I was more getting at the FDA's need for proof of the MOA, and...

I was more getting at the FDA's need for proof of the MOA, and that will need to come from a collection of surrogates rather than a single end point .

Mesoblast said the COVID trial was designed in consultation with the FDA and it has around 33 secondary end points of which some are surrogates, and some could be end points by themselves.
If you breakdown the data collection it appears the company will use the secondary endpoints to link:

Death / Clinical Improvement score / Improvement or resolution timeframe / Change in ARDS severity / IL 6 / IL 8 / TNFA / CRP .

They are mostly all checked on 7 day rolling period for a month which one would think the company will use to backup the MOA which also would vindicate the potency assays and possibly allay some of the manufacturing concerns depending on how many different donors / batches are used if successful.

They are very different trial end points when comparing MSB and Athersys, and I wonder if Athersys is collecting all of that data themselves anyway, or why they appear to have such different end points - Death for MSB, and safety/Ventilator free days for Athersys