Faculty Bibliography

Extracellular vesicles (EVs) play an important role in the cellular crosstalk by transferring bioactive molecules through biological barriers from a cell to another, thus influencing recipient cell functions and phenotype. Therefore, EVs are increasingly being explored as biomarkers of disease progression or response to therapy and as potential therapeutic agents in different contexts including in hematological malignancies. Recently, an EV role has emerged in allogeneic hematopoietic cell transplantation (allo-HCT) as well. Allogeneic hematopoietic cell transplantation often represents the only curative option in several hematological disorders, but it is associated with potentially life-threatening complications that can have a significant impact on clinical outcomes. The most common complications have been well-established and include graft-versus-host disease and infections. Furthermore, relapse remains an important cause of treatment failure. The aim of this review is to summarize the current knowledge, the potential applications, and clinical relevance of EVs in allo-HCT. Herein, we will mainly focus on the immune-modulating properties of EVs, in particular those derived from mesenchymal stromal cells, as potential therapeutic strategy to improve allo-HCT outcome. Moreover, we will briefly describe the main findings on EVs as biomarkers to monitor graft-versus-host disease onset and tumor relapse.

Contrary to tandem autologous transplant (auto-auto), autologous followed by reduced intensity conditioning allogenic transplantation (auto-allo) offers graft-versus-myeloma (GVM) effect but with higher toxicity. Trials comparing these two strategies relied on availability of HLA-matched sibling donors for arm allocation (biological randomization) and yielded conflicting results. A pooled analysis of multiple trials with extended follow up provides an opportunity to compare these strategies. We obtained individual patient data from participants of four trials comparing auto-auto vs. auto-allo after induction therapy. There were 899 patients in auto-auto and 439 in auto-allo. Median follow up of survivors was 118.5 months. Median overall survival (OS) was 78.0 months in auto-auto and 98.3 months in auto-allo (HR = 0.84, P = 0.02). OS was 36.4% vs. 44.1% at 10 years (P = 0.01) for auto-auto and auto-allo, respectively. Progression-free survival was also improved in auto-allo (HR = 0.84, P = 0.004). Risk of non-relapse mortality was higher in auto-allo (10 year 8.3% vs. 19.7%, P < 0.001), while risk of disease progression was higher in auto-auto (10 year 77.2% vs. 61.6%, P < 0.001). Median post relapse survival was 41.5 months in auto-auto and 62.3 months in auto-allo (HR = 0.71, P < 0.001). This supports the existence of durable GVM effect enhancing myeloma control with subsequent therapies.

Research on CAR T cells has achieved enormous progress in recent years. After the impressive results obtained in relapsed and refractory B-cell acute lymphoblastic leukemia and aggressive B-cell lymphomas, two constructs, tisagenlecleucel and axicabtagene ciloleucel, were approved by FDA. The role of CAR T cells in the treatment of B-cell disorders, however, is rapidly evolving. Ongoing clinical trials aim at comparing CAR T cells with standard treatment options and at evaluating their efficacy earlier in the disease course. The use of CAR T cells is still limited by the risk of relevant toxicities, most commonly cytokine release syndrome and neurotoxicity, whose management has nonetheless significantly improved. Some patients do not respond or relapse after treatment, either because of poor CAR T-cell expansion, lack of anti-tumor effects or after the loss of the target antigen on tumor cells. Investigators are trying to overcome these hurdles in many ways: by testing constructs which target different and/or multiple antigens or by improving CAR T-cell structure with additional functions and synergistic molecules. Alternative cell sources including allogeneic products (off-the-shelf CAR T cells), NK cells, and T cells obtained from induced pluripotent stem cells are also considered. Several trials are exploring the curative potential of CAR T cells in other malignancies, and recent data on multiple myeloma and chronic lymphocytic leukemia are encouraging. Given the likely expansion of CAR T-cell indications and their wider availability over time, more and more highly specialized clinical centers, with dedicated clinical units, will be required. Overall, the costs of these cell therapies will also play a role in the sustainability of many health care systems. This review will focus on the major clinical trials of CAR T cells in B-cell malignancies, including those leading to the first FDA approvals, and on the new settings in which these constructs are being tested. Besides, the most promising approaches to improve CAR T-cell efficacy and early data on alternative cell sources will be reviewed. Finally, we will discuss the challenges and the opportunities that are emerging with the advent of CAR T cells into clinical routine.

