Allogeneic Hematopoietic Transplantation Research Articles

Characterization and outcome of post-transplant lymphoproliferative disorders within a collaborative study.

Post-transplant lymphoproliferative disorders (PTLD) are heterogeneous lymphoid disorders ranging from indolent polyclonal proliferations to aggressive lymphomas that can arise after solid organ transplantation (SOT) and allogeneic hematopoietic transplantation (allo-HSCT). In this multi-center retrospective study, we compare patient characteristics, therapies, and outcomes of PTLD after allo-HSCT and SOT. Twenty-five patients (15 after allo-HSCT and 10 after SOT) were identified who developed PTLD between 2008 and 2022. Median age (57 years; range, 29-74 years) and baseline characteristics were comparable between the two groups (allo-HSCT vs SOT), but median onset of PTLD was markedly shorter after allo-HSCT (2 months vs. 99 months, P<0.001). Treatment regimens were heterogeneous, with reduction of immunosuppression in combination with rituximab being the most common first-line treatment strategy in both cohorts (allo-HSCT: 66%; SOT: 80%). The overall response rate was lower in the allo-HSCT (67%) as compared to the SOT group (100%). Consequently, the overall survival (OS) trended towards a worse outcome for the allo-HSCT group (1-year OS: 54% vs. 78%; P=0.58). We identified PTLD onset ≤150 days in the allo-HSCT (P=0.046) and ECOG >2 in the SOT group (P=0.03) as prognostic factors for lower OS. PTLD cases present heterogeneously and pose unique challenges after both types of allogeneic transplantation.

The impact of epigenetic modifications on allogeneic hematopoietic stem cell transplantation.

The field of epigenetics studies the complex processes that regulate gene expression without altering the DNA sequence itself. It is well established that epigenetic modifications are crucial to cellular homeostasis and differentiation and play a vital role in hematopoiesis and immunity. Epigenetic marks can be mitotically and/or meiotically heritable upon cell division, forming the basis of cellular memory, and have the potential to be reversed between cellular fate transitions. Hence, over the past decade, there has been increasing interest in the role that epigenetic modifications may have on the outcomes of allogeneic hematopoietic transplantation and growing enthusiasm in the therapeutic potential these pathways may hold. In this brief review, we provide a basic overview of the types of epigenetic modifications and their biological functions, summarizing the current literature with a focus on hematopoiesis and immunity specifically in the context of allogeneic hematopoietic stem cell transplantation.

Total Body Irradiation for Myeloablative Allogeneic Hematopoietic Transplantation in Acute Lymphoblastic Leukemia: How Important Is It Really?

Total Body Irradiation for Myeloablative Allogeneic Hematopoietic Transplantation in Acute Lymphoblastic Leukemia: How Important Is It Really?

Features of cytomegalovirus DNAemia and virus-specific T-cell responses in allogeneic hematopoietic stem-cell transplant recipients during prophylaxis with letermovir.

There is scarce information on the natural kinetics of cytomegalovirus (CMV) DNAemia and dynamics of CMV-specific T-cell reconstitution in allogeneic hematopoietic transplant recipients (allo-HSCT) undergoing letermovir (LMV) prophylaxis. Twelve adult CMV-seropositive high-risk recipients (median age, 53 years; 9 males/3 females) undergoing LMV prophylaxis and 13 non-LMV allo-HSCT controls (median age, 58 years; 7 males/6 females) were included. CMV DNAemia in plasma was monitored by real-time polymerase chain reaction. Preemptive antiviral therapy (PET) was administered upon detection of ≥1500IU/ml. CMV-specific interferon-gamma (IFN-γ)-producing CD8+ and CD4+ T cells were enumerated by flow cytometry around days +30, +60, and +90 after allo-HSCT. Ex vivo experiments assessing of the potential effect of LMV on CMV-specific T-cell expansion in a single CMV-seropositive donor were also conducted. Five LMV patients (41.6%) developed CMV DNAemia that cleared spontaneously. Four patients (33.3%) developed CMV DNAemia after LMV cessation, of which two required PET. Nine non-LMV patients (69.2%) developed CMV DNAemia (five required PET). The percentage of LMV and non-LMV patients exhibiting detectable CMV-specific T-cell responses was comparable (7/10 vs. 10/13; p=.71). Nevertheless, median CMV-specific CD4+ and CD8+ T-cell counts were lower in LMV patients by days +60 (p=.006 and .02, respectively) and +90 (p=.08 and .02). Ex vivo, CMV-specific CD8+ T cells expanded to the same level either in the presence (19.8%) or in the absence of LMV (20.6%). In our series, episodes of CMV DNAemia in LMV patients cleared spontaneously. A diminished degree of CMV-specific T-cell reconstitution in LMV patients compared to non-LMV patients was observed.

