Donor T cell DNMT3a regulates alloreactivity in mouse models of hematopoietic stem cell transplantation.

DNA methyltransferase 3a (DNMT3a) is an important part of the epigenetic machinery that stabilizes patterns of activated T cell responses. We hypothesized that donor T cell DNMT3a regulates alloreactivity after allogeneic blood and marrow transplantation (allo-BMT). T cell conditional Dnmt3a KO mice were used as donors in allo-BMT models. Mice receiving allo-BMT from KO donors developed severe acute graft-versus-host disease (aGVHD), with increases in inflammatory cytokine levels and organ histopathology scores. KO T cells migrated and proliferated in secondary lymphoid organs earlier and demonstrated an advantage in trafficking to the small intestine. Donor T cell subsets were purified after BMT for whole-genome bisulfite sequencing (WGBS) and RNA-Seq. KO T cells had global methylation similar to that of WT cells, with distinct, localized areas of hypomethylation. Using a highly sensitive computational method, we produced a comprehensive profile of the altered epigenome landscape. Hypomethylation corresponded with changes in gene expression in several pathways of T cell signaling and differentiation. Additionally, Dnmt3a-KO T cells resulted in superior graft-versus-tumor activity. Our findings demonstrate a critical role for DNMT3a in regulating T cell alloreactivity and reveal pathways that control T cell tolerance. These results also provide a platform for deciphering clinical data that associate donor DNMT3a mutations with increased GVHD, decreased relapse, and improved survival.

Trainee-led Engagement of the Care Team Improves Application of an Institutional Blood Culture Clinical Decision Algorithm to Pediatric Oncology Inpatients: A Single-institution Quality Improvement Project.

Meaningful engagement in quality improvement (QI) projects by trainees is often challenging. A fellow-led QI project aimed to improve adherence to a blood culture clinical decision algorithm and reduce unnecessary cultures in pediatric oncology inpatients. Methods: We visualized preintervention rates of blood cultures drawn on pediatric oncology inpatients using a control chart. Following the introduction of the algorithm to our division, an Ishikawa fishbone diagram of cause-and-effect identified two areas for improvement: prescriber education on the algorithm and targeted feedback on its use. We developed two interventions to support algorithm awareness and use: (1) bundled educational interventions and (2) targeted chart review and feedback. Fellows reviewed >750 blood culture episodes and adjudicated each as "adherent" or "nonadherent" to the algorithm. In addition, fellows provided direct feedback to prescribers regarding nonadherent episodes and discussed strategies for algorithm adherence. Results: Blood culture rates in preintervention, intervention, and follow-up periods were 33.35, 25.24, and 22.67 cultures/100 patient-days, respectively. The proportion of nonadherent culture episodes decreased from 47.14% to 11.11%. The use of the algorithm did not prolong the time to cultures drawn on patients with new fever. Seventy-five percent of fellows provided feedback to inpatient teams on algorithm use. Following this project, trainees reported feeling more qualified to apply QI principles to patient care. Conclusions: Implementation of a clinical decision algorithm reduced the rate of cultures drawn on pediatric oncology inpatients. Fellow-led education of the care team decreased the proportion of nonadherent culture episodes and provided active engagement in QI.

Pain Experiences of Adults With Sickle Cell Disease and Hematopoietic Stem Cell Transplantation: A Qualitative Study.

OBJECTIVE: Despite increasing use of hematopoietic stem cell transplantation (HSCT) for adults with sickle cell disease (SCD), little is known about pain management experiences throughout this process. The objective of this study was to explore patients' experiences with pain and pain management during and after HSCT for SCD. METHODS: We conducted a qualitative interview study with 10 patients who underwent HSCT for SCD. We transcribed interviews verbatim and inductively identified codes. We used thematic analysis alongside a constant comparative method to develop and refine a codebook that aided in the identification of themes. RESULTS: Four key themes emerged. (1) The pain trajectory: patients described a fluctuating course of pain during HSCT, which often extended long afterwards and impacted all aspects of life, particularly affected by pre-HSCT experiences; (2) The role of opioids-a double-edged sword: patients described opioids as reducing pain but insufficiently to balance significant adverse effects and burden; (3) Patient-centered decision making in pain management: patients described insufficient agency in decisions about opioid use and weaning; and (4) Consequences of health-related stigma: patients described experiences with stigma, mainly related to opioid use and weaning, as similar to pre-HSCT. CONCLUSIONS: From the perspective of patients who have undergone HSCT for SCD, clinicians should use a patient-centered approach, integrating non-opioid approaches into pain management, particularly psychosocial support. As transplant for SCD becomes increasingly available, incorporating patient perspectives may improve health care delivery and overall patient experiences.

