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Post-transplant cyclophosphamide (PTCY) is being increasingly used for graft-versus-host disease (GVHD) prophylaxis after hematopoietic cell transplantation (HCT) across various donor types. However, immune reconstitution after PTCY-based vs. conventional GVHD prophylaxis has not been well studied. We evaluated the pace of immune reconstitution (CD4+ T-cell, CD8+ T-cell, NK-cell and B-cell) at 3 months, 6 months and 1 year post-HCT in 583 adult patients receiving myeloablative (n=223) or reduced intensity conditioning (n=360) HCT (2012-2018). Haploidentical (Haplo; n=75) and 8/8 HLA-matched unrelated (MUD, n=508) donor types were included. GVHD prophylaxis was PTCY-based in 75 Haplo and 38 MUD (MUD-PTCY) HCT, while tacrolimus/methotrexate (TAC/MTX) was used in 89 and TAC/Sirolimus (TAC/SIR) in 381 MUD HCT. Clinical outcomes including viral infections, non-relapse mortality (NRM) and overall survival (OS) were compared across all four treatment groups. The recovery of absolute total CD4+ T-cell count after Haplo-PTCY and MUD-PTCY was significantly lower compared to MUD TAC/MTX or MUD TAC/SIR throughout 1 year of HCT (Figure). In contrast, CD19+ B-cell recovery at 6 months and thereafter was more rapid after Haplo-PTCY and MUD-PTCY HCT in comparison to MUD TAC/MTX and MUD TAC/SIR. In subgroup analysis compared to MUD TAC/MTX HCT, total CD8+ T-cell or NK-cell recovery was not significantly different after Haplo-PTCY or MUD-PTCY HCT. However, patients receiving MUD TAC/SIR vs. MUD TAC/MTX had significantly slower reconstitution of total CD8+ T-cells up to 6 months and CD19+ B-cells at 1 year of HCT, but no significant differences in CD4+ T-cell or NK-cell recovery. The distribution of recipient CMV serostatus was similar in all four groups: 72% in Haplo-PTCY, 62 % in MUD-PTCY HCT, 68% in MUD TAC/MTX and 63% in MUD TAC/SIR (p =0.11). Cumulative incidence of CMV reactivation/infection at 1-year of HCT was higher in patients receiving Haplo-PTCY (39.6%) or MUD TAC-MTX (37.7%) compared to those receiving MUD-PTCY (27.0%) or MUD TAC/SIR (22.8%; p <0.01). Whereas the incidence of EBV reactivation/infection was lower in patients receiving PTCY-based GVHD prophylaxis (5.2% in Haplo-PTCY and 8.1% in MUD-PTCY) as compared to patients receiving MUD TAC/MTX (19.7%) or MUD TAC/SIR (20.5%, p <0.01). The incidences of HHV6, BK- and other viruses were similar between the groups. Overall, the treatment groups had comparable NRM (p =0.27) and OS outcomes (p =0.78). Our data demonstrate that the pattern of immune reconstitution after HCT is different after PTCY-based vs. conventional GVHD prophylaxis with delayed total CD4+ T-cell but more rapid B-cell recovery after PTCY-based GVHD prophylaxis. The rates of CMV and EBV viral infections were different across the donor types. However, these differences had no significant influence on NRM or survival after HCT. [ABSTRACT FROM AUTHOR]

Mycophenolate mofetil (MMF) dose/kg can influence clinical outcomes of allogeneic hematopoietic cell transplantation (HCT) including acute graft-versus-host disease (GVHD) (Harnicar BBMT 2015; Bejanyan BBMT 2018). When used for GVHD prophylaxis in conjunction with post-transplant cyclophosphamide (PTCy), MMF is generally dosed at 15 mg/kg three times daily (capped at a maximum of 3 g/day) and combined with either tacrolimus or sirolimus. Thus, many adults receive the maximum dose and a variable dose/kg of MMF. We sought to investigate the impact of MMF dose/kg on clinical outcomes of HCT in the setting of PTCy-based GVHD prophylaxis, where the effect of MMF dose/kg is unknown. Included are 112 consecutive adult patients with hematologic malignancies who received myeloablative (n=70) or reduced intensity (n=42) HCT at the Moffitt Cancer Center between 2012-2018 with T-cell replete peripheral blood stem cells (n=94) or bone marrow (n=18). GVHD prophylaxis consisted of PTCy/MMF and either tacrolimus (n=57) or sirolimus (n=55). MMF dose relative to patient actual body weight (mg/kg/day), was stratified by tertiles into low (<30 mg/kg/day, n=31), intermediate (30-40 mg/kg/day, n=45) and high (>40 