Maddalena Noviello

Human herpesvirus 6 (HHV-6) can reactivate after allogeneic hematopoietic stem cell transplant (allo-HSCT) and may lead to severe symptoms. HHV-6–specific immune responses after HSCT are largely unexplored. We conducted a prospective observational study on 208 consecutive adult patients who received allo-HSCT to investigate HHV-6 reactivations and specific immune responses. Interferon gamma–producing HHV-6–specific T cells were quantified using enzyme-linked immunospot assay (ELISpot). HHV-6 reactivation occurred in 63% of patients, at a median of 25 days from allo-HSCT. Only 40% of these presented a clinically relevant infection, defined by the presence of classical HHV-6 end-organ diseases (EODs), based on European Conference on Infections in Leukaemia (ECIL) guidelines, and other possible HHV6-related EODs. Using multivariate analysis, we identified risk factors for HHV-6 reactivation: previous allo-HSCT, posttransplant cyclophosphamide (PT-Cy), and time-dependent steroids introduction. The use of PT-Cy and steroids were associated with clinically relevant infections, whereas higher CD3+ cell counts seemed to be protective. Interestingly, circulating HHV-6–specific T cells were significantly higher in patients with reactivated virus. Moreover, HHV-6–specific T-cell responses, quantified at >4 days after the first viremia detection, predicted clinically relevant infections (P < .0001), with higher specificity (93%) and sensitivity (79%) than polyclonal CD3+ cells per μL. Overall survival and transplant-related mortality were not affected by time-dependent HHV-6 reactivation, whereas a significant association was observed between clinically relevant infections and acute graft-versus-host disease. These results shed light on the role of HHV-6 in allo-HSCT and may affect HHV-6 monitoring and treatment.

Transplantation of hematopoietic cells from a healthy individual (allogeneic hematopoietic cell transplantation (allo-HCT)) demonstrates that adoptive immunotherapy can cure blood cancers: still, post-transplantation relapses remain frequent. To explain their drivers, we analyzed the genomic and gene expression profiles of acute myeloid leukemia (AML) blasts purified from patients at serial time-points during their disease history. We identified a transcriptional signature specific for post-transplantation relapses and highly enriched in immune-related processes, including T cell costimulation and antigen presentation. In two independent patient cohorts we confirmed the deregulation of multiple costimulatory ligands on AML blasts at post-transplantation relapse (PD-L1, B7-H3, CD80, PVRL2), mirrored by concomitant changes in circulating donor T cells. Likewise, we documented the frequent loss of surface expression of HLA-DR, -DQ and -DP on leukemia cells, due to downregulation of the HLA class II regulator CIITA. We show that loss of HLA class II expression and upregulation of inhibitory checkpoint molecules represent alternative modalities to abolish AML recognition from donor-derived T cells, and can be counteracted by interferon-γ or checkpoint blockade, respectively. Our results demonstrate that the deregulation of pathways involved in T cell-mediated allorecognition is a distinctive feature and driver of AML relapses after allo-HCT, which can be rapidly translated into personalized therapies.

The major cause of death after allogeneic Hematopoietic Stem Cell Transplantation (HSCT) for acute myeloid leukemia (AML) is disease relapse. We investigated the expression of Inhibitory Receptors (IR; PD-1/CTLA-4/TIM-3/LAG-3/2B4/KLRG1/GITR) on T cells infiltrating the bone marrow (BM) of 32 AML patients relapsing (median 251 days) or maintaining complete remission (CR; median 1 year) after HSCT. A higher proportion of early-differentiated Memory Stem (T_SCM) and Central Memory BM-T cells express multiple IR in relapsing patients than in CR patients. Exhausted BM-T cells at relapse display a restricted TCR repertoire, impaired effector functions and leukemia-reactive specificities. In 57 patients, early detection of severely exhausted (PD-1⁺Eomes⁺T-bet⁻) BM-T_SCM predicts relapse. Accordingly, leukemia-specific T cells in patients prone to relapse display exhaustion markers, absent in patients maintaining long-term CR. These results highlight a wide, though reversible, immunological dysfunction in the BM of AML patients relapsing after HSCT and suggest new therapeutic opportunities for the disease.

HLA-haploidentical haematopoietic stem cell transplantation (haplo-HSCT) is increasingly offered to patients with high-risk acute leukaemia. Unfortunately, haplo-HSCT is followed by a delayed immunoreconstitution. The aim of this EBMT registry study was to explore the clinical impact of lymphocyte subset counts after haplo-HSCT. We considered 144 leukaemic patients transplanted in the period 2001–2012. Pre-transplantation clinical variables and differential immune-cell counts (CD3, CD4, CD8 T cells, NK and B cells) measured before day 100 were evaluated for their capacity to predict overall survival, relapse mortality or non-relapse mortality (NRM). Negative prognostic factors for overall survival were advanced disease state at transplantation, host age and CMV seropositivity. Higher CD3, CD4 and CD8 counts were associated with a better overall survival and a lower NRM. Strikingly, when tested in multivariable analysis, higher CD3 and CD8 counts were still significantly associated with a lower NRM. These results indicate that an accelerated T-cell reconstitution correlates with less transplantation mortality, likely due to the protective role of T cells against viral infections. This observation suggests that CD8+ T-cell counts should be investigated as surrogate biomarkers of outcome in prospective haplo-HSCT trials.

Bone Marrow Transplantation is a high quality, peer-reviewed journal covering all aspects of clinical and basic haemopoietic stem cell transplantation.

RNA interference (RNAi) is a powerful tool for efficient and highly specific gene silencing. Transduction with lentiviral vectors provides stable and long-term gene expression in slowly and non-dividing cells. This chapter describes how to couple these two technologies to efficiently silence specific genes in primary acute myeloid leukemia (AML) cells for subsequent xenotransplantation in immunocompromised mice. This approach could be used for loss-of-function studies aimed at identifying oncogenic targets in AML.