Neoantigen-based EpiGVAX vaccine initiates antitumor immunity in colorectal cancer.

Metastatic colorectal cancer (CRC) is poorly immunogenic, with limited neoantigens that can be targeted by cancer vaccine. Previous approaches to upregulate neoantigen have had limited success. In this study, we investigated the role of a DNA methyltransferase inhibitor (DNMTi), 5-aza-2'-deoxycytidine (DAC), in inducing cancer testis antigen (CTA) expression and evaluated the antitumor efficacy of a combinatorial approach with an epigenetically regulated cancer vaccine EpiGVAX and DAC. A murine model of metastatic CRC treated with combination therapy with an irradiated whole-cell CRC vaccine (GVAX) and DAC was used to assess the antitumor efficacy. DAC significantly induced expression of CTAs in CRC, including a new CTA Tra-P1A with a known neoepitope, P1A. Epigenetically modified EpiGVAX with DAC improved survival outcomes of GVAX. Using the epigenetically regulated antigen Tra-P1A as an example, our study suggests that the improved efficacy of EpiGVAX with DAC may due in part to the enhanced antigen-specific antitumor immune responses. This study shows that epigenetic therapy with DNMTi can not only induce new CTA expression but may also sensitize tumor cells for immunotherapy. Neoantigen-based EpiGVAX combined with DAC can improve the antitumor efficacy of GVAX by inducing antigen-specific antitumor T cell responses to epigenetically regulated proteins.

Effect of increased dose of total body irradiation on graft failure associated with HLA-haploidentical transplantation in patients with severe haemoglobinopathies: a prospective clinical trial.

BACKGROUND: Although severe haemoglobinopathies can be cured with allogeneic blood or bone marrow transplantation, availability of matched donors and toxic effects can be problematic. We previously found that non-myeloablative haploidentical related bone marrow transplantation with post-transplantation cyclophosphamide expanded the donor pool while limiting graft-versus-host disease (GVHD). However, graft failure-albeit with full host haemopoietic recovery-occurred in 50% of patients. In this study, we investigated whether increasing total body irradiation from 200 cGy to 400 cGy would improve engraftment while maintaining the safety profile. METHODS: This study was done at Johns Hopkins Hospital (Baltimore, MD, USA). Patients aged 2-70 years receiving their first bone marrow transplant were eligible for inclusion in the study. Patients received rabbit-derived intravenous anti-thymocyte globulin 0·5 mg/kg on day -9 and 2 mg/kg on days -8 and -7, intravenous fludarabine 30 mg/m2 on days -6 to -2, intravenous cyclophosphamide 14·5 mg/kg on days -6 and -5, and total body irradiation 400 cGy administered as a single fraction on day -1. We collected unmanipulated bone marrow and infused on day 0. GVHD prophylaxis comprised intravenous cyclophosphamide 50 mg/kg per day on days 3 and 4 after transplantation, oral mycophenolate mofetil 15 mg/kg per dose (maximum 1 g) every 8 h on days 5 to 35, and oral sirolimus to maintain a level of 5-15 ng/dL for at least 1 year starting on day 5. The original planned primary objectives of this phase 2 clinical trial were transplant-related mortality and progression-free survival. However, the coverage decision by the Centers for Medicare and Medicaid Services to only provide payment for allogeneic bone marrow transplantation for patients with sickle cell disease on a clinical trial that had a comparison arm with patients not receiving bone marrow transplantation prompted the closure of this trial to accrual in 2017. Therefore, as we were unable to perform our planned statistical analysis, the primary objective was modified to evaluate engraftment, assessed by chimerism. This trial is registered with ClinicalTrials.gov, number NCT00489281. The study is closed to new participants and this is the primary analysis. FINDINGS: Between Sept 24, 2014, and Aug 1, 2017, we enrolled 17 consecutive patients: 12 (71%) with sickle cell disease and 5 (29%) with ß-thalassaemia major. The median patient age was 16 years (range 6-31, IQR 7·7-27·5). One (6%) of 17 patients had primary graft failure with recovery of host haemopoiesis. 13 (76%) of 17 patients achieved full donor chimerism and three (18%) had mixed donor-host chimerism. Five (29%) of 17 patients developed grade 2-4 acute GVHD, including four (24%) with maximal grade 2 GVHD and one (6%) with grade 3 GVHD. Chronic GVHD developed in three (18%) patients. As of their last follow-up visit, GVHD had resolved in all patients and no patients were receiving systemic GVHD therapy. All patients remained alive as of Aug 4, 2019, and the median follow-up duration was 705 days (range 355-1294; IQR 398-943). Only one (6%) of the 16 engrafted patients remained transfusion dependent, and 14 (88%) discontinued immunosuppression. INTERPRETATION: Increasing total body irradiation to 400 cGy substantially reduced graft failure while maintaining the safety of haploidentical bone marrow transplantation with post-transplantation cyclophosphamide. These results suggest that engraftment after haploidentical bone marrow transplantation for haemoglobinopathies is possible, and primary graft failure-the main problem previously reported-might be addressed by this strategy. Therefore, this curative approach should no longer be restricted to patients with HLA-matched donors. FUNDING: Maryland Stem Cell Research Fund and US National Institutes of Health.

