Transplantation-Associated Microangiopathy (TAM) in Recipients of HLA-Haploidentical Hematopoietic Stem Cell Transplants Using Ptcy, CNI and MMF for GvHD Prophylaxis
Authors: Fraccaroli Alessia , Prevalsek Dusan , Haebe Sarah , Bücklein Veit , Drolle Heidrun , Schoenermarck Ulf , Hiddemann Wolfgang , von Bergwelt Michael , Tischer Johanna 
Published: November 2019

Transplant-associated microangiopathy (TAM) is a life-threatening complication after allogeneic transplantation, related to endothelial toxicity caused by chemoradiotherapy, infections, immunosuppressive drugs and GvHD. Clinical manifestations include severe thrombocytopenia, microangiopathic hemolysis and organ dysfunction (e.g. renal, neurological) in the absence of disseminated intravascular coagulation. The reported incidence of TAM after allogeneic hematopoietic stem cell transplantation (HSCT) varies between 0,5 to 70%. Data for TAM occurrence and outcome in the context of HLA-haploidentical transplantation (haplo-HSCT) are rare. Here, we report our experience on TAM incidence, disease manifestation, treatment and outcome in T-cell-replete haplo-HSCT using PTCY as GvHD prophylaxis.
We retrospectively analyzed the treatment course of 148 adult patients undergoing haplo-HSCT with regard to the incidence of TAM at our center from January 2012 to April 2019. The diagnosis of TAM required the fulfillment of the criteria as defined by Ruutu et al., Haematologica 2007.
Median age of the entire cohort was 54 years (23-74). The majority of patients was transplanted for myeloid disease (60%). Postgrafting immunosuppression consisted of PTCY, CNI and MMF in all patients. Median follow-up time upon survivors was 3 years (4 months - 7 years). Twenty of 148 patients developed TAM, with a cumulative incidence of 10% at day 100. Median interval from haplo-HSCT to TAM onset was 63 days (23-295 days), with seven patients showing TAM after day +100. Median platelet count at diagnosis was 20 x 109/L (range: 6-116), predominantly de novo or worsening thrombocytopenia. Median LDH level was 437 IU/L (305-1445 IU/L). Serum haptoglobin levels were decreased in 85% of the TAM patients. 12/20 patients had active infection at the time of TAM diagnosis, most commonly viral (10/12). All but three patients presented with concurrent active acute GvHD requiring systemic steroid treatment in 16 patients Renal function abnormalities were diagnosed in 55% of the patients affected by TAM, with 4 patients requiring hemodialysis. Nine patients developed grade III hypertension and three patients showed neurologic dysfunction. Upon diagnosis of TAM, CNI dose was reduced (7 patients) or temporarily discontinued (7 patients). No switch to another CNI was performed. FFPs were transfused in nine patients, three patients underwent plasma exchange therapy without any effect. In four patients rituximab was applied. With a CI of 18% vs 2% (p0.002) using a PBSC graft was a risk factor for TAM development when compared to BM. Neither origin of disease (myeloid/lymphoid) nor sex of patient/donor or conditioning intensity (RIC/MAC) influenced the incidence significantly. Estimated one-year and three-year overall survival did not differ between the TAM and the non-TAM cohort (61% vs 61% and 46% vs 47%, p=0.9). Only one patient died because of TAM.
With an incidence of 10% at day +100 at our center TAM is a serious but not rare complication after haplo-HSCT using PTCY, CNI and MMF for GvHD prophylaxis. However, in our cohort disease course was moderate with low TAM-associated mortality. The use of a PBSC graft was the only factor influencing TAM incidence.

Disclosures
Hiddemann: F. Hoffmann-La Roche: Research Funding.