[Edaily Reporter NA EUN-KYUNG ] Development in the U.S. of the natural killer (NK) cell therapy “AB-101” (AlloNK), which GC CELL(144510)licensed out, has been completely halted. As recently as 12 days ago, its U.S. partner, Artiva Biotherapeutics, had announced plans to enter Phase 3 clinical trials, emphasizing efficacy comparable to existing chimeric antigen receptor T-cell (CAR-T) therapies. However, following the deaths of two patients and confirmation of a lack of long-term efficacy, the company announced it was abandoning the development.

Artiva is cutting 94% of its workforce and even considering liquidation, casting doubt on the future of other pipelines for which GC CELL has licensed the technology. Since GC CELL licensed AB-101 in 2019, the total revenue from upfront payments, milestones, and royalties has been 0 won. With this development halt, receiving the milestones allocated for the late-stage clinical trial has become virtually impossible.

Decision to Abandon Development Just One Week After Highlighting CAR-T-Level Efficacy

On the 27th (local time), Artiva announced that it was halting all clinical development of AB-101. It also canceled the Phase 3 clinical trial for patients with rheumatoid arthritis, which was scheduled to begin later this year. According to a filing with the U.S. Securities and Exchange Commission (SEC), Artiva’s board of directors approved the development halt on the 22nd.

Just a week earlier, on the 15th, the mood was completely the opposite. At that time, GC CELL highlighted the efficacy of AB-101 by introducing a clinical abstract that Artiva was set to present at the American College of Rheumatology (ACR 2026) conference. The presentation detailed that, in a study involving 34 patients with rheumatic diseases, the combination with rituximab demonstrated a potent B-cell depletion effect comparable to that of an autologous CAR-T therapy.

However, the assessment that it is comparable to CAR-T therapy refers solely to the pharmacological effect of eliminating B cells. It does not mean that the treatment is equivalent to CAR-T therapy in terms of how much it actually improves patients’ symptoms or how long those effects last. Nor has the long-term clinical efficacy of the two therapies been proven through direct comparison.

Artiva had planned to release clinical data from approximately 50 additional patients on November 9 and to enter Phase 3 trials by the end of the year. However, the company abandoned the development project altogether just before the clinical results were to be announced, raising growing questions about the discrepancy between the efficacy it had previously emphasized and the actual long-term therapeutic effects.

AB-101 is an allogeneic NK cell therapy developed by GC CELL. It involves mass-culturing and pre-stocking NK cells from healthy donors before administering them to patients, offering the advantage of easier production and supply compared to autologous CAR-T therapies, which are manufactured using the patient’s own cells.

Although initially developed as an anticancer drug, Artiva subsequently expanded its development scope to include autoimmune diseases such as rheumatoid arthritis. The strategy involves combining AB-101 with rituximab, an antibody therapy that targets B cells, to effectively eliminate B cells involved in the disease and maintain long-term therapeutic effects.

Early clinical results announced last May were also positive. In a Phase 2a clinical trial led by Artiva, 5 out of 7 (71%) rheumatoid arthritis patients followed for more than 6 months achieved a 50% improvement in symptoms (ACR50) according to the American College of Rheumatology criteria. At that time, there were no cases of disease recurrence or the need for new immunosuppressive therapy in this patient group.

Based on these results, Artiva reached an agreement with the U.S. Food and Drug Administration (FDA) on the design of a Phase 3 clinical trial for regulatory approval involving approximately 150 participants. However, the company stated that the durability of the therapeutic effect observed during long-term follow-up did not meet the criteria necessary to continue development.

The company explained that while the drug’s ability to eliminate B cells and the initial clinical response were consistent with previous announcements, the clinical response did not maintain the expected level over time. It stated that the decision to halt development was made after considering safety concerns arising from the fatalities, as well as the potential for development delays and commercial viability.

However, the company did not disclose specific figures, such as when and to what extent the therapeutic effect began to wane, or how many patients experienced a relapse of symptoms. Artiva also canceled the presentation of clinical results and the investor briefing scheduled for next month at the American College of Rheumatology.

Two patient deaths that occurred during the clinical trial also influenced this decision. The first patient was assessed as having likely died from leukoencephalopathy caused by the neurotoxicity of fludarabine, which had been administered prior to treatment to reduce lymphocyte counts. The second patient died suddenly approximately two months after the start of treatment, but the principal investigator determined that the death was unrelated to the trial treatment.

