The objective of this study is to assess the safety and tolerability of MRG002 in combination with HX008 in patients with HER2-expressed advanced malignant solid tumors; and to , explore the maximum tolerated dose (MTD), and to determine the recommended phase II dose (RP2D) of combination therapy; , and to evaluate the preliminary efficacy, pharmacokinetics, and immunogenicity of combination therapy in the targeted study population.

Inclusion Criteria:

1. Willing to sign the informed consent form and follow the requirements specified in the protocol.
2. Aged 18 to 75 (including 18 and 75), both genders.
3. Life expectancy ≥ 12 weeks.
4. Patients with histopathological or cytological confirmed HER2-expressed advanced solid tumors, and with at least one measurable lesion according to the Response Criteria in Solid Tumors (RECIST v1.1).
5. The score of ECOG for performance status is 0 or 1.
6. The toxicity of previous anti-tumor treatment has recovered to ≤ Grade 1 as defined by NCI-CTCAEv5.0.
7. No severe cardiac dysfunction.
8. Organ functions must meet the basic requirements.
9. Cumulative dose of anthracycline ≤ 450 mg/m2 doxorubicin or its equivalent.

Exclusion Criteria:

1. Prior treatment with chemotherapy, biological therapy, immunotherapy, radiotherapy, investigational drugs, attenuated live vaccines, immunomodulators, CYP3A4 inhibitors/inducers, antibody-drug conjugates, etc.
2. Treatment with immune checkpoint inhibitors or tumor vaccines within 60 days prior to the first dose.
3. Treatment with systemic corticosteroids or other immunosuppressive drugs within 14 days prior to the first dose or during the study period.
4. History of severe cardiac disease.
5. Poorly controlled hypertension and hyperglycemia.
6. Presence of peripheral neuropathy ≥ Grade 2.
7. History of moderate or severe dyspnea at rest due to advanced malignant tumor or its complications or severe primary pulmonary disease, or current need of continuous oxygen therapy, or current interstitial lung disease or pneumonia.
8. Central nervous system metastasis.
9. Received major surgery within 4 weeks prior to the first dose without complete recovery.
10. History of hypersensitivity to any component of MRG002 or HX008 or known history of hypersensitivity of ≥ Grade 3 to macromolecular protein products/monoclonal antibodies.
11. Evidence of active infection.
12. History of primary immunodeficiency or autoimmune disease.
13. Female patients with a positive serum pregnancy test or who are breast-feeding or who do not agree to take adequate contraceptive measures during the treatment and for 6 months after the last dose of study treatment.
14. Previous history of other primary malignancies.
15. Other conditions inappropriate for participation in this study, as deemed by the investigator.