Reduced-Intensity Haploidentical Bone Marrow Transplantation with Post-Transplant Cyclophosphamide for Solid Tumors in Pediatric and Young Adult Patients.

High-risk, recurrent, or refractory solid tumors in pediatric, adolescent, and young adult (AYA) patients have an extremely poor prognosis despite current intensive treatment regimens. We piloted an allogeneic bone marrow transplant platform using reduced-intensity conditioning (RIC) and partially HLA-mismatched (haploidentical) related donors for this population of pediatric and AYA solid tumor patients. Sixteen patients received fludarabine, cyclophosphamide, melphalan, and low-dose total body irradiation RIC haploidentical BMT (haploBMT) followed by post-transplantation cyclophosphamide (PTCy), mycophenolate mofetil, and sirolimus. All assessable patients were full donor chimeras on day 30 with a median neutrophil recovery of 19 days and platelet recovery of 21 days. One patient (7%) exhibited secondary graft failure associated with concomitant infection. The median follow-up time was 15 months. Overall survival was 88%, 56%, and 21% at 6, 12, and 24 months, respectively. Median survival from transplant date was 14 months with a median progression-free survival 7 months. We observed limited graft-versus-host disease in 3 patients and nonrelapse mortality in 1 patient. We demonstrated that RIC haploBMT with PTCy is feasible and has acceptable toxicities in patients with incurable pediatric and AYA solid tumors; thus, this approach serves as a platform for post-transplant strategies to prevent relapse and optimize progression-free survival.

mTORC1 Promotes T-bet Phosphorylation To Regulate Th1 Differentiation.

CD4+ T cells lacking the mTORC1 activator Rheb fail to secrete IFN-γ under Th1 polarizing conditions. We hypothesized that this phenotype is due to defects in regulation of the canonical Th1 transcription factor T-bet at the level of protein phosphorylation downstream of mTORC1. To test this hypothesis, we employed targeted mass-spectrometry proteomic analysis-multiple reaction monitoring mass spectrometry. We used this method to detect and quantify predicted phosphopeptides derived from T-bet. By analyzing activated murine wild-type and Rheb-deficient CD4+ T cells, as well as murine CD4+ T cells activated in the presence of rapamycin, a pharmacologic inhibitor of mTORC1, we were able to identify six T-bet phosphorylation sites. Five of these are novel, and four sites are consistently dephosphorylated in both Rheb-deficient CD4+ T cells and T cells treated with rapamycin, suggesting mTORC1 signaling controls their phosphorylation. Alanine mutagenesis of each of the six phosphorylation sites was tested for the ability to impair IFN-γ expression. Single phosphorylation site mutants still support induction of IFN-γ expression; however, simultaneous mutation of three of the mTORC1-dependent sites results in significantly reduced IFN-γ expression. The reduced activity of the triple mutant T-bet is associated with its failure to recruit chromatin remodeling complexes to the Ifng gene promoter. These results establish a novel mechanism by which mTORC1 regulates Th1 differentiation, through control of T-bet phosphorylation.