In neither case was AB-101 itself confirmed as the cause of death. However, after the first death was reported, the FDA requested a temporary suspension of new patient enrollment and dosing in the Phase 2a clinical trial. Subsequently, Artiva reviewed the overall clinical benefits and safety risks and decided to discontinue development.

A GC CELL official explained, “We understand that the investigation into the deaths is just beginning,” adding, “This was not an official clinical hold ordered by the FDA, but rather a decision by Artiva to suspend the trial on its own.”

No Advance Payment, No Milestones… Even If Technology Is Returned, Resumption of Development Remains Uncertain

Following the news of Artiva’s development halt, GC CELL’s stock price also plummeted. As of 2:40 p.m. on the 28th, GC CELL was trading at a price approximately 19% lower than the previous trading day.

GC CELL and Artiva are linked not only by a simple technology export relationship but also through equity investment. The two companies signed a comprehensive agreement in September 2019 for the joint development of NK cell therapies, and in November of the same year, GC CELL transferred the exclusive development and commercialization rights for AB-101 in major regions, including the U.S., to Artiva.

Under the AB-101 agreement, GC CELL was eligible to receive a total of $77 million (approximately 103.1 billion won), including up to $22 million (approximately 29.5 billion won) in development-stage milestones and up to $55 million (approximately 73.6 billion won) in sales milestones. The agreement also provides for royalties tied to sales following commercialization.

However, the actual revenue GC CELL has secured from the AB-101 technology export to date is 0 won. No upfront payment was received at the time of the 2019 contract, and Artiva’s interim report for this year shows no amounts recognized as development or sales milestones or royalties as of the end of June.

In other words, the $77 million was not an amount actually received at the time the contract was signed, but rather a contingent technology fee that could have been received based on future development and sales performance. Since Artiva halted development just before entering Phase 3 clinical trials, the possibility of receiving technology fees linked to late-stage clinical progress and commercialization has effectively vanished. However, compensation for separate research, development, and manufacturing services must be distinguished from technology export revenue.

There are also complex equity relationships involved. According to SEC filings submitted by Artiva last August, as of July 20, GC CELL and GC Corp. collectively held a 12.3% stake in Artiva. The total number of shares held was 5,999,703, comprising 1,607,734 shares held by GC CELL and 4,391,969 shares held by GC Corp.

The issue is that Artiva is even reevaluating whether to continue its existing new drug development business. The company is considering strategic alternatives ranging from reducing its workforce by approximately 94% to mergers, business combinations, asset sales, and technology transfers—as well as corporate dissolution and liquidation. Although the company held approximately $319.1 million (about 427.3 billion won) in cash, cash equivalents, and investment assets as of the end of September, it intends to explore other options rather than continuing its existing business.

Consequently, the future of the remaining candidate compounds for which GC CELL has licensed out the technology has also become uncertain. In addition to AB-101, the two companies had signed licensing agreements for a total of four candidate compounds, including AB-201—a HER2-targeted CAR-NK therapy for solid tumors such as breast cancer—as well as AB-202 and AB-205.

According to Artiva’s SEC filing, should the AB-101 agreement be terminated, Artiva is required to transfer the relevant regulatory documents and approvals to GC CELL and grant GC CELL the right to use the preclinical and clinical data. However, the fact that Artiva has halted development does not automatically terminate the agreement or guarantee the return of the technology.

Even if the technology is returned, whether GC CELL will resume its own development is a separate issue. This is because the company must first identify the cause of AB-101’s failure to maintain the initial efficacy observed in previous clinical trials over the long term. Factors such as the timing and extent of the decline in efficacy after six months, as well as the potential for improvement through additional dosing or changes to the clinical trial design, are likely to determine future development strategies.

In particular, the key issue is what differences existed between the clinical data GC CELL presented on the 15th and the long-term follow-up data Artiva reviewed when deciding to halt development on the 22nd. This is because the possibility of further developing the technology can only be assessed once it is confirmed when the latest data was obtained and in which metrics it fell short of previous expectations.

A GC CELL official stated, “We understand that Artiva decided to halt development after comprehensively considering the clinical data, safety, and commercial viability,” adding, “There are no additional details confirmed beyond what Artiva has already announced.” The representative added, “No decision has yet been made regarding the return of rights to AB-101 or whether we will pursue in-house development,” and noted, “We will review the rights related to the exported pipeline and the direction of future development while maintaining close communication with Artiva.”