Graft dysfunction in compassionate use of genetically engineered pig-to-human cardiac xenotransplantation: a case report.

BACKGROUND: A genetically engineered pig cardiac xenotransplantation was done on Jan 7, 2022, in a non-ambulatory male patient, aged 57 years, with end-stage heart failure, and on veno-arterial extracorporeal membrane oxygenation support, who was ineligible for an allograft. This report details our current understanding of factors important to the xenotransplantation outcome. METHODS: Physiological and biochemical parameters critical for the care of all heart transplant recipients were collected in extensive clinical monitoring in an intensive care unit. To ascertain the cause of xenograft dysfunction, we did extensive immunological and histopathological studies, including electron microscopy and quantification of porcine cytomegalovirus or porcine roseolovirus (PCMV/PRV) in the xenograft, recipient cells, and tissue by DNA PCR and RNA transcription. We performed intravenous immunoglobulin (IVIG) binding to donor cells and single-cell RNA sequencing of peripheral blood mononuclear cells. FINDINGS: After successful xenotransplantation, the graft functioned well on echocardiography and sustained cardiovascular and other organ systems functions until postoperative day 47 when diastolic heart failure occurred. At postoperative day 50, the endomyocardial biopsy revealed damaged capillaries with interstitial oedema, red cell extravasation, rare thrombotic microangiopathy, and complement deposition. Increased anti-pig xenoantibodies, mainly IgG, were detected after IVIG administration for hypogammaglobulinaemia and during the first plasma exchange. Endomyocardial biopsy on postoperative day 56 showed fibrotic changes consistent with progressive myocardial stiffness. Microbial cell-free DNA testing indicated increasing titres of PCMV/PRV cell-free DNA. Post-mortem single-cell RNA sequencing showed overlapping causes. INTERPRETATION: Hyperacute rejection was avoided. We identified potential mediators of the observed endothelial injury. First, widespread endothelial injury indicates antibody-mediated rejection. Second, IVIG bound strongly to donor endothelium, possibly causing immune activation. Finally, reactivation and replication of latent PCMV/PRV in the xenograft possibly initiated a damaging inflammatory response. The findings point to specific measures to improve xenotransplant outcomes in the future. FUNDING: The University of Maryland School of Medicine, and the University of Maryland Medical Center.

Preclinical Immunopharmacologic Assessment of KPL-404, a Novel, Humanized, Non-Depleting Antagonistic Anti-CD40 Monoclonal Antibody.

The CD40/CD40L pathway plays a major role in multiple inflammatory processes involving different immune and stromal cells. Abnormal activation of this pathway has been implicated in pathogenesis of complex autoimmune diseases including systemic lupus erythematosus, rheumatoid arthritis, Graves' disease, and Sjogren's Syndrome. We completed in vitro and in vivo preclinical characterization of KPL-404, a novel humanized anti-CD40 IgG4 monoclonal antibody, to demonstrate its potency, efficacy, and pharmacokinetic profile; safety was also assessed. In vitro, KPL-404 bound recombinant human and cynomolgus monkey CD40 with comparable affinity in the nanomolar range. KPL-404 binding to cell surface CD40 did not induce antibody- or complement-mediated cytotoxicity of CD40-expressing cells. Pharmacological antagonistic activity of KPL-404 was demonstrated in vitro by inhibition of CD40-mediated downstream NF-kB activation. In the in vivo study with cynomolgus monkeys, KPL-404, administered intravenously as a single dose (10 mg/kg) or two monthly doses of 1 or 5 mg/kg, did not elicit observable safety findings, including thrombocytopenia over 8 weeks. KPL-404 engaged CD40 expressed on peripheral B cells for 2 and 4 weeks after a single administration of 5 or 10 mg/kg IV, respectively, without depletion of peripheral B cells. At 5 mg/kg IV, KPL-404 blocked both primary and secondary responses to T-cell dependent antibody responses to test antigens, KLH, and tetanus toxoid. These data illustrated the relationship between KPL-404 serum concentration and pharmacodynamic effects of CD40-targeting in circulation and in lymphoid tissues. These data support clinical development of KPL-404 in autoimmune diseases. SIGNIFICANCE STATEMENT: We aimed to develop a potent and efficacious CD40 antagonist. In vitro and in vivo findings show that KPL-404 blocks the anti-CD40 antibody that potently inhibits primary and secondary antibody responses at pharmacologically relevant concentrations, has a favorable pharmacokinetic profile, and does not deplete B cells by antibody-dependent cellular cytotoxicity or apoptosis ("nondepleting"). These findings support clinical development of KPL-404 as a potential therapeutic in autoimmune diseases.

Blocking GM-CSF receptor α with mavrilimumab reduces infiltrating cells, pro-inflammatory markers and neoangiogenesis in ex vivo cultured arteries from patients with giant cell arteritis.

