New Treg Therapy Earns FDA Orphan Drug Designation in Myelofibrosis

The FDA has granted orphan drug designation to CK0804, an investigational Treg cell therapy, as a treatment for patients with myelofibrosis, according to a press release from the developer, Cellenkos® Inc.¹

Developers designed CK0804 as an allogenic, off-the-shelf agent that exploits the CXCR4/CXCL12 axis to interact with the antigen presenting cell and administer a targeted payload of suppressing cytokine IL-10, thereby resolving inflammation in a non-MHC dependent fashion. In myelofibrosis, the novel agent has demonstrated disease-modifying effects based on a decrease of pathogenic monocytes in plasma and bone marrow.

Compared with other therapies, CK0804 does not require HLA matching with recipients and can be cryopreserved and stored with a shelf life exceeding 2 years. Additionally, the agent can be thawed and infused whenever needed, and it can be administered intravenously in the outpatient setting via a peripheral line.

“Receiving orphan drug designation is an important milestone in the clinical development of CK0804 for myelofibrosis and underscores our commitment to advance CK0804 into phase 2 trials to address the unmet need for patients who have not responded to currently available therapies,” Simrit Parmar, MD, founder of Cellenkos, stated in the press release.¹ “The observed increase in IL-10 and decreases in TGFβ levels in CK0804 responders, together with reductions in pathogenic monocytes in plasma and bone marrow, support the disease modifying potential of CK0804 Tregs as a distinct and differentiated therapeutic class in myelofibrosis.”

Investigators presented early findings from a clinical trial assessing CK0804 among a small cohort of patients with myelofibrosis at the 2025 American Society of Hematology (ASH) Annual Meeting and Exposition.² Among 8 evaluable patients in the initial safety run-in portion of the study, 5 (62.5%) achieved a response. Additionally, data showed a 49% (range, 37%-65%) average decrease in symptom burden among patients with a response at 12 months following the initial dose of CK0804.

The median baseline levels of TGF- β1, β2, and β3 were elevated among patients who achieved a response, which decreased to more than 50% by the conclusion of study therapy. Additionally, pro-fibrotic and pro-inflammatory disease markers such as FGF, sCD40L, PDGF AA and PDGF AB/BB decreased by more than 50% among patients with a response vs those who did not respond.

“This more in-depth analysis of the safety run-in phase of evaluating CXCR4 enriched Tregs cell therapy as addition to ruxolitinib in [patients with myelofibrosis] with sub-optimal response shows that the immune system of responders changed markedly in ways that were different than and complementary to JAK inhibition, with safety and no myelosuppressive adverse events [AEs],” lead study author Lucia Masarova, MD, co-leader of the Myeloproliferative Neoplasms Session in the Division of Cancer Medicine at The University of Texas MD Anderson Cancer Center, wrote with coauthors.²

The expansion cohort of this study included a dose-intensive regimen of CK0840 Tregs administered as 4 weekly infusions followed by 5 monthly infusions. Additionally, all patients initiated ruxolitinib (Jakafi) at 5 mg twice daily or higher, which was stable for at least 8 weeks.

The study’s primary end point was safety. A secondary end point was the overall response rate at 24 weeks based on International Working Group-Myeloproliferative Neoplasms Research and Treatment criteria.

There were 4 patients in the expansion cohort who had a median age of 69.5 years (range, 66-78). Investigators reported 28 infusions with no grade 3/4 treatment-related AEs in the outpatient setting. Among 3 evaluable patients, 1 achieved a spleen volume reduction of more than 25%; all 3 experienced a decrease in symptom burden.

References

1. FDA grants orphan drug designation to Cellenkos' CK0804 Treg therapy for treatment of myelofibrosis. News release. Cellenkos Inc. January 6, 2026. Accessed January 6, 2026. https://tinyurl.com/bd783dk7
2. Masarova L, Abedi M, Pemmaraju N, et al. Dose intensive regimen of CK0804 tregs in myelofibrosis. Blood. 2025;146(suppl 1):5602. doi:10.1182/blood-2025-5602