Fostamatinib in the Treatment of Chronic Active Antibody Mediated Rejection

Inclusion Criteria * Signed informed consent prior to any study specific screening procedures. * Male or female, at least 18 years of age * Females must be either post-menopausal, surgically sterile (hysterectomy, bilateral salpingectomy or bilateral oophorectomy), or, if of child-bearing potential, must not be pregnant or lactating. * Patients must be established on tacrolimus maintenance immunosuppression * A pre-study renal biopsy obtained within 3 months prior to Baseline (Visit 1) will be reviewed by a renal pathologist to ensure subjects meet the following Banff histologic entry criteria: If C4d positive: Microcirculation inflammation score (g+ptc) ≥1 If C4d negative: Microcirculation inflammation score (g+ptc) ≥2 Chronic glomerulopathy (cg) score ≥1b or significant Peritubular Capillary Basement Membrane Multilayering (PTCBML) Chronic tubulo-interstitial scarring ≤50% Glomerular global obsolescence ≤50% Sample must contain at least 7 glomeruli and 1 artery * Otherwise in stable health as determined by the Investigator based on medical history and laboratory tests during the screening period. See Exclusion Criteria for specific exclusions. * In the Investigator's opinion, understand the duration of the study (up to 52 weeks), including the requirements for renal biopsies, and has the ability to understand the nature of the study and any hazards of participation and to communicate satisfactorily with the Investigator. Exclusion Criteria: * Co-existing Banff Category 4 T-cell mediated rejection * History of or active, clinically significant, respiratory, gastrointestinal (including pancreatitis), hepatic, neurological, psychiatric, musculoskeletal, genitourinary, dermatological, or other disorder that, in the Investigator's opinion, could affect the conduct of the study or the absorption, metabolism or excretion of the study drug. * Have had any major cardiovascular event within the 180 days prior to randomisation, including but not limited to: myocardial infarction, unstable angina, cerebrovascular accident, pulmonary embolism, or New York Heart Association Class III or IV heart failure. * An absolute neutrophil count of \< 1,500/μL, Hgb \< 9 g/L, ALT or AST of \> 1.5x ULN, total bilirubin \> 2.0 mg/dL at Baseline (Visit 1). * Acute gastrointestinal symptoms (e.g., nausea, vomiting, diarrhoea) at Baseline (Visit 1). The subject may be reassessed after full recovery from the acute gastrointestinal illness. * Co-existing BK nephropathy or pyelonephritis on screening biopsy. * Active bacterial, viral or parasitic infections, including tuberculosis. Where CMV viral infection is defined as replicating DNA ≥3000 copies/ml and EBV viral infection is defined as replicating DNA ≥10000 copies/ml. * Evidence of active or previous invasive fungal infection. * Positive serologic tests suggestive of active hepatitis B or hepatitis C or hepatitis E(subjects may be included if confirmed hepatitis C recombinant immunoblot assay negative or hepatitis C virus RNA negative \[qualitative\]) or hepatitis E virus RNA negative by PCR), or subjects with suspected human immunodeficiency virus (HIV). * Have active malignancy. * Currently enrolled in an investigational drug or device study or have used an investigational drug or device within 30 days or 5 half-lives (whichever is longer) from Baseline (Visit 1). * Are unable or unwilling to follow instructions, including participation in all study assessments and visits. * Have a history of alcohol or substance abuse that, in the judgment of the Investigator, may impair or risk the subject's full participation in the study. * Have a condition or be in a situation that the Investigator feels may put the subject at significant risk, may confound the study results, or may interfere significantly with the subject's participation in the study. * Have a known allergy and/or sensitivity to the study drug or its excipients. * Pregnancy or for women that are sexually active, unable to take highly effective contraception (please see inclusion criteria 3 for more information regarding what classifies as a highly effective contraception method) * Women who are breastfeeding