Improved efficacy of mesenchymal stromal cells stably expressing CXCR4 and IL-10 in a xenogeneic graft versus host disease mouse model.

Previous clinical trials have shown that mesenchymal stromal cells (MSCs) can modulate graft versus host disease (GvHD) after allogeneic hematopoietic transplantation, although with variable efficacy. To improve the anti-GvHD effect of these cells, adipose tissue derived-human MSCs (Ad-MSCs) were transduced with a lentiviral vector conferring stable expression of CXCR4, a molecule involved in cell migration to inflamed sites, and IL-10, a cytokine with potent anti-inflammatory properties. In vitro experiments showed that the expression of these molecules in Ad-MSCs (named CXCR4-IL10-MSCs) efficiently enhanced their migration towards SDF-1α and also improved their immunomodulatory properties compared to unmodified Ad-MSCs (WT-MSCs). Moreover, using a humanized GvHD mouse model, CXCR4-IL10-MSCs showed improved therapeutic effects, which were confirmed by histopathologic analysis in the target organs. Additionally, compared to WT-MSCs, CXCR4-IL10-MSCs induced a more marked reduction in the number of pro-inflammatory Th1 and Th17 cells, a higher polarization towards an anti-inflammatory T cell profile (CD3+-IL10+ cells), and increased the number of regulatory T and B cells. Our in vitro and in vivo studies strongly suggest that CXCR4-IL10-MSCs should constitute an important new generation of MSCs for the treatment of GvHD in patients transplanted with allogeneic hematopoietic grafts.

449 - Long-Term Follow-up Outcomes of Patients That Underwent Allogeneic or Autologous Hematopoietic Transplant Shortly after a COVID-19 Infection

449 - Long-Term Follow-up Outcomes of Patients That Underwent Allogeneic or Autologous Hematopoietic Transplant Shortly after a COVID-19 Infection

PP 3.16 – 00209 Prolonged persistence of HIV-infected cells in tissues after allogeneic hematopoietic transplant

PP 3.16 – 00209 Prolonged persistence of HIV-infected cells in tissues after allogeneic hematopoietic transplant

Role of endothelial cells in graft-versus-host disease.

To date, the only curative treatment for high-risk or refractory hematologic malignancies non-responsive to standard chemotherapy is allogeneic hematopoietic transplantation (allo-HCT). Acute graft-versus-host disease (GVHD) is a donor T cell-mediated immunological disorder that is frequently fatal and the leading cause of non-relapse mortality (NRM) in patients post allo-HCT. The pathogenesis of acute GVHD involves recognition of minor and/or major HLA mismatched host antigens by donor T cells followed by expansion, migration and finally end-organ damage due to combination of inflammatory cytokine secretion and direct cytotoxic effects. The endothelium is a thin layer of endothelial cells (EC) that line the innermost portion of the blood vessels and a key regulator in vascular homeostasis and inflammatory responses. Endothelial cells are activated by a wide range of inflammatory mediators including bacterial products, contents released from dying/apoptotic cells and cytokines and respond by secreting cytokines/chemokines that facilitate the recruitment of innate and adaptive immune cells to the site of inflammation. Endothelial cells can also be damaged prior to transplant as well as by alloreactive donor T cells. Prolonged EC activation results in dysfunction that plays a role in multiple post-transplant complications including but not limited to veno-occlusive disease (VOD), transplant associated thrombotic microangiopathy (TA-TMA), and idiopathic pneumonia syndrome. In this mini review, we summarize the biology of endothelial cells, factors regulating EC activation and the role of ECs in inflammation and GVHD pathogenesis.

