Your immune system is constantly working to clean up faulty cells and damaged tissues. It's working, right now, to mop up pathogenic microbes and cancer cells before they can gain a foothold in your body. The search-and-destroy capabilities of immune cells have long made them ideal candidates for novel medical interventions, but we've only recently gained enough control over biology to make it a reality.

Two biopharma companies eager to take advantage of the potential of cellular medicines are Iovance Biotherapeutics (NASDAQ:IOVA) and Fate Therapeutics (NASDAQ:FATE). Each is working on unique cell types in specific types of cancer, but recent and upcoming data readouts make these two of the top biotech stocks to buy in December. 

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Basking in the glory of promising data

Iovance Biotherapeutics is developing cellular medicines based on tumor infiltrating lymphocytes (TILs). These special T cells harbor unique anti-tumor capabilities, but can be rendered powerless by rapidly mutating cancer cells. To address the immune-suppressing defenses of tumors, the company has developed a unique process to extract, amplify, and armor TILs naturally produced by cancer patients. The reinvigorated TILs are reinjected into the patient to rally the immune system against malignant cells.

Even targeting difficult-to-treat cancers, Iovance has demonstrated promising results in clinical trials. The lead drug candidate, lifileucel, achieved an objective response rate (ORR) of 36% in 66 individuals with metastatic melanoma in a phase 2 trial. The median duration of response (DOR) had not been reached at the median follow-up of 11.3 months. Additionally, the drug candidate notched an ORR of 41% in 42 individuals who were resistant to anti-PD-1 therapies.  

That's a pretty solid update. Melanoma is easily treated when caught on the surface of the skin, but once it spreads (metastasizes) to other areas of the body, the five-year survival rates plummet, making metastatic melanoma one of the deadliest cancers. Anti-PD-1 drugs such as Keytruda from Merck have improved outcomes in recent years, but patients who don't respond or become resistant have few options. 

Iovance expects to complete enrollment of a pivotal phase 3 trial for lifileucel in metastatic melanoma in early 2020. That could allow the company to file a biologics license application (BLA) with the U.S. Food and Drug Administration by the end of 2020. 

Investors can also look forward to a potential BLA filing for LN-145 in cervical cancer by the end of 2020. That drug candidate earned Breakthrough Therapy designation from the FDA to speed up its development. There are a host of other clinical trials underway, too. 

Iovance is studying LN-145 in head and neck cancer in a phase 2 trial, while another study is looking at combinations of lifileucel and LN-145, each with Keytruda, against several solid-tumor cancers. The biotech also recently announced a new asset, a peripheral blood lymphocyte (PBL) called IOV-2001, that will begin clinical trials in chronic lymphocytic leukemia by the end of 2019. 

Simply put, this biotech stock has surged in 2019, and the $3.1 billion company appears to have a bright future with its novel approach to cellular medicines.

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Are natural killer cells ready for prime time? 

While Iovance is riding recent data readouts higher, Fate Therapeutics is looking to end the year strong by releasing a barrage of results. The biopharma will make six presentations on its pipeline at the American Society of Hematology (ASH) annual meeting Dec. 7 to 10. 

Fate Therapeutics is developing an ambitious pipeline of cellular medicines. Its lead drug candidates are based on natural killer (NK) cells, which are special immune cells that are potentially more valuable immunotherapy candidates than T cells. NK cells can be dosed multiple times (CAR-T cells are typically only dosed once), aren't attacked by a recipient's immune system (T cells usually require strict donor-patient matching), and can target cancer cells with less risk of triggering mutations that lead to resistance. 

The only obstacle is that NK cells have delivered mixed results in clinical trials to date. Fate Therapeutics thinks it can leverage recent advances in stem cells and bioprocessing to succeed where predecessors have failed. The December updates will provide investors with a glimpse of what's possible, although the biopharma has been moving full steam ahead in 2019.

It opened a dedicated manufacturing facility for producing induced pluripotent stem cells (iPSC), which are the starting points for many of its immunotherapies. It dosed the first patients with FT516, an NK-cell-based drug candidate aimed at treating blood cancers. The FDA cleared its investigational new drug (IND) application for FT596, a targeted therapy based on NK cells, paving the way for clinical trials to start in blood cancers. And the company ended September with over $300 million in cash. 

In total, Fate Therapeutics has 13 different programs in various stages of development. Whether that means the company lacks focus or has many shots on goal, Wall Street appears to be waiting for more concrete evidence that any of its drug candidates actually work. Given the tumbling stock price and a market valuation of only $1 billion, the risk-reward presented by this small-cap biotech stock could turn a small position into a long-term stroke of genius for patient investors. 

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.