Targeting HLA class II in allogeneic stem cell transplantation

Abstract

Allogeneic stem cell transplantation (alloSCT) is a curative treatment for a variety of hematologic diseases. The mechanism of curation by an alloSCT is the induction of an immune response of donor T cells attacking patients hematopoiesis, including the malignant hematopoietic cells. This is called the graft-versus-leukemia (GVL) reactivity. However, donor T cells can also be directed against healthy tissue cells of the recipient, causing graft-versus-host disease (GVHD). In this thesis we focused on targeting HLA class II by donor CD4 T cells to induce GVL without GVHD, because under non-inflammatory conditions, HLA class II is mainly expressed on hematopoietic cells and not on other tissue cells. We showed that CD4 T cells from HLA-identical sibling donors can induce conversion from mixed to full donor chimerism with GVL reactivity, but without GVHD, by targeting HLA class II restricted minor histocompatibility antigens. We also analyzed the immunopeptidome of different HLA-DP alleles. HLA-DP peptide binding motifs showed a clear association with the HLA-DP allele specific sequences of the binding groove. Functional hierarchies among HLA-DP alleles were unravelled, providing new molecular insights into HLA-DP classification. Permissiveness of mismatches between donor and recipient is not a black and white phenomenon, but rather gradual based on similarities and differences in the peptidomes.