There is some positive info out there about Alpha 2...

There is some positive info out there about Alpha 2 Macroglobulin (A2M), but one could question its durability. Being a human recombinant protein it might also encounter supply/manufacturing issues and it may also face degradation challenges, whether in vivo or in storage.

There will also be a major difference in the costs of manufacturing A2M vs PPS and I think PPS will have a better chance of meeting the scale required to treat OA than A2M. A2M appears to have a similar MOA to PPS, but it may be limited in the required dosage that can be given, however empirical evidence suggests this won't be much of an issue. It's easier to give a higher dose of a chemical such as PPS than a recombination human protein such as A2M. The ultimate test will be a randomised double blind trial.

Just some of my thoughts.