*2.1. Animal Experiments*

The present study was performed with permission of the State of Hesse, Regierungspraesidium Giessen, according to section 8 of the German Law for the protection of animals and conforms to the NIH guide for the care and use of laboratory animals. All experiments were approved by the committee on the ethics of animal experiments of the Regierungspraesidium Giessen, Germany (permit number: V54-19c 20 15c GI20/10 Nr. G21\_2016 and JLU Nr. 532\_M). Col-HSV-TK mice were generated at the Max Planck Institute for Heart and Lung Research animal facility (Bad Nauheim, Germany), as described previously [38]. In brief, purified Col1-HSV-TK-IRES-EGFP plasmids (Supplementary Figure S1a) were microinjected into the pronucleus of a fertilized ovum obtained from super-ovulated female mice. Subsequently, groups of injected embryos were re-implanted into the oviducts of pseudo-pregnant female mice. The litters were bred with wild-type C57BL/6J mice. Female, positively genotyped mice were paired again with wild-type mice to create a heterozygous Col-HSV-TK colony. After genotyping, offspring were used for the experiments. All mice were housed in a pathogen-free environment under a constant 12-hour light-dark cycle at 22 ◦C temperature and 50% humidity. The mice were fed standard chow (ALTROMIN, Lage, Germany) and water ad libitum.

5 <sup>×</sup> 10<sup>6</sup> bone marrow (BM) cells were transplanted from male Col-HSV-TK (FC-Ablation) or C57BL/6J wild-type mice (Control) into 12 weeks old lethally irradiated (11 Gy, 60Co) female C57BL/6J mice via tail vein injection (*n* = 16 for each group). For FC depletion during fibrogenesis after 4 weeks of reconstitution 300 mg/l TAA (Sigma-Aldrich, Munich, Germany) and 8.3 mg/l VCV (Roche, Basel, Switzerland) were administered orally via drinking water for 18 weeks. Mice were sacrificed at the age of 34 weeks. A summary of the animal experiment is depicted schematically in Figure 1a.

**Figure 1.** Suicide gene strategy enabled fibrocyte depletion. (**a**) Schematic representation of the animal experiments including lethal irradiation, bone marrow transplantation (BM-Tx), and treatment with valganciclovir (VCV) and thioacetamide (TAA). While TAA induces hepatic fibrosis, VCV is metabolized into toxic compounds by all cells expressing herpes simplex virus thymidine kinase (HSV-TK). (**b**) Successful depletion was confirmed by RNA in situ hybridization. Fibrocytes (FC, black arrows) were identified by the simultaneous expression of *Col1a1* (red) and *Ptprc* (CD45, blue) transcripts. The details in boxes were enlarged in individual panels in the lower right part of the micrograph. Note that individual and possibly *Col1a1*/*Ptprc* co-expressing cells were detected in the fibrocyte-ablated group. Magnification 1000×, bars 10 μm.

For FC ablation during regeneration, TAA but not VCV was given until the age of 34 weeks. Thereafter, the TAA-administration was stopped and VCV was added during a 4-week regeneration period. Untreated female C57BL/6J mice, sacrificed at the age of 34 and 38 weeks, served as supercontrols (SC). Liver samples were shock frosted and stored at −80 ◦C or preserved for histology as indicated below. Serum samples were stored at −80 ◦C until analysis of alanine aminotransferases (ALT) by routine clinical chemistry on a Reflotron Plus Analyzer (Roche, Mannheim, Germany).
