Chimerism Revisited: Perspective of an Immunopathologist

Abstract

Introduction: Chimerism analysis is an important diagnostic tool not only for assessing the risk of relapse after allo-Haematopoietic Stem Cell Transplant (HSCT) in patients with malignant diseases, it is also the predominant method for monitoring post-transplant engraftment status in both haematological malignancies and non malignant haematological disorders. Aim: To show the chimerism data observed in post-HSCT cases of our hospital over last four years and to emphasise on timely and close monitoring of these patients in the laboratory. Materials and Methods: The present study was a retrospective study in which 40 HSCT cases comprising of both haematological malignancies and non malignant haematological disorders were monitored in the molecular laboratory of Army Hospital (Research and Referral), at regular intervals by Short Tandem RepeatsPolymerase Chain Reaction (STR-PCR) for quantification of donor chimerism. The pretransplant workup included Human Leukocyte Antigens (HLA) typing of all recipients and donors, serum Panel Reactive Antibody (PRA) testing and Single Antigen Bead (SAB) assays for detecting donor specific antibodies in all haploidentical transplants. Results: Male patients formed majority, with only nine female cases. After complete HLA matching and preconditioning, 35 patients underwent matched related stem cell transplant, two were Matched Unrelated Donor (MUD) and three haploidentical transplants. Complete donor chimerism at D+90 was reported in 19 patients (73%) of haematologic malignancies with two cases of relapse and five showing evidence of Graft Versus Host Disease (GVHD). Amongst non malignant disorders 10 patients (71.4%) showed complete donor chimerism at D+90 with two cases of GVHD. Conclusions: Post-HSCT, progressive chimerism monitoring is an essential molecular test that predicts engraftment status of the patient by verifying the dynamic relationship between recipient and donor cells.