LB-ARHGDIB-1R as a novel minor histocompatibility antigen for therapeutic application

In HLA-matched allogeneic hematopoietic stem cell transplantation (SCT), donor T cells can mediate graft-versus-leukemia/lymphoma (GvL) reactivity and graft-versus-host disease (GvHD) by recognition of minor histocompatibility antigens (MiHA).1–4 Only a minority of MiHA shows hematopoiesis-restricted expression, and donor T cells for these MiHA may induce beneficial GvL reactivity without GvHD. The number of well-characterized MiHA with therapeutic relevance based on hematopoiesis-restricted expression remains limited and only 25% and 40% of recipients transplanted with grafts from sibling and unrelated donors, respectively, are eligible for therapies targeting known hematopoietic MiHA.3,4 Thus, in order to increase the efficacy and applicability of cellular therapy for selective GvL induction, more hematopoiesis-restricted MiHA with balanced population frequencies in common HLA molecules must be identified. Here, we investigated the therapeutic significance of a MiHA encoded by ARHGDIB.5 We demonstrated hematopoiesis-restricted gene expression with the exception of intermediate mRNA expression in endothelial cells and showed that T cells recognized LB-ARHGDIB-1R presented by HLA-B*07:02 on primary leukemic cells, but not on [interferon-gamma (IFN-γ)]-treated fibroblasts and keratinocytes. To evaluate potential toxicity against endothelial cells, we tested T cell recognition of LB-ARHGDIB-1R on human umbilical vein endothelial cells (HUVEC) and found only limited reactivity under inflammatory conditions. Furthermore, we demonstrated in vivo targeting of LB-ARHGDIB-1R in eight out of ten patients who were screened for post-transplant specific T-cell responses. In one patient with relapsed lymphoma, high T-cell frequencies were induced after donor lymphocyte infusion (DLI), coinciding with long-lasting anti-lymphoma immunity without GvHD. Our data thus support the relevance of LB-ARHGDIB-1R as a therapeutic target with the potential to induce selective GvL reactivity.