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The combination of hypomethylating agents with the selective Bcl-2 inhibitor venetoclax (HMA-VEN) has emerged as a highly active regimen in patients with acute myelogenous leukemia (AML) in both the upfront and relapsed/refractory (r/r) settings. We report our early experience with a cohort of patients who were able to proceed to allogeneic hematopoietic cell transplantation (alloHCT) after HMA-VEN therapy. Thirty-two patients with AML (19 r/r and 13 de novo) with a median age of 62 years underwent alloHCT after HMA-VEN therapy. Twenty-two (68.8%) were in complete remission (CR)/CR with incomplete count recovery at time of HCT. With a median follow up of 14.4 months, the 1-year overall survival (OS) was 62.5%, and disease-free survival was 43.8%. The 1-year nonrelapse mortality rate was 18.8%, and the cumulative incidence of relapse was 37.5%. Among patients who underwent alloHCT in CR, the 1-year OS was 77.3%, and the cumulative incidence of nonrelapse mortality was 9.1%. The cumulative incidence of grade II-IV acute graft-versus-host disease was 43.8%. We conclude that alloHCT after HMA-VEN is therapy associated with favorable allogeneic HCT outcomes in newly diagnosed older patients with AML, as well as those with r/r AML.

Philadelphia chromosome–like (Ph-like) acute lymphoblastic leukemia (ALL) is a subset of high-risk B cell ALLs. A large proportion of Ph-like ALL cases carry activating kinase mutations that could potentially allow them to be targeted by tyrosine kinase inhibitors. Ph-like ALL is not an uncommon entity, especially among adults, with a frequency exceeding 20%, including in older patients (>60 years old) with ALL. Ph-like ALL is associated with inferior outcomes across all ages, and studies have consistently shown a higher incidence of persistent postinduction minimal residual disease in patients carrying Ph-like ALL compared with other subgroups of ALL, and this translates into inferior leukemia-related outcomes. The inferior outcome of conventional chemotherapy for Ph-like ALL in adults raises the fundamental question of whether all adults with Ph-like ALL require an allogeneic hematopoietic cell transplantation (HCT) in first complete remission (CR1) regardless of other presenting features and treatment response parameters. Here we present and discuss several scenarios in which adults with Ph-like ALL underwent or were considered for HCT in CR1 for various reasons. Although the decision to proceed with HCT was clear and indisputable in some of these situations, in others we struggled with the decision to transplant in CR1 because of the lack of published data regarding the efficacy of allogeneic HCT as consolidation for Ph-like ALL. We emphasize the urgent need for developing well-designed studies to address this important question.

Allogeneic hematopoietic cell transplantation (HCT) is recommended for patients with T cell acute lymphoblastic leukemia (T-ALL) in second or later complete remission (CR) and high-risk patients in first CR. Given its relative rarity, data on outcomes of HCT for T-ALL are limited. We conducted a multicenter retrospective cohort study using data from 208 adult patients who underwent HCT between 2000 and 2014 to describe outcomes of allogeneic HCT for T-ALL in the contemporary era. The median age at HCT was 37 years, and the majority of patients underwent HCT in CR, using total body irradiation (TBI)-based myeloablative conditioning regimens. One-quarter of the patients underwent alternative donor HCT using a mismatched, umbilical cord blood, or haploidentical donor. With a median follow up of 38 months, overall survival at 5 years was 34%. The corresponding cumulative incidence of non-relapse mortality and relapse was 26% and 41%, respectively. In multivariable analysis, factors significantly associated with overall survival were the use of TBI (HR, 0.57; P = .021), age >35 years (HR, 1.55; P = .025), and disease status at HCT (HR, 1.98; P = .005 for relapsed/refractory disease compared with CR). Relapse was the most common cause of death (58% of patients). Allogeneic HCT remains a potentially curative option in selected patients with adult T-ALL, although relapse is a major cause of treatment failure.

