Development of ISB 1442, a CD38 and CD47 bispecific biparatopic antibody innate cell modulator for the treatment of multiple myeloma.

Antibody engineering can tailor the design and activities of therapeutic antibodies for better efficiency or other advantageous clinical properties. Here we report the development of ISB 1442, a fully human bispecific antibody designed to re-establish synthetic immunity in CD38+ hematological malignancies. ISB 1442 consists of two anti-CD38 arms targeting two distinct epitopes that preferentially drive binding to tumor cells and enable avidity-induced blocking of proximal CD47 receptors on the same cell while preventing on-target off-tumor binding on healthy cells. The Fc portion of ISB 1442 is engineered to enhance complement dependent cytotoxicity, antibody dependent cell cytotoxicity and antibody dependent cell phagocytosis. ISB 1442 thus represents a CD47-BsAb combining biparatopic targeting of a tumor associated antigen with engineered enhancement of antibody effector function to overcome potential resistance mechanisms that hamper treatment of myeloma with monospecific anti-CD38 antibodies. ISB 1442 is currently in a Phase I clinical trial in relapsed refractory multiple myeloma.

Neuronal activity induction of the stathmin-like gene RB3 in the rat hippocampus: possible role in neuronal plasticity.

Synaptic activity induces a rapid transcriptional response that is essential for the establishment of long-term neuronal plasticity. Using a differential cloning technique, we have identified a gene induced by seizure activity in the brain as RB3. RB3 is a recently cloned gene belonging to the stathmin family of phosphoproteins. Like SCG10, RB3 is brain-specific, although in situ hybridization results show that the expression of RB3 is more ubiquitous than is that of SCG10. Using genomic DNA sequencing, we show that the 27 amino acid sequence unique to the RB3" transcript is encoded by an alternatively spliced exon, exon 2'. Using a peptide antibody raised against exon 2' to detect RB3" and an anti-Flag antibody to detect an epitope-tagged version of RB3, we show that both proteins are localized to the Golgi apparatus of transfected COS7 cells. Of particular interest, RB3 mRNA, but not SCG10 mRNA, is rapidly induced in the dentate gyrus granule layer of the hippocampus after electrically induced seizure activity as well as stimuli leading to long-term potentiation (LTP). In addition, RB3 mRNA is induced in pheochromocytoma (PC12) cells treated with 250 ng/ml NGF. These results suggest that RB3 may play a role in activity-induced neuronal plasticity and neuronal differentiation.

Contribution to global protein stabilization of the N-capping box in human growth hormone.

In this work we have investigated the contribution to protein stability of residues forming the boundaries of alpha-helices. At the N-terminus of helix 2 of human growth hormone there are two residues, Ser71 and Glu74, which form two reciprocal hydrogen bonds between the side chains and the backbone nitrogens of either residue (the N-capping box). In order to evaluate the stabilizing effect of each hydrogen bond, site-directed mutagenesis was employed. In addition, the effect of side-chain negative charge on helix stabilization, via charge dipole interaction, was assessed. Ultraviolet spectroscopy and near- and far-UV CD spectroscopy as well as guanidine hydrochloride protein denaturation were used as assays to monitor the conformational and free energy of stabilization changes induced by the point mutations. The results of these experiments can be summarized as follows: (a) receptor binding studies showed that the tertiary conformation of each mutant was similar to that of the native hormone, (b) far-UV CD spectroscopic analyses showed that the overall alpha-helical content was unchanged in the mutants, (c) UV absorption and CD spectroscopic analyses indicated small alterations in helical packing in those mutants in which the hydrogen bond between the side chain of Ser71 and backbone NH of Glu74 was disrupted, (d) the hydrogen bond involving the side chain of Ser71 contributes at least 1.0 kcal/mol to protein stabilization and has a 2-fold larger stabilizing effect than that of the hydrogen bond involving the Glu74 side chain, and (e) the putative charge-dipole interaction of Glu74 with the alpha-helix dipole does not contribute to the stabilization of the tertiary conformation of human growth hormone.

Changing the location of the Schiff base counterion in rhodopsin.

Rhodopsin and all of the vertebrate visual pigments have a carboxylic acid residue, Glu113, in the third transmembrane segment that serves as a counterion to the protonated Schiff base nitrogen of the chromophore. We show here that the counterion in bovine rhodopsin can be moved from position 113 to 117 without significantly changing the wild-type spectral properties of the protein. A series of double mutants were constructed where the Glu113 counterion was changed to Gln and an Asp residue was substituted for amino acid residues from position 111 to 121 in the third transmembrane segment of the protein. Only at position 117 can an Asp fully substitute for the counterion at position 113. The double mutant E113Q,-A117D has an absorption maximum at 493 nm which is independent of pH in the range 5.6-8.4 and independent of the presence of external chloride anions. An Asp at no other position tested in the third transmembrane segment can fully substitute for the Glu counterion at position 113. Partial substitution is observed for an Asp at position 120. Residues 113, 117, and 120 are expected to lie along the same face of an alpha-helix. These results suggest that the Schiff base nitrogen in rhodopsin is located between residues 113 and 117 but there is enough flexibility in the protein to allow partial interaction with an Asp at position 120. Position 117 is the same location of the counterion in the related biogenic amine receptors.

