Inclusion Criteria:

   - HLA-A*02-positive, unless being enrolled in the third non-HLA-A*02 arm

   - Histologically confirmed diagnosis of HER2/neu positive primary breast cancer

   - Completion of both neoadjuvant and adjuvant trastuzumab-based standard of care breast
   cancer therapy

   - Stage I, II, or III at presentation with pathologic evidence of residual invasive
   carcinoma in the breast or axillary lymph nodes (residual disease) at surgery
   following completion of neoadjuvant therapy -OR- Stage III at presentation with
   pathologic complete response (pCR) at surgery following completion of neoadjuvant
   therapy

   - The subject can begin study therapy within one year of completion of adjuvant
   trastuzumab-based therapy and any other standard therapies, but, study therapy can be
   administered concurrently with endocrine therapy.

   - No clinical evidence of residual or persistent breast cancer per treating physician
   assessment

   - ECOG 0-2

   - Adequate organ function

   - Negative pregnancy test or evidence of post-menopausal status

   - If of childbearing potential, willing to use a form of highly effective contraception

Exclusion Criteria:

   - Stage IV cancer or metastatic breast cancer at any time

   - Inflammatory breast cancer

   - Receiving other investigational agents

   - Receiving chemotherapy

   - Requiring long-term systemic treatment with corticosteroids or other immunosuppressive
   therapy

   - History of immunodeficiency or active autoimmune disease

   - A history of serious allergic reactions, including anaphylaxis, to human
   granulocyte-macrophage colony-stimulating factors such as sargramostim, yeast-derived
   products, or any component of the investigational product

   - Other malignancies except adequately treated in situ carcinoma of the cervix or basal
   cell or squamous cell carcinoma of the skin

   - Active infection

   - Known HIV infection with a detectable viral load within 6 months of the anticipated
   start of treatment. Note: Subjects on effective antiretroviral therapy with an
   undetectable viral load within 6 months of the anticipated start of treatment are
   eligible for this trial.