RecruitingPhase 1Drug trialCD40 Agonist, Flt3 Ligand, and Chemotherapy in HER2 Negative Breast CancerThis research study is being done to find out if the immunotherapy drugs called CDX-301 and CDX-1140 in combination with the standard chemotherapy treatment pegylated liposomal doxorubicin (PLD, Doxil) are safe and effective at controlling the cancer in patients with metastatic triple Human Epidermal Growth Factor Receptor 2 (HER2) negative breast cancer, and to determine a safe dose and treatment schedule of the three drugs. This research study will also test how your immune system responds to these treatments alone and in combination.