John M. Delaney

APRIL and TALL-1 and receptors BCMA and TACI: system for regulating humoralimmunity

We report that the tumor neurosis factor homolog APRIL (a proliferation-inducing ligand) stimulates in vitro proliferation of primary B and T cells and increases spleen weight due to accumulation of B cells in vivo. APRIL functions via binding to BCMA (B cell maturation antigen) and TACI (transmembrane activator and CAML-interactor) and competes with TALL-1 (also called BLyS or BAFF) for receptor binding. Soluble BCMA and TACI specifically prevent binding of APRIL and block APRIL-stimulated proliferation of primary B cells. BCMA-Fc also inhibits production of antibodies against keyhole limpet hemocyanin and Pneumovax in mice, indicating that APRIL and/or TALL-1 signaling via BCMA and/or TACI are required for generation of humoral immunity. Thus, APRIL–TALL-1 and BCMA-TACI form a two ligands–two receptors pathway involved in stimulation of B and T cell function.

GFRalpha-2 and GFRalpha-3 are two new receptors for ligands of the GDNF family.

The receptor for glial cell line-derived neurotrophic factor (GDNF) consists of GFRα-1 and Ret. Neurturin is a GDNF-related neurotrophin whose receptor is presently unknown. Here we report that neurturin can bind to either GFRα-1 or GFRα-2, a novel receptor related to GFRα-1. Both GFRα-1 and GFRα-2 mediate neurturin-induced Ret phosphorylation. GDNF can also bind to either GFRα-1 or GFRα-2, and activate Ret in the presence of either binding receptor. Although both ligands interact with both receptors, cells expressing GFRα-1 bind GDNF more efficiently than neurturin, while cells expressing GFRα-2 bind neurturin preferentially. Cross-linking and Ret activation data also suggest that while there is cross-talk, GFRα-1 is the primary receptor for GDNF and GFRα-2 exhibits a preference for neurturin. We have also cloned a cDNA that apparently codes for a third member of the GFRα receptor family. This putative receptor, designated GFRα-3, is closely related in amino acid sequence and is nearly identical in the spacing of its cysteine residues to both GFRα-1 and GFRα-2. Analysis of the tissue distribution of GFRα-1, GFRα-2, GFRα-3, and Ret by Northern blot reveals overlapping but distinct patterns of expression. Consistent with a role in GDNF function, the GFRαs and Ret are expressed in many of the same tissues, suggesting that GFRαs mediate the action of GDNF family ligands in vivo.

Fusion partners can increase the expression of recombinant interleukins via transient transfection in 2936E cells.

The expression levels of five secreted target interleukins (IL‐11, 15, 17B, 32, and IL23 p19 subunit) were tested with three different fusion partners in 2936E cells. When fused to the N‐terminus, human serum albumin (HSA) was found to enhance the expression of both IL‐17B and IL‐15, cytokines which did not express at measurable levels on their own. Although the crystallizable fragment of an antibody (Fc) was also an effective fusion partner for IL‐17B, Fc did not increase expression of IL‐15. Fc was superior to HSA for the expression of the p19 subunit of IL‐23, but no partner led to measurable levels of IL‐32γ secretion. Glutathione S‐transferase (GST) did not enhance the expression of any target and suppressed the production of IL‐11, a cytokine which expressed robustly both on its own and when fused to HSA or Fc. Cleavage of the fusion partner was not always possible. The use of HSA or Fc as N‐terminal fusions can be an effective technique to express difficult proteins, especially for applications in which the fusion partner need not be removed.

Fusion Partners as a Tool for the Expression of Difficult Proteins in Mammalian Cells

The expression of proteins which do not express well on their own can be enhanced by linking them to human serum albumin (HSA) or antibody crystallizable fragment (Fc). The constructs shown here are designed to secrete the proteins after transient transfection of mammalian cell lines. The fusion partners are appended to the N-terminus of the proteins and contain a linker designed to be proteolytically cleaved. Transient transfection and purification protocols are provided as well as experimental results with five interleukins.

Interleukin‐21 Receptor Blockade Inhibits Secondary Humoral Responses and Halts the Progression of Preestablished Disease in the (NZB × NZW)F1 Systemic Lupus Erythematosus Model

Systemic lupus erythematosus (SLE) is a complex autoimmune disease that is driven in part by chronic B and T lymphocyte hyperresponsiveness to self antigens. A deficiency of interleukin‐21 (IL‐21) or IL‐21 receptor (IL‐21R) in mice dramatically reduces inflammation and B and T cell activation in models of autoimmunity, including SLE. However, whether IL‐21 is essential for the maintenance and amplification of preestablished inflammation has not been widely examined in various animal models. The purpose of this study was to examine the impact of novel mouse IL‐21R neutralizing antibodies on recall responses to antigen challenge and on disease progression in the (NZB × NZW)F1 (NZB/NZW) mouse model of SLE.

Agonistic Human Antibodies Binding to Lecithin-Cholesterol Acyltransferase Modulate High Density Lipoprotein Metabolism.

Drug discovery opportunities where loss-of-function alleles of a target gene link to a disease-relevant phenotype often require an agonism approach to up-regulate or re-establish the activity of the target gene. Antibody therapy is increasingly recognized as a favored drug modality due to multiple desirable pharmacological properties. However, agonistic antibodies that enhance the activities of the target enzymes are rarely developed because the discovery of agonistic antibodies remains elusive. Here we report an innovative scheme of discovery and characterization of human antibodies capable of binding to and agonizing a circulating enzyme lecithin cholesterol acyltransferase (LCAT). Utilizing a modified human LCAT protein with enhanced enzymatic activity as an immunogen, we generated fully human monoclonal antibodies using the XenoMouseTM platform. One of the resultant agonistic antibodies, 27C3, binds to and substantially enhances the activity of LCAT from humans and cynomolgus macaques. X-ray crystallographic analysis of the 2.45 Å LCAT-27C3 complex shows that 27C3 binding does not induce notable structural changes in LCAT. A single administration of 27C3 to cynomolgus monkeys led to a rapid increase of plasma LCAT enzymatic activity and a 35% increase of the high density lipoprotein cholesterol that was observed up to 32 days after 27C3 administration. Thus, this novel scheme of immunization in conjunction with high throughput screening may represent an effective strategy for discovering agonistic antibodies against other enzyme targets. 27C3 and other agonistic human anti-human LCAT monoclonal antibodies described herein hold potential for therapeutic development for the treatment of dyslipidemia and cardiovascular disease.