Cyclophosphamide improves engraftment in patients with SCD and severe organ damage who undergo haploidentical PBSCT.

Peripheral blood stem cell transplantation (PBSCT) offers a curative option for sickle cell disease (SCD). Although HLA-matched sibling transplantation is promising, the vast majority of patients lack such a donor. We sought to develop a novel nonmyeloablative HLA-haploidentical PBSCT approach that could safely be used for patients with severe organ damage. Based on findings in our preclinical model, we developed a phase 1/2 trial using alemtuzumab, 400 cGy total body irradiation, and escalating doses of posttransplant cyclophosphamide (PT-Cy): 0 mg/kg in cohort 1, 50 mg/kg in cohort 2, and 100 mg/kg in cohort 3. A total of 21 patients with SCD and 2 with ß-thalassemia received a transplant. The mean hematopoietic cell transplant-specific comorbidity index of 6 reflected patients with cirrhosis, heart failure, and end-stage renal disease. The engraftment rate improved from 1 (33%) of 3 in cohort 1 to 5 (63%) of 8 in cohort 2 and 10 (83%) of 12 in cohort 3. Percentage of donor myeloid and CD3 chimerism also improved with subsequent cohorts. There was no transplant-related mortality, and overall survival was 87%. At present, 0% in cohort 1, 25% in cohort 2, and 50% in cohort 3 remain free of their disease. There was no grade 2 to 4 acute or extensive chronic graft-versus-host disease (GVHD). Therefore, PT-Cy improves engraftment and successfully prevents severe GVHD after nonmyeloablative conditioning in patients with SCD who are at high risk for early mortality. Additional strategies are necessary to decrease the graft rejection rate and achieve a widely available cure for all patients with SCD. This trial was registered at www.clinicaltrials.gov as #NCT00977691.

Nonmyeloablative Haploidentical Bone Marrow Transplantation with Post-Transplantation Cyclophosphamide for Pediatric and Young Adult Patients with High-Risk Hematologic Malignancies.

Lower-intensity conditioning regimens for haploidentical blood or marrow transplantation (BMT) are safe and efficacious for adult patients with hematologic malignancies. We report data for pediatric/young adult patients with high-risk hematologic malignancies (n = 40) treated with nonmyeloablative haploidentical BMT with post-transplantation cyclophosphamide from 2003 to 2015. Patients received a preparative regimen of fludarabine, cyclophosphamide, and total body irradiation. Post-transplantation immunosuppression consisted of cyclophosphamide, mycophenolate mofetil, and tacrolimus. Donor engraftment occurred in 29 of 32 (91%), with median time to engraftment of neutrophils >500/µL of 16 days (range, 13 to 22) and for platelets >20,000/µL without transfusion of 18 days (range, 12 to 62). Cumulative incidences of acute graft-versus-host disease (GVHD) grades II to IV and grades III and IV at day 100 were 33% and 5%, respectively. The cumulative incidence of chronic GVHD was 23%, with 7% moderate-to-severe chronic GVHD, according to National Institutes of Health consensus criteria. Transplantation-related mortality (TRM) at 1 year was 13%. The cumulative incidence of relapse at 2 years was 52%. With a median follow-up of 20 months (range, 3 to 148), 1-year actuarial overall and event-free survival were 56% and 43%, respectively. Thus, we demonstrate excellent rates of engraftment, GVHD, and TRM in pediatric/young adult patients treated with this regimen. This approach is a widely available, safe, and feasible option for pediatric and young adult patients with high-risk hematologic malignancies, including those with a prior history of myeloablative BMT and/or those with comorbidities or organ dysfunction that preclude eligibility for myeloablative BMT.

De novo DNA methylation by DNA methyltransferase 3a controls early effector CD8+ T-cell fate decisions following activation.

DNMT3a is a de novo DNA methyltransferase expressed robustly after T-cell activation that regulates plasticity of CD4(+) T-cell cytokine expression. Here we show that DNMT3a is critical for directing early CD8(+) T-cell effector and memory fate decisions. Whereas effector function of DNMT3a knockout T cells is normal, they develop more memory precursor and fewer terminal effector cells in a T-cell intrinsic manner compared with wild-type animals. Rather than increasing plasticity of differentiated effector CD8(+) T cells, loss of DNMT3a biases differentiation of early effector cells into memory precursor cells. This is attributed in part to ineffective repression of Tcf1 expression in knockout T cells, as DNMT3a localizes to the Tcf7 promoter and catalyzes its de novo methylation in early effector WT CD8(+) T cells. These data identify DNMT3a as a crucial regulator of CD8(+) early effector cell differentiation and effector versus memory fate decisions.

