Image source: Getty Images.

Investors in cellular therapy developer Bellicum Pharmaceuticals, Inc. (NASDAQ:BLCM) and targeted cancer treatment specialist Celldex Therapeutics (NASDAQ:CLDX) watched in horror this spring as both biotech stocks lost over 50% of their value. Bellicum has recovered somewhat but is still down 22% year to date. For Celldex, a clinical upset in March continues pushing the stock about 70% lower than its value at the beginning of the year.

Both companies are advancing unique therapies while burning through cash, and neither has any products to sell yet, but the similarities end there. Let's look closer at their pipelines in light of the recent price divergence to see which is a better buy right now.

The case for Bellicum Pharmaceuticals

Bellicum is one of several biotechs bent on modifying T-cells to improve a range of outcomes. Blood stem cell transplants, sometimes called bone marrow transplants, have been a treatment option for a range of blood disorders, including cancers, for over 50 years, but there's a catch: The new cells sometimes recognize their surroundings as foreign and attack everything.

T-cells attacking cancer image source: Getty Images.

One type of immune cell, the T-cells you see attacking cancer above, is thought the be the main trouble-starter, and depletion of this important immune system component is a standard pre-transplant procedure. This reduces chances of deadly graft-vs.-host disease (GVHD), but also leaves patients highly exposed to infections.

Bellicum's lead candidate, BPX-501, consists of modified T-cells with a suicide switch, called CaspaCIDe. Giving them to patients after stem cell transplants should reduce opportunistic infections, and if they go berserk and cause GVHD, an infusion of rimiducid shuts them down fast.

Earlier this year, Bellicum presented early data suggesting BPX-501 works as planned. Although the trial is expected to enroll 180 patients, interim results from 17 high-risk pediatric patients with blood cancers, and 24 patients with non-cancerous blood disorders, were positive at a median follow-up of seven months. There was no transplant-related mortality due to infection or GVHD complications.

Image source: Bellicum Pharmaceuticals.

Acute GVHD occurs in 30% to 60% of patients receiving donor stem cell transplants, which makes the lack of transplant-related deaths in this many patients nothing short of miraculous. It's still early, but BPX-501 could make donor stem cell transplants a more common treatment option. Just how popular it could be is hard to say, but an approval would almost certainly justify the company's recent market cap of just $463 million.

The case for Celldex Therapeutics

This clinical-stage biotech's first shot at approval with Rintega bounced off the goalpost. The targeted brain cancer therapy performed consistently with earlier data, but patients on standard therapy performed unusually well, rendering its registrational trial a failure, and the stock plummeted.

With Rintega out of the picture, Celldex still has five more targeted cancer candidates in 13 clinical trials. Closest to the finish line is Glemba, a protein that targets and binds to gpNMB (a protein commonly expressed on the surface of different cancer cells) attached to a chemo-bomb that doesn't drop until the protein side binds to gpNMB and is carried inside like a Trojan horse.

Investigators noticed something very interesting during a previous study with 124 heavily pre-treated advanced breast cancer patients. There were 16 patients in the study with triple negative tumors that overexpress gpNMB. Among this group, patients receiving Glemba survived without disease progression for 3.5 months. That's a huge improvement over just 1.5 months among patients receiving an investigator's choice of existing therapies.

Roughly 170,000 breast cancer patients worldwide have triple negative tumors, but the number that also express gpNMB at high levels is unclear. Glemba is currently enrolling up to 300 of these patients for a phase 2b trial designed to support an application to treat this underserved population. The trial is measuring progression-free survival against a single chemo drug, Roche's Xeloda, and if it performs as well in the larger study as it did in the 16-patient subgroup, this stock's current market cap of about $463 million will seem like a joke.

Reasons to be nervous

Bellicum's only clinical-stage candidate, BPX-501, has some uphill battles to face. First, it's in mid-stage trials -- and probably years away from an application. If approved, its rate of adoption is anybody's guess; different cellular therapies have entered the marketplace in the past only to fail.

Bellicum investors will also want to watch bluebird bio and its Lentiviral vector-based stem cell transplant solutions. Bluebird's approach avoids GVHD complications by replacing faulty genes in patients' own stem cells before transplant procedures, which could render BPX-501 redundant.

In contrast, Celldex's Glemba is an antibody-drug conjugate, a class of cancer therapies that have proven successful in the real world. Beyond this candidate's registrational study, the drug is in four other clinical trials, three of which have been sponsored by investigators themselves.

Image source: Celldex Therapeutics.

I think Glemba's odds of success are better than average, but there's also a chance that results from the 16 patients separated from others in its previous breast cancer trial were simply a case of data mining. If Glemba does fail, though, Celldex has four more clinical-stage candidates all aimed at different targets.

Both biotech stocks look fairly cheap compared to their potential. Glemba's proximity to the finish line, though, and a stable of backup candidates make Celldex Therapeutics the better buy today, hands down.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.