This is an open-label, single-arm phase I dose-escalation study designed to evaluate the safety, tolerability, pharmacokinetic profile, and preliminary efficacy of MT027 in patients with advanced primary peritoneal malignancies or abdominal metastases secondary to malignant solid tumors. The study primarily focuses on determining the maximum tolerated dose and recommended phase II dose through sequential cohort dose escalation, while secondarily characterizing the pharmacokinetic parameters and collecting initial efficacy data regarding tumor response.

This investigation comprehensively evaluates the pharmacodynamic and pharmacokinetic profile of MT027 cellular therapy through three primary objectives: (1) systematic monitoring of treatment-emergent adverse events and clinically significant laboratory parameter deviations; (2) assessment of antitumor activity with correlative biomarker analysis; and (3) characterization of cellular kinetics including biodistribution patterns, mechanistic pathways of therapeutic activity, and comprehensive immunogenicity assessment measuring both cellular/humoral immune responses against MT027 cells. The protocol further investigates potential host-versus-product immune reactions through longitudinal monitoring of donor-specific antibodies and cytokine release profiles, while employing advanced molecular tracking methodologies to elucidate cellular persistence and functional modulation within the tumor microenvironment.

This single-arm, dose-escalation phase I clinical trial aims to assess the tolerability, safety, pharmacokinetic profile, and preliminary efficacy of MT027 in patients with advanced primary peritoneal malignancies or secondary abdominopelvic metastatic solid tumors.

This phase I study implements a tripartite dose-escalation framework (1×10⁷, 3×10⁷, and 6×10⁷ cells/administration) with biweekly intravenous dosing. Post-initial dosing requires a 4-week observation period for dose-limiting toxicities (DLT) graded per NCI-CTCAE v5.0 criteria, followed by subsequent 14-day interval administrations. Following 6 completed treatment cycles (12 weeks), participants may either transition to surveillance follow-up or continue therapy per investigator-determined risk-benefit analysis.

The hybrid accelerated titration "3+3" design initiates with single-patient cohorts for preliminary dose evaluation, transitioning to conventional 3+3 methodology (minimum 3 patients/cohort) for subsequent dose levels. Protocol-defined dose escalation beyond predetermined thresholds requires documented consensus between investigators and sponsors, contingent upon comprehensive review of cumulative safety parameters (including DLT absence) and emerging efficacy indicators.

The trial progresses through sequential Phase IA (dose-finding) and Phase IB (dose-expansion) stages. Phase Ia cessation triggers include either confirmation of Recommended Phase II Dose (RP2D) or investigator-verified favorable therapeutic index at any dose level.

An interim analysis will be conducted upon Phase IA completion, followed by submission of an ethical amendment application prior to initiating Phase IB. Phase IB will be initiated with multi-cohort expansion (n=9-18 per cohort) across prespecified malignancies: colorectal adenocarcinoma (CRC), gastric carcinoma (GC), high-grade serous ovarian carcinoma (HGSOC), breast cancer (BC), non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC), metastatic castration-resistant prostate cancer (mCRPC), clear cell renal cell carcinoma (ccRCC), and cervical squamous cell carcinoma (CSCC), etc.

Inclusion Criteria:

• Patients must meet all of the following inclusion criteria to be enrolled in this study:

  1. Voluntarily participate in this study and provide a signed and dated written informed consent form before undergoing any study-specific procedures, sampling, or analyses;

  2. Aged 18-70 years (inclusive), regardless of gender;

  3. Diagnosed with primary malignancy confirmed by pathology and/or histology (with complete pathological report provided), including:Advanced solid tumors that have failed ≥2 lines of prior standard therapy;Advanced solid tumors (e.g., gastric cancer, colorectal cancer, platinum-resistant advanced ovarian cancer, fallopian tube cancer, etc.) with no standard treatment available, or for which accessible treatments have failed, or for which the investigator deems the patient intolerant to accessible treatments based on comprehensive risk-benefit assessments (intolerance defined as ≥Grade 3 adverse reactions post-treatment, or reactions below Grade 3 but persistent or recurrent, impacting continued treatment). All related adverse reactions must resolve to ≤Grade 1 or return to baseline before screening or the first dose.Primary malignant peritoneal tumors confirmed by pathology and/or histology, including primary peritoneal cancer, peritoneal mesothelioma, etc., with failed or intolerable standard therapy;Other solid tumors with peritoneal metastasis judged by the investigator to lack standard treatment options.

