Marian van de Meent

HLA class II upregulation during viral infection leads to HLA-DP–directed graft-versus-host disease after CD4+ donor lymphocyte infusion

CD8+ T cell-depleted (TCD) donor lymphocyte infusion (DLI) after TCD allogeneic hematopoietic stem cell transplantation (alloSCT) has been associated with a reduced risk of graft-versus-host disease (GVHD) while preserving conversion to donor hematopoiesis and antitumor immunity, providing a rationale for exploring CD4+ T cell-based immunotherapy for hematologic malignancies. Here, we analyzed the clinical course and specificity of T cell immune responses in 2 patients with acute myeloid leukemia (AML) who converted to full-donor chimerism but developed severe acute GVHD after prophylactic CD4+ DLI after 10/10-HLA-matched, but HLA-DPB1-mismatched TCD-alloSCT. Clonal analysis of activated T cells isolated during GVHD demonstrated allo-reactivity exerted by CD4+ T cells directed against patient-mismatched HLA-DPB1 molecules on hematopoietic cells and skin-derived fibroblasts only when cultured under inflammatory conditions. At the time of CD4+ DLI, both patients contained residual patient-derived T cells, including cytomegalovirus (CMV)-specific T cells as a result of CMV reactivations. Once activated by CMV antigens, these CMV-specific T cells could stimulate HLA-DPB1-specific CD4+ T cells, which in turn could target nonhematopoietic tissues in GVHD. In conclusion, our data demonstrate that GVHD after HLA-DPB1-mismatched CD4+ DLI can be mediated by allo-reactive HLA-DPB1-directed CD4+ T cells and that ongoing viral infections inducing HLA class II expression on nonhematopoietic cells may increase the likelihood of GVHD development. This trial is registered at http://www.controlled-trials.com/ISRCTN51398568/LUMC as #51398568.

Monocyte‐derived dendritic cells can induce autoreactive CD4+ T cells showing myeloid lineage directed reactivity in healthy individuals

T cells against self‐antigens can be detected in peripheral blood of healthy individuals, although intrathymic negative selection removes most high‐avidity T cells specific for self‐antigens from the peripheral repertoire. Moreover, spontaneous T‐cell proliferation following stimulation with autologous monocyte‐derived dendritic cells (autoDCs) has been observed in vitro. In this study, we characterized the nature and immunological basis of the autoDC reactivity in the T‐cell repertoire of healthy donors. We show that a minority of naive and memory CD4+ T cells within the healthy human T‐cell repertoire mediates HLA‐restricted reactivity against autoDCs, which behave like a normal antigen‐specific immune response. This reactivity appeared to be primarily directed against myeloid lineage cells. Although cytokine production by the reactive T cells was observed, this did not coincide with overt cytotoxic activity against autoDCs. AutoDC reactivity was also observed in the CD8+ T‐cell compartment, but this appeared to be mainly cytokine‐induced rather than antigen‐driven. In conclusion, we show that the presence of autoreactive T cells harboring the potential to react against autologous and HLA‐matched allogeneic myeloid cells is a common phenomenon in healthy individuals. These autoDC‐reactive T cells may help the induction of primary T‐cell responses at the DC priming site.

High Mutation Frequency of the PIGA Gene in T Cells Results in Reconstitution of GPI Anchor−/CD52− T Cells That Can Give Early Immune Protection after Alemtuzumab-Based T Cell–Depleted Allogeneic Stem Cell Transplantation

Alemtuzumab (ALM) is used for T cell depletion in the context of allogeneic hematopoietic stem cell transplantation (alloSCT) to prevent acute graft-versus-host disease and graft rejection. Following ALM-based T cell–depleted alloSCT, relatively rapid recovery of circulating T cells has been described, including T cells that lack membrane expression of the GPI-anchored ALM target Ag CD52. We show, in a cohort of 89 human recipients of an ALM-based T cell–depleted alloSCT graft, that early lymphocyte reconstitution always coincided with the presence of large populations of T cells lacking CD52 membrane expression. In contrast, loss of CD52 expression was not overt within B cells or NK cells. We show that loss of CD52 expression from the T cell membrane resulted from loss of GPI anchor expression caused by a highly polyclonal mutational landscape in the PIGA gene. This polyclonal mutational landscape in the PIGA gene was also found in CD52− T cells present at a low frequency in peripheral blood of healthy donors. Finally, we demonstrate that the GPI−/CD52− T cell populations that arise after ALM-based T cell–depleted alloSCT contain functional T cells directed against multiple viral targets that can play an important role in immune protection early after ALM-based T cell–depleted transplantation.