Antibody expression in bacteriophage systems: the future of monoclonal antibodies?

Bacteriophage systems have been utilized to express and isolate antibodies. This promising technology has been evolving rapidly and has the potential to revolutionize the way in which monoclonal antibodies are generated. This review focuses on the many recent advances that have been made in obtaining monoclonal antibodies from bacteriophage systems.

Constitutively active mutants of rhodopsin.

Two critical amino acids in the visual pigment rhodopsin are Lys-296, the site of attachment of retinal to the protein through a protonated Schiff base linkage, and Glu-113, the Schiff base counterion. Mutation of Lys-296 or Glu-113 results in constitutive activation of opsin, as assayed by its ability to activate transducin in the absence of added chromophore. We conclude that opsin is constrained to an inactive conformation by a salt bridge between Lys-296 and Glu-113. Recently, one of the mutants, K296E, was found in a family with retinitis pigmentosa, suggesting that degeneration of the photoreceptor cells in individuals with this mutation may result from persistent stimulation of the phototransduction pathway.

Transducin activation by rhodopsin without a covalent bond to the 11-cis-retinal chromophore.

Rhodopsin and the visual pigments are a distinct group within the family of G-protein-linked receptors in that they have a covalently bound ligand, the 11-cis-retinal chromophore, whereas all of the other receptors bind their agonists through noncovalent interactions. The retinal chromophore in rhodopsin is bound by means of a protonated Schiff base linkage to the epsilon-amino group of Lys-296. Two rhodopsin mutants have been constructed, K296G and K296A, in which the covalent linkage to the chromophore is removed. Both mutants form a pigment with an absorption spectrum close to that of the wild type when reconstituted with the Schiff base of an n-alkylamine and 11-cis-retinal. In addition, the pigment formed from K296G and the n-propylamine Schiff base of 11-cis-retinal was found to activate transducin in a light-dependent manner, with 30 to 40% of the specific activity measured for the wild-type protein. It appears that the covalent bond is not essential for binding of the chromophore or for catalytic activation of transducin.

Neonatal and adult primary B cells use the same germ-line VH and V kappa genes in their (T,G)-A-L-specific repertoire.

Although there is a nonrandom usage of VH gene families by primary B cells early in ontogeny, at issue is whether the preferential rearrangement of 3' germ-line VH genes, e.g., VH7183 and VHQ52 family genes, influences the neonatal B cell repertoire that can be expressed in response to Ag. In order to address this issue, and to determine whether neonatal B cells can use the same germ-line VH and V kappa genes as adult B cells in their primary response, we have analyzed at the molecular level the neonatal antibody response to (T,G)-A-L and compared it with the adult primary response. Among the TGB5 Id+, GT+ antibodies, which dominate the neonatal response to (T,G)-A-L, two VH gene families were used: J558 (high frequency) and 36-60 (low frequency). The majority of Id+ neonatal hybridomas used the same germ-line VH gene (H10, from the VHJ558 family), but with enormous diversity in the D region, and one of two germ-line V kappa 1 genes (V kappa 1A, V kappa 1C). These are the same germ-line V-genes used by most primary adult Id+ hybridomas, and the frequency of expression of this germ-line V-gene combination appears equivalent in the neonatal and adult primary repertoires. Therefore, it is clear from this study that as early as day 5, neonatal B cells can use the same germ-line V-genes as adult primary B cells in their Ag-specific repertoire.

Effect of carboxylic acid side chains on the absorption maximum of visual pigments.

The proposal that the absorption maximum of the visual pigments is governed by interaction of the 11-cis-retinal chromophore with charged carboxylic acid side chains in the membrane-embedded regions of the proteins has been tested by mutating five Asp and Glu residues thought to be buried in rhodopsin. Changing Glu113 to Gln causes a dramatic shift in the absorption maximum from 500 nanometers to 380 nanometers, a decrease in the pKa (acidity constant) of the protonated Schiff base of the chromophore to about 6, and a greatly increased reactivity with hydroxylamine. Thus Glu113 appears to be the counterion to the protonated Schiff base. Wavelength modulation in visual pigments apparently is not governed by electrostatic interaction with carboxylate residues, other than the counterion.