A phase 2 study of interleukin-22 and systemic corticosteroids as initial treatment for acute GVHD of the lower GI tract

AbstractGraft-versus-host disease (GVHD) is a major cause of morbidity and mortality following allogeneic hematopoietic transplantation. In experimental models, interleukin-22 promotes epithelial regeneration and induces innate antimicrobial molecules. We conducted a multicenter single-arm phase 2 study evaluating the safety and efficacy of a novel recombinant human interleukin-22 dimer, F-652, used in combination with systemic corticosteroids for treatment of newly diagnosed lower gastrointestinal acute GVHD. The most common adverse events were cytopenias and electrolyte abnormalities, and there were no dose-limiting toxicities. Out of 27 patients, 19 (70%; 80% confidence interval, 56%-79%) achieved a day-28 treatment response, meeting the prespecified primary endpoint. Responders exhibited a distinct fecal microbiota composition characterized by expansion of commensal anaerobes, which correlated with increased overall microbial α-diversity, suggesting improvement of GVHD-associated dysbiosis. This work demonstrates a potential approach for combining immunosuppression with tissue-supportive strategies to enhance recovery of damaged mucosa and promote microbial health in patients with gastrointestinal GVHD. This trial was registered at www.clinicaltrials.gov as NCT02406651.

Sequential Use of Flamsa, FLAG, CLAG or TEC-Based Conditioning Regimen Followed By Allogeneic Hematopoietic Transplantation Results in Favorable Outcome for High Risk Acute Myeloid Leukemia, Myelodysplastic Syndrome and Myeloproliferative Neoplasia Patients: 15 Year Follow-up of the Multicenter Study in Singapore

