On April 17, 2026 Pheast Therapeutics, a clinical-stage biotechnology company advancing macrophage-directed immunotherapies for cancer, reported the presentation of initial Phase 1a clinical data and new preclinical findings for PHST001, an IgG4 anti-CD24 macrophage checkpoint inhibitor, at the American Association for Cancer Research (AACR) (Free AACR Whitepaper) Annual Meeting 2026.
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"The data presented at AACR (Free AACR Whitepaper) suggest that PHST001 may address a longstanding challenge in translating the therapeutic potential of macrophage biology into a cancer treatment with the right balance of activity and tolerability," said Roy Maute, Ph.D., CEO and Co-founder of Pheast Therapeutics. "The preclinical data further support rationally designed therapeutic combinations informed by CD24 biology, reinforcing the breadth of PHST001’s development potential."
In the ongoing Phase 1a first-in-human study, PHST001 was generally well-tolerated across dose-escalation cohorts. Most treatment-related adverse events were Grade 1 or 2, with a subset of patients experiencing transient neutrophil decreases that were manageable and not associated with clinical complications. The dataset demonstrated linear pharmacokinetics, increasing CD24 receptor occupancy at higher dose levels, and pharmacodynamic changes consistent with innate immune activation. Early signs of clinical activity were observed, including disease stabilization and tumor shrinkage.
In preclinical studies including patient-derived tumor xenograft models, PHST001 enhanced macrophage-mediated tumor control and prolonged survival in combination with chemotherapies and antibody-drug conjugates. PHST001 also inhibited metastatic spread and reduced metastatic burden across multiple in vivo models.
"Taken together, these clinical and preclinical findings begin to build the profile we are looking for in a macrophage checkpoint inhibitor: favorable tolerability, evidence of biological activity, and meaningful combination potential," said Raphaël Rousseau, M.D., Ph.D., Chief Medical Officer of Pheast Therapeutics. "These data support continued development of PHST001 as a monotherapy and in combination with cytotoxic agents, where it may enhance macrophage-mediated clearance of treatment-damaged tumor cells."
Pheast plans to present updated clinical data from the ongoing PHST001-101 study at a future medical meeting.
The AACR (Free AACR Whitepaper) posters can be viewed at https://www.pheast.com/pipeline.
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 evade 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 forms the basis for therapeutic strategies targeting CD24 to activate 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 in many human cancers and high expression of CD24 is associated with poor prognosis across multiple tumor types. PHST001 is designed to promote macrophage-mediated phagocytosis of cancer cells and initiate a broader immune response. PHST001-101 is an open-label, multicenter Phase 1 study in patients with advanced solid tumors (ClinicalTrials.gov Identifier: NCT06840886). Primary objectives include safety, tolerability, and dose optimization, with secondary objectives evaluating pharmacokinetics and preliminary anti-tumor activity. PHST001 received FDA Fast Track Designation for the treatment of ovarian cancer in June 2025. The phase 1b portion of the study combining PHST001 with chemotherapies is actively recruiting patients.
(Press release, Pheast Therapeutics, APR 17, 2026, View Source [SID1234664512])