Patients receive HER2 intracellular domain (ICD) protein mixture intradermally and sterile water injected intradermally (as a negative control) at 6 months post-vaccination with pNGVL3-hICD vaccine. Vital signs and injection site will be monitored prior to skin test and at 60 minutes post-test. Patients return 48-72 hours after skin test for delayed-type hypersensitivity (DTH) measurements. The injection site is biopsied and examined by immunohistochemistry for infiltrating T-cell and antigen-presenting cell populations.