Introduction: Allogeneic hematopoietic cell transplant (allo-HCT) is an effective consolidative treatment for patients with certain hematological malignancies and gives the best outcome when done in remission. However, patients with refractory acute myeloid leukemia (AML) or some myeloproliferative neoplasia (MPN) and myelodysplastic syndrome (MDS) deemed unable to achieve remission with standard induction are often excluded from allo-HCT with conventional conditioning regimen as pre-transplant remission could not be achieved. Recently, a sequential transplant approach, as developed by the Munich group, comprising of intensive cytoreductive chemotherapy FLAMSA (Fludarabine/Amsacrine/Cytarabine) to decrease leukemia cell burden shortly prior to conditioning regimen, has been successfully used for high-risk (HR) AML/MDS with promising results. Methods: We studied 72 patients (median age 51 years, range 17-68) with HR AML (n=57), as defined by refractory, relapsed disease, secondary leukemia, complete remission with adverse-risk cytogenetics according to ELN criteria, or high/very risk refined Disease Risk Index (DRI), MPN (n=3) and HR MDS (n=12) according to IPSS-R, undergoing allo-HCT using the sequential transplant approach in 2 transplant centers in Singapore between January 2009 and July 2022. The sequential transplant approach combined a cytoreductive chemotherapy, which consisted of either FLAMSA (n=21), FLAG [Fludarabine/Cytarabine/Granulocyte Colony Stimulating Factor (GCSF)] +/- Idarubicin (n=30), CLAG (Clofarabine +/- Cytarabine +/- GCSF) (n=18), or TEC (Thiotepa, Etoposide, Cyclophosphamide) (n=3) followed by reduced intensity (RIC) (n=61) or myeloablative (MAC) (n=11) conditioning regimen. All patients received peripheral blood stem cell from matched related donors (MRD) (n=36), mismatched related donors (MMRD) (n=7), matched unrelated donors (MUD) (n=21), or mismatched unrelated donors (MMURD) (n=8). Post-grafting immunosuppression consisted of calcineurin inhibitor and mycophenolate mofetil (MMF) in all patients. Thymoglobulin and post-transplant cyclophosphamide were added for GVHD prophylaxis for MUD/MMURD and MMRD transplant, respectively. One MMRD had selective ex vivo T-cell depleted transplant followed by MMF as GVHD prophylaxis. Results: The median time to neutrophil > 1000/μL was 11 days (range, 8-25). With a median follow-up duration of 51 months (range, 1-148), the Kaplan-Meier estimate of overall survival (OS) and leukemia-free survival (LFS) at 5 years were 42% (95% CI, 30-54) and 32% (95% CI 20-44), respectively. The cumulative incidence of relapse and non-relapse mortality (NRM) at 2 years were 47% (95% CI, 35-59) and 16% (95% CI, 9-26), respectively. Patients receiving FLAG, CLAG or TEC-based sequential regimen showed a trend towards lower NRM and relapse compared to FLAMSA-based regimen, although the difference was not statistically significant. This translated into a more favorable 5-year LFS (40% vs 13%, p=0.04), but no statistically significant difference in 5-year OS (42% vs 40%, p=0.56). Patients with refractory disease (n=49) were at higher risk of relapse compared to patients whom had achieved at least a partial remission prior to sequential allo-HCT (n=17) (2-year cumulative incidence of relapse: 59.0% vs 34.0%, p=0.02). This resulted in an inferior 5-year OS (31% vs 66%; p=0.02) and LFS (20% vs 75%, p<0.01). On multivariable analysis, only refined DRI showed significant impact on OS (p=0.01) and LFS (p=0.02) but had no significant impact on NRM and relapse. The 5-year OS for patients with intermediate/high risk and very high risk DRI were 51% and 21% (p<0.01), and the corresponding 5-year LFS were 42% and 10% (p<0.01), respectively (Figure 1 and Figure 2). Conclusions: Sequential transplant conditioning with FLAMSA, FLAG, CLAG or TEC-based cytoreductive regimen followed by allo-HCT is an effective strategy in overcoming the dismal prognosis of HR AML, MDS and MPN, including patients with high risk DRI, and enabling favorable long-term disease-free survival. More studies on effective strategies such as optimising the conditioning regimen intensity or post-transplant maintenance therapy with prophylactic donor lymphocyte infusion, are needed to further eliminate the risk of relapse, without increasing risk of treatment-related toxicity. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Tracking Immune Reconstitution in the Bone Marrow Following Allogeneic Hematopoietic Transplantation in Humans Reveals Early Dominance of Innate Lymphoid Populations

Tracking Immune Reconstitution in the Bone Marrow Following Allogeneic Hematopoietic Transplantation in Humans Reveals Early Dominance of Innate Lymphoid Populations

Attenuation of Graft-Versus-Host-Disease Via Genetic or Pharmacologic Inhibition of the RNA Splicing Factor RBM39

