FDA Grants Orphan Drug Designation to CK0804 for Myelofibrosis

The U.S. Food and Drug Administration (FDA) has granted orphan drug designation to CK0804, an investigational regulatory T cell therapy developed by Cellenkos Inc., for the treatment of myelofibrosis, a rare blood cancer, the company announced. The designation is intended to support development of therapies for rare diseases and comes as CK0804 continues to be evaluated in patients with myelofibrosis who have not responded to currently available treatments.

Myelofibrosis is characterized by scarring in the bone marrow, enlarged spleen and symptoms such as anemia and fatigue that can significantly affect quality of life. Cellenkos is developing CK0804 as an allogeneic, off-the-shelf regulatory T cell therapy designed to reduce inflammation and address disease-related changes in the bone marrow and other tissues.

Main Data That Support the Findings

The orphan drug designation is supported by results from a 13-patient clinical study in myelofibrosis that were presented at the 67th Annual Meeting of the American Society of Hematology in December 2025. Patients enrolled in the study had a median age of 68 years, with ages ranging from 55 to 84 years, and had previously failed a median of two prior therapies, with a range of one to six.

Among the patients who were evaluable for response, 45% of 11 patients experienced a spleen volume reduction greater than 10%. In addition, 78% of nine evaluable patients had a symptom burden reduction greater than 50%. Improvement in transfusion burden was reported in all three of three evaluable patients.

At a median follow-up of 195 days, which ranged from 41 to 809 days, 10 patients were alive. During this period, three patients proceeded to stem cell transplant, two switched to a different class of therapy and the remaining patients continued their initial treatment with Jakafi (ruxolitinib).

Beyond clinical measures such as spleen size and symptom burden, investigators observed biological changes among patients who responded to CK0804. Responders demonstrated decreased circulating levels of several inflammatory and disease-associated markers, including transforming growth factor beta 1, transforming growth factor beta 2, fibroblast growth factor, platelet-derived growth factor and soluble CD40 ligand. Reductions in pathogenic monocytes were also seen in both plasma and bone marrow, along with normalization of the bone marrow myeloid-to-erythroid ratio.

According to the company, these findings suggest a potential disease-modifying effect of CK0804 in myelofibrosis.

What Are the Trial Details?

CK0804 is composed of regulatory T cells that express high levels of the CXCR4 receptor, allowing the cells to preferentially home to CXCL12, a ligand that is overexpressed in the bone marrow and in sites of extramedullary hematopoiesis such as the spleen in myelofibrosis.

Once the cells reach target tissues, CK0804 regulatory T cells interact with antigen-presenting cells and undergo in vivo proliferation. Through this process, the cells secrete interleukin-10, a suppressor cytokine, which is intended to reduce local and systemic inflammation through a non–major histocompatibility complex–restricted mechanism. The therapy is also designed to regulate platelet-derived growth factor–driven pathways involved in disease remodeling.

CK0804 is derived from clinical-grade umbilical cord blood and manufactured using Cellenkos’ proprietary CRANE process. According to the company, the therapy does not require human leukocyte antigen matching, can evade innate immune surveillance and can be cryopreserved with a shelf life of more than two years while retaining viability and suppressor function. The product is designed to be thawed and infused on demand through a peripheral intravenous line in an outpatient setting.

Dr. Simrit Parmar, founder of Cellenkos, said the designation supports further development of the therapy for patients with myelofibrosis who have limited options. She noted that observed increases in interleukin-10 and decreases in transforming growth factor beta levels among responders, along with reductions in pathogenic monocytes, support the potential of CK0804 as a distinct therapeutic approach in this disease.

Safety

The press release did not report specific safety events related to CK0804. No treatment-related adverse events or safety signals were detailed in the announcement. The company stated that CK0804 is being advanced into phase 2 clinical trials for myelofibrosis as part of its ongoing development program.

Reference

1. “FDA Grants Orphan Drug Designation to Cellenkos' CK0804 Treg Therapy for Treatment of Myelofibrosis.” News Release. Cellenkos. Jan 6, 2026.

Editor's note: This article is for informational purposes only and is not a substitute for professional medical advice, as your own experience will be unique. Use this article to guide discussions with your oncologist. Content was generated with AI, reviewed by a human editor, but not independently verified by a medical professional.

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