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Investigation of the impact of donor lymphocyte infusions on T cell reconstitution after allogeneic haematopoietic stem cell transplantation with alemtuzumab

Student thesis: Doctoral ThesisDoctor of Philosophy

Lymphocyte depletion with alemtuzumab effectively reduces the incidence of graft versus host disease after allogeneic haematopoietic stem cell transplantation (HSCT), but risk of infections and malignant disease relapse is high. Our group has previously reported that pre-emptive donor lymphocyte infusions (pDLI), given to patients after allogeneic HSCT to reverse falling donor T cell chimerism, improves overall and relapse-free survival. To investigate the basis for better outcome after pDLI, the recovery of lymphocyte subsets, T cell receptor (TCR) diversity and T cell functional competence after allogeneic HSCT with alemtuzumab were assessed. A key finding was that naïve T cells were absent for at least six months after transplantation and subsequent recovery was very slow, unless patients received pDLI. Both naïve CD4 and CD8 T cell populations were significantly increased after pDLI, but did not reach levels present in age matched healthy individuals and abnormalities within other lymphocyte subsets persisted. Sequential analysis of the TCR β chain repertoire showed domination by a small number of high abundance clones, and the abnormal profiles persisted after pDLI. Repertoire skewing was most pronounced in patients that experienced reactivation of cytomegalovirus (CMV) or Epstein Barr Virus (EBV) viraemia. In vitro stimulation with CMV and EBV peptide libraries followed by assessment of activation marker expression and interferon-γ, MIP-1β and TNF-α production showed that virus-specific T cell responses were robust and sometimes increased in magnitude and polyfunctionality after pDLI. The frequency of T cells that expressed PD1 was often high, but they retained function. Emergence and rapid expansion of donor-derived CD8 T cell clones specific for CMV and EBV antigens after DLI was seen in virus-positive patients whose donors were virus-negative. This suggests that naïve T cells present in the DLI had been primed upon encounter with virus in the patient. These findings show that naïve T cells can be primed and give rise to strong functional responses, and that pDLI replenishes naïve T cells. By inference, this may extend to leukaemia antigens and underlie the reduced rate of malignant disease relapse seen in patients given pDLI after allogeneic HSCT with alemtuzumab.
Original languageEnglish
Awarding Institution
Award date1 Oct 2019

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