Gemcitabine and Ex Vivo Expanded Allogenic Universal Donor, TGFβi Natural Killer (NK) Cells With or Without Naxitamab (Danyelza) for the Treatment of Patients With Metastatic, GD2 Expressing, HER2 Negative Breast Cancer

This trial is testing a combination of a chemotherapy drug (gemcitabine) and donated immune cells called Natural Killer (NK) cells, with or without a targeted antibody (naxitamab/Danyelza), for people with metastatic HER2-negative breast cancer. The NK cells are specially grown to be more effective at fighting cancer. The cancer cells must express a surface protein called GD2 (common in triple-negative breast cancer). **You may be eligible if...** - You are 18 or older with metastatic, HER2-negative breast cancer (e.g., triple-negative breast cancer) - Your cancer is historically associated with GD2 expression (archival tissue required) - You have received at least one prior treatment for metastatic disease - Your blood counts, kidney, and liver function are within acceptable ranges - You have measurable tumors on scans **You may NOT be eligible if...** - You have active brain metastases without prior treatment or recent progression - You have an active autoimmune disease requiring systemic treatment - You have received chemotherapy or radiation in the past 3 weeks - You have had a recent heart attack, serious heart failure, or significant heart disease Talk to your doctor to see if this trial is right for you.