The timing of immunosuppressive therapy used in combination with post-transplantation cyclophosphamide (PTCY) in haploidentical hematopoietic stem cell transplant (haplo-HSCT) is not standardized. We evaluated the schedules of immunosuppression therapy after haplo-HSCT in 509 patients with acute leukemia receiving PTCY on days +3 and +4 along with tacrolimus (group 1; n = 215), with cyclosporine A (CSA) and mycophenolate mofetil (MMF) from day +5 (group 2; n = 170), or CSA + MMF from day 0 or 1 with PTCY on days +3 and +5 (group 3; n = 124). Compared with the other 2 groups, patients in group 3 were younger (median age, 46 years; P = .02) and more often received bone marrow (77%; P < .01) and a regimen containing thiotepa, fludarabine, and busulfan (84%; P< .01). At 2 years, overall survival was 44% was in group 1, 48% in group 2, and 59% in group 3 (P= .15); leukemia-free survival (LFS) was 43%, 46%, and 53% (P= .05); and refined graft-versus-host disease-free, relapse-free survival (rGRFS) was 33%, 39%, and 36% (P = .02). The incidence of grade II-IV acute GVHD was 25% in group 1, 39% in group 2, and 18% in group 3 (P< .01); incidence of chronic GVHD was 25%, 21%, and 24% (P= .50); relapse incidence was 36%, 37%, and 26% (P= .02); and nonrelapse mortality was 26%, 20%, and 21% (P= .35). On multivariate analysis, early start of immunosuppression therapy at day +1 followed by PTCY was associated with a better LFS (hazard ratio [HR], .58; P= .02) and improved rGRFS (HR, .62; P = .02). In this study, the timing of immunosuppression influenced the outcomes of haplo-HSCT with PTCY. An early start of CSA + MMF with PTCY administered on days +3 and +5 improves LFS and rGRFS.

To define the role of spleen stiffness (SS) and liver stiffness (LS) in myelofibrosis and other Philadelphia (Ph)-negative myeloproliferative neoplasms (MPNs), we studied, by ultrasonography (US) and elastography (ES), 70 consecutive patients with myelofibrosis (MF) (no.43), essential thrombocythemia (ET) (no.10), and polycythemia vera (PV) (no.17). Overall, the median SS was not different between patients with MF and PV (p = 0.9); however, both MF and PV groups had significantly higher SS than the ET group (p = 0.011 and p = 0.035, respectively) and healthy controls (p < 0.0001 and p = 0.002, respectively). In patients with MF, SS values above 40 kPa were significantly associated with worse progression-free survival (PFS) (p = 0.012; HR = 3.2). SS also correlated with the extension of bone marrow fibrosis (BMF) (p < 0.0001). SS was higher in advanced fibrotic stages MF-2, MF-3 (W.H.O. criteria) than in pre-fibrotic/early fibrotic stages (MF-0, MF-1) (p < 0.0001) and PFS was significantly different in the two cohorts, with values of 63% and 85%, respectively (p = 0.038; HR = 2.61). LS significantly differed between the patient cohort with MF and healthy controls (p = 0.001), but not between the patient cohorts with ET and PV and healthy controls (p = 0.999 and p = 0.101, respectively). We can conclude that organ stiffness adds valuable information to the clinical work-up of MPNs and could be employed to define patients at a higher risk of progression.

