Mesothelin CAR-Mix therapy enters phase 1 with intraperitoneal dosing for peritoneal metastasis
A phase 1 study from Zhejiang University is preparing to test SY001, an autologous mesothelin-targeted CAR-Mix cell product, in adults with advanced solid tumors that have spread to the peritoneum. The design is exploratory, open-label, and single-arm, with an emphasis on safety, tolerability, pharmacokinetics, pharmacodynamics, and early antitumor activity rather than comparative efficacy. Enrollment is planned for 10 to 24 participants, and the study is listed as not yet recruiting.
The choice of target is biologically coherent. Mesothelin is a cell-surface glycoprotein with limited expression in normal tissues and overexpression across several solid tumors, making it a logical antigen for cell-based immunotherapy. In this protocol, the product is intended to combine two immune effector populations in one autologous treatment: predominantly chimeric antigen receptor-modified macrophages, with T cells making up at least 15% of the final cell count. The macrophage component is designed to bind mesothelin-positive tumor cells, intensify phagocytosis and antigen presentation, and reshape the suppressive tumor microenvironment. The T-cell fraction is expected to add complementary cytotoxic activity.
Why the peritoneal compartment may shape this trial’s biology
Peritoneal metastasis creates a distinct therapeutic setting. Drug exposure in the peritoneal cavity can differ from systemic circulation, and diffuse surface disease often resists standard approaches because of tumor heterogeneity and local immune suppression. Intraperitoneal delivery may help place engineered cells directly where disease burden is concentrated, potentially improving cellular contact with malignant implants and ascites-associated tumor cells. The protocol also includes assessment of malignant ascites using protocol-defined WHO criteria, a reminder that fluid burden is part of the clinical phenotype here and not just a radiographic detail.
The underlying rationale is straightforward: if mesothelin is present on the surface of peritoneal tumor deposits, and if engineered macrophages can engage that antigen in situ, then both direct cellular killing and local immune reprogramming become plausible. Preclinical work described in the record showed tumor-cell killing in vitro and antitumor activity after intraperitoneal administration in a xenograft model. Those data do not predict human benefit, but they do explain why the product is being moved into an early clinical setting.
Dose escalation will move through four planned cell levels
Investigators plan to evaluate four dose levels of SY001: 1×10⁹, 2×10⁹, 4×10⁹, and 6×10⁹ CAR-Mix cells. The dose-escalation strategy combines accelerated titration with a conventional 3+3 design, a familiar structure in first-in-human oncology studies when the central question is where toxicity begins to emerge. The primary objective is to define safety and tolerability during a 28-day dose-limiting toxicity observation period and to determine the maximum tolerated dose.
The 28-day window is clinically important because cell therapies can produce acute inflammatory toxicity, delayed immune effects, or organ-specific complications after initial infusion. In a setting where the cells are administered intraperitoneally, investigators will need to watch not only for systemic events but also for abdominal complications linked to delivery into a diseased peritoneal cavity. The study excludes patients with extensive intra-abdominal adhesions, complete intestinal obstruction, severe intra-abdominal infection, and several other gastrointestinal conditions that could increase procedural risk or confound safety interpretation.
A single sentence captures the core uncertainty: no one yet knows where the therapeutic window will sit.
Eligibility criteria narrow the population to mesothelin-positive, treatment-experienced disease
The protocol is built around a highly selected population. Eligible participants must be 18 to 75 years old, have histologically or pathologically confirmed advanced, metastatic, or recurrent malignant solid tumors with peritoneal metastasis, and have mesothelin positivity confirmed by immunohistochemistry or immunocytochemistry in at least 10% of tumor cells. Tumor types may include gastric cancer, colorectal cancer, fallopian tube cancer, and mesothelioma, although the list is not limited to those diagnoses.
Prior therapy status also matters. Participants must have failed second-line or later standard therapy, have no available standard therapy, have failed available therapy, or be judged unsuitable for further standard treatment after a benefit-risk assessment that takes prior toxicity, performance status, comorbidities, and organ function into account. Measurable disease is required under RECIST 1.1, and the record specifies either a non-lymph-node lesion at least 10 mm in longest diameter or a lymph node at least 15 mm in short axis, with imaging slice thickness no greater than 5 mm.
Safety filters reflect the risks of cell therapy and intraperitoneal administration
The exclusion criteria reveal how much caution accompanies this first-in-human development stage. Patients with recent myocardial infarction, unstable angina, stroke, coronary angioplasty, or stent placement within 6 months are excluded, as are those with New York Heart Association class III or IV heart failure, left ventricular ejection fraction below 50%, uncontrolled hypertension, significant arrhythmia, or a prolonged QTc interval. Pulmonary reserve matters as well: participants with FEV1/FVC at or below 60% or any need for supplemental oxygen cannot enroll.
Infection screening is equally strict. Active uncontrolled infection is exclusionary, although prophylactic antibacterial, antiviral, and antifungal therapy is allowed. The protocol also excludes certain viral and bacterial serologies, symptomatic central nervous system or leptomeningeal metastases, autoimmune disease, active substance abuse that cannot be discontinued, and any prior mesothelin-targeted therapy. Participants who received immune cell therapy within 6 months before screening are also ineligible. These filters are not ornamental; they reduce the chance that the safety signal will be obscured by unrelated organ dysfunction, competing inflammation, or prior immune manipulation.
What the early readout will need to clarify
The planned secondary and exploratory endpoints reach beyond toxicity. Investigators will examine preliminary antitumor activity, pharmacokinetic and pharmacodynamic characteristics, and the relationship between mesothelin expression, immune microenvironment change, and clinical outcomes. That kind of translational framework is common in early cell therapy, but in solid tumors it is especially important because target expression alone does not guarantee response. Tumor architecture, immune exclusion, ascites dynamics, and local suppressive signaling all influence whether engineered cells can persist and function.
The study completion date is estimated for 2030, with primary completion expected in mid-2029. Until then, the central questions remain basic and bedside-relevant: whether intraperitoneal CAR-Mix cells can be delivered safely, whether a maximum tolerated dose can be defined, and whether mesothelin-directed cellular activity can be detected in a disease compartment that has been historically difficult to treat. The protocol is explicit about what comes next, but it leaves the clinical answer unresolved until patients are treated and observed.