Selected Inclusion Criteria:

          -  Histological diagnosis of synovial sarcoma

          -  Immunohistochemistry (IHC) results from tumor biopsy for New York esophageal squamous
             cell carcinoma 1 (NY-ESO-1) are positive

          -  Participants have received at least 4 but no more than 8 cycles of first-line
             anthracycline or ifosfamide-containing systemic anti-cancer therapy regimen

          -  Must have documentation of no evidence of disease progression of the tumor during or
             after completion of first line systemic anti-cancer therapy

          -  ECOG (Eastern Cooperative Oncology Group) performance status of 0 or 1

          -  Age >/= 12 years

          -  Life expectancy of at least 6 months

        Selected Exclusion Criteria:

          -  Have received last dose of first-line systemic anti-cancer therapy or date of most
             recent local regional therapy >28 days prior to day 1

          -  Have received prior anti-NY-ESO-1 therapy

          -  Have received first-line systemic anti-cancer therapy with an agent other than
             anthracycline or ifosfamide

          -  Have received treatment with systemic immunomodulatory agents within 28 days prior to
             administration of the first dose of CMB305, or 5 half-lives of the drug, whichever
             occurs sooner.

          -  Have significant immunosuppression from concurrent, recent, or anticipated need for
             chronic treatment with systemic immunosuppressive dose of corticosteroids or
             immunosuppressive medications.

          -  Have psychiatric or other medical illness, or any other condition that in the opinion
             of the investigator prevents compliance with the study procedures or ability to
             provide valid informed consent.

          -  Have history of uncontrolled autoimmune disease.

          -  Have a significant electrocardiogram finding or cardiovascular disease

          -  have inadequate organ function per protocol

          -  History of other cancer within 3 years

          -  Evidence of active tuberculosis or recent clinically-significant infection requiring
             systemic therapy.

          -  Evidence of active Hepatitis B, Hepatitis C, or Human Immunodeficiency virus (HIV)
             infection

          -  Have a history of brain metastasis

          -  Have received cancer therapies including chemotherapy, radiation, biologic, or kinase
             inhibitors, granulocyte-colony stimulating factor (G-CSF), or granulocyte-macrophage
             colony-stimulating factor (GM-CSF) within 3 weeks prior ot the first scheduled dose of
             CMB305

          -  Female of child bearing potential who is pregnant, is planning to become pregnant, or
             is breast feeding; or male who is sexually active with a female of child bearing
             potential who is planning to become pregnant.