Analysis of human biologics with a mouse skin transplant model in humanized mice.

Preclinical testing of human therapeutic monoclonal antibodies has been limited in murine models due to species differences in pharmacokinetics and biologic responses. To overcome these constraints we developed a murine skin transplant model in humanized mice and used it to test human monoclonal antibody therapy. Neonatal NOD/SCID/IL2Rγc(null) mice (NSG) were reconstituted with human CD34(+) hematopoietic stem cells (hNSG). When adult, these mice rejected MHC mismatched murine C57BL/6J skin grafts. Rejection required adequate reconstitution with human cells. There was diffuse infiltration of the epidermis and dermis with hCD8 and hCD4 cells in rejected grafts by immunohistochemistry. Studies with B6/MHC class I and II knockout mice donors indicated that neither is required for rejection. Graft rejection was associated with the development of effector and central memory T cells and an increase in serum immunoglobulins. We also tested the effects of teplizumab (anti-CD3 mAb) and found it could delay skin graft rejection, whereas ipilimumab (anti-CTLA-4 [cytotoxic T-lymphocyte antigen-4] mAb) treatment accelerated rejection. These findings demonstrate that hNSG mice reliably and predictably reject a xenogenic mouse skin graft by a human T cell mediated mechanism. The model can be utilized to investigate the ability of human immunotherapies to enhance or suppress functional human immune responses.

Monoclonal antibodies directed against a synthetic peptide corresponding to the alpha-bungarotoxin binding region of the acetylcholine receptor.

Murine monoclonal antibodies have been produced against a 32 amino acid synthetic peptide corresponding to residues 173-204 on the alpha-subunit of the nicotinic acetylcholine receptor from Torpedo californica. All of the monoclonal antibodies were of the IgM subtype and most cross-reacted with the purified native receptor. None of the antibodies were effective in blocking alpha-bungarotoxin binding to the receptor nor, conversely, did alpha-bungarotoxin interfere with antibody binding. However, two monoclonal antibodies, previously shown to bind near the ligand binding site on the native receptor, did compete partially (50%) with the binding of one of the IgM monoclonal antibodies.

The role of tyrosine at the ligand-binding site of the nicotinic acetylcholine receptor.

Identification of the critical residues in a receptor's ligand-binding site provides valuable structural information important for understanding the basis for ligand recognition. The design of specific ligands targeted for receptor action will depend to a great extent on detailed structural knowledge of this kind. Although the nicotinic acetylcholine receptor (nAChR) is perhaps the best characterized of all receptors, the detailed configuration of the ligand-binding site remains unknown. Structural comparisons of nicotinic agonists and antagonists have long predicted a negative subsite on the receptor to interact with the positively charged alkyl-ammonium moiety common to nearly all nicotinic agents. We have used intrinsic fluorescence spectroscopic analyses together with binding studies of selectively modified peptide fragments of the nAChR to suggest that one or two invariant tyrosine residues at positions 190 and 198 on the alpha-subunit provide the critical negative subsite required for ligand binding. Tyrosines may similarly be part of the negative subsite of muscarinic receptors and other neurotransmitter receptors that bind cationic ligands.

Relapsing and remitting severe hypoglycemia due to a monoclonal anti-insulin antibody heralding a case of multiple myeloma.

CONTEXT: We report a novel case of insulin autoimmune syndrome (IAS) presenting with hypoglycemia due to production of a monoclonal anti-insulin antibody in a patient subsequently found to have multiple myeloma (MM). OBJECTIVE: The aim of the study was to describe the 5-yr clinical course of a patient with IAS and MM and to characterize the origin and function of the pathogenic antibody. METHODS: We conducted a longitudinal case history with laboratory investigations to characterize the anti-insulin antibody subtype, specificity, affinity, and origin. RESULTS: The patient presented with IAS, which worsened during treatment of hepatitis C. The patient was then discovered to have a monoclonal gammopathy that progressed to MM. Treatment of the MM induced remission of the neoplasia and IAS, which then followed a synchronized course of progression and response to therapy. An anti-insulin IgG(3)-λ that bound specifically but with low affinity to the insulin B chain (amino acids 9-30) and that was distinct from the primary MM IgG(3)-κ clone was recovered from the patient and cloned. The antibody bound insulin and showed mutations of normal affinity maturation. CONCLUSIONS: We describe a case of MM heralded by IAS, where full characterization of the pathogenic antibody revealed that the monoclonal anti-insulin antibody had originated from a self-reactive clone.

A human homologue of the Drosophila Toll protein signals activation of adaptive immunity.

