Longitudinal Analysis of VWF Multimerization Patterns In a well-defined TTP Cohort

Abstract 4308

VWF function has long been implicated in TTP's pathogenesis. Initial study reported unusually large (UL)VWF multimers in patients with relapsing TTP. Later, ULVWF were demonstrated in TTP patients during remission that are acutely consumed at the onset of disease. However, many detailed steps concerning the timely relationship between VWF multimerization and clinical courses such as disease onset, mortality, disease refractoriness, and treatment response are still missing. In this study, we performed VWF multimeric analyses in over 400 serial samples longitudinally collected from more than 20 TTP patients at various clinical stages, including initial presentation, acute treatment, clinical remission, and clinical visits prior to TTP relapses. At the time of acute presentation, approximately 50% of cases show presence of ULVWF multimer patterns, while around 35% demonstrate acute consumption of UL and high molecular weight VWF multimers. The other 15% of cases however reveal normal VWF multimer patterns at the time of disease presentation. For the TTP patients who normally respond to plasma exchange (PE) therapy, a mild ULVWF multimer pattern may be present after discontinuation of daily PE therapy. Upon restoration of ADAMTS13 activity and achievement of sustained remission, VWF multimer patterns are normalized. During the period of daily plasma exchange for acute episodes of TTP, a persistent presence of ULVWF multimer patterns appears indicative of disease refractoriness and is associated with disease mortality. In the course of this study, ADAMTS13 activity levels (reportable range of 0.5 % –100%) in these longitudinal samples were also precisely determined using SELDI-TOF mass spectrometry to establish the correlation between ADAMTS13 activity measured in vitro and VWF multimeric patterns formed in vivo. Our study for the first time defines the dynamic changes of VWF multimeric patterns in relation to the evolution and natural history of TTP in a large well-defined clinical cohort. These novel observations provide new implications into the pathobiology of TTP and may help to develop new biomarkers for monitoring therapeutic responses and for screening for TTP relapses.