Inclusion Criteria:

          -  Signed written informed consent obtained prior to study procedures

          -  Histologically-confirmed Her2 positive advanced solid tumor malignancy with documented
             disease progression during or immediately following the immediate prior therapy, or
             within 6 months of completing adjuvant therapy for subjects with breast cancer

          -  Subjects must have previously received adequate standard therapy for treatment of
             their malignancy

               -  For those with metastatic breast cancer, must have received HER2-directed therapy
                  including trastuzumab, pertuzumab and ado-trastuzumab in any breast cancer
                  disease setting

               -  For those with advanced gastric cancer, adequate prior treatment with
                  HER2-directed chemotherapy is required

          -  At least 1 measurable lesion by iRECIST

          -  Able to provide fresh tumor biopsy or archived block specimen taken since time of most
             recent anti-HER2 mAb-directed therapy

          -  ECOG of 0 or 1

          -  Life expectancy ≥ 6 months

          -  LVEF ≥ 50% by MUGA or ECHO

          -  Absolute neutrophil (ANC) count ≥ 1500/ µL

          -  Platelet count ≥ 100,000/µL

          -  Hemoglobin ≥ 9g/dL

          -  Estimated GFR >30mL/min/1.73m2

        Exclusion Criteria:

          -  glioblastoma multiforme or other primary CNS tumors are excluded

          -  clinically significant cardiac disease

          -  clinically significant active infection

          -  clinical history, prior diagnosis, or overt evidence of autoimmune disease

          -  current use of more than 5mg/day of prednisone (or an equivalent glucocorticoid)

          -  Prior treatment as follows:

               -  prior cumulative doxorubicin dose greater than or equal to 300 mg/m^2 or
                  equivalent

               -  chemotherapy within 2 weeks of enrollment

               -  external beam radiation within 2 weeks of enrollment (28 days if CNS-directed
                  therapy)

               -  any monoclonal antibody (mAb) or other protein therapeutic containing Fc-domains
                  within 4 weeks of enrollment

               -  pertuzumab within 4 months of enrollment

               -  Experimental agents within 3 half-lives or 28 days prior to enrollment, whichever
                  is shorter

               -  allogeneic hematopoietic stem cell transplant (HSCT)

               -  prior infusion of a genetically modified therapy

          -  Pregnant or breastfeeding