OR37 Persistence of T cells from the first donor after a second allogeneic stem cell transplantation

Abstract

The monitoring of chimerism is a standard procedure to help assess engraftment and achievement of full donor lymphoid cells after allogeneic stem cell transplantation. T cell chimerism analysis is essential since T cells support the engraftment of hematopoietic stem cells and progenitor cells. TCRαβ T cells provide anti-tumor activity but can also cause graft vs. host disease (GVHD). In contrast, TCRγδ T cells have been found not to be associated with GVHD. Here we report a case in which residual T cells from the first donor were identified in a patient who received a second conditioning regiment and a subsequent second hematopoietic stem cell transplant. These cells from the first donor need to be closely monitored since they are TCRαβ T cells. A 10-year old male with high risk Acute Myeloid Leukemia received a 10/10 matched unrelated donor peripheral stem cell transplant (PSCT) with TCRαβ T cell depletion in May of 2015. He had been doing well until July 2016 when he relapsed. The patient underwent one dose of donor lymphocyte infusion in August 2016, with no improvement. He then received the second conditioning regimen and a KIR favorable maternal haplo-identical CD3/CD19 depleted PSCT on 11/9/16. The patient has done well overall post-transplant. He remains in remission with 100% donor engraftment without GVHD. Interestingly, his T cell engraftment analysis indicates he has T cell chimerism. 9% of his T cells are from the first unrelated donor and 91% are from the second donor. A subsequent analysis of TCRγδ T cell enriched engraftment showed that 100% of the TCRγδ T cells were from the second donor. This result suggests that the residual T cells identified from the first donor were most likely TCRαβ T cells. These results demonstrated that even after TCRαβ-depletion of the first graft and intensified immunosuppressive therapy conditioning regiment prior to the second transplant, CD3 + TCRαβ T cells from the first donor persisted. The patient is currently in remission. The expansion of the first donor T cells would strongly suggest a high risk of GVHD. Thus, it is clinically relevant to closely monitor these cells.