BACKGROUND: Effective and safe therapies are needed for the treatment of patients with giant cell arteritis (GCA). Emerging as a key cytokine in inflammation, granulocyte-macrophage colony stimulating factor (GM-CSF) may play a role in promoting inflammation in GCA. OBJECTIVES: To investigate expression of GM-CSF and its receptor in arterial lesions from patients with GCA. To analyse activation of GM-CSF receptor-associated signalling pathways and expression of target genes. To evaluate the effects of blocking GM-CSF receptor α with mavrilimumab in ex vivo cultured arteries from patients with GCA. METHODS: Quantitative real time PCR, in situ RNA hybridisation, immunohistochemistry, immunofluorescence and confocal microscopy, immunoassay, western blot and ex vivo temporal artery culture. RESULTS: GM-CSF and GM-CSF receptor α mRNA and protein were increased in GCA lesions; enhanced JAK2/STAT5A expression/phosphorylation as well as increased expression of target genes CD83 and Spi1/PU.1 were observed. Treatment of ex vivo cultured GCA arteries with mavrilimumab resulted in decreased transcripts of CD3ε, CD20, CD14 and CD16 cell markers, and reduction of infiltrating CD16 and CD3ε cells was observed by immunofluorescence. Mavrilimumab reduced expression of molecules relevant to T cell activation (human leukocyte antigen-DR [HLA-DR]) and Th1 differentiation (interferon-γ), the pro-inflammatory cytokines: interleukin 6 (IL-6), tumour necrosis factor α (TNFα) and IL-1ß, as well as molecules related to vascular injury (matrix metalloprotease 9, lipid peroxidation products and inducible nitric oxide synthase [iNOS]). Mavrilimumab reduced CD34 + cells and neoangiogenesis in GCA lesions. CONCLUSION: The inhibitory effects of mavrilimumab on multiple steps in the GCA pathogenesis cascade in vitro are consistent with the clinical observation of reduced GCA flares in a phase 2 trial and support its development as a therapeutic option for patients with GCA.

Crystal structure of interleukin-21 receptor (IL-21R) bound to IL-21 reveals that sugar chain interacting with WSXWS motif is integral part of IL-21R.

IL-21 is a class I cytokine that exerts pleiotropic effects on both innate and adaptive immune responses. It signals through a heterodimeric receptor complex consisting of the IL-21 receptor (IL-21R) and the common γ-chain. A hallmark of the class I cytokine receptors is the class I cytokine receptor signature motif (WSXWS). The exact role of this motif has not been determined yet; however, it has been implicated in diverse functions, including ligand binding, receptor internalization, proper folding, and export, as well as signal transduction. Furthermore, the WXXW motif is known to be a consensus sequence for C-mannosylation. Here, we present the crystal structure of IL-21 bound to IL-21R and reveal that the WSXWS motif of IL-21R is C-mannosylated at the first tryptophan. We furthermore demonstrate that a sugar chain bridges the two fibronectin domains that constitute the extracellular domain of IL-21R and anchors at the WSXWS motif through an extensive hydrogen bonding network, including mannosylation. The glycan thus transforms the V-shaped receptor into an A-frame. This finding offers a novel structural explanation of the role of the class I cytokine signature motif.

Rational design of interleukin-21 antagonist through selective elimination of the gammaC binding epitope.

The cytokine interleukin (IL)-21 exerts pleiotropic effects acting through innate as well as adaptive immune responses. The activities of IL-21 are mediated through binding to its cognate receptor complex composed of the IL-21 receptor private chain (IL-21Ralpha) and the common gamma-chain (gammaC), the latter being shared by IL-2, IL-4, IL-7, IL-9, and IL-15. The binding energy of the IL-21 ternary complex is predominantly provided by the high affinity interaction between IL-21 and IL-21Ralpha, whereas the interaction between IL-21 and gammaC, albeit essential for signaling, is rather weak. The design of IL-21 analogues, which have lost most or all affinity toward the signaling gammaC chain, while simultaneously maintaining a tight interaction with the private chain, would in theory represent candidates for IL-21 antagonists. We predicted the IL-21 residues, which compose the gammaC binding epitope using homology modeling and alignment with the related cytokines, IL-2 and IL-4. Next we systematically analyzed the predicted binding epitope by a mutagenesis study. Indeed two mutants, which have significantly impaired gammaC affinity with undiminished IL-21Ralpha affinity, were successfully identified. Functional studies confirmed that these two novel hIL-21 double mutants do act as hIL-21 antagonists.

Comparison of the ability of wild type and stabilized human IgG(4) to undergo Fab arm exchange with endogenous IgG(4)in vitro and in vivo.