High-dose Cyclophosphamide is Effective Therapy for Pediatric Severe Aplastic Anemia.

OBJECTIVE: Use of high-dose cyclophosphamide without hematopoietic stem cell transplant to treat severe aplastic anemia (SAA) has been controversial due to concern for increased infectious toxicity as compared with antithymocyte globulin and cyclosporine A. As children often tolerate dose-intensive therapy better than adults, we sought to perform a detailed retrospective analysis of both treatment response and toxicity in 28 patients younger than 22 years of age treated with 29 courses of high-dose cyclophosphamide as the sole form of immunosuppression. STUDY DESIGN: Children and adolescents with SAA who lacked an human leukocyte antigen-matched sibling donor were treated with cyclophosphamide 50 mg/kg/d for 4 consecutive days then received daily granulocyte colony stimulating factor until neutrophil recovery, transfusion support, and antimicrobial prophylaxis. RESULTS: Overall survival was 85%, with hematologic response of 79% and complete response of 66%. Cumulative incidences of bacterial infection (86%) and fungal infection (62%) were high but deaths due to infection were rare, as were clonal evolution (1/28), clinically relevant paroxysmal nocturnal (1/28), and relapse (2/28). CONCLUSIONS: Response rates and survival following high-dose cyclophosphamide in pediatric patients with SAA exceed those seen in adults and compare favorably to antithymocyte globulin/cyclosporine A with manageable infectious toxicity.

Single-Agent Post-Transplantation Cyclophosphamide as Graft-versus-Host Disease Prophylaxis after Human Leukocyte Antigen-Matched Related Bone Marrow Transplantation for Pediatric and Young Adult Patients with Hematologic Malignancies.

High-dose cyclophosphamide given after HLA-matched related and unrelated allogeneic bone marrow transplantation (BMT) for patients with hematologic malignancies is effective single-agent graft-versus-host disease (GVHD) prophylaxis in adults. Data describing outcomes for pediatric and young adult patients have not been reported. Between the years 2007 and 2013, 29 pediatric and young adult patients ages ≤21 years of age treated at our institution for high-risk hematologic malignancies underwent myeloablative HLA-matched related T cell-replete BMT. Eleven patients received post-transplantation cyclophosphamide (PTCy) as single-agent GVHD prophylaxis and were followed prospectively. Eighteen patients received calcineurin inhibitor (CNI)-based standard GVHD prophylaxis and were studied retrospectively as a control group. No acute GVHD (aGVHD) developed in patients receiving PTCy, whereas patients receiving CNI-based GVHD prophylaxis had cumulative incidences of grades II to IV and grades III and IV aGVHD of 27% and 5%, respectively. No patients receiving PTCy developed chronic GHVD, compared to 1 in the control group. Two-year overall survival was similar between the 2 groups (54% PTCy versus 58% CNI-based prophylaxis), as was event-free survival (42% PTCy versus 47% CNI-based). The 5-year cumulative incidence of relapse was 58% for PTCy and 42% for CNI-based GVHD prophylaxis (P = .45). These results suggest that PTCy is a safe and efficacious method of GVHD prophylaxis after an HLA-matched related BMT in the pediatric and young adult population that affords patients to be off all post-transplantation immunosuppression on day +5.

Successful Treatment of Recurrent Autoimmune Cytopenias in the Context of Sinus Histiocytosis With Massive Lymphadenopathy Using Sirolimus.

Sinus histiocytosis with massive lymphadenopathy (SHML), or Rosai-Dorfman disease (RDD), is a non-neoplastic, lymphoproliferative disorder that usually resolves spontaneously or with minimal conventional chemotherapy. Rarely, SHML can be associated with autoimmune findings. Such cases are often treatment resistant and have high rates of morbidity and mortality. We present a case of a patient with long-standing autoimmunity in the context of SHML, dependent on standard-treatment until he was transitioned to novel monotherapy with sirolimus. Sirolimus treatment resulted in a complete remission, now sustained after discontinuation of all treatments for over 23 months, with no observable long-term sequelae.

