Gal epitope expression and immunological properties in iGb3S deficient mice

α-Gal antigen-deficient rabbits with GGTA1 gene disruption via CRISPR/Cas9

BACKGROUND

Previous studies have identified the carbohydrate epitope Galα1-3Galβ1-4GlcNAc-R (termed the α-galactosyl epitope), known as the α-Gal antigen as the primary xenoantigen recognized by the human immune system. The α-Gal antigen is regulated by galactosyltransferase (GGTA1), and α-Gal antigen-deficient mice have been widely used in xenoimmunological studies, as well as for the immunogenic risk evaluation of animal-derived medical devices. The objective of this study was to develop α-Gal antigen-deficient rabbits by GGTA1 gene editing with the CRISPR/Cas9 system.

RESULTS

The mutation efficiency of GGTA1 gene-editing in rabbits was as high as 92.3% in F0 pups. Phenotype analysis showed that the α-Gal antigen expression in the major organs of F0 rabbits was decreased by more than 99.96% compared with that in wild-type (WT) rabbits, and the specific anti-Gal IgG and IgM antibody levels in F1 rabbits increased with increasing age, peaking at approximately 5 or 6 months. Further study showed that GGTA1 gene expression in F2-edited rabbits was dramatically reduced compared to that in WT rabbits.

CONCLUSIONS

α-Gal antigen-deficient rabbits were successfully generated by GGTA1 gene editing via the CRISPR/Cas9 system in this study. The feasibility of using these α-Gal antigen-deficient rabbits for the in situ implantation and residual immunogenic risk evaluation of animal tissue-derived medical devices was also preliminarily confirmed.

Bile Duct Ligation Impairs Function and Expression of Mrp1 at Rat Blood-Retinal Barrier via Bilirubin-Induced P38 MAPK Pathway Activations

Liver injury is often associated with hepatic retinopathy, resulting from accumulation of retinal toxins due to blood-retinal barrier (BRB) dysfunction. Retinal pigment epithelium highly expresses MRP1/Mrp1. We aimed to investigate whether liver injury affects the function and expression of retinal Mrp1 using bile duct ligation (BDL) rats. Retinal distributions of fluorescein and 2,4-dinitrophenyl-S-glutathione were used for assessing Mrp1 function. BDL significantly increased distributions of the two substrates and bilirubin, downregulated Mrp1 protein, and upregulated phosphorylation of p38 and MK2 in the retina. BDL neither affected the retinal distribution of FITC-dextran nor expressions of ZO-1 and claudin-5, demonstrating intact BRB integrity. In ARPE-19 cells, BDL rat serum or bilirubin decreased MRP1 expression and enhanced p38 and MK2 phosphorylation. Both inhibiting and silencing p38 significantly reversed the bilirubin- and anisomycin-induced decreases in MRP1 protein. Apparent permeability coefficients of fluorescein in the A-to-B direction (Papp, A-to-B) across the ARPE-19 monolayer were greater than Papp, B-to-A. MK571 or bilirubin significantly decreased Papp, A-to-B of fluorescein. Bilirubin treatment significantly downregulated Mrp1 function and expression without affecting integrity of BRB and increased bilirubin levels and phosphorylation of p38 and MK2 in rat retina. In conclusion, BDL downregulates the expression and function of retina Mrp1 by activating the p38 MAPK pathway due to increased bilirubin levels.

SMAD4-201 transcript as a putative biomarker in colorectal cancer

Background

Transcripts with alternative 5′-untranslated regions (UTRs) result from the activity of alternative promoters and they can determine gene expression by influencing its stability and translational efficiency, thus executing complex regulation of developmental, physiological and pathological processes. Transcriptional regulation of human SMAD4, a key tumor suppressor deregulated in most gastrointestinal cancers, entails four alternative promoters. These promoters and alternative transcripts they generate remain unexplored as contributors to the SMAD4 deregulation in cancer. The aim of this study was to investigate the relative abundance of the transcript SMAD4–201 in colorectal cell lines and tissues in order to establish if its fluctuations may be associated with colorectal cancer (CRC).