Fab arm exchange by a stabilized anti-IL-31 IgG(4)S228P monoclonal antibody (mAb) was studied using physiologically relevant antibody concentrations and thiol exchange conditions, and directly compared to that of matched wild type IgG(4) (IgG(4)wt) and IgG(1) control antibodies. In vitro arm exchange between the test mAbs and a purified IgG(4)wt exchange partner was monitored using capillary isoelectric focusing and a size-exclusion peak shift assay. Arm exchange between the test mAbs and IgG exchange partners with unknown specificity was monitored using only the shift assay. Studies were performed using single isotype human and mouse mAbs, unfractionated human, mouse, and cynomolgus monkey IgG, and human serum as the sources of the exchange partners. In vitro studies using human serum demonstrated that anti-IL-31 IgG(4)S228P did not undergo significant Fab arm exchange with endogenous human IgG(4) whereas anti-IL-31 IgG(4)wt underwent rapid and extensive Fab arm exchange. The in vitro results were corroborated by in vivo studies in which mice were injected with a mixture of either form of the test mAb and an excess of non-specific human IgG(4) exchange partner.

Crystal structure of a prolactin receptor antagonist bound to the extracellular domain of the prolactin receptor.

The crystal structure of the complex between an N-terminally truncated G129R human prolactin (PRL) variant and the extracellular domain of the human prolactin receptor (PRLR) was determined at 2.5A resolution by x-ray crystallography. This structure represents the first experimental structure reported for a PRL variant bound to its cognate receptor. The binding of PRL variants to the PRLR extracellular domain was furthermore characterized by the solution state techniques, hydrogen exchange mass spectrometry, and NMR spectroscopy. Compared with the binding interface derived from mutagenesis studies, the structural data imply that the definition of PRL binding site 1 should be extended to include residues situated in the N-terminal part of loop 1 and in the C terminus. Comparison of the structure of the receptor-bound PRL variant with the structure reported for the unbound form of a similar analogue ( Jomain, J. B., Tallet, E., Broutin, I., Hoos, S., van Agthoven, J., Ducruix, A., Kelly, P. A., Kragelund, B. B., England, P., and Goffin, V. (2007) J. Biol. Chem. 282, 33118-33131 ) demonstrates that receptor-induced changes in the backbone of the four-helix bundle are subtle, whereas large scale rearrangements and structuring occur in the flexible N-terminal part of loop 1. Hydrogen exchange mass spectrometry data imply that the dynamics of the four-helix bundle in solution generally become stabilized upon receptor interaction at binding site 1.

The existence of multiple conformers of interleukin-21 directs engineering of a superpotent analogue.

The high resolution three-dimensional structure of human interleukin (hIL)-21 has been resolved by heteronuclear NMR spectroscopy. Overall, the hIL-21 structure is dominated by a well defined central four-helical bundle, arranged in an up-up-down-down topology, as observed for other cytokines. A segment of the hIL-21 molecule that includes the third helical segment, helix C, is observed to exist in two distinct and interchangeable states. In one conformer, the helix C segment is presented in a regular, alpha-helical conformation, whereas in the other conformer, this segment is largely disordered. A structure-based sequence alignment of hIL-21 with receptor complexes of the related cytokines, interleukin-2 and -4, implied that this particular segment is involved in receptor binding. An hIL-21 analog was designed to stabilize the region around helix C through the introduction of a segment grafted from hIL-4. This novel hIL-21 analog was demonstrated to exhibit a 10-fold increase in potency in a cellular assay.

Recognition of privileged structures by G-protein coupled receptors.

Privileged structures are ligand substructures that are widely used to generate high-affinity ligands for more than one type of receptor. To explain this, we surmised that there must be some common feature in the target proteins. For a set of class A GPCRs, we found a good correlation between conservation patterns of residues in the ligand binding pocket and the privileged structure fragments in class A GPCR ligands. A major part of interior surface of the common ligand binding pocket of class A receptors, identified in many GPCRs, is lined with variable residues that are responsible for selectivity in ligand recognition, while other regions, typically located deeper into the binding pocket, are more conserved and retain a predominantly hydrophobic and aromatic character. The latter is reflected in the chemical nature of most GPCR privileged structures and is proposed to be the common feature that is recognized by the privileged structures. Further, we find that this subpocket is conserved even in distant orthologs within the class A family. Three pairs of ligands recognizing widely different receptor types were docked into receptor models of their target receptors utilizing available structure- activity relationships and mutagenesis data. For each pair of ligands, the ligand-receptor complexes reveal that the nature of the privileged structure binding pocket is conserved between the two complexes, in support of our hypothesis. Only part of the privileged structures can be accommodated within the conserved subpocket. Some contacts are established between the privileged structure and the nonconserved parts of the binding pocket. This implies that any one particular privileged structure can target only a subset of receptors, those complementary to the full privileged structure. Our hypothesis leads to a valuable novelty in that ligand libraries can be designed without any foreknowledge of the structure of the endogenous ligand, which in turn means that even orphan receptors can in principle now be addressed as potential drug targets.

