We determined the efficacy of tocilizumab (TCZ) in preventing grade II-IV acute GVHD (aGVHD) in patients with acute-leukemia or myelodysplasia undertaking matched-related-sibling (MSD) or volunteer-unrelated-donor (VUD) allogeneic-SCT after myeloablative or reduced-intensity conditioning across five Australian centers. 145 patients (50 MSD, 95 VUD) were randomly assigned to placebo or TCZ on day-1. All patients received T-cell-replete PBSC grafts and GVHD-prophylaxis with cyclosporin/methotrexate. A planned sub-study analyzed the VUD cohort. With a median follow up of 746 days, the incidence of grade II-IV aGVHD at day 100 for the entire cohort was 36% versus 27% for placebo versus TCZ (HR 0.69; CI:0.38-1.26, p=0.23) and 45% versus 32% (HR 0.61; CI:0.31-1.22, p=0.16) for the VUD subgroup. The incidence of grade II-IV aGVHD at day 180 for the entire cohort was 40% versus 29% for placebo versus TCZ (HR 0.68; CI:0.38-1.22, p=0.19) and 48% versus 32% (HR 0.59; CI:0.30-1.16, p=0.13) for the VUD subgroup. Reductions in aGVHD were predominantly in grade II disease. A trend to improved aGVHD-free survival (aGVHD-FS) was noted in the TCZ-treated VUD subgroup, 52% versus 68% for placebo versus TCZ (p=0.13). For the entire cohort, transplant-related-mortality occurred in 8% versus 11% of placebo versus TCZ-treated patients respectively (p=0.56) and overall-survival was 79% versus 71% (p=0.27). Median day to neutrophil and platelet engraftment was delayed by 2-3 days in TCZ-treated patients while liver toxicity and infectious complications were similar between groups. In this phase-3 randomized, double-blind trial (ACTRN12614000266662), tocilizumab showed non-significant trends to reduced incidence of grade II-IV aGVHD and improved aGVHD-FS in recipients of HLA-matched VUD donors, but no improvements in long term-survival.

Key Points Th17 cells differentiate early after allo-SCT in both mouse and man and display a high degree of cytokine plasticity. IL-12/IL-23 drives further differentiation of Th17 toward an inflammatory phenotype that is inhibited by cyclosporine treatment.

Key Points DCs are the principal source of IL-6 dysregulation after alloSCT. IL-6–dependent GVHD is driven by classical signaling of IL-6R on donor T cells but is regulated by trans signaling.

Mice reconstituted with human hematopoietic stem cells are valuable models to study aspects of the human immune system in vivo. We describe a humanized mouse model (hu mice) in which fully functional human CD141 and CD1c myeloid and CD123 plasmacytoid dendritic cells (DC) develop from human cord blood CD34 cells in immunodeficient mice. CD141 DC are the human equivalents of murine CD8 /CD103 DC which are essential for the induction of tumor-inhibitory cytotoxic T lymphocyte responses, making them attractive targets to exploit for the development of new cancer immunotherapies. We used CD34 -engrafted NSG-A2 mice to investigate activation of DC subsets by synthetic dsRNA or ssRNA analogs polyinosinic-polycytidylic acid/poly I:C and Resiquimod/R848, agonists for TLR3 and TLR8, respectively, both of which are expressed by CD141 DC. Injection of hu mice with these agonists resulted in upregulation of costimulatory molecules CD80, CD83 and CD86 by CD141 and CD1c DC alike, and their combination further enhanced expression of these molecules by both subsets. When combined, poly I:C and R848 enhanced serum levels of key cytokines associated with cross-presentation and the induction of cytotoxic T lymphocyte responses including IFN-α, IFN-β, IL-12 and CXCL10. These data advocate a combination of poly I:C and R848 TLR agonists as means of activating human DC for immunotherapy.

Graft-versus-host disease (GVHD) is the major cause of nonrelapse morbidity and mortality after allogeneic stem cell transplantation (allo-SCT). Prevention and treatment of GVHD remain inadequate and commonly lead to end-organ dysfunction and opportunistic infection. The role of interleukin (IL)-17 and IL-22 in GVHD remains uncertain, due to an apparent lack of lineage fidelity and variable and contextually determined protective and pathogenic effects. We demonstrate that donor T cell-derived IL-22 significantly exacerbates cutaneous chronic GVHD and that IL-22 is produced by highly inflammatory donor CD4 T cells posttransplantation. IL-22 and IL-17A derive from both independent and overlapping lineages, defined as T helper (Th)22 and IL-22 Th17 cells. Donor Th22 and IL-22 Th17 cells share a similar IL-6-dependent developmental pathway, and while Th22 cells arise independently of the IL-22 Th17 lineage, IL-17 signaling to donor Th22 directly promotes their development in allo-SCT. Importantly, while both IL-22 and IL-17 mediate skin GVHD, Th17-induced chronic GVHD can be attenuated by IL-22 inhibition in preclinical systems. In the clinic, high levels of both IL-17A and IL-22 expression are present in the skin of patients with GVHD after allo-SCT. Together, these data demonstrate a key role for donor-derived IL-22 in patients with chronic skin GVHD and confirm parallel but symbiotic developmental pathways of Th22 and Th17 differentiation.