I know this is more so speculation rather than anything else but...

I know this is more so speculation rather than anything else but came across this Vox article about human challenge trials (yes I know Vox aren't the most reliable but it's more so the subject of the article that I care for). Here's an excerpt - "Bioethicist Nir Eyal and epidemiologists Marc Lipsitch and Peter Smith suggested conducting “human challenge trials” on willing volunteers. In such trials, volunteers are dosed with either the candidate vaccine or a placebo and then directly exposed to the coronavirus. That way, researchers would know that 100 percent of participants had been exposed, making it easier to judge the vaccine’s effectiveness. In normal vaccine trials, the treatment group is given the vaccine and the control group a placebo, and the volunteers in both groups go about their regular lives, where they may or may not encounter the virus in the wild.".
Interesting isn't it...
However, one of the big problems currently lies in that human challenge trials are only done "where enough is known about the disease or the strain that was selected that the risks to participants are lower and can be managed”, and with Covid-19 there is no treatment that can prevent death and other large risks... yet.
And as you have probably put 2 and 2 together already, Mesoblast's treatment could be 1 of many the safety barriers that is needed to allow human challenge trials to be given the go ahead, a very big safety barrier.
Interesting times...