Inclusion Criteria:
1. Voluntarily sign the informed consent form and agree to comply with the requirements of the protocol;
2. No gender restriction;
3. Age: ≥18 years and ≤75 years;
4. Expected survival time ≥3 months;
5. Diagnosed with recurrent or metastatic head and neck squamous cell carcinoma (HNSCC) and other solid tumors;
6. Agree to provide archived tumor tissue specimens or fresh tissue samples from the primary or metastatic lesions obtained within 3 years;
7. Must have at least one measurable lesion as defined by RECIST v1.1;
8. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1, with no deterioration within 2 weeks prior to the first dose;
9. Toxicities from prior anti-tumor therapy have recovered to ≤ Grade 1 as defined by NCI-CTCAE v6.0;
10. No severe cardiac dysfunction; left ventricular ejection fraction (LVEF) ≥50%;
11. Organ function levels must meet the protocol-specified requirements;
12. Coagulation function: international normalized ratio (INR) ≤1.5, and activated partial thromboplastin time (aPTT) ≤1.5 × upper limit of normal (ULN);
13. Urine protein ≤1+ or ≤1000 mg/24h;
14. For premenopausal women of childbearing potential, a serum pregnancy test must be performed within 7 days prior to the start of treatment, with a negative result, and must be non-lactating; all trial participants (both male and female) must agree to use adequate barrier contraceptive measures throughout the entire treatment period and for 6 months after the completion of treatment;
15. Participants must be capable of and willing to comply with the scheduled visits, treatment plan, laboratory tests, and other study-related procedures as required by the protocol.
Exclusion Criteria:
1. Received chemotherapy, biotherapy, immunotherapy, or other anti-tumor therapies within 4 weeks or 5 half-lives prior to the first dose;
2. History of severe cardiac or cerebrovascular disease;
3. Prolonged QTc interval, complete left bundle branch block, third-degree atrioventricular block, or frequent and uncontrolled arrhythmias;
4. Active autoimmune diseases and inflammatory diseases;
5. Diagnosed with another malignant tumor within 5 years prior to the first dose;
6. Unstable thrombotic events requiring therapeutic intervention within 6 months prior to the first dose;
7. Hypertension poorly controlled by antihypertensive medication;
8. Poorly controlled blood glucose;
9. History of interstitial lung disease (ILD) requiring corticosteroid therapy, or currently diagnosed with ILD, or grade ≥2 radiation pneumonitis;
10. Severe impairment of respiratory function;
11. Active central nervous system (CNS) metastases;
12. Prior or concurrent central nervous system lesions;
13. Participants with a history of allergy to recombinant humanized antibodies or human-mouse chimeric antibodies, or allergy to any excipient component of BL-M08D1;
14. Prior history of organ transplantation or allogeneic hematopoietic stem cell transplantation (Allo-HSCT);
15. Positive for human immunodeficiency virus (HIV) antibody, active tuberculosis, active hepatitis B virus (HBV) infection, or active hepatitis C virus (HCV) infection;
16. Active infections requiring systemic therapy within 4 weeks prior to the first dose of study drug;
17. Pleural, peritoneal, or pericardial effusion requiring drainage and/or accompanied by symptoms within 4 weeks prior to the first dose of study drug;
18. Imaging findings suggest tumor invasion or encasement of abdominal, thoracic, or other major vessels;
19. Received another investigational drug within 4 weeks or 5 half-lives prior to the first dose;
20. Pregnant or breastfeeding women;
21. Other conditions deemed by the investigator to be unsuitable for participation in this clinical trial.
