Donor Hematopoietic Stem Cells Did No Major Contribution to Hair Follicle Repair Either in Short or in Long Term Allogeneic Hematopoietic Stem Cell Transplants Recipients.
Authors: Rovo Alicia , Meyer-Monard Sandrine , Heim Dominik , Arber Caroline , Passweg Jakob R. , Gratwohl Alois , Tichelli Andre 
Published: October 2019

Abstract
Several reports suggest that hematopoietic stem cell (HSC) develops unexpected plasticity and can form non-hematopoietic tissue. However the intrinsic plasticity of these cells has been questioned suggesting that such cells might fuse with other cells giving the appearance of differentiation. Most of the controversy over the mechanism arises from the techniques that are used to track and characterize the progenitor cell in different tissues. In the clinical setting there are no prospective quantitative studies in the human being. Objective: we assessed in a prospective study the incidence and extent of donor type chimerism in blood and non-hematopoietic cells tissue in allogeneic HSC transplants irrespective of donor type, stem cell source, conditioning and disease category. We focused on tissues with high need of organ repair: following conditioning and free of blood contamination: hair follicles. In a preliminary report we showed hair chimerism results from 53 long term survivors of allogeneic HSCT. In those recipients donor cells did not contribute to hair follicle repair. We now extend the study by increasing the number of long term patients and including short term survivors after successful engraftment. Methods: all consecutive male and female patients above 18 years old, with a full donor chimerism of hemopoiesis at last control were included. The visit included: anamnesis, clinical examination and chimerism from peripheral blood and hair follicles. Chimerism was analyzed by PCR-based amplification of 9 different short tandem repeat (STR) loci and the amelogenin locus, detecting a minor cell population ≥3%. We minimized the risk of blood contamination by careful hair follicles washing according to the procedure used in forensic medicine. The protocol was approved by the Ethics Committee. Results: between April 2003 and July 2004, 145 patients were invited to participate in this study, 119 patients (82%) accepted, 4 patients were excluded due to insufficient hair DNA; therefore the study included 100 long term (≥ 24 months of follow-up) and 15 short term (1–12 month follow-up) patients.
Population demographic characteristics and results
Conclusions: we observed a high grade of acceptance for participation in the study. In this population all hair follicles chimerism showed 100% recipient alleles, there was no difference between recipients with short or long term follow-up after HSCT. Hematopoietic stem cells from donor did not make a major contribution to repair hair growth in recipients. Contamination by hematopoietic cells can be excluded in this study due to the fact that we found no donor alleles in the hair analyzed.
Follow up after HSCT(months) ≥ 24 1–12 N 100 15 Gender Male/Female 59/41 10/ 5 Median age at HSCT 36 (range 6–63) 40 (range 17–50) Median age at follow up 43 (range 20–66) 40 (range 18–51) Median follow up (months) 96 (range 24–264) 8 (range 2–12) Donor gender Male/Female 58/42 9/6 Diagnosis to transplantation Severe aplastic anemia 6 0 Hematological malignancy 94 15 HLA Type donor identical sibling 85 12 matched related 1 0 mismatched related 3 1 matched unrelated 11 2 Source PB/BM 33/67 15/0 Conditioning High intensity 85 13 Low intensity 15 2 Acute GVHD no/yes 25/75 5/10 Chronic GVHD no/yes 41/59 6/9 Blood chimerism 100% donor alleles 98 15 90–95% donor alleles 2 0 Hair chimerism 100% recipient alleles 100 15