Parallel solid-phase synthesis of disubstituted (5-biphenyltetrazolyl) hydantoins and thiohydantoins targeting the growth hormone secretagogue receptor.

An efficient solid-phase protocol for the synthesis of substituted (5-biphenyltetrazolyl)-hydantoins and -thiohydantoins has been developed. Suzuki cross-coupling between resin-bound 2-(tetrazol-5-yl)-phenylborinane and 4-bromobenzaldehyde gave the corresponding tetrazolylbiphenyl aldehyde. Subsequent reductive amination using amino acid esters gave the pivotal resin bound amino acid esters which were transformed to hydantoins or thiohydantoins via two routes: (i) treatment with isocyanates or isothiocyanates or (ii) successive treatment with triphosgene and primary amines. Using molecular modeling, we were able to jump from L-692,429, a well known non-peptidyl growth hormone secretagogue (GHS), to biphenyltetrazolyl hydantoins, obtaining compounds with IC(50) values below 600 nM after two iterative cycles only.

Structural characterization of LNA and alpha-L-LNA hybridized to RNA.

LNA and alpha-L-LNA are promising candidates for the development of efficient oligonucleotide-based therapeutic agents. Here, we present a short overview of the structural results we have obtained for LNA:RNA and alpha-L-LNA:RNA hybrids. Specifically, we have shown that LNA acts as an A-type mimic, while alpha-L-LNA acts as a B-type mimic when built into oligonucleotides.

The global conformation of the hammerhead ribozyme determined using residual dipolar couplings.

The global structure of the hammerhead ribozyme was determined in the absence of Mg(2+) by solution NMR experiments. The hammerhead ribozyme motif forms a branched structure consisting of three helical stems connected to a catalytic core. The (1)H-(15)N and (1)H-(13)C residual dipolar couplings were measured in a set of differentially (15)N/(13)C-labeled ribozymes complexed with an unlabeled noncleavable substrate. The residual dipolar couplings provide orientation information on both the local and the global structure of the molecule. Analysis of the residual dipolar couplings demonstrated that the local structure of the three helical stems in solution is well modeled by an A-form conformation. However, the global structure of the hammerhead in solution in the absence of Mg(2+) is not consistent with the Y-shaped conformation observed in crystal structures of the hammerhead. The residual dipolar couplings for the helical stems were combined with standard NOE and J coupling constant NMR data from the catalytic core. The NOE data show formation of sheared G-A base pairs in domain 2. These NMR data were used to determine the global orientation of the three helical stems in the hammerhead. The hammerhead forms a rather extended structure under these conditions with a large angle between stems I and II ( approximately 153 degrees ), a smaller angle between stems II and III ( approximately 100 degrees ), and the smallest angle between stems I and III ( approximately 77 degrees ). The residual dipolar coupling data also contain information on the dynamics of the molecule and were used here to provide qualitative information on the flexibility of the helical domains in the hammerhead ribozyme-substrate complex.

Locked nucleic acid (LNA) recognition of RNA: NMR solution structures of LNA:RNA hybrids.

Locked nucleic acids (LNAs) containing one or more 2'-O,4'-C-methylene-linked bicyclic ribonucleoside monomers possess a number of the prerequisites of an effective antisense oligonucleotide, e.g. unprecedented helical thermostability when hybridized with cognate RNA and DNA. To acquire a detailed understanding of the structural features of LNA giving rise to its remarkable properties, we have conducted structural studies by use of NMR spectroscopy and now report high-resolution structures of two LNA:RNA hybrids, the LNA strands being d(5'-CTGAT(L)ATGC-3') and d(5'-CT(L)GAT(L)AT(L)GC-3'), respectively, T(L) denoting a modified LNA monomer with a thymine base, along with the unmodified DNA:RNA hybrid. In the structures, the LNA nucleotides are positioned as to partake in base stacking and Watson-Crick base pairing, and with the inclusion of LNA nucleotides, we observe a progressive change in duplex geometry toward an A-like duplex structure. As such, with the inclusion of three LNA nucleotides, the hybrid adopts an almost canonical A-type duplex geometry, and thus it appears that the number of modifications has reached a saturation level with respect to structural changes, and that further incorporations would furnish only minute changes in the duplex structure. We attempt to rationalize the conformational steering induced by the LNA nucleotides by suggesting that the change in electronic density at the brim of the minor groove, introduced by the LNA modification, is causing an alteration of the pseudorotational profile of the 3'-flanking nucleotide, thus shifting this sugar equilibrium toward N-type conformation.