Bellicum Pharmaceuticals, Inc. (NASDAQ:BLCM) and Achaogen, Inc. (NASDAQ:AKAO) were big movers during the middle of the week, with both companies moving on fresh inputs relating to their respective development pipelines.

Here’s what you need to know.

Bellicum

Shortly after the markets closed out in the US on Tuesday, Bellicum reported that the US Food and Drug Administration (FDA) has placed a clinical hold on U.S. studies of its lead development asset. The drug is called BPX-501 and it’s currently under investigation as a potential therapy to improve the outcomes of patients undergoing haploidentical (partial match) hematopoietic stem cell transplants (HSCT).

These sorts of transplants can be a life-saving treatment for patients with certain conditions but, at the same time, are very risky because they are only partial matches. The chances of graft versus host disease (GvHD) developing is high because of the non-match element of the procedure and GvHD can be deadly.

BPX-501 is designed to turn off T cells that would otherwise attack the cells that are introduced as part of the stem cell transplant and, in doing so, designed to make the process safer for patients that need it.

And there’s a fair amount of early stage data that points towards it being effective towards that aim.

So what’s with the clinical hold?

Reports have hit press that certain patients who have undergone treatment with BPX-501 have developed encephalopathy, a general term that means brain disease, damage, or malfunction, generally characterized by an altered mental state. It’s a serious development and one that, if shown to be directly caused by the BPX-501 treatment, could be a nail in the coffin for the asset long term.

Is it BPX-501 that is causing the encephalopathy?

This is the key question and, at a glance, it looks as though the decision to put this program on hold may be more of a risk minimization move than anything else. According to reports, only three patients have been diagnosed with the encephalopathy that’s causing the concern and the company has treated more than 240 patients with the drug as part of its human clinical trials program. That’s around a 1.25% incidence rate, which is enough to raise concerns but likely not enough to completely derail the program – even if the drug is shown to be the root cause of the complication. The issue is risk/benefit.

Regardless of this fact, however, markets are taking the development as bad news and are trading down on the company as a result.

After hours on Tuesday (the announcement didn’t hit press until markets ended the day in the US), Bellicum shares slid just shy of 40% and will enter today’s session in and around $5.10 a piece.

Chances are we’ll see some further weakness as normal participation gets underway. But for investors who believe in the asset and think the risk/benefit profile for patients will hold, it could be a good chance to buy the discount.

Achaogen

This one is more positive than that which Belicum reported.

The company said on Tuesday that the FDA has completed its review of a manufacturing facility that’s owned by Pfizer – one at which Achaogen intends to produce its lead development asset if and when it picks up a green light for commercialization in the US subsequent to PDUFA – and that the outcome of the review is a classification of Voluntary Action Indicated (VAI).

AVAI outcome indicates that although objectionable conditions were found, the problems do not justify further regulatory action and any corrective action is left to the investigator to take voluntarily.

Why is this important?

Achaogen has an NDA with the FDA for the above-mentioned lead asset, a drug called plazomicin, which it’s trying to get approved a new treatment option for patients with serious bacterial infections, including those due to CRE and ESBL-producing Enterobacteriaceae.

The review of the manufacturing facility was hanging as a dark cloud over the NDA, with the uncertainty surrounding the outcome translating to uncertainty surrounding the chances of the NDA picking up a regulatory approval.

With the VAI outcome in place, the dark cloud is lifted and it’s now all about safety and efficacy as opposed to any manufacturing concerns.

Markets now look towards the upcoming PDUFA data as the next catalyst for Achaogen, which is slated for June 25, 2018.

Enjoyed this? Read this next: Biotech Movers: Aradigm Corporation, Theravance Biopharma, Inc. and Mylan NV