Does Microangiopathy Predict Chronic GvHD After Allogeneic Stem Cell Transplantation? A Clinical and Immunohistochemical Study on Bone Marrow Biopsies
Authors: Hill Wolfgang , Sotlar Karl , Kolb Hans Jochem , Hausmann Andreas , Tischer Johanna , Rank Andreas 
Published: October 2019

Abstract
Abstract 4540
Microangiopathy (MA) and graft-versus-host disease (GvHD) are serious complication after allogeneic hematopoietic cell transplantation (HCT). MA is comparable to a slight form of thrombotic thrombocytopenic purpura (TTP), characterized as de novo thrombocytopenia, hemolysis, evidence of fragmentocytes in the blood, hypertension, cerebral confusion and uremic syndrome. Conglomerates of platelets and uncleaved multimere of vWillebrand-Factor (vWf)) are the pathophysiological correlate and result in multiple occlusions of microvessels. Up to now the exact pathomechanism for chronic GvHD (cGvHD) is unknown but oftenly associated with decreasing platelets counts. In patients (pts) with cGvHD we previously described an increased number of vWf +and CD34+ microvessels and of CD8+ T-cells in the bone marrow (Hill,W Blood 112 abstract No 1166, 2008). The aim of this study is to screen bone marrow biopsies of pts after HCT for histological changes of vascular quality regarding to MA and correlate these findings with the development of cGvHD. Bone marrow biopsies of 36 pts (25 male, 11 female, 45 years median, range 18–64) after HCT (day 105 to 4623) were screened for overall number of vWf+ vessels, the number of sinus with a thick wall of vWf + deposit with a size > 15 × 8μ (plaquesinus) and the number of vWf+ deposit without evidence of sinus (plaques) as well as the number of megakaryocytes between Oct 2001 and Jul 2006. Morphological findings were correlated with GvHD or non-GvHD and with MA by the well known grading (aMA) at the time of acute GvHD (aGvHD) and with as a modificated grading (cMA) at the time of simultaneous cGvHD.

Results:
26 of 36 pts had cGvHD (6 with limited and 20 with extensive disease). 22 had aGvHD before and 4 did not. 8 of the 36 pts had neither aGvHD nor cGvHD, 2 pts suffered from aGvHD. Regarding to aMA a moderate grade was found in 14 pts, a mild form was detected in 15 pts, and 7 pts did not have any signs of aMA. The levels of maximal elevation of lactatdehydrogenase (LDH) and maximal decrease of platelets (each p value < 0,02) were as followed: absent grade LDH mean 248 U/L and platelets decrease mean 36 %; mild grade LDH 299 U/L and platelets 52 % and moderate grade LDH 505 U/L and platelets 70%. Additional parameters (each p<0,01) were evidence of fragmentocytes, increase of retikulocytes, anemia, minimal aPTT and minimal fibrinogen. 20 of 36 pts had aGvHD stage II-IV. 14 of these had moderate grade of aMA (5 mild, 1 absent). Otherwise none of 16 pts without aGvHD had moderate aMA (p=0,000). 10 had mild and 6 absent aMA. Additionally 14 of the 26 pts with cGvHD had a moderate grade of aMA before in contrast to none of the 10 pts with or without aGvHD (p=0,003). The grading of MA at the time of cGvHD based of minimal platelets count and maximal LDH elevation (cMA) as followed: for grade absent platelets 163 G/L and LDH 219 U/L, for mild platelets 98 G/L and LDH 331 U/L and for moderate platelets 38 G/L and LDH 344 U/L. Additional parameters were platelet decrease, anemia, elevation of reticulocytes as well as level of vWf in serum (169, 308 respectively 480%) (p < 0,04).11 of 26 pts with cGvHD had a moderate grade cMA vs none of 10 pts without cGvHD (p=0,013). The cumulative level of Ciclosporin A in serum was higher in mild and moderate grade of cMA vs absent (13,3 vs 7,3g p=0,036). The duration were 190 vs 88 days (p=0,06). The numbers of vWf+ vessels, of plaqesinus and plaques were higher in pts with cGvHD than non-cGvHD (16 vs 7/mm2 p=0,000, 3,4 vs 0,7/mm2, p=0,000, respectively 1,2 vs 0,3/mm2 p=0,054). cMA mild and moderate grade had more vWf+ vessels, plaquesinus and plaques than absent grade (each p<0,022). A change into severe grade of MA was prevented by discontinuation of immunosuppression and infusions of fresh frozen plasma (3 pts) as well as of IVIG for suspected ITP.

Conclusion:
Low grade MA was more often observed than expected from the literature. MA can be demonstrated morphologically by vWf+ deposits in endothelial-cells in bone marrow and can be graded also at the time of cGvHD. The high frequency of moderate grade at the time after engraftment with or without aGvHD is remarkable for development of a cGvHD with prognostic, pathogenetic and therapeutic relevance. From clinical, laboratory and morphological point of view microangiopathy seems to be part of aGvH reaction, followed by deposits of vWf+ material in the bone marrow, consumption of platelets by fixation to uncleaved multimere of vWf with the consequence of thrombocytopenia.

Disclosures:
Hill: Novartis: Research Funding.