Telomere length of donors influences granulocyte recovery in children after hematopoietic stem cell transplantation

Abstract

Dear Editor,Telomeres (terminal restriction fragments, TRF) are non-coding repetitive DNA sequences located at the end ofchromosomes in order to prevent end-to-end fusion andrearrangements [ 1]. Telomere length is widely recognizedas a critical factor in determining the replicative potential ofmitotic cells. Accelerated TRF shortening due to excessivereplicative stem cell turnover may represent a likelyindicator of hematopoietic stem cell (HSC) prematureaging, ultimately leading to increased incidence of graftfailure and/or clonal disorders [ 2–6]. Since the clinicalcourse of transplanted patients depends on the rapidrecovery of hematopoiesis immediately after engraftmentand because correlation between telomere length andgranulocyte recovery remains controversial [ 7, 8], wemeasured HSC reconstitution of recipients as well astelomere length from donors and recipients at differentintervals from hematopoietic stem cell transplantation(HSCT). Nineteen children with various disorders referredto the HSCT Unit of the “G. Gaslini ” Children ’s ResearchInstitute to receive allogeneic HSCT were entered in thestudy after approval of the protocol by the InstitutionalEthics Committee. Relevant clinical findings are detailed inTable 1. Thirteen had acute or poor prognosis chronicleukemia and six had other diseases associated with bonemarrow failure. Average age of patients at HSCT was9.5 years (range 1 –18) and that of donors 31.1 years (range10 –45). Five patients received HSCT from a humanleukocyte antigen (HLA) identical sibling, 11 from anHLA-matched unrelated donor, and three from a mis-matched relative; bone marrow was the source of HSC inall cases but three, who received peripheral blood stemcells.Childrenwereconditionedwithamyeloablativeregimenbased on total body irradiation plus cyclophosphamide –thiotepa. Among patients with malignancy, nine were intheir first complete remission/chronic phase (CR/CP) at thetime of transplant and six in second or subsequent CR/CP.Peripheral blood samples were separated into a light-density mononuclear cell (MNC) fraction and granulocyte(polymorphonuclear leukocyte, PMN)-rich pellets. Unfrac-tionated MNCs were used because previous authors haveshown that telomere loss of monocytes is similar to that inlymphocytes with aging [ 9]. Genomic DNA was isolatedfrom PMN and MNC using a DNA purification kit(Amersham, Little Chalfont, UK). TRF were evaluatedwith a chemiluminescent assay kit (Telo-TAGGG telomerelength assay, Roche, Mannheim, Germany) as describedbefore [ 10 ]. Complete engraftment was obtained in all cases