mg/kg/day, n=36). The median age at transplant was 57.8 (range: 21-75) years. Median follow-up was 12 months (range: 0.3-39). Donors were haploidentical related (n=74), mismatched unrelated (n=26), and matched related/unrelated (n=12). MMF dose groups had similar characteristics, except the low dose group having a higher proportion of males (p<0.01), higher body mass index (p<0.01), and patients receiving <3g/day MMF (p<0.01). Cumulative incidence rate (CIR) of neutrophil engraftment was 96% and of platelet engraftment was 89% for all patients. For the entire cohort, CIR was 41% for grade II-IV and 11% for grade III-IV acute GVHD at day 100 and 46% for chronic GVHD at 2-years. MMF dose had no significant effect on acute (Figure 1) or chronic GVHD (Table). Probability of 2-year non-relapse mortality (NRM) was 17% and relapse was 31% for all patients. Corresponding 2-year overall survival (OS) was 60% and disease-free survival (DFS) was 52% (Figure 2). While MMF dose did not significantly influence NRM, relapse or OS, we observed significantly better DFS in patients receiving intermediate vs. low weight-based MMF dose (HR=0.5, CI: 0.25-0.998, p=0.049). In patients receiving PTCy based GVHD prophylaxis, MMF dose/kg had no significant effect on GVHD. However, lower MMF dose/kg was associated with worse DFS. This study suggests that <30 mg/kg/day may lead to inferior clinical outcomes. Larger studies are needed to confirm these findings. [ABSTRACT FROM AUTHOR]

Haploidentical hematopoietic cell transplantation (haplo-HCT) with post-transplant cyclophosphamide (PTCy) is increasingly offered as a curative treatment for patients with hematological malignancies. In a recent registry study (Bashey et al. JCO 2017), peripheral blood (PB) as a graft source compared to bone marrow reduced the risk of relapse but increased acute and chronic GVHD after haplo-HCT with PTCy in combination with calcineurin inhibitor (CNI) and mycophenolate mofetil (MMF). In this phase II trial we aimed to assess the efficacy of Sirolimus (Sir) in combination with PTCy and MMF as a CNI-free GVHD prophylaxis after PB haplo-HCT (NCT03018223). The primary end point was the cumulative incidence of grade II-IV acute GVHD at day 100 after HCT. With 32 evaluable patients enrolled, the study had a 90% power (α = 0.1) to demonstrate a reduction in 100-day grade II-IV acute GVHD from the historical benchmark of 40% (haplo-HCT and PTCy/Tac/MMF) to 20%. Sir was administrated from days +5 to +90 at target level of 8-14 ng/ml, followed by taper by day +180 in the absence of acute GVHD. A total of 32 patients with hematological malignancies were treated on trial 2/2017- 8/2018. The median age at HCT was 50 years (range, 23-75) and 59% of patients were racial/ethnic minorities. AML (50.0%) was the most common indication for HCT. The majority (66%) received myeloablative Fludarabine (Flu) and Busulfan (AUC of 5300), while 34% received non-myeloablative Flu/Cy/TBI 200 cGy. There were no graft failure events and the median time of neutrophil engraftment was 17 days (range, 12 - 30). With a median follow-up of 15.4 months, the primary endpoint was met with day 100 grade II-IV acute GVHD cumulative incidence of 18.8% (95% CI 7.5 - 34.0; grade III-IV = 9.4%). The cumulative incidence of 1-year NIH moderate/severe chronic GVHD was 20.0% (95% CI 7.9-36.0) (Figure). Only 3 patients required systemic glucocorticoids for chronic GVHD therapy. At last follow up, all immunosuppression was successfully discontinued in 43% (n=12) of all surviving study patients. The 1-year probability of non-relapse mortality was 19.7% (95% CI 7.8 - 35.5), relapse was 23.7% (95% CI 10.2 - 40.4), disease-free survival was 56.6% (95% CI 41.3 - 77.7) and overall survival was 70.2% (95% CI 55.5 - 88.6) for the entire cohort. These data demonstrate that PTCy/Sir/MMF GVHD prophylaxis effectively prevents grade II-IV acute GVHD after PB haplo-HCT and results in successful hematopoietic engraftment. Furthermore, the initial chronic GVHD, relapse and survival outcomes appear favorable. These findings warrant prospective comparison of PTCy/Sir/MMF with PTCy/Tac/MMF after PB haplo-HCT. [ABSTRACT FROM AUTHOR]