Feasibility of treating post-transplantation minimal residual disease in children with acute leukemia.

Outcomes are poor for patients with hematologic malignancies who experience overt relapse after allogeneic hematopoietic stem cell transplantation (HCT). Data on outcomes of post-transplantation minimal residual disease (MRD) are limited. In this single-institution, retrospective cohort analysis of children with acute leukemia and myelodysplastic syndrome, we document the pattern of relapse with a primary focus on outcomes of post-transplantation MRD. Forty of 93 patients (43%) who underwent a first allogeneic HCT and had systematic pretransplantation and post-transplantation MRD evaluations at +30, +60, +90, +180 days and +1 and +2 years post-transplantation experienced relapse. The median time to relapse was 4.8 months post-transplantation, with a median survival of 4 months post-relapse. Despite frequent, systematic, routine post-HCT disease restaging evaluation, 31 patients (78%) presented with overt disease at the time of relapse. Seven patients with acute leukemia who had post-transplantation MRD presented at a median of 1 month post-transplantation. Owing to rapid disease progression or treatment-related mortality, there was no improvement in survival in those patients whose leukemia was detected in a state of MRD post-transplantation. Our results suggest that early intervention strategies targeting post-transplantation MRD for relapse prevention in acute leukemia may not be feasible.

Factors predictive of relapse of acute leukemia in children after allogeneic hematopoietic cell transplantation.

The presence of minimal residual disease (MRD) before transplantation is the most important prognostic risk factor predictive of post-transplantation relapse in hematologic malignancies. However, MRD alone does not adequately predict relapse in all patients. To improve upon the ability to identify patients likely to relapse, we evaluated risk factors, in addition to MRD, that may be associated with development of post-transplantation relapse. In this single institution, retrospective cohort study of children with acute leukemia or myelodysplastic syndrome who had undergone a first allogeneic transplantation and had pretransplantation MRD evaluation, 40 of 93 patients (43%) experienced relapse. Univariate analysis demonstrated that African American race, high initial white blood cell count, central nervous system (CNS) disease at diagnosis, short first complete remission, nonmyeloablative (NMA) conditioning, lack of remission, and MRD before transplantation were associated with worse relapse-free survival (RFS). In a Cox multivariable analysis, CNS disease (P = .009), lack of remission (P = .01), and NMA conditioning (P = .04) were independently associated with inferior RFS. Among those in a morphologic complete remission who underwent a myeloablative transplantation, having both CNS disease at diagnosis (specifically in acute lymphoblastic leukemia) and MRD positivity was an independent risk factor predictive of relapse, which has not been previously reported. Results from our study support the existence of risk factors complimentary to pretransplantation MRD. Validation in a larger independent homogenous cohort is needed to develop a prognostic tool for clinical use to predict post-transplantation relapse.

All PI3Kinase signaling is not mTOR: dissecting mTOR-dependent and independent signaling pathways in T cells.

The mechanistic target of rapamycin (mTOR) is emerging as playing a central role in regulating T cell activation, differentiation, and function. mTOR integrates diverse signals from the immune microenvironment to shape the outcome of T cell receptor (TCR) antigen recognition. Phosphatidylinositol 3-kinase (PI3K) enzymes are critical mediators of T cell activation through their generation of the second messenger phosphatidylinositol (3,4,5) triphosphate (PIP3). Indeed, PIP3 generation results in the activation of Protein Kinase B (PKB, also known as AKT), a key activator of mTOR. However, recent genetic studies have demonstrated inconsistencies between PI3K disruption and loss of mTOR expression with regard to the regulation of effector and regulatory T cell homeostasis and function. In this review, we focus on how PI3K activation directs mature CD4 T cell activation and effector function by pathways dependent on and independent of mTOR signaling. Importantly, what has become clear is that targeting both mTOR-dependent and mTOR-independent PI3K-induced signaling distally affords the opportunity for more selective regulation of T cell differentiation and function.

HLA-haploidentical bone marrow transplantation with posttransplant cyclophosphamide expands the donor pool for patients with sickle cell disease.