Recent studies have identified pharmacologic modulation of RNA splicing via degradation of the splicing factor RBM39 to mediate anticancer effects and enhance responses to immune checkpoint blockade through generation of novel RNA-splicing derived immunogenic peptides in tumors. However rigorous evaluation of the role of RBM39 in immune cells has not been performed. Here we identify that RBM39 modulates exon recognition in T cells to regulate their function. Although essential for the survival of hematopoietic precursors and tumors, RBM39 is dispensable for peripheral T cell survival. Functional evaluation of the T cell alloantigen response in allogeneic hematopoietic stem transplantation (allo-HSCT) revealed that Rbm39 loss attenuated graft-versus-host-disease (GVHD) and improved overall survival while partially sparing graft-versus-tumor (GVT) effects. To rigorously evaluate the role of RBM39 in immune cells, we generated an Rbm39 conditional knockout mouse by floxing Rbm39 exon 7, which encodes its first RNA recognition motif. Pan-hematopoietic deletion of Rbm39 resulted in rapid complete failure of hematopoiesis and impaired hematopoietic stem cell (HSC) self-renewal. We next analyzed the phenotype of animals with T cell specific deletion of RBM39 and compared this with the effects of pharmacologic RBM39 degradation on T cells. Strikingly, in contrast to the profound effects of genetic RBM39 loss in HSCs and the inability of cancer cells to tolerate RBM39 deletion, RBM39 deletion under CD4-cre (deletion early in thymopoiesis) or distal Lck-cre (late in thymopoiesis) yielded modestly fewer viable peripheral T cells, which skewed towards a CD44+ effector/memory phenotype. This observation was also recapitulated with extended treatment of mice with the RBM39 degrader E7820 (in phase II trials currently; clinicaltrials.gov NCT05024994). Deep RNA-seq analysis of splenic CD3+ T cells from distal Lck-cre Rbm39fl/fl mice revealed widespread decreased efficiency of RNA splicing in Rbm39 null T cells compared to controls, indicative of altered RNA splicing in T cells with Rbm39 deletion. Rbm39 KO T cells experienced global increases in exon skipping at genomic regions where upstream introns had reduced GC content. These data identify that RBM39 is required in a cell and tissue-specific manner for cell survival and further highlights the selectivity of therapeutic approaches targeting RBM39. We next assessed the functional consequences of pharmacologic RBM39 degradation or genetic RBM39 deletion in T cells. Consistent with observations in genetic mouse models, T cells could tolerate extensive pharmacologic RBM39 degradation without loss of proliferative capacity in response to PMA/Ionomycin or anti-CD3+CD28 stimulation. Similarly, genetic Rbm39 null T cells had an intact proliferative response to PMA/Ionomycin. Furthermore, when we evaluated the effects of RBM39 loss in the MHC-mismatched C57BL/6 => Balb/c allo-HSCT system, Rbm39 deletion in donor T cells under either CD4- or distal Lck-cre profoundly reduced GVHD severity and improved overall survival in recipients (Fig. A). These genetic findings were recapitulated via pharmacologic degradation of RBM39 in the same HSCT system (Fig. B). Similar experiments performed in the setting of Balb/c hosts engrafted with A20 lymphoma cells revealed partial preservation of GVT activity using Rbm39 KO T cells. Single cell RNA sequencing analyses of CD4-cre Rbm39fl/fl primary T cells revealed upregulation of the integrin beta1 subunit in both CD4 and CD8 T cells. This suggests alteration of T cell trafficking away from GVHD target organs as one mechanism by which RBM39 loss may alter T cell alloreactivity in allo-HSCT. Our results identify cell-type specific roles for RBM39 in hematopoiesis and immune cells and suggest a therapeutic approach for GVHD via direct modulation of RNA splicing. Of note, as the RBM39 degrader E7820 is currently in phase II clinical trials for relapsed myeloid neoplasms, our previous studies and this data identify a treatment for myeloid neoplasms in the post-transplant setting, where RBM39 degraders mediate both direct and immune-mediated anti-tumor effects while also attenuating GVHD via modulation of RNA splicing in T cells. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Efficacy of Azacitidine Post-Transplant Maintenance for FLT3-Negative Acute Myeloid Leukemia and Myelodysplastic Syndrome

