Monoclonal antibody drugs will flood the market soon and usher in a new era of treatment for several diseases (MS, AD, certain cancers, etc).
What you mention about cell division rates being slow was solved by the hybridoma protocol where you fuse two cells, one of which is a myeloma (cancer that is a rapidly reproducing cell line) and another is a B cell that produces Antibodies that are specific for your intended target. Since then there have been a lot of strides in monoclonal antibody production. [https://en.wikipedia.org/wiki/Monoclonal_antibody#Production]
It's still cell division, nowhere near the speed and cost of chemically produced drugs.