Immune Response and Potential Booster for Patients Who Have Received HER2-pulsed DC1

Inclusion Criteria:

* Patients with a diagnosis of nonmetastatic or metastatic breast cancer in complete clinicla response classic HER2pos (ie, IHC 3+ or FISHpos) breast cancer (BC) who have previously been vaccinated with DC1 HER2-pulsed vaccines on any of several prior clinical trials for ductal carcinoma in situ (DCIS) or inflammatory breast cancer (IBC) are eligible; however, we also allowed HER2 2+ patients in many of these prior trials and they will also be allowed to participate in this trial. Note: HER2pos BC is defined by tumor tissue HER2 overexpression and or tumor HER2 amplification. The lack of HER2 overexpression by IHC is defined as 0 or 1+ whereas overexpression is defined as 3+. In the event of equivocal IHC, 2+, the tumor must be gene-amplified by fluorescent in situ hybridization (FISH) performed upon the primary tumor or metastatic lesion (ratio \> 2 and HER2 copy number \> 4 define HER2negdisease).
* Patients with nonmetastatic HER posBC must have completed all standard-of-care treatment for nonmetastatic BC (e.g., surgery, chemotherapy, radiation therapy, and HER2-targeted therapy). Note: antiestrogen therapy is permitted while on trial. Note: antiestrogen therapy is permitted while on trial.
* Patients with diagnosis of metastatic HER2 pos breast cancer must have complete tumor response to current treatment per RECIST 1.1 and completed all standard-of-care chemotherapy. Note: maintenance treatment with approved HER2-targeted agents and/or antiestrogen therapy is permitted while on trial.
* Age ≥ 18 years.
* Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1.
* Participants must have normal organ and marrow function within 2 weeks of registration.
* For both male and female patients, effective methods of contraception must be used throughout the study and for 3 months following the last dose.
* Must have the ability to understand and the willingness to sign a written informed consent prior to registration on study.

Exclusion Criteria:

* Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, congenital prolonged QT syndrome, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.
* Uncontrolled congenital or acquired immune deficiency that is requiring treatment that would interfere with study treatment will not be allowed on study. Topical, ocular, intra-articular, intranasal, inhalational corticosteroids (with minimal systemic absorption) are allowed. Patients who have received systemic corticosteroids ≤ 30 days prior to starting study drug will be excluded.
* No other prior malignancy is allowed except for the following:

  * Adequately treated basal cell or squamous cell skin cancer
  * In situ cervical cancer
  * Any other cancer from which the patient has been disease free for at least 3 years.
* Pregnant or breast feeding.
* Known to be HIV positive.
* Known current or a history of hepatitis B or C virus, including chronic and dormant states, unless disease has been treated and confirmed cleared.
* Major surgery within 4 weeks of initiation of study drug.
* Have not recovered to ≤ Grade 1 or tolerable Grade 2 adverse events (AEs) due to agents administered ≥ 28 days earlier, as documented by the treating investigator.
* Currently enrolled in any other clinical protocol or investigational trial that involves administration of experimental therapy and/or therapeutic devices, or investigational drug. Note: patients enrolled on another HER2 vaccine trial but not receiving active therapy can enroll in this study.
* Not able to comply with the treatment schedule and study procedures for any reason.