The slow pace of progress towards clearance of amyloid, in that only in the past year has one of the immunotherapy trials actually looked promising, has provoked a lot of alternative theorizing these past five years. Some it is clearly not so great, such as the fellow who argues that it is caused by rising use of paracetamol (see http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3921468/ ), but some lines of theory are much more compelling. A more encompassing synthesis is emerging in which microbial infection by spirochetes and gum disease bacteria (e.g. see https://doi.org/10.3389/fnagi.2017.00336 ) that can provoke amyloid formation as well as failing drainage of cerebrospinal fluid (e.g. see https://doi.org/10.1002/ana.24271, https://www.ethz.ch/en/news-and-events/eth-news/news/2017/11..., etc) that stops removal of amyloid, tau, etc are as important as purely cell focused considerations of the biochemistry of amyloid beta.

For an example of the new type of venture emerging now as a result of all of this you might look at Leucadia Therapeutics, working on a way to restore drainage through the cribiform plate, but there will be more in the years ahead to complement the immunotherapy for amyloid and tau mainstream.