A Retrospective Study of C5b-9 and MASP2 Deposition in Skin Microvasculature As a Prognostic and Diagnostic Tool for Transplant-Associated Thrombotic Microangiopathy
Authors: Daunov Michael , Sumodi John , Agarwal Nikki , Gallogly Molly Megan , Metheny Leland , Tomlinson Ben K. , Klisovic Rebecca B. , Bseiso Ali W. , Glotzbecker Brett , Honda Kord , van Besien Koen 
Published: December 2024

Introduction
Transplant-associated thrombotic microangiopathy (TA-TMA) is a rare but serious complication of stem cell transplantation (SCT) which presents an urgent and life-threatening diagnostic dilemma. Skin biopsies with detectable deposition of terminal complement component C5b-9 and lectin pathway of complement enzyme mannose-binding lectin-associated serine protease 2 (MASP2) have been described in small cohorts of TA-TMA patients as correlating with a clinical diagnosis of TA-TMA. We sought to verify the role of skin microvasculature with C5b-9 and MASP2 deposition as a diagnostic tool, assess its specificity for TA-TMA in the setting of Graft vs Host Disease (GVHD), and examine its predictive role differentiation standard vs high-risk TA-TMA.
Methods
We identified patients who had undergone alloSCT and had had skin biopsies for various reasons. Data regarding diagnostic criteria for TA-TMA and GVHD were collected and three cohorts were identified: those with suspected TA-TMA, those without TA-TMA but with histological evidence of GVHD, and those without either TA-TMA or GVHD. Skin biopsies were evaluated by IHC for C5b-9 and MASP2 and read by a dermatopathologist blinded to their TA-TMA status. C5b-9 and MASP2 deposition in skin biopsies were tabulated and comparison between groups was performed using chi-squared analysis.
Results
We identified 30 patients: 9 with confirmed or suspected TA-TMA, 13 with histological evidence of GVHD, and 8 without GVHD or TA-TMA. Half (50%) of the 8 control cases stained positive for C5b-9 or MASP2. Of the 13 cases with histological evidence of GVHD, 5 (21%) stained positive for either C5b-9 or MASP2. Of the 9 patients with confirmed or suspected TA-TMA, 4 met modified Jodele criteria for TA-TMA, 4 had incomplete evaluations or did not meet diagnostic criteria, and 1 met criteria but had skin biopsy 4 months after diagnosis. Three of 4 patients (75%) with confirmed TA-TMA stained positive for C5b-9 or MASP2 which was not statistically significant relative to the GVHD cohort; χ2=0.53, p=.468, or the control cohort; χ2=0.1723, p=.68. All of the cases that met criteria for high-risk TA-TMA (n=3) stained positive for C5b-9 or MASP2 while the one patient with standard risk TA-TMA did not stain positive for C5b-9 or MASP2. Three of 4 (75%) patients with suspected TA-TMA stained positive for C5b-9 or MASP2. One patient who had TA-TMA four months prior did not stain positive for either C5b-9 or MASP2.
Conclusions
In this retrospective evaluation of skin biopsies for patients who had undergone alloSCT with suspected TA-TMA or GVHD, C5b-9 and MASP2 deposition in skin microvasculature was not correlated with clinical diagnosis of TA-TMA as defined by the modified Jodele criteria, albeit with small numbers. Patients with high-risk disease had more staining of C5b-9 and MASP2 vs standard risk TA-TMA but this was not statistically significant. We could not confirm initial reports of C5b-9 or MASP2 in skin microvasculature as a diagnostic tool for TA-TMA. In our hands, the assay lacks sensitivity and specificity.