The tyrosine kinase inhibitor dasatinib is often used after allogeneic hematopoietic cell transplantation to treat minimal residual disease in Philadelphia chromosome–positive (Ph+) acute lymphoblastic leukemia (ALL). Colitis, sometimes hemorrhagic, has occasionally been described with the use of dasatinib for both chronic myeloid leukemia and Ph+ ALL. The pathogenesis of dasatinib-induced colitis is unclear but may be related to effects of dasatinib on immune function. We describe a series of 5 patients who had 7 episodes of colitis during dasatinib use. No patient had obvious large granular lymphocytosis in peripheral blood. The histopathologic and immunohistochemical features of these cases were indistinguishable from control cases of gut graft-versus-host disease (GVHD). In all patients symptoms resolved upon discontinuation of dasatinib in addition to therapy with local or low-dose systemic steroids. An additional 3 patients who developed cytomegalovirus (CMV) colitis while on dasatinib therapy were identified and studied. Dasatinib colitis may have an immune-mediated mechanism similar to GVHD, and dasatinib use may be associated with CMV colitis. Awareness of this association is important for avoiding unnecessary intensification of immunosuppression for suspected gut GVHD.

The prognostic relevance of cytogenetics at diagnosis on the outcome of allogeneic hematopoietic stem cell transplantation (alloHCT) for adult acute lymphoblastic leukemia (ALL) remains unclear. We retrospectively analyzed outcomes of 333 adult ALL patients who underwent alloHCT at our institution over a 10-year period. Patients were classified according to disease status at transplantation (complete response [CR] 1 [n = 202] or > CR1) and according to cytogenetic risk, defined as good (2%), intermediate (42%), poor (46%), or unknown (10%) based on available outcome data for each of the cytogenetic abnormalities. Three-year overall survival (OS), leukemia-free survival (LFS), and relapse incidence (RI) were 55.7%, 47.9% and 27.5%, respectively; 1-year nonrelapse mortality (NRM) was 17.3%. For patients undergoing alloHCT in CR1, 3-year OS, LFS, and RI were 69.8%, 62.3%, and 17.1%, respectively. In multivariable analysis, cytogenetic risk did not impact OS or LFS for the whole cohort or for patients who underwent transplantation in CR1. Disease status at alloHCT was an independent predictor for LFS (CR1 versus others: hazard ratio [HR], 3.17; P

Chronic graft-versus-host disease (cGVHD) is a late-occurring inflammatory condition post- allogeneic hematopoietic cell transplantation (HCT), which involves multiple distinct interactions among alloreactive dysregulated T and B cells. Prior studies have shown that autoantibodies to platelet-derived growth factor receptor (PDGFR) induce tyrosine phosphorylation and accumulation of Reactive Oxygen Species (ROS), causing expression of collagen type-1 gene through the Ha-Ras-Erk1/2–ROS signaling pathway. We hypothesize that antioxidant markers of inflammation (8-OHdG, total antioxidant levels, CXCL4 and pH2Ax) will be elevated in patients with scleroderma cGVHD compared to patients who do not develop cGVHD or have non-scleroderma cGVHD. Patients (n=36) were consented on an IRB-approved protocol for a cross-sectional single time point biospecimen collection. Patients with established cGVHD (n=29) or ≥2 years post-HCT without clinical manifestations of cGVHD (n=7) were included. Patients with cGVHD were divided into Scleroderma cGVHD (n=14) and Non-scleroderma cGVHD (n=15). Median age was 49 (range: 21-69) and 56 years (range: 18-72) for patients with scleroderma (group 1) and without scleroderma or no GVHD (group 2), respectively. Median prior lines of therapy was 3.2 (range: 2-5) for patients in group 1. All patients is group 1 and 77% of patients in group 2 received PBCSs as the graft source. Transplant was from a matched unrelated (group 1: 75%, group 2: 73%) or a matched sibling donor (group 1: 25%, group 2: 23%). Tacrolimus/sirolimus was the most commonly used GVHD prophylactic regimen in both groups (group 1: 83% and group 2: 64%). Peripheral blood samples were drawn at a single time point post-HCT, and serum samples were used for ELISA assays for levels of total antioxidants, 8-OHdG, and CXCL4. Flow cytometric analysis was performed to investigate percentage of Tregs and pH2AX+ cells. There were no differences in the total antioxidant levels, CXCL4 and Tregs between groups 1 and 2. Using a cutoff threshold of 10 ng/ml of 8-OHdG, 11 patients (78%) in group 1 and 9 patients (40.9%) in groups 2 had elevated levels of 8-OHdG (p=0.029, Fisher's exact). Percentage of pH2AX expressing cells was lower in group 2. At the cutoff threshold of 37%, only one patient (7%) in group 1 and 13 patients (59%) in group 2 had more than 37% pH2AX-expressing CD45+ cells in their peripheral blood (p=0.002, Fisher's exact). In conclusion, our pilot cross-sectional study showed that scleroderma cGVHD is associated with increased ROS levels (8-OHdG) without elevation of pH2AX cells in peripheral blood T cells. Our results indicate that ROS elevation in scleroderma patients may be a stress response to inflammatory milieu and is independent of DNA damage. Our data justify further prospective cohort studies to define the role of ROS markers in scleroderma cGVHD and to develop novel strategies to treat/prevent cGVHD.

