Safety and Efficacy Study of PF-06835375 in Primary Immune Thrombocytopenia

This is a Phase 2, open-label, multicenter, multiple subcutaneous injection, safety and efficacy study of PF-06835375 in adult participants with primary immune thrombocytopenia (ITP). This study will focus on participants with persistent (\>3 months and ≤12 months), or chronic (\>12 months) ITP

This study is designed to elucidate the effects of PF-06835375 on platelet counts in participants with moderate to severe primary ITP. Based on the experience with other B-cells depleting agents, it is expected that the platelet counts will increase following a standard treatment. Each participant in cohort 1 received 1 subcutaneous injection of dose 1 every month for 3 months during the 12-week treatment period. Each participant in cohorts 2, 3, or 4 (will) receive(d) subcutaneous injection(s) of dose 2, 3, or 4 every month for 4 months during the 16-week treatment period. This should provide sufficient levels of exposure and depletion of CXCR5 positive cells to sustain the effects of PF-06835375 during the treatment period. Additional depletion of Tfh cells may provide sustained increase in platelet count following the last treatment.

Inclusion Criteria: * Diagnosis of Primary ITP. Ongoing ITP (platelet counts \<50 x 109/L) \[No severe bleeding within 1 month or during screening\] AND Persistent ITP (3 to 12 months) or Chronic ITP \>12 months Exclusion Criteria: * Bleeding event according to the WHO grading scale ≥2 occurring ≤4 weeks prior to screen OR a current bleeding event that, in the opinion of the investigator, requires treatment with standard of care therapy OR require blood or blood products during screening * Splenectomy within 3 months of randomization or planned during the study duration.