A Study to Assess YH003 in Combination with Pebolizumab and Albumin Paclitaxel Injection in Subjects with Unresectable/metastatic Mucosal Melanoma

Inclusion Criteria:

* 1.Subjects must have the ability to understand and willingness to sign a written informed consent document.
* 2\. Subjects must have histologically advanced or cytologically confirmed metastatic or unresectable mucosal melanoma;
* 3.Subjects have not received standard systemic therapy; patients have disease progression 6 months or more after the end of neoadjuvant or adjuvant therapy (except nab-paclitaxel), and can be enrolled in the clinical study;
* 4\. Subject must have at least 1 unidimensional measurable disease by RECIST 1.1;
* 5\. Subjects must be age 18 years or older;
* 6\. Subjects must have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
* 7\. Life expectancy ≥3 months based on investigator's judgement；
* 8\. Subjects must have adequate organ function;
* 9\. Women of childbearing potential need to have a negative pregnancy test and need to take contraceptive/contraceptive measures including their partners.

Exclusion Criteria:

* 1.Subjects have another active invasive malignancy within 5 years；
* 2.The subject has received anti-tumor therapy or other investigational drug therapy or traditional Chinese medicine (herbal medicine) with anti-tumor indications prior to the first dose;
* 3.Subjects with a history of ≥ Grade 3 immune-related adverse events resulted from previous immunotherapy.
* 4.History of clinically significant sensitivity or allergy ；
* 5.Primary central nervous system (CNS) malignancies or symptomatic CNS metastases.；
* 6.History of (non-infectious) pneumonitis that required corticosteroids or current pneumonitis, or history of interstitial lung disease；
* 7.Subjects have active pulmonary embolism with hemodynamic changes 12 weeks before the first dose;
* 8\. Subjects must not have a known or suspected history of autoimmune disease within 3 years prior to the first dose of study treatment;
* 9\. Subjects have clinically uncontrolled diseases;
* 10\. Subjects have severe cardiovascular disease;
* 11\. Subjects have evidence of active infection;
* 12\. Subjects must not have a known or suspected history of an autoimmune disorder；
* 13.Major surgery within 4 weeks prior to study entry and Minor surgery within 2 weeks prior to the first dose.
* 14\. Any condition that the investigator assesses as inappropriate for participation in the study.