Acute lymphoblastic leukemia (ALL) with a history of central nervous system (CNS) involvement, either at diagnosis or relapse, poses challenges when the decision is made to proceed with allogeneic hematopoietic cell transplantation (alloHCT), as there is no evidence-based consensus on the best peri-transplantation approach to reduce subsequent CNS relapse risk. Here, we retrospectively analyzed outcomes of 87 patients with ALL and a history of CNS involvement who later underwent alloHCT. Patients with pretransplantation CNS involvement had higher risk of CNS relapse after transplantation (2-year CNS relapse: 9.6% versus 1.4%, P.0001), inferior event-free survival (EFS) (hazard ratio [HR], 1.52; P = .003), and worse overall survival (OS) (HR, 1.55; P = .003) compared with patients without pretransplantation CNS involvement (n = 543). There was no difference in post-transplantation CNS relapse, EFS, or OS among patients presenting with CNS involvement at diagnosis, those with isolated CNS relapse, and those with combined bone marrow and CNS relapse before HCT. Interestingly, neither pretransplantation cranial irradiation, use of total body irradiation-based conditioning, nor post-transplantation prophylactic intrathecal chemotherapy were associated with a reduction of CNS relapse risk after transplantation. Thus, among the patients in the cohort studied, there was no clear benefit of CNS-directed therapy in the peri-transplantation period among patients who had prior CNS involvement and underwent subsequent alloHCT.

Chronic GVHD remains as the major cause of morbidity and mortality after allogeneic hematopoietic cell transplantation. Systemic corticosteroids are the first line of therapy, but outcomes are poor in steroid refractory (SR) patients. Previous reports show that in SR patients, IL-2 therapy results in partial response (PR) associated with increase in regulatory T cells (Tregs). ECP has been used for cGVHD with skin response rates of 40-100%. Based on non-overlapping toxicities and, we prospectively studied a combination of low dose IL-2 + ECP to treat SR-cGVHD. Patients with SR-cGVHD, were treated with low dose IL-2 (1 × 106 U/m2, daily) + ECP for 12 weeks. IL-2 was provided by Prometheus Laboratories. ECP was administered 2 times/week for 4 weeks followed by 2 treatments every 2 weeks for the next 8 weeks. The NIH consensus criteria was used to assess cGVHD severity. PBMC and plasma samples were banked at baseline and on 3-week intervals to assess regulatory T cell (Tregs) and reactive oxygen species (ROS). Of the 12 consented patients, 9 completed the study (2 were not treated due to rapid disease progression before enrollment and 1 died from sepsis at week 11). All enrolled patients (n=10) had scleroderma as the predominant cGVHD manifestation. Median age was 45.6 years (range: 23-66). Median prior lines of therapy were 4.2(range 3-6), 5 patients had prior exposure to ruxolitinib and 4 were on ECP at the enrollment. Donors were fully matched unrelated (n=8), matched sibling (n=1) or mismatched unrelated (n=1). Conditioning regimen was myeloablative (n=5) or reduced intensity (n=4). GVHD prophylaxis was tacrolimus/Sirolimus (tac/sir) (n=6), tac/methotrexate (MTX) (n=2), or Tac/sir/MTX (n=1). Of the 10 enrolled patients, 9 responded to IL-2 + ECP combination (all classified as PR). A 37% dose reduction in steroid dose was noted among 7 patients. The remaining 3 patients were on stable steroid dose at end of study. Only 1 patient had progressive cGVHD in form of scleroderma. ECP+IL-2 therapy was well tolerated with no drug related serious adverse events (SAE). Grade 3-4 AEs included grade 3 metabolic and nutrition (n=8), grade 3 anemia (n=3), and grade 4 atrial flutter (n=1). Infectious complications were noted in 3 patients (one grade 4 [sepsis]). There was a robust increase in Tregs from the baseline mean of 0.755% (range 0.08-1.88) to end of treatment 6.999% (range 0.78-17.13) [p=0.02] Fig 1. Increment in Tregs was seen in patients who were on ECP therapy prior to enrollment (n=4) and in one patient who progressed while on therapy. No correlation was found between the treatment response and ROS levels. In conclusion, the combination of ECP +IL-2 is well tolerated in patients with SR-cGVHD with no apparent increase in infectious complications or other toxicities. Clinical response correlates with a robust increase in Tregs, but no correlation was found with ROS levels.

