Poor solubility is a common challenge encountered during the development of high concentration monoclonal antibody (mAb) formulations, but there are currently no methods that can provide predictive information on high-concentration behavior of mAbs in early discovery. We explored the utility of methodologies used for determining extrapolated solubility as a way to rank-order mAbs based on their relative solubility properties. We devised two approaches to accomplish this: 1) vapor diffusion technique utilized in traditional protein crystallization practice, and 2) polyethylene glycol (PEG)-induced precipitation and quantitation by turbidity. Using a variety of in-house mAbs with known high-concentration behavior, we demonstrated that both approaches exhibited reliable predictability of the relative solubility properties of these mAbs. Optimizing the latter approach, we developed a format that is capable of screening a large panel of mAbs in multiple pH and buffer conditions. This simple, material-saving, high-throughput approach enables the selection of superior molecules and optimal formulation conditions much earlier in the antibody discovery process, prior to time-consuming and material intensive high-concentration studies.

Self-association of monoclonal antibodies (mAbs) at high concentrations can result in developability challenges such as poor solubility, aggregation, opalescence and high viscosity. There is a significant unmet need for methods that can evaluate self-association propensities of concentrated mAbs at the earliest stages in antibody discovery to avoid downstream issues. We have previously developed a method (affinity-capture self-interaction nanoparticle spectroscopy, AC-SINS) that is capable of detecting weak antibody self-interactions using unusually dilute mAb solutions (tens of µg/ml). Here we optimize and implement this assay for characterization of unpurified and highly dilute mAbs directly in cell culture media. This assay was applied to screen 87 mAbs obtained via immunization. Our measurements reveal a wide range of self-associative propensities for mAbs that bind to the same antigen and which differ mainly in their complementarity-determining regions. The least associative mAbs identified by AC-SINS were confirmed to be highly soluble when purified and concentrated by three to five orders of magnitude. This approach represents a key advance in screening mAb variants using unpurified antibody samples, and it holds significant potential to both improve initial candidate selection as well as to guide protein engineering efforts to improve the properties of specific mAb candidates.

A myriad of innovative bispecific antibody (BsAb) platforms have been reported. Most require significant protein engineering to be viable from a development and manufacturing perspective. Single-chain variable fragments (scFvs) and diabodies that consist only of antibody variable domains have been used as building blocks for making BsAbs for decades. The drawback with Fv-only moieties is that they lack the native-like interactions with CH1/CL domains that make antibody Fab regions stable and soluble. Here, we utilize a redesigned Fab interface to explore 2 novel Fab-based BsAbs platforms. The redesigned Fab interface designs limit heavy and light chain mixing when 2 Fabs are co-expressed simultaneously, thus allowing the use of 2 different Fabs within a BsAb construct without the requirement of one or more scFvs. We describe the stability and activity of a HER2×HER2 IgG-Fab BsAb, and compare its biophysical and activity properties with those of an IgG-scFv that utilizes the variable domains of the same parental antibodies. We also generated an EGFR × CD3 tandem Fab protein with a similar format to a tandem scFv (otherwise known as a bispecific T cell engager or BiTE). We show that the Fab-based BsAbs have superior biophysical properties compared to the scFv-based BsAbs. Additionally, the Fab-based BsAbs do not simply recapitulate the activity of their scFv counterparts, but are shown to possess unique biological activity.