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.