synthetic-antigen-controls-for-immunohistochemistry

Synthetic Antigen Controls for Immunohistochemistry

Immunohistochemistry (IHC) assays provide valuable insights into protein expression patterns, the reliable interpretation of which requires ...

Genentech, Inc.

Local delivery of therapeutic angiogenic agents that stimulate blood vessel formation represents a promising strategy for the treatment of peripheral vascular disease (PVD). At present, requirements for temporal and spatial parameters for localized delivery are unclear, with a variety of sustained delivery approaches being examined. Two polymer-based sustained formulations containing the 165 amino acid isoform of human recombinant vascular endothelial growth factor-A (rhVEGF(165)) were evaluated for their potential application in the treatment of PVD following intramuscular injection. Microspheres prepared from a 50:50 ratio of polylactic-co-glycolic acid (PLGA) and a gel of PLGA polymer solubilized in N-methyl pyrrolidone (PLGA:NMP) were each loaded with rhVEGF(165) and tested in vitro and in vivo. PLGA microspheres averaged ∼30 μm in diameter and contained 8.9% (w/w) rhVEGF(165), while the PLGA:NMP gel was formulated with varying amounts of spray freeze-dried rhVEGF(165) to result in final gel formulations having concentrations of 0.36, 0.72, or 3.6 mg/mL rhVEGF(165). In vitro release of rhVEGF(165) from PLGA microspheres showed ∼10% cumulative release by day 6, whereas the cumulative release of rhVEGF(165) from the PLGA:NMP gel matrices (0.65% w/w loading) was less than 0.25% at this same time point. While the in vitro release characteristics of these two sustained release formulations were broadly different, the plasma rhVEGF(165) concentration-time profiles following hind-limb intramuscular (IM) injection of these formulations in non-compromised rats revealed similar in vivo pharmacokinetics. Three-dimensional resin casts of vascular architecture were prepared at days 3, 7, 14, 21, 28, 60, and 75 following a single IM dosing of these sustained release microsphere and gel matrix formulations in the gastrocnemius muscle of immune-compromised mice. Scanning electron microscopic visualization of these vascular casts demonstrated spatial arrangement of capillary sprouts and vessel enlargement consistent with profound vascular changes occurring within 3 days of dosing that persisted for 2 months, approximately 1 month beyond the anticipated completion of rhVEGF(165) release from these sustained delivery formulations. Vascular re-modeling events were correlated with histological and immunohistochemical parameters attributed to known biological actions of rhVEGF(165) signaling. Together, these pharmacokinetic and pharmacodynamic results support the use of sustained release PLGA-based formulations for the local delivery of rhVEGF(165) to achieve a durable vascular re-modeling response.

Sustained release formulations of rhVEGF₁₆₅ produce a durable response in a murine model of peripheral angiogenesis.

Protein secretion to the periplasm of Escherichia coli offers an attractive route for producing heterologous proteins including antibodies. In this approach, a signal peptide is fused to the N-terminus of the heterologous protein. The signal peptide mediates translocation of the heterologous protein from the cytoplasm to the periplasm and is cleaved during the translocation process. It was previously shown that optimization of the translation initiation region (TIR) which overlaps with the nucleotide sequence of the signal sequence improves the production of heterologous proteins. Despite the progress, there is still room to improve yields using secretion as a means to produce protein complexes such as full-length monoclonal antibodies (mAbs).

Enhancing full-length antibody production by signal peptide engineering.

Optimization and standardization of immunohistochemistry (IHC) protocols within and between laboratories requires reproducible positive and negative control samples. In many situations, suitable tissue or cell line controls are not available. We demonstrate here a method to incorporate target antigens into synthetic protein gels that can serve as IHC controls. The method can use peptides, protein domains, or whole proteins as antigens, and is compatible with a variety of fixation protocols. The resulting gels can be used to create tissue microarrays (TMAs) with a range of antigen concentrations that can be used to objectively quantify and calibrate chromogenic, fluorescent, or mass spectrometry-based IHC protocols. The method offers an opportunity to objectively quantify IHC staining results, and to optimize and standardize IHC protocols within and between laboratories. (J Histochem Cytochem 58:XXX-XXX, 2019).

Linda K. Rangell

Research Pathology

Genentech, Inc.

Synthetic Antigen Controls for Immunohistochemistry