Induction of the adaptive immune response depends on the expression of co-stimulatory molecules and cytokines by antigen-presenting cells. The mechanisms that control the initial induction of these signals upon infection are poorly understood. It has been proposed that their expression is controlled by the non-clonal, or innate, component of immunity that preceded in evolution the development of an adaptive immune system in vertebrates. We report here the cloning and characterization of a human homologue of the Drosophila toll protein (Toll) which has been shown to induce the innate immune response in adult Drosophila. Like Drosophila Toll, human Toll is a type I transmembrane protein with an extracellular domain consisting of a leucine-rich repeat (LRR) domain, and a cytoplasmic domain homologous to the cytoplasmic domain of the human interleukin (IL)-1 receptor. Both Drosophila Toll and the IL-1 receptor are known to signal through the NF-kappaB pathway. We show that a constitutively active mutant of human Toll transfected into human cell lines can induce the activation of NF-kappaB and the expression of NF-kappaB-controlled genes for the inflammatory cytokines IL-1, IL-6 and IL-8, as well as the expression of the co-stimulatory molecule B7.1, which is required for the activation of naive T cells.

Truncation variants of peptides isolated from MHC class II molecules suggest sequence motifs.

T cells recognize foreign protein antigens in the form of peptide fragments bound tightly to the outer aspect of molecules encoded by the major histocompatibility complex (MHC). Most of the amino-acid differences that distinguish MHC allelic variants line the peptide-binding cleft, and different allelic forms of MHC molecules bind distinct peptides. It has been demonstrated that peptide-binding to MHC class I involves anchor residues in certain positions and that antigenic peptides associated with MHC class I exhibit allele-specific structural motifs. We have previously reported an analysis of MHC class II-associated peptide sequences. Here we extend this analysis and show that certain amino-acid residues occur at particular positions in the sequence of peptides binding to a given MHC class II molecule. These sequence motifs require the amino terminus to be shifted one or two positions to obtain alignment; such shifts occur naturally for a single peptide sequence without qualitatively altering CD4 T-cell recognition.

Sequence analysis of peptides bound to MHC class II molecules.

CD4 T cells recognize peptide fragments of foreign proteins bound to self class II molecules of the major histocompatibility complex (MHC). Naturally processed peptide fragments bound to MHC class II molecules are peptides of 13-17 amino acids which appear to be precessively truncated from the carboxy terminus, perhaps after binding to the MHC class II molecule. The finding of predominant self peptides has interesting implications for antigen processing and self-non-self discrimination.

On the complexity of self.

Self peptides bound to self major histocompatibility complex (MHC) molecules have been implicated both in positive and in negative selection of T cells during intrathymic development. We report here that the novel MHC-restricted monoclonal antibody Y-Ae detects the MHC class II bound form of a major self peptide. Y-Ae binds approximately 12% of the relevant MHC class II molecules on self antigen presenting cells. The peptide detected by Y-Ae is one of several major peptides eluted from the MHC molecule. These data suggest that self peptides presented by self MHC class II molecules at densities sufficient to signal a CD4 T cell are of very limited complexity. Furthermore, as Y-Ae stains antigen presenting cells that mediate negative selection but not thymic cortical epithelial cells that drive positive selection, differential expression of self peptide:self MHC class II complexes may be a key feature of intrathymic selection.

MyD88 is an adaptor protein in the hToll/IL-1 receptor family signaling pathways.

The Toll-mediated signaling cascade using the NF-kappaB pathway has been shown to be essential for immune responses in adult Drosophila, and we recently reported that a human homolog of the Drosophila Toll protein induces various immune response genes via this pathway. We now demonstrate that signaling by the human Toll receptor employs an adaptor protein, MyD88, and induces activation of NF-kappaB via the Pelle-like kinase IRAK and the TRAF6 protein, similar to IL-1R-mediated NF-kappaB activation. However, we find that Toll and IL-1R signaling pathways are not identical with respect to AP-1 activation. Finally, our findings implicate MyD88 as a general adaptor/regulator molecule for the Toll/IL-1R family of receptors for innate immunity.

The specificity and orientation of a TCR to its peptide-MHC class II ligands.

A T cell-mediated immune response is mainly determined by the 3-5 aa residues that protrude upwards from a peptide bound to an MHC molecule. Alterations of these peptide residues can diminish, eliminate or radically alter the signal that the T cell receives through its T cell receptor (TCR). We have used peptide immunizations of normal mice and mice carrying alpha or beta chain TCR transgenes to identify three distinct peptide contact points. One, near the carboxyl terminus of the peptide, involves the beta chain CDR3 region; the second was centrally located and interacted with both the alpha and beta chain CDR3 loops; the third was near the amino terminus of the peptide, and affected V alpha gene usage, but not the structure of CDR3 of either TCR chain. Based on these results, we propose an orientation for the TCR of this cloned line and argue for its generality.