Increased Effector CD4+ T-Cells Early Post Hematopoietic Stem Cell Transplantation Using an Alemtuzumab-Based Reduced Intensity Conditioning Regimen Correlate with Subsequent Development of Graft Versus Host Disease.
Authors: Matthews Katie , Lim ZiYi , Pearce Laurence , Tobal Khalid , Madrigal Alejandro , Mufti Ghulam J. , Barber Linda D. 
Published: October 2019

Lymphocyte depletion using the anti CD52 monoclonal antibody alemtuzumab reduces the incidence of graft versus host disease (GvHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT), but some patients still develop this potentially life-threatening complication. We previously reported that patients achieving rapid full donor T cell chimerism after fludarabine, busulphan and alemtuzumab (FBC) conditioned allo-HSCT have a significantly increased risk of GvHD compared to patients with prolonged mixed donor chimerism beyond day 100 (Lim et al. Br. J. Haematology 2007). We performed a prospective study of 29 patients who received allo-HSCT with FBC conditioning (median age: 53 years; range: 34 – 69 presenting with AML or MDS) to examine the kinetics of lymphocyte reconstitution in relation to T-cell chimerism patterns and incidence of GvHD. Naïve, memory, effector and terminally differentiated CD4+ and CD8+ T-cells, activated T-cells (CD25+ HLA-DR+); putative regulatory CD4+ CD25high Foxp3+ T-cells, B-cells and NK cells were enumerated in whole peripheral blood of patients at days 30, 60, 90, 180, 270 and 360 after HSCT. Chimerism analysis of purified T-cells was performed by genetic profiling of polymorphic short tandem repeat loci. Ten patients developed GvHD (acute or chronic). Although alemtuzumab induced profound depletion of all T-cell subsets, significantly higher numbers of CD4+ effector (CD45RO+ CD27−) T-cells were detected at day 30 post transplant in patients who later developed GvHD (24 cells/μl; range: 1 – 84 cells/μl) compared to patients without GvHD (5 cells/μl; range: 1 – 40 cells/μl) (p = 0.026). In contrast, there were no significant differences in the numbers or rate of reconstitution of CD8+ T-cell sub-populations, NK cells or B-cells in patients that developed GvHD and those who did not at any time points. T-cells present at day 30 in patients that subsequently developed GvHD were 100% donor whereas the majority of patients that did not develop GvHD exhibited mixed donor and recipient T cell chimerism. Development of GvHD pathology was associated with expansion of these donor effector CD4+ T-cells (at day 60: 35 cells/μl; range: 9 – 154 cells/μl compared to 7 cells/μl; range: 1 – 56 cells/μl for patients without GvHD, p = 0.04). Absolute numbers of CD4+ CD25high Foxp3+ T-cells at day 30 were similar in both groups of patients (p = 0.8). However, of note, a significant deficit of these putative regulatory T-cells in the group that developed GvHD was apparent when numbers were considered relative to CD4+ effector T cells at day 30 (41 CD4+ effector T-cells; range: 28 – 51 /per regulatory CD4+ T cell for the GvHD group compared to 12 CD4+ effector T-cells; range: 2 – 33 /per regulatory CD4+ T-cell for patients without GvHD, p = 0.03). We speculate the higher numbers of effector CD4+ T-cells detected in patients at day 30 post HSCT are donor-derived mature T cells that alemtuzumab fails to deplete. In the solid organ transplant setting, alemtuzumab has been shown to be relatively sparing of effector memory CD4+ T-cells. Our correlation of donor-derived effector CD4+ T-cells with subsequent development of GvHD suggests they are alloreactive and that a deficit of T-regs relative to CD4+ effector T-cells early post HSCT contributes to GvHD.