The optimal myeloablative conditioning (MAC) for patients undergoing haploidentical hematopoietic cell transplantation (haplo-HCT) is unknown. We studied the outcomes of total body irradiation (TBI) vs chemotherapy (CT) based MAC regimens in acute myeloid leukemia (AML) patients. The study included 1008 patients who underwent first haplo-HCT with post-transplant cyclophosphamide, following TBI (N = 89, 9%) or CT (n = 919, 91%) based MAC. Patients in the TBI cohort were younger (median age, 38 vs 47 years, P < .01) and more likely to receive BM graft (57% vs 43%, P = .01). Two-year overall chronic GVHD (cGVHD) incidence was 42% vs 27% (P < .01) and extensive cGVHD incidence was 9% vs 12% (P = .33) in TBI and CT cohorts, respectively. Graft failure was reported in two (2%) TBI- and 65 (7%) CT-MAC recipients (P = .08). Death from veno-occlusive disease was reported in one (3%) TBI and 11 (3%) CT patients who died during the study period. In the multivariate analysis, TBI was associated with increased risk for overall cGVHD (hazard ratio = 1.95, 95% confidence interval:1.2-3.1, P < .01) compared to CT-based MAC. The choice of conditioning regimen did not impact relapse incidence, leukemia-free survival, non-relapse mortality, overall survival or GVHD-relapse-free survival in multivariate analysis. In conclusion, major transplant outcomes were not statistically different between TBI-based MAC and CT-based MAC in patients with AML after haplo-HCT/PTCy.

Donor selection contributes to improve clinical outcomes of T-cell-replete haploidentical stem cell transplantation (haplo-SCT) with posttransplant cyclophosphamide (PT-Cy). The impact of donor age and other non-HLA donor characteristics remains a matter of debate. We performed a multicenter retrospective analysis on 990 haplo-SCTs with PT-Cy. By multivariable analysis, after adjusting for donor/recipient kinship, increasing donor age and peripheral blood stem cell graft were associated with a higher risk of grade 2 to 4 acute graft-versus-host-disease (aGVHD), whereas 2-year cumulative incidence of moderate-to-severe chronic GVHD was higher for transplants from female donors into male recipients and after myeloablative conditioning. Increasing donor age was associated with a trend for higher nonrelapse mortality (NRM) (hazard ratio [HR], 1.05; P = .057) but with a significant reduced risk of disease relapse (HR, 0.92; P = .001) and improved progression-free survival (PFS) (HR, 0.97; P = .036). Increasing recipient age was a predictor of worse overall survival (OS). Risk of relapse was higher (HR, 1.39; P < .001) in patients aged ≤40 years receiving a transplant from a parent as compared with a sibling. Moreover, OS and PFS were lower when the donor was the mother rather than the father. Pretransplant active disease status was an invariably independent predictor of worse clinical outcomes, while recipient positive cytomegalovirus serostatus and hematopoietic cell transplant comorbidity index >3 were associated with worse OS and PFS. Our results suggest that younger donors may reduce the incidence of aGVHD and NRM, though at higher risk of relapse. A parent donor, particularly the mother, is not recommended in recipients ≤40 years.

Haploidentical stem cell transplantation with T cell-replete grafts and post-transplant cyclophosphamide (PTCy) is increasingly used with encouraging outcome. Natural killer (NK) cell alloreactivity, predicted by missing killer cell immunoglobulin-like receptor (KIR) ligands in the recipient that are present in their donor improves outcome of T cell-depleted haploidentical transplants. We explored the role of KIR ligand mismatching in 444 acute leukemia patients after T cell-replete transplants with PTCy. Thirty-seven percent of all patients had KIR ligand mismatching. Patients were in first remission (CR1) (39%), second remission (CR2) (26%), or active disease (35%). Stem cell source was peripheral blood (PBSC, 46%) or bone marrow (54%). The 2-year relapse, non-relapse mortality (NRM), and survival rates were 36.0% (95% confidence interval (CI), 31.4-40.7), 23.9% (20.0-28.0), and 45.9% (40.8-51.0), respectively. Multivariate analysis identified acute myeloid leukemia compared with acute lymphoblastic leukemia (hazard ratio (HR) 0.55, P = 0.002), female gender (HR 0.72, P = 0.04), and good performance status (HR 0.71, P = 0.04) as factors associated with better survival, while advanced age (HR 1.13, P = 0.04), active disease (HR 3.38, P < 0.0001), and KIR ligand mismatching (HR 1.41, P = 0.03) as associated with worse survival. KIR ligand mismatching was associated with a trend for higher relapse but not with graft-versus-host disease or NRM. The KIR ligand-mismatching effect was more prominent in patients given PBSC. In conclusion, there is no evidence that KIR ligand mismatching results in better outcome in the PTCy setting.