Production of a recombinant monoclonal antibody to Herpes Simplex Virus glycoprotein D for immunoaffinity purification of tagged proteins

Measurement of specific and nonspecific tissue uptake of antibodies in tumor by SPECT imaging and nonlinear compartmental modeling

BACKGROUND

Understanding the mechanisms driving specific and nonspecific tissue uptake of antibodies can inform protein engineering strategies that maximize therapeutic efficacy in target tissues while minimizing off-target tissue toxicities. While in vitro cell assays are typically used to study these internalization mechanisms, there are few methods readily available to evaluate these pathways in vivo. Single photon emission computed tomography (SPECT) imaging with a non-residualizing radiohalogen probe can measure total levels of intact antibody, and a residualizing radiometal-chelate probe, in combination with a non-residualizing probe, can measure catabolized antibody associated with receptor-mediated and nonspecific internalization processes. Here, we describe a SPECT imaging study in human epidermal growth factor receptor 2 (HER2)-expressing tumor-bearing mice aimed at measuring whole body disposition kinetics of tumor-targeting trastuzumab (anti-HER2) and non-targeting (anti-gD) antibodies. Mice received these molecules labeled with either a non-residualizing prosthetic group ([125I]SIB) or with a residualizing radiometal-chelate (111In-DOTA).

RESULTS

SPECT imaging data confirmed significant HER2-mediated tumor uptake and catabolism of anti-HER2, evidenced by the high 111In-DOTA-anti-HER2 signal over time relative to 111In-DOTA-anti-gD and the respective [125I]SIB-labeled molecules. [125I]SIB-anti-HER2 still showed noticeably higher tumor signal than [125I]SIB-anti-gD, demonstrating a meaningful pool of intact anti-HER2 in the interstitial tumor compartment. Spleen showed the greatest catabolism of both mAbs amongst all non-tumor tissues. Compartmental modeling of the SPECT data demonstrated that cell-associated anti-HER2 was primarily receptor-bound, with a peak receptor occupancy of 35% at 13 h post administration of a 10 mg/kg dose, with minimal free and pinocytosed mAb.

CONCLUSION

Here, we successfully developed an imaging and modeling approach to capture anti-HER2 antibody receptor binding as well as specific and nonspecific internalization over time in vivo. These data and analyses demonstrate the power of SPECT imaging using both non-residualizing and residualizing radioisotopes to better characterize the different biological states (free, bound, and catabolized) of antibodies within interstitial and intracellular compartments. Understanding these distinct antibody internalization mechanisms in tumor and non-tumor tissues enables more informed decisions on dose selection to optimize treatment of tumors with heterogeneous antigen expression while minimizing nonspecific toxicities.

Recent Advances in Supramolecular Affinity Separations: Affinity Chromatography and Related Methods

Affinity chromatography is a technique that uses a stationary phase based on the supramolecular interactions that occur in biological systems or mimics of these systems. This method has long been a popular tool for the isolation, measurement, and characterization of specific targets in complex samples. This review discusses the basic concepts of this method and examines recent developments in affinity chromatography and related supramolecular separation methods. Topics that are examined include advances that have occurred in the types of supports, approaches to immobilization, and binding agents that are employed in this method. New developments in the applications of affinity chromatography are also summarized, including an overview on the use of this method for biochemical purification, sample preparation or analysis, chiral separations, and biointeraction studies.

Gene editing in CHO cells to prevent proteolysis and enhance glycosylation: Production of HIV envelope proteins as vaccine immunogens

Several candidate HIV subunit vaccines based on recombinant envelope (Env) glycoproteins have been advanced into human clinical trials. To facilitate biopharmaceutical production, it is necessary to produce these in CHO (Chinese Hamster Ovary) cells, the cellular substrate used for the manufacturing of most recombinant protein therapeutics. However, previous studies have shown that when recombinant Env proteins from clade B viruses, the major subtype represented in North America, Europe, and other parts of the world, are expressed in CHO cells, they are proteolyzed and lack important glycan-dependent epitopes present on virions. Previously, we identified C1s, a serine protease in the complement pathway, as the endogenous CHO protease responsible for the cleavage of clade B laboratory isolates of -recombinant gp120s (rgp120s) expressed in stable CHO-S cell lines. In this paper, we describe the development of two novel CHOK1 cell lines with the C1s gene inactivated by gene editing, that are suitable for the production of any protein susceptible to C1s proteolysis. One cell line, C1s-/- CHOK1 2.E7, contains a deletion in the C1s gene. The other cell line, C1s-/- MGAT1- CHOK1 1.A1, contains a deletion in both the C1s gene and the MGAT1 gene, which limits glycosylation to mannose-5 or earlier intermediates in the N-linked glycosylation pathway. In addition, we compare the substrate specificity of C1s with thrombin on the cleavage of both rgp120 and human Factor VIII, two recombinant proteins known to undergo unintended proteolysis (clipping) when expressed in CHO cells. Finally, we demonstrate the utility and practicality of the C1s-/- MGAT1- CHOK1 1.A1 cell line for the expression of clinical isolates of clade B Envs from rare individuals that possess broadly neutralizing antibodies and are able to control virus replication without anti-retroviral drugs (elite neutralizer/controller phenotypes). The Envs represent unique HIV vaccine immunogens suitable for further immunogenicity and efficacy studies.

Identification and CRISPR/Cas9 Inactivation of the C1s Protease Responsible for Proteolysis of Recombinant Proteins Produced in CHO Cells

Proteolysis associated with recombinant protein expression in Chinese Hamster Ovary (CHO) cells has hindered the development of biologics including HIV vaccines. When expressed in CHO cells, the recombinant HIV envelope protein, gp120, undergoes proteolytic clipping by a serine protease at a key epitope recognized by neutralizing antibodies. The problem is particularly acute for envelope proteins from clade B viruses that represent the major genetic subtype circulating in much of the developed world, including the US and Europe. In this paper, we have identified complement Component 1's (C1s), a serine protease from the complement cascade, as the protease responsible for the proteolysis of gp120 in CHO cells. CRISPR/Cas9 knockout of the C1s protease in a CHO cell line was shown to eliminate the proteolytic activity against the recombinantly expressed gp120. In addition, the C1s^-/- MGAT1^- CHO cell line, with the C1s protease and the MGAT1 glycosyltransferase knocked out, enabled the production of unclipped gp120 from a clade B isolate (BaL-rgp120) and enriched for mannose-5 glycans on gp120 that are required for the binding of multiple broadly neutralizing monoclonal antibodies (bN-mAbs). The availability of this technology will allow for the scale-up and testing of multiple vaccine concepts in regions of the world where clade B viruses are in circulation. Furthermore, the proteolysis issues caused by the C1s protease suggests a broader need for a C1s-deficient CHO cell line to express other recombinant proteins that are susceptible to serine protease activity in CHO cells. Similarly, the workflow described here to identify and knockout C1s in a CHO cell line can be applied to remedy the proteolysis of biologics by other CHO proteases.