Conduit CAR: Redirecting CAR T-Cell Specificity with A Universal and Adaptable Bispecific Antibody Platform.

The success of chimeric antigen receptor (CAR) T-cell therapy against hematologic malignancies has altered the treatment paradigm for patients with these diseases. Nevertheless, the occurrence of relapse due to antigen escape or heterogeneous antigen expression on tumors remains a challenge for first-generation CAR T-cell therapies as only a single tumor antigen can be targeted. To address this limitation and to add a further level of tunability and control to CAR T-cell therapies, adapter or universal CAR T-cell approaches use a soluble mediator to bridge CAR T cells with tumor cells. Adapter CARs allow simultaneous or sequential targeting of multiple tumor antigens, control of immune synapse geometry, dose control, and the potential for improved safety. Herein, we described a novel CAR T-cell adapter platform that relies on a bispecific antibody (BsAb) targeting both a tumor antigen and the GGGGS (G4S) linker commonly used in single-chain Fv (ScFv) domains expressed on CAR T-cell surfaces. We demonstrated that the BsAb can bridge CAR T cells to tumor cells and potentiate CAR T-cell activation, proliferation, and tumor cell cytolysis. The cytolytic activity of CAR T-cells was redirected to different tumor antigens by changing the BsAb in a dose-dependent manner. This study highlights the potential of G4S-displaying CAR T cells to be redirected to engage alternative tumor-associated antigens (TAA). Significance: New approaches are needed to address relapsed/refractory disease and manage potential toxicities associated with CAR T-cell therapy. We describe an adapter CAR approach to redirect CAR T cells to engage novel TAA-expressing cells via a BsAb targeting a linker present on many clinical CAR T-cell therapeutics. We anticipate the use of such adapters could increase CAR T-cell efficacy and reduce potential CAR-associated toxicities.

Monitoring the disulfide bond formation of a cysteine-rich repeat protein from Helicobacter pylori in the periplasm of Escherichia coli.

Helicobacter pylori infection increases the risk of cardiovascular diseases besides leading to duodenal and gastric peptic ulcerations. H. pylori cysteine-rich protein B (HcpB) is a disulfide-rich repeat protein that belongs to the family of Sel1-like repeat proteins. HcpB contains four pairs of anti-parallel alpha helices that fold into four repeats with disulfide bonds bridging the helices of each repeat. Recent in vitro oxidative refolding of HcpB identified that the formation and folding of the disulfide bond in the N-terminal repeat are the rate limiting step. Here we attempted to understand the disulfide formation of HcpB in the periplasm of Escherichia coli. The protein was expressed in wild type (possessed enzymes DsbA, B, C, and D) and knock out (Dsb enzymes deleted one at a time) E. coli strains. The soluble part of the periplasm when analyzed by SDS-PAGE and Western Blot showed that the wild type and DsbC/D knock out strains contained native oxidized HcpB while the protein was absent in the DsbA/B knock out strains. Hence the recombinant expression of HcpB in E. coli requires DsbA and DsbB for disulfide bond formation and it is independent of DsbC and DsbD. Prolonged cell growth resulted in the proteolytic degradation of the N-terminal repeat of HcpB. The delayed folding of the N-terminal repeat observed during in vitro oxidative refolding could be the reason for the enhanced susceptibility to proteolytic cleavage in the periplasm. In summary, a good correlation between in vivo and in vitro disulfide bond formation of HcpB is observed.

The effects of intramolecular and intermolecular electrostatic repulsions on the stability and aggregation of NISTmAb revealed by HDX-MS, DSC, and nanoDSF.

The stability and aggregation of NIST monoclonal antibody (NISTmAb) were investigated by hydrogen/deuterium exchange mass spectrometry (HDX-MS), differential scanning calorimetry (DSC), and nano-differential scanning fluorimetry (nanoDSF). NISTmAb was prepared in eight formulations at four different pHs (pH 5, 6, 7, and 8) in the presence and absence of 150 mM NaCl and analyzed by the three methods. The HDX-MS results showed that NISTmAb is more conformationally stable at a pH near its isoelectric point (pI) in the presence of NaCl than a pH far from its pI in the absence of NaCl. The stabilization effects were global and not localized. The midpoint temperature of protein thermal unfolding transition results also showed the CH 2 domain of the protein is more conformationally stable at a pH near its pI. On the other hand, the onset of aggregation temperature results showed that NISTmAb is less prone to aggregate at a pH far from its pI, particularly in the absence of NaCl. These seemingly contradicting results, higher conformational stability yet higher aggregation propensity near the pI than far away from the pI, can be explained by intramolecular and intermolecular electrostatic repulsion using Lumry-Eyring model, which separates folding/unfolding equilibrium and aggregation event. The further a pH from the pI, the higher the net charge of the protein. The higher net charge leads to greater intramolecular and intermolecular electrostatic repulsions. The greater intramolecular electrostatic repulsion destabilizes the protein and the greater intermolecular electrostatic repulsion prevents aggregation of the protein molecules at pH far from the pI.

Discovery and characterization of single-domain antibodies for polymeric Ig receptor-mediated mucosal delivery of biologics.

Mucosal immunity is dominated by secretory IgA and IgM, although these are less favorable compared to IgG molecules for therapeutic development. Polymeric IgA and IgM are actively transported across the epithelial barrier via engagement of the polymeric Ig receptor (pIgR), but IgG molecules lack a lumen-targeted active transport mechanism, resulting in poor biodistribution of IgG therapeutics in mucosal tissues. In this work, we describe the discovery and characterization of single-domain antibodies (VHH) that engage pIgR and undergo transepithelial transport across the mucosal epithelium. The anti-pIgR VHH panel displayed a broad range of biophysical characteristics, epitope diversity, IgA competition profiles and transcytosis activity in cell and human primary lung tissue models. Making use of this diverse VHH panel, we studied the relationship between biophysical and functional properties of anti-pIgR binders targeting different domains and epitopes of pIgR. These VHH molecules will serve as excellent tools for studying pIgR-mediated transport of biologics and for delivering multispecific IgG antibodies into mucosal lumen, where they can target and neutralize mucosal antigens.

In Pursuit of Stability Enhancement of a Prostate Cancer Targeting Antibody Derived from a Transgenic Animal Platform.

Accelerated timelines necessitate the discovery of fully human antibodies as biotherapeutics using transgenic animals with a notion that such mAbs bypass humanization. A transgenic animal derived mAb (PCa75) targeted against a prostate cancer antigen had several 'unusual residues' (rare somatic hypermutations, rSHM, with positional frequency of <1%) that resulted in compromised biophysical properties (Tm = 61 °C and intrinsic stability ΔGu = 24.3 kJ/mol) and a sub-optimal immunogenicity profile. In our quest for quality medicine, we pursued antibody engineering strategies to enhance the stability of PCa75. PCa62, an engineered variant of PCa75, retained function while significantly improving the drug-like attributes of the molecule (Tm = 75 °C and intrinsic stability ΔGu = 63.5 kJ/mol). rSHM is rather prevalent, 18 out the 21 approved transgenic animal-derived antibodies have at least one 'unusual residue'. Thus, engineering of rSHM remains critical to enhance the stability and minimize immunogenicity risk of biotherapeutics.