Bortezomib in the treatment of refractory thrombotic thrombocytopenic purpura

Acquired thrombotic thrombocytopenic purpura (TTP) is a rare, life-threatening condition caused by autoantibody-mediated inhibition of ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type-1 motif, 13). Therapeutic plasma exchange (TPE) improves survival, but disease may be refractory despite therapy. Management and treatment response of refractory TTP is variable, with rituximab and other immunosuppression often being used. Case reports have suggested a benefit of the proteasome inhibitor, bortezomib, possibly due to elimination of the autoreactive plasma cells producing anti-ADAMTS13 antibodies. We evaluated the effect of bortezomib in a series of primary refractory TTP patients unresponsive to intensive therapy. Bortezomib-treated patients were identified from consecutive cases managed at two UK referral centres. Demographic and clinical data were extracted from hospital records. ADAMTS13 activity was measured using a fluorescence resonance energy transfer VWF73 assay, and anti-ADAMTS13 IgG using enzyme-linked immunosorbent asssay. We identified six bortezomib-treated patients out of 51 consecutive cases of acute, acquired TTP. All patients received TPE, methylprednisolone and rituximab. Five of the six achieved complete remission with bortezomib, and one died of cardiac arrest due to underlying disease. No treatment-related adverse events were observed. Mean follow-up time after hospital discharge was 17 months (range: 3-33). Bortezomib appears effective in the treatment of a subgroup of cases with severe, refractory TTP. Prospective trials are required to further investigate this effect.