Pheast Therapeutics Reports Initial Phase 1a Data for PHST001 at AACR 2026

Early clinical data show promising safety, pharmacology, and signs of activity for novel macrophage checkpoint inhibitor

Apr. 20, 2026 at 4:19am

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A minimalist, neon-outlined illustration of an immune cell, possibly a macrophage, glowing against a dark background, conceptually representing the potential of Pheast Therapeutics' PHST001 to activate the innate immune system to fight cancer.Pheast Therapeutics' novel macrophage checkpoint inhibitor PHST001 shows promise in early clinical trials, hinting at new ways to harness the immune system's innate defenses against cancer.Redwood City Today

Pheast Therapeutics, a clinical-stage biotech company, presented initial Phase 1a data and new preclinical findings for its anti-CD24 macrophage checkpoint inhibitor PHST001 at the AACR 2026 Annual Meeting. The data highlighted PHST001's differentiated safety and pharmacologic profile, including target engagement, innate immune activation, and early signs of clinical activity in patients with advanced solid tumors. Preclinical studies also supported PHST001's potential in metastatic models and combination with other cancer therapies.

Why it matters

Macrophage-directed immunotherapies represent a promising but challenging area of cancer research. The data on PHST001 suggest it may address key translational hurdles by achieving the right balance of anti-tumor activity and tolerability. If further developed, PHST001 could offer a new approach to harnessing macrophage biology to treat aggressive and difficult-to-treat cancers.

The details

In the ongoing Phase 1a study, PHST001 was generally well-tolerated, with mostly Grade 1-2 adverse events and manageable neutropenia. The data showed linear pharmacokinetics, increasing CD24 receptor occupancy at higher doses, and pharmacodynamic changes consistent with innate immune activation. Early signs of clinical activity, including disease stabilization and tumor shrinkage, were also observed. Preclinical studies demonstrated PHST001's ability to enhance macrophage-mediated tumor control, inhibit metastatic spread, and combine effectively with chemotherapies and antibody-drug conjugates.

  • The AACR posters were presented on April 17, 2026.
  • Pheast plans to present updated clinical data from the ongoing PHST001-101 study at a future medical meeting.

The players

Pheast Therapeutics

A clinical-stage biotechnology company advancing macrophage-directed immunotherapies for cancer.

Roy Maute, Ph.D.

CEO and Co-founder of Pheast Therapeutics.

Raphaël Rousseau, M.D., Ph.D.

Chief Medical Officer of Pheast Therapeutics.

Amira Barkal

Principal founder of Pheast and the researcher who identified CD24 as a novel macrophage checkpoint.

Irving Weissman

Co-founder of Pheast and an expert in innate immunity and cancer immunotherapy.

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What they’re saying

“The data presented at AACR 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.”

— Roy Maute, Ph.D., CEO and Co-founder of Pheast Therapeutics

“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.”

— Raphaël Rousseau, M.D., Ph.D., Chief Medical Officer of Pheast Therapeutics

What’s next

Pheast plans to present updated clinical data from the ongoing PHST001-101 study at a future medical meeting.

The takeaway

The initial data on Pheast's PHST001 suggest it may offer a promising new approach to harnessing macrophage biology to treat cancer, with a favorable safety profile and early signs of clinical activity. If these findings are borne out in further development, PHST001 could represent an important advance in the challenging field of macrophage-directed immunotherapies.