A Vaccine (STEMVAC) for Improving Survival in Patients With Triple-Negative Breast Cancer and Moderate or Extensive Residual Cancer Burden

Inclusion Criteria:

* At least 18 years of age
* Eastern Cooperative Oncology Group (ECOG) performance status score of ≤ 2
* Triple-negative breast cancer as determined by the treating oncologist
* Completed standard of care neoadjuvant chemotherapy in the opinion of their treating oncologist
* Patients whose tumors progress on neoadjuvant therapy may be enrolled
* No clinical evidence of local or distant recurrence
* Plan to receive standard of care adjuvant directed therapy
* Completed standard of care locoregional treatment, including definitive breast and lymph node surgery followed by standard radiation therapy, if recommended
* Residual cancer burden (RCB) index 2 or 3 as calculated per routine anatomic pathology clinical standards
* Absolute neutrophil count (ANC) ≥ 800/μL (within 30 days of first study vaccine administration)
* Hemoglobin (Hgb) ≥ 8 g/dL (within 30 days of first study vaccine administration)
* Platelets ≥ 75,000/ μL (within 30 days of first study vaccine administration)
* Total bilirubin ≤ 1.5 x institutional upper limit of normal (ULN), except patients with Gilbert's syndrome, in whom total bilirubin must be \< 3.0 mg/dL (within 30 days of first study vaccine administration)
* Aspartate aminotransferase (AST)/alanine aminotransferase (ALT) ≤ 1.5 x institutional ULN (within 30 days of first study vaccine administration)
* Creatinine ≤ 1.5 x ULN mg/dL or creatinine clearance \> 60 mL/min (within 30 days of first study vaccine administration)
* At least 28 days post systemic steroids prior to enrollment, unless used as part of prophylaxis to prevent intravenous (IV) contrast reactions.

  * Topical, ocular, intra-articular, intranasal, inhalational corticosteroids (with minimal systemic absorption) are allowed
* Must have recovered from major infections and/or surgical procedures; and in the opinion of the investigator, not have any significant active concurrent medical illnesses or condition precluding protocol treatment
* Patients of child-bearing potential must agree to use dual methods of contraception and have a negative urine pregnancy test at screening, and male patients must use an effective barrier method of contraception if sexually active with a person of child-bearing potential. Acceptable methods of contraception are abstinence, condoms with contraceptive foam, oral, implantable or injectable contraceptives, contraceptive patch, intrauterine device, diaphragm with spermicidal gel, or a sexual partner who is surgically sterilized or post-menopausal

Exclusion Criteria:

* Toxicities related to prior exposure to immune checkpoint inhibitors for which immune checkpoint inhibitors cannot be safely continued as determined by study investigator
* Germline BRCA1 or BRCA2 mutations with adjuvant olaparib planned within the study period

  * NOTE: If olaparib is not planned, then these patients are eligible
* Any known cardiac conditions:

  * Symptomatic restrictive cardiomyopathy
  * Dilated cardiomyopathy
  * Unstable angina within 4 months prior to enrollment
  * New York Heart Association functional class III-IV heart failure on active treatment
  * Symptomatic pericardial effusion
* Autoimmune disease requiring active systemic treatment
* Known hypersensitivity reaction to the GM-CSF adjuvant; any known contra-indication to GM-CSF
* Pregnant or breast feeding
* Known history of human immunodeficiency virus (HIV) infection, hepatitis B (e.g., hepatitis B virus surface antigen \[HBsAg\] reactive), or hepatitis C (e.g., hepatitis C virus \[HCV\] ribonucleic acid \[RNA\] is detected)
* Major surgery within the 4 weeks prior to initiation of first study vaccine
* Enrollment in any other clinical protocol or investigational trial that involves concurrent administration of experimental therapy and/or therapeutic devices, or investigational drug. Patients who completed prior clinical trials (such as neoadjuvant treatment, surgery or radiation trials) and are on long term follow up are permitted