Inclusion Criteria:
* Male or female patients aged ≥18 years and ≤70 years.
* Histopathologically confirmed advanced recurrent/metastatic malignant solid tumors that are refractory to second-line treatment and have no available standard clinical therapeutic options (e.g., advanced soft tissue sarcoma, advanced head and neck squamous cell carcinoma, malignant melanoma, etc.).
* Eastern Cooperative Oncology Group (ECOG) performance status score of 0-1.
* Expected overall survival ≥3 months.
* Interval from the last chemotherapy, radiotherapy, or surgery ≥28 days.
* Interval from the last use of nitrosourea or mitomycin C ≥6 weeks.
* Adequate organ function, defined by the following laboratory parameters within 14 days prior to enrollment:
* Hemoglobin ≥90 g/L (no blood transfusion within 14 days).
* Absolute neutrophil count \>1.5 × 10⁹/L.
* Platelet count ≥80 × 10⁹/L.
* Total bilirubin ≤1.5 × upper limit of normal (ULN).
* Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) ≤2.5 × ULN (≤5 × -ULN in case of liver metastasis).
* Creatinine clearance ≥60 mL/min (calculated by Cockcroft-Gault formula).
* Left ventricular ejection fraction (LVEF) ≥50%.
* Signed written informed consent.
Exclusion Criteria:
* Participation in another investigational drug clinical trial within 4 weeks.
* Tumor located adjacent to major blood vessels or trachea.
* Uncontrolled cardiac clinical symptoms or diseases, including New York Heart Association (NYHA) Class ≥2 heart failure, unstable angina, myocardial infarction within 1 year, or clinically significant supraventricular/ventricular arrhythmias requiring treatment or intervention.
* Female patients who are pregnant or lactating.
* Active pulmonary tuberculosis, bacterial or fungal infection (≥Grade 2 per NCI-CTCAE version 5.0), active human immunodeficiency virus (HIV) infection, active hepatitis B virus (HBV) infection, or hepatitis C virus (HCV) infection.
* History of uncontrollable psychoactive substance abuse or presence of mental disorders.
* Any active autoimmune disease or history of autoimmune disease, including but not limited to uveitis, enteritis, hypophysitis, nephritis, hyperthyroidism, and hypothyroidism.
* Subjects with vitiligo or childhood asthma in complete remission (no adult intervention required) are eligible; subjects with asthma requiring bronchodilator therapy are excluded.
* Receiving immunosuppressive therapy.
* History of drug abuse or known medical, psychological, or social conditions that interfere with study compliance (e.g., alcoholism or illicit drug addiction).
* Known hypersensitivity, allergy, or intolerance to the study drug CPIL22BP mRNA (including any excipients), or history of severe allergic reactions to any drugs, foods, or vaccines (e.g., anaphylactic shock, allergic laryngeal edema, allergic dyspnea, allergic purpura, thrombocytopenic purpura, local Arthus reaction, etc.).
* Female subjects planning pregnancy, or male subjects whose partner plans pregnancy, from screening until 12 months after the last study drug injection.
* Any concomitant disease that, in the investigator's judgment, may seriously compromise patient safety or prevent the subject from completing the study.
