Human G‐CSF‐mobilized CD34‐positive peripheral blood progenitor cells can stimulate allogeneic T‐cell responses: implications for graft rejection in mismatched transplantation

Abstract

To investigate mechanisms of stem cell graft rejection we studied the allo‐stimulatory potential of G‐CSF mobilized peripheral blood progenitor cells (PBPC). CD34+ cells were purified (> 95%) in a two‐step procedure using immunoaffinity columns for CD34 selection and T‐depletion. The capacity of CD34+ cells to stimulate allogeneic T‐cell responses was compared with other cells from the same individual. CD34+ cells induced potent proliferative responses at stimulator:responder ratios of 1:20, but were approximately 50‐fold less efficient compared to dendritic cells. Furthermore, CD34+ cells primed responses from partially matched allogeneic T cells in bulk cultures. Dual‐colour flow cytometry showed that the co‐stimulatory molecules B7.1, CD40 and ICAM‐1 were absent on resting CD34‐positive progenitor cells, but were induced during incubation with allogeneic lymphocytes due to a cytokine‐mediated effect. Up‐regulation of accessory molecules on CD34+ cells was reproduced by incubation with interferon‐γ or GM‐CSF which enhanced the allo‐stimulatory activity of CD34+ cells. Blocking studies with inhibitory antibodies suggested co‐stimulatory functions for B7.2, ICAM‐3, CD40 and LFA‐3. CD34+ cells were more efficient in inducing allogeneic T‐cell responses when compared to the unprocessed leukapheresis products. The reduced allo‐stimulatory ability of G‐CSF mobilized PBPC could be explained by the presence of CD3+4+ and CD3+8+ lymphocytes with suppressor activity. We conclude that current methods of stem cell selection for transplantation do not avoid allo‐sensitization of the recipient and that further graft manipulation with add‐back of lymphocytes or selection of subsets of CD34+ cells with reduced allo‐stimulatory ability may reduce graft rejection.

Human iPS cell–derived hematopoietic progenitor cells induce T-cell anergy in in vitro–generated alloreactive CD8+ T cells

“…40 It is this characteristic that forms a formidable barrier to successful bone marrow transplantation. Because we did not observe lysis of the iPS-HPCs by alloreactive T cells, we wondered about the impact of iPS-HPCs on alloreactive T cells.…”

Higher doses of CD34+ peripheral blood stem cells are associated with increased mortality from chronic graft-versus-host disease after allogeneic HLA-identical sibling transplantation

“…15,17 It has been shown that granulocyte colony-stimulating factor (G-CSF)-mobilized CD34+ hematopoietic stem cells not only participate in engraftment, but also have an immunogenic role. [18][19][20][21] In the setting of T-cell-depleted allogeneic transplants using CD34+ positive selection as T-cell-depletion method, Urbano-Ispizua et al 22 could show that a high CD34+ cell dose not only does not improve the clinical results, but also actually may be associated with a poorer outcome. With this background, we therefore hypothesized that variations in the cell composition of PBSC grafts could lead to differences in graft-versus-host immune reactions, thereby affecting transplant related events also in the context of non-T-cell-depleted allogeneic transplants.…”

Allogeneic transplantation of CD34+selected cells from peripheral blood from human leukocyte antigen–identical siblings: detrimental effect of a high number of donor CD34+ cells?

“…Although a beneficial effect of increasing numbers of CD34 ϩ cells on engraftment and survival has been demonstrated for autografting, 3,11,12 that association might be different in the context of allogeneic transplantation, where CD34 ϩ cells not only participate in engraftment, but also have an immunogenic role. [13][14][15][16] With this background, we have analyzed the effect on the clinical outcome of the number of CD34 ϩ cells in 84 consecutive adult patients submitted to allo-PBT/CD34 ϩ from HLAidentical siblings. This study, for the first time, reports that a high CD34 ϩ cell dose not only does not improve the clinical result, but actually might have a deleterious effect.…”