Allogeneic marrow transplantation can cure sickle cell disease; however, HLA-matched donors are difficult to find, and the toxicities of myeloablative conditioning are prohibitive for most adults with this disease. We developed a nonmyeloablative bone marrow transplantation platform using related, including HLA-haploidentical, donors for patients with sickle cell disease. The regimen consisted of antithymocyte globulin, fludarabine, cyclophosphamide, and total body irradiation, and graft-versus-host disease prophylaxis with posttransplantation high-dose cyclophosphamide, mycophenolate mofetil, and tacrolimus or sirolimus. After screening 19 patients, we transplanted 17, 14 from HLA-haploidentical and 3 from HLA-matched related donors. Eleven patients engrafted durably. With a median follow-up of 711 days (minimal follow up 224 days), 10 patients are asymptomatic, and 6 patients are off immunosupression. Only 1 patient developed skin-only acute graft-versus-host disease that resolved without any therapy; no mortality was seen. Nonmyeloablative conditioning with posttransplantation high-dose cyclophosphamide expands the donor pool, making marrow transplantation feasible for most patients with sickle cell disease, and is associated with a low risk of complications, even with haploidentical related donors. Graft failure, 43% in haploidentical pairs, remains a major obstacle but may be acceptable in a fraction of patients if the majority can be cured without serious toxicities.

De novo DNA methylation is required to restrict T helper lineage plasticity.

Naïve CD4+ T cells are highly plastic and can differentiate into discrete lineages with unique functions during an immune response. Once differentiated, helper T cells maintain a stable transcriptional memory of their initial lineage choice and resist redifferentiation. During embryogenesis, de novo DNA methylation operates on the hypomethylated genome of the blastocyst to achieve tissue-specific patterns of gene expression. Similarly, the ifnγ promoter is hypomethylated in naïve T cells, but Th2, Th17, and iTreg differentiation is accompanied by substantial de novo DNA methylation at this locus. To determine whether de novo DNA methylation is required to restrict T helper lineage plasticity, we used mice with T cell-specific deletion of the methyltransferase DNMT3a. Induction of lineage-specific cytokines occurred normally in the absence of DNMT3a, however, DNMT3a-deficient Th2, Th17, and iTreg completely failed to methylate the ifnγ promoter. This was accompanied by an increase in the transcriptionally permissive trimethyl H3K4 mark, and a reduction in inhibitory H3K27 methylation at the ifnγ locus. Failed de novo methylation resulted in failed silencing of the ifnγ gene, as DNMT3a-deficient Th2, Th17, and iTreg cells produced significant levels of IFNγ following restimulation in the presence of IL-12. Therefore, DNMT3a-mediated DNA methylation restricts T helper plasticity by establishing an epigenetically silent chromatin structure at regulatory regions of the ifnγ gene.

Genetic and biochemical regulation of CD4 T cell effector differentiation: insights from examination of T cell clonal anergy.

The two-signal model of T cell activation states that antigen recognition by TCR provides a tolerogenic signal (termed Signal 1) unless the T cell receives simultaneous costimulation (Signal 2) that permits antigen recognition to prime activation. Our efforts to characterize genetic and biochemical factors resulting from Signal 1 alone have identified signaling molecules, transcription factors, and an epigenetic regulator that each contribute to the anergic phenotype observed. However, our most striking finding is that the same factors identified using anergy to model T cell activation versus tolerance also participate in determining the outcome of the effector phenotype of fully activated T cells. We summarize our own findings and other recent advances in the genetic and biochemical understanding of T cell activation, tolerance, and plasticity in this review.

Identification of DNA methyltransferase 3a as a T cell receptor-induced regulator of Th1 and Th2 differentiation.

Ag-specific T cell cytokine expression is dictated by the context in which TCR engagement occurs. Recently it has become clear that epigenetic changes play a role in this process. DNA methyltransferase 3a (DNMT3a) is a de novo methyltransferase important to the epigenetic control of cell fate. We have determined that DNMT3a expression is increased following TCR engagement and that costimulation mitigates DNMT3a protein expression. T cells lacking DNMT3a simultaneously express IFN-gamma and IL-4 after expansion under nonbiasing conditions. While global methylation of DNA from wild-type and knockout T cells is similar, DNMT3a-null T cells demonstrate selective hypomethylation of both the Il4 and Ifng loci after activation. Such hypomethylated knockout Th2 cells retain a greater capacity to express IFN-gamma protein when they are subsequently exposed to Th1-biasing conditions. Based on these findings we propose that DNMT3a is a key participant in regulating T cell polarization at the molecular level by promoting stable selection of a context-specific cell fate through methylation of selective targets in T cells.