Methods

Relative abundance of SMAD4–201 in total SMAD4 mRNA was analyzed using quantitative PCR in a set of permanent human colon cell lines and tumor and corresponding healthy tissue samples from patients with CRC.

Results

The relative abundance of SMAD4–201 in analyzed cell lines varied between 16 and 47%. A similar relative abundance of SMAD4–201 transcript was found in the majority of analyzed human tumor tissue samples, and it was averagely 20% lower in non-malignant in comparison to malignant tissue samples (p = 0.001). Transcript SMAD4–202 was not detectable in any of the analyzed samples, so the observed fluctuations in the composition of SMAD4 transcripts can be attributed to transcripts other than SMAD4–201 and SMAD4–202.

Conclusion

The expression profile of SMAD4–201 in human tumor and non-tumor tissue samples may indicate the translational potential of this molecule in CRC, but further research is needed to clarify its usability as a potential biomarker for early diagnosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09186-z.

Human immune reactivity of GGTA1/CMAH/A3GALT2 triple knockout Yucatan miniature pigs

In this study, we investigated the effect of a triple knockout of the genes alpha-1,3-galactosyltransferase (GGTA1), cytidine monophosphate-N-acetylneuraminic acid hydroxylase (CMAH), and alpha 1,3-galactosyltransferase 2 (A3GALT2) in Yucatan miniature pigs on human immune reactivity. We used the CRISPR/Cas9 system to create pigs lacking GGTA1 (GTKO) and GGTA1/CMAH/A3GALT2 triple gene knockout (TKO). The expression of all three xenoantigens was absent in TKO pigs, but there was no additional reduction in the level of Galα1,3Gal (αGal) epitopes expression in the A3GALT2 gene KO. Peripheral blood mononuclear cells (PBMCs), aorta endothelial cells (AECs), and cornea endothelial cells (CECs) were isolated from these pigs, and their ability to bind human IgM/IgG and their cytotoxicity in human sera were evaluated. Compared to wild type (WT) pigs, the level of human antibody binding of the PBMCs, AECs, and CECs of the transgenic pigs (GTKO and TKO) was significantly reduced. However, there were significant differences in human antibody binding between GTKO and TKO depending on the cell type. Human antibody binding of TKO pigs was less than that of GTKO on PBMCs but was similar between GTKO and TKO pigs for AECs and CECs. Cytotoxicity of transgenic pig (GTKO and TKO) PBMCs and AECs was significantly reduced compared to that of WT pigs. However, TKO pigs showed a reduction in cytotoxicity compared to GTKO pigs on PBMCs, whereas in AECs from both TKO and GTKO pigs, there was no difference. The cytotoxicity of transgenic pig CECs was significantly decreased from that of WT at 300 min, but there was no significant reduction in TKO pigs from GTKO. Our results indicate that genetic modification of donor pigs for xenotransplantation should be tailored to the target organ and silencing of additional genes such as CMAH or A3GALT2 based on GTKO might not be essential in Yucatan miniature pigs.

Selective Identification of α-Galactosyl Epitopes in N-Glycoproteins Using Characteristic Fragment Ions from Higher-Energy Collisional Dissociation

The α-galactosyl epitope is a terminal N-glycan moiety of glycoproteins found in mammals except in humans, and thus, it is recognized as an antigen that provokes an immunogenic response in humans. Accordingly, it is necessary to analyze the α-galactosyl structure in biopharmaceuticals or organ transplants. Due to an identical glycan composition and molecular mass between α-galactosyl N-glycans and hybrid/high-mannose-type N-glycans, it is challenging to characterize α-galactosyl epitopes in N-glycoproteins using mass spectrometry. Here, we describe a method to identify α-galactosyl N-glycopeptides in mice glycoproteins using liquid chromatography with tandem mass spectrometry with higher-energy collisional dissociation (HCD). The first measure was an absence of [Y_HM] ion peaks in the HCD spectra, which was exclusively observed in hybrid and/or high-mannose-type N-glycopeptides. The second complementary criterion was the ratio of an m/z 528.19 (Hex₂HexNAc₁) ion to m/z 366.14 (Hex₁HexNAc₁) ion (I_m/z528/I_m/z366). The measure of [I_m/z528/I_m/z366 > 0.3] enabled a clear-cut determination of α-galactosyl N-glycopeptides with high accuracy. In Ggta1 knockout mice, we could not find any α-galactosyl N-glycoproteins identified in WT mice plasma. Using this method, we could screen for α-galactosyl N-glycoproteins from mice spleen, lungs, and plasma samples in a highly sensitive and specific manner. Conclusively, we suggest that this method will provide a robust analytical tool for determination of α-galactosyl epitopes in pharmaceuticals and complex biological samples.

