H. R. Hoogenboom, Ph.D., CSO of Merus Biopharmaceuticals (Driebergen, The Netherlands), discussed his company's plans for development of defined recombinant antibody mixtures, using cell lines engineered to simultaneously produce several different antibodies.
Traditionally, companies have shied away from the use of antibody mixtures because of cost, and the complexity of manufacturing and regulatory issues. Merus seeks to develop and commercialize proprietary technology for human antibody-based therapeutics using Oligoclonics, defined mixtures of human antibodies.
The Oligoclonic technology is designed to achieve the performance of polyclonal antibodies combined with consistency and cost saving of monoclonal antibodies. This format places multiple genes in the same host cell, rather than growing a number of cell lines concurrently, where they might compete with one another.
A clonal cell line capable of generating different antibodies is produced by simultaneously transfecting cells with multiple antibody heavy and light encoding genes (in one or more expression vectors) and selecting for stable integration.
By carefully screening a number of cell lines, clones are identified that express multiple antibodies, and at a total expression level typical for a monoclonal antibody. Biological assays are used to find the most optimal composition of each of the antibody components in the mixture.
The Merus team demonstrated that when two antibodies sharing the same light chain are encoded in a single host cell (PER.C6), the two homodimers will be produced as well as the heterodimer, composed of the two dissimilar heavy chains and coding for a bifunctional antibody.
In cell lines producing three different antibodies the different species can be distinguished in isoelectric focusing gels. Moreover, peptides encoded by the different antibody genes can be separated out using mass spectrometry.
Using these tools, it was demonstrated that some of the cell lines stably produced the different antibody for 30 generations of cell culture growth. Therefore the assumptions upon which the technology is based appear to be valid.
There are a variety of potential applications of the Merus technology. Oligoclonics cell lines could effectively target multiple epitopes on the same protein target, or they could target different antigens, such as CD20 and CD22 on the same leukemic cell line.
Other potential applications include multiple cytokines or a collective group of antigens on an infectious disease entity. Moreover, this technology has the potential to generate higher affinity and avidity antibodies that could function more vigorously in a variety of tasks, including synergy in apoptosis and antigen-dependent cell cytotoxicity, and suppression of multiply redundant cellular pathways.
This approach has the potential to serve as a means to boost antibody efficacy yet retain a natural, nonmodified antibody format and build on existing antibody production facilities.
While the technology has great appeal, there are substantial challenges that the Merus team is addressing. These include establishment of stability of the antibody-producing cell lines, proof of performance as compared to standard monoclonal and polyclonal antibodies, and the formidable issue of overcoming regulatory hurdles.