Adoptive T Cell Therapy Following HER2-Pulsed Dendritic Cell Vaccine & Pepinemab /Trastuzumab in Patients w/ Metastatic HER2+ Breast Cancer

Participants will receive a DC1 vaccine injection at 1.0-2.0 x 10\^7 cells, either to groin lymph notes or to tumor if accessible once a week for 3 weeks on days 1, 8 and 15. Participants will receive DC1 vaccine boosters every 3 weeks x 3.

Participants will receive trastuzumab 8 mg/kg by IV week 1, then 6 mg/kg by IV beginning week 4 and continuing every 3 weeks until disease progression or intolerable toxicity.

Participants will receive pepinemab 20 mg/kg by IV beginning week 1 and continuing every 3 weeks until disease progression or intolerable toxicity.

Participants will receive IL-15 expanded CD4 T cells infusion by IV Day 1 at week 8, 2 weeks from last DC1 vaccine, and IL-7 expanded CD4 T cells infusion IV at week 8 day 8.