GGTA1/iGb3S Double Knockout Mice: Immunological Properties and Immunogenicity Response to Xenogeneic Bone Matrix

Background

Animal tissues and tissue-derived biomaterials are widely used in the field of xenotransplantation and regenerative medicine. A potential immunogenic risk that affects the safety and effectiveness of xenografts is the presence of remnant α-Gal antigen (synthesized by GGTA1 or/and iGb3S). GGTA1 knockout mice have been developed as a suitable model for the analysis of anti-Gal antibody-mediated immunogenicity. However, we are yet to establish whether GGTA1/iGb3S double knockout (G/i DKO) mice are sensitive to Gal antigen-positive xenoimplants.

Methods

α-Gal antigen expression in the main organs of G/i DKO mice or bovine bone substitutes was detected via a standardized ELISA inhibition assay. Serum anti-α-Gal antibody titers of G/i DKO mice after immunization with rabbit red blood cells (RRBC) and implantation of raw lyophilized bone substitutes (Gal antigen content was 8.14 ± 3.17 × 10¹²/mg) or Guanhao Biotech bone substitutes (50% decrease in Gal antigen relative to the raw material) were assessed. The evaluation of total serum antibody, inflammatory cytokine, and splenic lymphocyte subtype populations and the histological analysis of implants and thymus were performed to systematically assess the immune response caused by bovine bone substitutes and bone substitute grafts in G/i DKO mice.

Results

α-Gal epitope expression was reduced by 100% in the main organs of G/i DKO mice, compared with their wild-type counterparts. Following immunization with RRBC, serum anti-Gal antibody titers of G/i DKO mice increased from 80- to 180-fold. After subcutaneous implantation of raw lyophilized bone substitutes and Guanhao Biotech bone substitutes into G/i DKO mice, specific anti-α-Gal IgG, anti-α-Gal IgM, and related inflammatory factors (IFN-γ and IL-6) were significantly increased in the raw lyophilized bone substitute group but showed limited changes in the Guanhao Biotech bone substitute group, compared with the control.

Conclusion

G/i DKO mice are sensitive to Gal antigen-positive xenogeneic grafts and can be effectively utilized for evaluating the α-Gal-mediated immunogenic risk of xenogeneic grafts.

The Possible Role of Anti-Neu5Gc as an Obstacle in Xenotransplantation

Seventy to ninety percentage of preformed xenoreactive antibodies in human serum bind to the galactose-α(1,3)-galactose Gal epitope, and the creation of Gal knockout (KO) pigs has eliminated hyperacute rejection as a barrier to xenotransplantation. Now other glycan antigens are barriers to move ahead with xenotransplantation, and the N-glycolyl neuraminic acid, Neu5Gc (or Hanganutziu-Deicher antigen), is also a major pig xenoantigen. Humans have anti-Neu5Gc antibodies. Several data indicate a strong immunogenicity of Neu5Gc in humans that may contribute to an important part in antibody-dependent injury to pig xenografts. Pig islets express Neu5Gc, which reacted with diet-derived human antibodies and mice deleted for Neu5Gc reject pancreatic islets from wild-type counterpart. However, Neu5Gc positive heart were not rejected in Neu5Gc KO mice indicating that the role of Neu5Gc-specific antibodies has to be nuanced and depend of the graft situation parameters (organ/tissue, recipient, implication of other glycan antigens). Recently generated Gal/Neu5Gc KO pigs eliminate the expression of Gal and Neu5Gc, and improve the crossmatch of humans with the pig. This review summarizes the current and recent experimental and (pre)clinical data on the Neu5Gc immunogenicity and emphasize of the potential impact of anti-Neu5Gc antibodies in limiting xenotransplantation in humans.