Historically, outcomes of adult patients (pts) with ALL who fail to enter remission with standard induction chemotherapy are very poor. Blinatumomab, a bispecific CD3/CD19 antibody, has shown remarkable activity in relapsed/refractory (r/r) ALL. While allogeneic HCT is the recommended consolidation therapy for r/r ALL pts who respond to salvage therapy, HCT and toxicity outcomes for those who received blinatumomab salvage and HCT remains largely unknown. A retrospective review of r/r ALL pts medical records, who received blinatumomab salvage therapy from 2012 to 2018 at our institution was obtained. Only pts who responded to blinatumomab and underwent HCT were included (n=29). Kaplan-Meier curves and the log-rank test were used to evaluate the overall survival (OS) and progression-free survival (PFS). Cumulative incidence (CI) curves and the Gray test were used to examine the differences in relapse rates and non-relapse mortality (NRM). The median age at the time of HCT was 29 years (range: 19-65), and 8 pts (28%) were over 50 years old. HCT was done in complete remission- (CR)-1 (n=14, 48%) or ≥CR-2, with 2pts receiving blinatumomab salvage after relapse from a prior HCT. Pts received transplant from a matched sibling (n=11), matched unrelated (n= 12), haploidentical donor (n=5) or double umbilical cord blood (n=1) after myeloablative (n=20, including TBI+VP16, n=15) or reduced intensity (n=9) conditioning. The graft source was PBSCs in 25 pts (86.2%). Graft-versus-host disease (GVHD) prophylaxis was tacrolimus/sirolimus-based (n=19, 66%), and post-HCT cyclophosphamide (n=5, 17%) for haploidentical transplants. At the time of salvage therapy initiation, pts had either gross residual (n=22) or minimal residual disease (MRD+) (n=7). Negative MRD remission status was achieved prior to HCT in 15 pts, including those who were MRD+ before blinatumomab salvage. With a median follow up of 21.7 months (mo) (range: 1.1-55.7) for all pts and 6.4 mo for surviving pts, the 1-year OS and PFS were 72.8% (95% CI: 48.5-87.0) and 63.0% (95% CI: 38.8-79.8), respectively (Fig 1). Causes of death post-HCT were GVHD (n=3); NRM (n=4; 3 sepsis and 1 regimen related toxicity) and relapse (n=3). The CI of relapse at 1 and 2 years were 24.9% (95% CI: 8.6-45.3) and 45.9%, (95% CI: 20.3-68.3), respectively. NRM at 100 days was 6.9% (95% CI: 1.2-20.0) and at 12 mo was 12.1% (95% CI: 2.7-29.0). The incidence of grades 3-4 acute GVHD and extensive chronic GVHD at 24 mo were 25.0% (95% CI: 8.7-45.5) and 38.8% (95% CI: 14.2-63.1), respectively. No cases of veno-occlusive disease post-HCT were reported. We present here, for the 1st time, detailed data showing the tolerability and efficacy of HCT following salvage therapy with blinatumomab. No unexpected toxicities were noted post-HCT and the study showed encouraging 1-year OS and PFS with. Longer-term follow-up is ongoing for these patients.

