Pheast Therapeutics, a clinical-stage biotechnology company advancing next-generation macrophage-directed immunotherapies for cancer, today announced a peer-reviewed publication in Clinical Cancer Research, a journal of the American Association for Cancer Research (AACR), detailing the preclinical foundation for its lead program, PHST001, a novel, high-affinity IgG4 anti-CD24 monoclonal antibody currently in Phase 1 clinical development for multiple solid tumor types.
The published findings demonstrate that PHST001 binds CD24 with high affinity, blocks CD24-Siglec-10 signaling, and drives macrophage phagocytosis of tumor cells. PHST001 showed robust anti-tumor activity across six solid tumor models — ovarian, breast, endometrial, pancreatic, lung, and cholangiocarcinoma — and enhanced the effects of chemotherapy, radiotherapy, and antibody-drug conjugates, including in treatment-resistant tumor models. The findings also reveal crucial crosstalk between the adaptive immune system and macrophages activated by PHST001.
“Cancer cells survive in part by expressing cell surface ‘don’t eat me’ signals that suppress critical immune surveillance functions of the immune system’s macrophages. CD24 is one of the most important of these signals expressed on several types of human cancer cells; this publication shows that blocking it with PHST001 can mobilize macrophages against a broad range of solid tumors,” said Irving Weissman, M.D., co-founder of Pheast Therapeutics. “This is a significant advance for the field of innate immune therapy against cancer and is critical for the next stages to determine the potential of PHST001 to become an important new cancer treatment.”
“The combination benefit outlined in this publication is exactly what we are now testing in patients, where PHST001 has already shown promising early signs of activity,” said Roy Maute, Ph.D., co-founder and Chief Executive Officer of Pheast. “These peer-reviewed data underpin our conviction in CD24 as a critical target and Pheast’s leadership in macrophage checkpoint immunotherapy.”
PHST001 is being evaluated in the ongoing Phase 1 PHST001-101 trial (NCT06840886) in patients with relapsed or refractory solid tumors. The monotherapy dose-escalation is nearly complete, and the chemotherapy combination cohorts are underway. Pheast expects to present initial clinical data at an upcoming medical meeting. PHST001 received FDA Fast Track Designation for the treatment of ovarian cancer in June 2025.
The Clinical Cancer Research publication is available here: https://aacrjournals.org/clincancerres/article/doi/10.1158/1078-0432.CCR-26-0481/786889/Targeting-CD24-activates-macrophages-to-reduce
About CD24
CD24 is a cell surface protein that plays a key role in tumor immune evasion by engaging Siglec-10, an inhibitory receptor on macrophages. This interaction suppresses macrophage-mediated clearance of cancer cells, allowing tumors to escape destruction by the innate immune system. CD24 was identified as a novel macrophage checkpoint through foundational work by Dr. Amira Barkal, principal founder of Pheast. Along with other co-founders, Drs. Irving Weissman, Ravi Majeti, and Roy Maute, Pheast’s research opened the door to therapeutic strategies targeting CD24 to drive innate immune responses against cancer.
About PHST001
PHST001 is an anti-CD24 macrophage checkpoint inhibitor designed to overcome immune suppression in the tumor microenvironment. CD24 is highly expressed across many cancers, where high expression is associated with poor prognosis. Pheast has engineered PHST001 to be a potential best-in-class antibody designed to induce macrophages to phagocytose cancer cells and initiate a powerful immune response. PHST001-101 is an open-label, multicenter Phase 1 study in patients with advanced solid tumors (ClinicalTrials.gov Identifier: NCT06840886) evaluating safety, tolerability, and dose optimization, with secondary objectives assessing pharmacokinetics and preliminary anti-tumor activity. PHST001 received FDA Fast Track Designation for the treatment of ovarian cancer in June 2025.
About Pheast Therapeutics
Pheast is a clinical-stage immuno-oncology company focused on activating the innate immune system in the fight against cancer. Founded as a spinout from Stanford University and led by scientific experts in innate immunity and cancer immunotherapy, Pheast is developing novel therapies for some of the most difficult-to-treat and aggressive cancers. Pheast is backed by leading life sciences investors, Catalio Capital Management and ARCH Venture Partners. For more info, visit Pheast.com and connect on LinkedIn.
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