New Mesoblast “COVID kid” stem cell study

Dr Fred Grossman, CMO Mesoblast, stem cells for COVID-19
Dr Fred Grossman, CMO Mesoblast.

The biotech Mesoblast is starting an expanded access study of its stem cell product for kids with a severe offshoot of COVID-19.

The cellular drug in this case is remestemcel-L (more below).

While most children fare better than adults in dealing with COVID-19, the rare subset of kids with COVID-19 for this study have more severe disease than the average COVID patient and some die.

Physicians need more potential treatment options here for these children. In that sense one could argue that testing more new drugs including cellular therapies is a high priority.

Tidal wave of cell medicine trials for COVID

MSCs mesenchymal stem cells stromal cells Rose Spear
MSCs (mesenchymal stem cells and stromal cells). Blue is DAPI, Green is actin, and Red is fibrin filaments on which the cells were grown. Photo credit: Rose Spear open source image on Flickr.

Mesoblast is one of a growing group of cell medicine biotech companies and universities that have started various trials for COVID-19, most often using stem cells, but sometimes other kinds of cells including immune cells.

In fact, doing a search on for MSCs and COVID-19 produces an astonishing number of trial listings, although not all seem to refer to MSCs somehow. I expect that number will soon be 200, which adds up to a ton of patients getting cells and most often MSCs for their COVID-19.

Do this boatload of MSC-related trials make sense?

What are the risks?

How much data was needed to get FDA clearance for the various INDs (or equivalent in other countries)?

New Mesoblast clinical experiment

The new FDA-cleared Mesoblast study (technically an Expanded Access Protocol or compassionate use program) seems fairly unique in its focus on children with that rare, but very severe COVID-19-related condition called Multisystem Inflammatory Syndrome in Children (MIS-C).

The trial listing is entitled, “Intermediate-size Expanded Access Program (EAP), Mesenchymal Stromal Cells (MSC) for Multisystem Inflammatory Syndrome in Children (MIS-C) Associated With Coronavirus Disease (COVID-19).” I only found 3 total trial listings using any product for MIS-C in a recent search.

The MSCs here are remestemcel-L, which is approved for use in graft-versus-host disease (GvHD), where recipients of stem cell transplants (e.g. bone marrow) end up having the “graft” (donor immune cells) attack the host (the person who got the transplant). remestemcel-L suppresses the graft from attacking the patient.

How could a GvHD cellular drug possibly help COVID-19 or MIS-C?

How could the same product used for GvHD potentially help COVID-19 patients and more specifically the pediatric patients with MIS-C? The basic premise seems to be that remestemcel-L may suppress the overactive immune response of COVID-19 patients, limiting “friendly fire” damage from the immune system and perhaps turning down the cytokine storm of COVID.

However, GvHD is a very different disease than COVID-19 or MIS-C. For one thing, in GvHD it is someone else’s immune cells causing the damage, while in COVID-19 it is our own cells that overdo it. Also, of course, COVID-19 disease is caused by a massive infection with the novel coronavirus, while GvHD patients most often are battling cancer. The patient population is very different. These things present challenges to the new work. A commonality though is some role for cytokine storm, which remestemcel-L may  target.

Here’s the firm’s view of the road to efficacy in this COVID context:

“Mesoblast Chief Medical Officer Dr Fred Grossman said: “The extensive body of safety and efficacy data generated to date using remestemcel-L in children with graft versus host disease suggest that our cellular therapy could provide a clinically important therapeutic benefit in MIS-C patients, especially if the heart is involved as a target organ for inflammation. Use of remestemcel-L in children with COVID-19 builds on and extends the potential application of this cell therapy in COVID-19 cytokine storm beyond the most severe adults with acute respiratory distress syndrome.”

So maybe it could help?

It’s very hard to predict based on so little data. It’s also hard to know safety of stem cell products for COVID-19 patients yet.

As to the larger Mesoblast COVID-19 study (the earlier one that is not just for kids), Motley Fool of all places highlighted a potential challenge for the company in that an increasing number of hospitals may be avoiding putting COVID patients on ventilators since that step could lead to more negative outcomes for some kinds of patients, and the company’s study is focused on patients on ventilators.

Maybe the firm will expand the scope of patients for that study to also include those not on ventilators.

FDA and cell therapy clearances during COVID-19 pandemic

During a pandemic it seems the FDA has really changed how it handles cell therapy clearances, requiring less data for COVID-19-related IND applications and perhaps for other mechanisms of moving products forward, like expanded access.

Expanded access applications can proceed with much less data in general. The initial earlier clearance of the remestemcel-L IND to be tested in COVID-19 in general is also the foundation for this new “COVID kids” effort.


The kids in this protocol will also get steroids. I have to wonder if the steroids alone might do enough on their own for some patients given recent results. Between the steroids and because this is expanded access and I don’t think there will be any controls in that context, I also wonder if Mesoblast will be able to get a clear signal on whether the stem cells specifically did something useful for the children.

Looking ahead

remestemcel-L and other MSC approaches could also have risks for these COVID pediatric patients. It’s hard to anticipate potential risks, but some kind of over-suppression of the immune system comes to mind. That could make the kids less able to fight off the virus. Just because a drug has a certain safety profile in GvHD also does not mean that translates to kids with severe COVID-19 and MISC-C. As a result, we should keep both efficacy and potential adverse events in mind as the clinical work proceeds.

In about 6 months we’ll know quite a bit more from all the MSC studies for COVID-19 and the other cell medicine trials. I hope at least some of the data from the different studies suggest both efficacy and that the hoped-for good safety profile remains solid.

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