Identification of anti-apoptotic properties of the Bcl2 protein has offered novel treatment options in many malignancies including AML. Venetoclax, a Bcl2 inhibitor, has shown promising results as upfront therapy in elderly patients (pts) and relapse/refractory (R/R) AML, when combined with hypomethylating agents (HMA). Yet, due to the high relapse risk, allogenic HCT remains as the only curative option for these high risk populations. To date, outcomes of HCT after prior therapy with Venetoclax + HMA have not been described. Also, as Venetoclax induces aplasia of antigen presenting cells expressing Bcl2, we hypothesized that pre-HCT treatment with venetoclax may be associated with a lower risk for GvHD. We retrospectively analyzed 26 consecutive AML pts who underwent HCT at our institution from 2016 to 2018 with final line of systemic therapy of venetoclax + HMA. Pts were not eligible for upfront standard induction chemotherapy (n=8) or had R/R disease (n=18). Fifteen pts received ≥2 lines of therapy and 3 had previous HCT. CR/CRi was achieved in 62% (n=16), of which 3 pts had minimal residual disease and the rest (n=10) had persistent disease prior to HCT. Donors were matched related (n=8), matched unrelated (n=16), or haploidentical (n=2). Conditioning regimen was myeloablative (38.5%) or reduced intensity (61.5%). Most pts (n=24, 92.3%) received PBMCs as the graft source. Tacrolimus/Sirolimus (Tac/Sir) was administered in most pts (n=20, 77%) for GvHD prophylaxis. Descriptive statistics were used for baseline characteristics. Kaplan-Meier and cumulative incidence curves were constructed for overall survival (OS), progression-free survival (PFS), relapse, none-relapse mortality (NRM), and aGvHD. Median age at the time of HCT was 59 years (range: 18-73). Median time to neutrophil and platelet engraftment were 17 days (range: 14-20) and 20 days (range: 16-61), respectively. With a median follow up of 4.5 months (range: 1.4-18.6), 6 months relapse rate was 12% (95% CI: 0.16-0.54) and 100 day NRM was 4% (95% CI: 0.02-0.34). Grade II-IV aGvHD at 100 days was noted in 34% (95% CI: 0.15-0.51). One-year OS and PFS for all pts were 72% (95% CI: 0.43-0.88) and 40% (95% CI: 0.16-0.63), respectively. For patients in CR at the time of HCT, 1-year OS was 80% (95%CI: 37-95) and PFS was 38% (95%CI: 0.08-0.69) (Fig 1). Only one patient who had been treated with three lines of systemic therapy prior to HCT experienced veno-occlusive disease. Thus, administration of Venetoclax-based salvage regimen as a bridge to HCT is safe with no added immediate toxicities post-HCT. Our early outcome data are promising for this otherwise high-risk population. Our data also justify further studies on the role and impact of Venetoclax and its anti-Bcl2 properties as a component of the conditioning regimen or as post-HCT maintenance.

CMVi leads to significant morbidity in R+ HCT and preemptive therapy (PET) has been the standard of care. LTV was FDA-approved in Nov. 2017 for CMVi prevention in R+ HCT. Besides the clinical trials, there is are real world data on LTV. Upon IRB approval, we retrospectively studied consecutive R+ HCT pts with their first HCT between 1/1/2017 and 6/30/2018. LTV group included pts with HCT between 2/20/18 and 6/30/2018, who had LTV Px started within 28 days of HCT (n=59), and R+ HCT between 1/1/2017 and 2/19/2018 (n=307) served as control (ctrl). We compared CMVi rates in first 100 days of HCT, and time to engraftment between the 2 groups. Risk stratification: high risk - haplo/cord HCT & ATG use, low risk - all others. CMVi was defined as viral load (VL) of 625 IU/ml to 1250 IU/ml or higher (CMV assay conversion factor of 1 genomic copy/ml = 2.5 IU/ml). CMV VL less than 625 IU/ml is reported negative, VL between 625 and 1250 IU/ml is qualitative positive but numeric value is provided only for VL ≥ 1250 IU/ml. PET was recommended for VL >1250 IU/ml (500 copies/ml) in high risk and > 3750 IU/ml (1500 copies/ml) in low risk HCT (including those on LTV requiring PET). Descriptive statistics was done for baseline characteristics. Cumulative incidence curves were generated for CMVi within 100 days post-HCT and Gray's test was used to compare the difference between the 2 groups. In both groups, median age was 54 years and HCT indications were similar. Donor type in LTV/ Ctrl groups: MRD (27 vs 36%), MUD (44 vs 47%), haplo (27 vs 15%), cord (1.7 vs 1.6%). PBMC was graft source in 90% of both groups. Myeloablative conditioning: 40.7% in LTV and 35% in Ctrl. GVHD Px: Cellcept (32 vs 25%), methotrexate (7 vs 9%), tacro/siro (58 vs 65), and others (3.4 vs 0.3%) in LTV & Ctrl respectively. A majority (n=36) received both intravenous & oral LTV formulation while 23 received oral only. Median time from HCT to LTV start was 13 days (range: 4-26). LTV group had significant reduction in CMVi rate (22.4% [95%CI: 12.7-34.0]) compared with ctrl group (41.1% [95%CI: 35.4-46.7], p=0.008, Fig 1). In a subgroup of high-risk HCT LTV was significantly reduced CMVi rate (22.2%) compared with ctrl (62.8%, p=0.004, Fig 2) while statistical difference was not reached in low-risk HCT pts (22.8% vs. 35.6%, p=0.11). In the LTV Px, clinically significant (CS)-CMVi requiring PET occurred in 8.4% (n=5) and on excluding 2 pts who were not on LTV at the time of CMVi, the rate was 5% (Fig 1). CMVi cleared without PET in 8/13 LTV pts and LTV was continued; all pts had VL LTV use in a real world setting is associated with significant reduction of CMVi and CS-CMVi without any discernible myelosuppression. The low level CMVi resolved spontaneously in majority with continued LTV Px and PET was not necessary. The high-risk HCT had most benefit with LTV Px.

