hyperacute rejection (HAR), acute humoral xenograft rejection (AHXR), and acute cellular xenograft rejection (ACXR). The main components in HAR are natural xenoreactive antibodies in combination with complement activation. This is evident from the prevention of HAR in recipients in whom either antibodies or complement activation is depleted or inhibited. However, these strategies generally fail to prevent AHXR, which occurs later. AHXR is a multifactorial process in which natural and elicited antibodies may play roles, possibly in conjunction with complement, coagulation factors, and white blood cells. A main target appears to be the microvasculature which, in kidney grafts, is associated with a glomerular thrombotic microangiopathy. It is not clear to what extent species-specific physiologic disparities in complement and coagulation processes may play a role, separate from antibody-initiated processes. As rejection of solid organ xenografts is currently from AHXR, ACXR has not yet received close attention. In addition to intragraft rejection events, systemic complications following host-graft interactions have emerged, including (often fatal) consumptive coagulopathy and immune complex disease. It is anticipated that rejection processes will change when pigs with new genetic modifications become available. For instance, the precise role of natural antibodies to Galalpha1,3Gal will be able to be distinguished from other factors when pigs that lack the target antigen are available, and their organs can be evaluated in large animal xenotransplantation models.

Elimination of porcine hemopoietic cells by macrophages in mice.

The difficulty in achieving donor hemopoietic engraftment across highly disparate xenogeneic species barriers poses a major obstacle to exploring xenograft tolerance induction by mixed chimerism. In this study, we observed that macrophages mediate strong rejection of porcine hemopoietic cells in mice. Depletion of macrophages with medronate-encapsulated liposomes (M-liposomes) markedly improved porcine chimerism, and early chimerism in particular, in sublethally irradiated immunodeficient and lethally irradiated immunocompetent mice. Although porcine chimerism in the peripheral blood and spleen of M-liposome-treated mice rapidly declined after macrophages had recovered and became indistinguishable from controls by wk 5 post-transplant, the levels of chimerism in the marrow of these mice remained higher than those in control recipients at 8 wks after transplant. These results suggest that macrophages that developed in the presence of porcine chimerism were not adapted to the porcine donor and that marrow-resident macrophages did not phagocytose porcine cells. Moreover, M-liposome treatment had no effect on the survival of porcine PBMC injected into the recipient peritoneal cavity, but was essential for the migration and relocation of these cells into other tissues/organs, such as spleen, bone marrow, and peripheral blood. Together, our results suggest that murine reticuloendothelial macrophages, but not those in the bone marrow and peritoneal cavity, play a significant role in the clearance of porcine hemopoietic cells in vivo. Because injection of M-liposomes i.v. mainly depletes splenic macrophages and liver Kupffer cells, the spleen and/or liver are likely the primary sites of porcine cell clearance in vivo.