PD-1(Programmed Death-1) Antibody +GP as First Line Treatment for Triple Negative Breast Cancer(TNBC) Patients

There will be 3 stages in this trial. Stage 1 is the dose escalation stage. JS001 will be tested in combination with GP in 3 dose levels. Level 1: 120mg Level 2: 240mg Level 3: 480mg Patients will receive JS001+GP for 6 cycles and JS001 maintenance therapy for up to approximately 2 years. JS001 will be given on d1 every 3 weeks with GP and every 2 weeks in maintenance therapy. The first group of participants will receive the lowest dose level of JS001 at 120mg. Each new group will receive a higher dose of JS001 than the group before it until 480mg. Stage 2 is the dose expansion stage. Dose expansion will be carried out to expand to 12 patients in the highest dose level at which the patient can tolerate well. This dose will also be recommended as phase 2 dose(RP2D). Stage 3 is the sequential treatment stage. Patients receive 6 cycles of GP without JS001 and then receive JS001 maintenance therapy for up to approximately 2 years.