Background AlloHCT is the only curative therapy for primary and secondary myelofibrosis (MF). Pulmonary arterial hypertension (PAH) can be seen in 30% of patients with MF. PAH can eventually lead to right heart failure and may be associated with complications after alloHCT. The primary objective was to determine the association of PAH with alloHCT outcome in patients with MF. Secondary objectives included the effect of HCT on the underlying PAH as well as incidence of specific transplant-related complications in these patients. Methods All patients with MF who underwent alloHCT from 2008 to early 2018 at the City of Hope Medical Center with evaluable pre-HCT echocardiography were considered for this retrospective analysis. Pre and postHCT echocardiograms were reviewed to evaluate the pulmonary arterial systolic pressure (PASP). Descriptive statistics were used for baseline patient and transplant related characteristics stratified by PAH. Paired t-test was used to detect the change in the pulmonary vascular pressure after HCT. Kaplan-Meier and cumulative incidence curves were constructed for OS and NRM), respectively. Log-rank test and Gray's test were used whenever appropriate. Results 65 patients with MF that met the inclusion criteria were studied. Median age at HCT was 61 years with 36 (55%) males. 39 (60%) patients had intermediate 2 or high DIPPS score at the time of HCT. 37 (57%) had JAK2 positive MF. . Median PASP was 37.0 mmHg (range: 16.0-57.9) prior to HCT with 37 out of 65 patients (57%) meeting the diagnostic criteria for PAH. With median follow-up of 35.0 months (range: 3.3 – 119.4), PAH was significantly associated with inferior OS (58.9% vs. 88.8%, p=0.025), primarily due to increased NRM (21.6% vs. 7.1%, p= 0.007). 57% of deaths (8 of 14) in patients with PAH occurred within day 100 after HCT. In patients with available post-HCT echocardiogram (n=33) eight patients (24%) had persistent PAH with the median pulmonary artery pressure of 30mmHg. Compared with pre-HCT values pulmonary arterial pressure was significantly reduced after HCT (p Conclusion PAH is associated with inferior survival due to increased NRM in patients with MF undergoing alloHCT. About half of deaths in patients with PAH occurred within 100 days of HCT. PAH appears at least partially reversible after successful alloHCT. Based on our data, PAH should be considered a risk factor for early mortality after alloHCT and surveillance of pulmonary artery pressure in MF patients being considered for alloHCT may be useful.

We undertook a prospective longitudinal study to examine humoral and cellular immune responses to influenza vaccination in hematopoietic cell transplant (HCT) patients and healthy adults. Healthy volunteers and HCT patients had blood samples taken prior to influenza vaccination and 30, 90, and 180 days postvaccination. Serum from pre- and postvaccination time points were tested for influenza A IgG and IgM by ELISA as well as tested for neutralizing antibody (NAb) titers via hemagglutination inhibition assay. Polychromatic flow cytometry was used to examine CD4(+) T cells for levels of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and CD154 (CD40 ligand) expression after stimulation with inactivated flu virus. In healthy subjects, we found a significant increase in Influenza A IgG and IgM levels as well as an increase in NAb titers pre- and post-influenza vaccination. Notably, NAb titers of most HCT patients did not rise to a protective level postvaccination. CD4(+) T cell expression of CD154 and cytokine responses were significantly reduced in HCT recipients compared to healthy adults. A lack of B cell reconstitution and dysfunctional CD4 T cell costimulation (as marked by low CD154 expression) is associated with low NAb levels postvaccination in HCT patients.