A Study to Assess Safety, Tolerability, Pharmacokinetics and Pharmacodynamics of Multiple- Dose BIVV009 in Participants With Chronic Immune Thrombocytopenia (ITP)

An AE is any untoward medical occurrence in a participant participating in a clinical study that does not necessarily have a causal relationship with the pharmaceutical/biological agent under study. A serious adverse event (SAE) is any AE that results in: death, persistent or significant disability/incapacity, requires inpatient hospitalization or prolongation of existing hospitalization, is life-threatening experience, is a congenital anomaly/birth defect and may jeopardize participant and/or may require medical or surgical intervention to prevent one of the outcomes listed above.

Number of participants with premature study terminations will be assessed.

Clinical laboratory abnormalities including one or more specific target-organs for toxicity of BIVV009, abnormalities in D-dimer, thrombin-anti-thrombin assay, and Systemic Lupus Erythematosus (SLE) panel.

Change from baseline in peripheral blood platelet count at A-EOT will be assessed.

Change from baseline in peripheral blood platelet count during BIVV009 treatment will be assessed.

Number of participants who are independent from using combination ITP therapy during A-EOT but receive combination ITP therapy after A-EOT will be assessed.

Complete response (CR) is defined as a platelet count greater than or equal to (>=) 100*10^9/liter (L) measured on 2 occasions at least 7 days apart and the absence of bleeding on and through these two visits and the lack of combination ITP therapy on and through these two visits.

Response or Better: Response (R) is defined as a platelet count >= 30*10^9/L and a greater than 2-fold increase from baseline measured on 2 occasions at least 7 days apart and the absence of bleeding on and through these two visits and the lack of combination ITP therapy on and through these two visits; and CR: A platelet count >=100*10^9/L measured on 2 occasions at least 7 days apart and the absence of bleeding on and through these two visits and the lack of combination ITP therapy on and through these two visits.

Duration of CR is defined as the number of consecutive days in which a patient's peripheral blood platelet count is >= 100*10^9/L and the absence of bleeding, and the lack of platelet transfusions or other ITP therapy.

Duration of response is defined as the number of consecutive days in which a patient's peripheral blood platelet count is >= 30*10^9/L and the absence of bleeding, and the lack of platelet transfusions or other ITP therapy.

Time to first platelet response is defined as greater than or equal to 30*10^9/L, 50*10^9/L, 100*10^9/L (confirmed by a consecutive platelet response at least 7 days apart).

Number of participants who report loss of response among those who achieve response will be reported. For a participant with a response (R), the loss of the response is defined as a platelet count < 30*10^9/L measured on 2 consecutive occasions at least 1 day apart, or a less than 2-fold increase in platelet count from baseline measured on 2 consecutive occasions at least 1 day apart, or the presence of bleeding, or use of the combination ITP therapy.

Number of participants who report loss of complete response among those who achieve complete response will be reported. For a participant with a complete response (CR), loss of complete response is defined as a platelet count less than (<) 100*10^9/L measured on 2 consecutive occasions more than 1 day apart and/or the presence of bleeding or use of the combination ITP therapy.

Change from baseline (Part B) in peripheral blood platelet count to B-EOT will be assessed.

Number of participants who achieve CR and the lack of platelet transfusions or other ITP therapy during Part B treatment period will be reported. Complete response (CR): A platelet count >= 100*10^9/L measured on 2 occasions at least 7 days apart and the absence of bleeding on and through these two visits and the lack of combination ITP therapy on and through these two visits.

Number of participants who achieve response through B-EOT will be reported.

Duration of CR is defined as the number of consecutive days in which a participant's peripheral blood platelet count is >= 100*10^9/L and the absence of bleeding, and the lack of platelet transfusions or other ITP therapy.

Duration of response is defined as the number of consecutive days in which a participant's peripheral blood platelet count is >= 30*10^9/L and the absence of bleeding, and the lack of platelet transfusions or other ITP therapy.

Number of participants who achieve a platelet count >= 100*10^9/L on 2 consecutive occasions at least 7 days apart and have the absence of bleeding on and through these two visits and use any combination ITP therapy through B-EOT will be assessed.

Number of participants who achieve a platelet count >= 30*10^9/L and a greater than (>) 2-fold increase from baseline measured on 2 consecutive occasions at least 7 days apart and have the absence of bleeding on and through these two visits and use any combination ITP therapy through B-EOT will be assessed.

Number of Participants who do not require other ITP therapy (non-transfusion) following the last BIVV009 dose will be assessed.

Number of Participants who do not require platelet transfusions during the Part B treatment period will be reported.

Number of participants who experience any bleeding episode, bleeding by grade or serious bleeding according to the International Working Group (IWG) Bleeding Assessment Tool (BAT) will be reported.

Plasma concentrations of BIVV009 will be assessed.

Maximum observed concentration of BIVV009 in plasma will be assessed.

Time to Reach Maximum Observed Plasma Concentration (Tmax) of BIVV009 will be assessed.

AUC (0-t) is the area under the Concentration-time curve (AUC) from hour 0 to the last quantifiable time point of BIVV009.

Blood samples will be collected to determine number of participants with anti-drug antibodies (ADAs) against BIVV009.

Inhibition by BIVV009 of the complement system classical pathway measured by the WIESLAB assay.

Complement CH50 is a blood test that helps us determine whether protein abnormalities and deficiencies in the complement system are responsible for any increase in autoimmune activity. It will be assessed using complement assays.

Total C4 Levels will be assessed in plasma using complement assays.

C1q Levels will be assessed in plasma using complement assays.

Thrombopoietin level will be assessed in plasma using complement assays.