  4. Clear systemic treatment plan for primary and metastatic lesions, with no anticipated changes during the study;

  5. Confirmed peritoneal metastasis via biopsy, cytology, CT, or prior evidence;

  6. Enhanced CT shows intraperitoneal space-occupying lesions with ≥1 measurable lesion (per iRECIST criteria); or evaluable malignant peritoneal effusion via ultrasound (per WHO criteria);

  7. Willingness to provide recent FFPE tissue samples, pathological slides (8 consecutive unstained slides), or ascites tumor cells for B7-H3 expression testing, with confirmed B7-H3 positivity;

  8. No intraperitoneal drug injections (including hyperthermic intraperitoneal chemotherapy) within 1 month before signing the informed consent, except diagnostic paracentesis;

  9. Expected survival ≥3 months;

  10. ECOG performance status (PS) score of 0-2;

  11. Laboratory results during screening meeting the following criteria:

      Blood tests (within 14 days):

      WBC ≥3.0×10^9/L; ANC ≥1.5×10^9/L; Lymphocytes ≥0.8×10^9/L; Platelets ≥90×10^9/L; Hemoglobin ≥90 g/L (transfusions or erythropoietin allowed). Patients requiring repeated transfusions due to active bleeding or chronic conditions must be discussed with the sponsor.

      Liver function (within 7 days):

      Total bilirubin ≤1.5×ULN; ALT/AST ≤2.5×ULN (≤5×ULN if liver metastases present).

      Renal function (within 7 days):

      Serum creatinine ≤1.5×ULN; or CrCL ≥30 mL/min (Cockcroft-Gault formula).

      Coagulation (within 7 days):

      INR/PT ≤1.3×ULN; APTT ≤1.5×ULN.

  12. Recovery of prior systemic treatment toxicity to ≤Grade 1 or baseline (except alopecia);

  13. Fertile males and females must agree to use contraception from informed consent until 180 days post-last MT027 cell infusion.

Exclusion Criteria:

• 1. Known allergy to the investigational drug or its excipients; 2. Contraindications to peritoneal puncture or deemed unlikely to benefit from intraperitoneal therapy; 3. MSI-H/dMMR colorectal cancer patients not previously treated with immunotherapy; 4. Extensive liver metastases (>70% liver involvement); 5. Confirmed portal vein thrombosis; 6. Bowel obstruction within 4 weeks before dosing; 7. Conditions limiting drug diffusion (e.g., compartmentalized or gelatinous ascites); 8. Surgery or radiotherapy within 4 weeks before the first dose; 9. Systemic steroids (excluding replacement therapy) or immunosuppressants within 1 week before treatment; 10. Participation in other drug trials within 4 weeks before screening; 11. Prior B7-H3-targeted therapy (antibody/ADC/cell therapy) without confirmed B7-H3 positivity via biopsy; 12. Severe allergy to any component of the investigational drug or biologics; 13. Concurrent malignancies (except cured cervical carcinoma in situ or basal cell carcinoma); 14. Severe autoimmune diseases; 15. Prior allogeneic tissue/organ transplant; 16. Live vaccines within 2 weeks before cell therapy or planned during the study; 17. Active HBV, HCV (unless RNA-negative), HIV, syphilis, EBV, or CMV infection; 18. Active systemic infection or coagulation disorders; 19. Severe cardiac (NYHA Class III+), hepatic (Child-Pugh C+), renal (CKD ≥Stage 4), or pulmonary insufficiency; 20. Pregnancy or lactation; 21. Any condition deemed unsuitable by the investigator