Introduction: For patients with myeloid malignancies undergoing allogeneic hematopoietic transplantation (alloHCT), disease relapse remains the most common cause of transplant failure and mortality. Treatment of relapse after alloHCT remains extremely challenging. Post-transplant maintenance with fms-like tyrosine kinase 3 (FLT3) inhibitors has shown benefit in preventing relapse in the minority of patients with FLT3 mutated acute myeloid leukemia (AML). For the remaining patients, the efficacy of hypomethylating agents (HMA) as post-transplant maintenance yields conflicting results. There is a paucity of data regarding the role of HMA as post-transplant maintenance administered outside the context of a clinical trial. We aimed to evaluate the efficacy of azacitidine (AZA) as post-alloHCT maintenance in a real-world setting in patients with FLT3-negative AML or myelodysplastic syndrome (MDS). Methods: We conducted a single center retrospective matched-control comparative analysis. The study group (AZA group) included adults, aged ³18, with FLT3-negative AML or MDS who received their first alloHCT between 2013 and 2020; and were treated post-transplant with AZA maintenance therapy, initiated within 180 days after alloHCT. All patients in the AZA group initiated maintenance while in complete remission (CR) without minimal residual disease (MRD), assessed by multi-color flow cytometry. We compared the AZA group to a matched control group of contemporaneous patients with AML or MDS who did not receive any maintenance. We matched the control group according to disease type (AML or MDS), disease risk category (by ELN12 for AML and IPSS-R for MDS) and disease status at transplant. Matched controls were required to have count recovery (ANC>1000 X 106 cells/L and PLT>20K/µL) within ±7 days of initiation of AZA in their counterparts. We excluded controls if they had positive MRD, overt relapse or if they died prior to the initiation of AZA in their counterparts; grade 2-4 acute graft versus host disease (GVHD) within +/-7 days, or chronic GVHD within +/-15 days of initiation of AZA in their counterparts. The primary endpoint was disease progression, evaluated considering death before progression as a competing event. Results: We identified 93 consecutive patients who received AZA maintenance. A total of 357 unique matched controls were identified at a 2/1, 3/1, 4/1 matching ratio for 1 (1%), 13 (14%), and 79 (85%) of cases, respectively. The AZA and control groups had comparable patient and disease characteristics except for older age (median: 61 vs. 57 years, p=0.01) and lower hematopoietic comorbidity index (HCT-CI) (median: 2 vs. 3, p=0.04) in the AZA group (Table 1). Patients in the AZA group received a median of 8 (range 1-60) cycles of AZA. Outcomes were compared starting at the time of initiation of AZA in the case. Median follow-up among surviving patients was 35 and 44 months in the AZA and control groups, respectively. The 3-year cumulative incidence of disease progression was 29% and 33% (HR 0.7, 95% CI 0.4-1.1; p=0.09), respectively. Subset analyses showed that the protective effect of AZA on disease progression was limited to patients with high risk AML or MDS [HR 0.4, 95% CI 0.2-0.8, p=0.009] (Figure 1 B,D).There was no beneficial effect for AZA for patients with low or intermediate risk disease [HR 1.04, 0.6-1.8, p=0.9] (Figure 1 A,C). The use of AZA was also associated with a lower rate (4% vs. 22%, p=0.001) of non-relapse mortality independent of the disease risk category. These effects translated into a significantly superior overall (74% vs. 51%, p<0.001) and progression-free (67% vs. 46%, P<0.001) survival in the AZA group compared to the control group. Results were consistent when the analyses were repeated using a second independently selected matched control group (data not shown). Conclusion: Post-alloHCT AZA maintenance was associated with lower progression rate in patients with high-risk FLT3-negative AML or MDS. This effect is remarkable considering that matched controls had been in MRD-negative CR prior to initiation of AZA in their matched counterparts. Our results also indicate a low rate of non-relapse mortality associated with AZA maintenance which warrants evaluation in prospective studies. Collectively, our data suggest that AZA maintenance should be considered for post-alloHCT maintenance in high risk FLT3-negative AML and MDS patients. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Ageing-resembling phenotype of long-term allogeneic hematopoietic cells recipients compared to their donors

BackgroundAgeing is a complex phenomenon that leads to decreased proliferative activity, loss of function of the cells, and cellular senescence. Senescence of the immune system exacerbates individual’s immune response, both humoral and cellular but increases the frequency of infections. We hypothesized that physiological ageing of adaptive immune system occurs in recipients of allogeneic hematopoietic cells transplant (allo-HCT) at faster rate when compared to their respective donors since the small number of donor cells undergo immense proliferative stress restoring recipients hematopoiesis. We compared molecular characterizations of ageing between recipients and donors of allo-HCT: telomeric length and immunophenotypic changes in main lymphocyte subsets – CD4+, CD8+, CD19+, CD56+.ResultsMedian telomeric length (TL) of CD8+ lymphocytes was significantly longer in donors compared to recipients (on average 2,1 kb and 1,7 kb respectively, p = 0,02). Similar trends were observed for CD4+ and CD19+ although the results did not reach statistical significance. We have also found trends in the immunophenotype between recipients and donors in the subpopulations of CD4+ (naïve and effector memory), CD8+ Eomes+ and B-lymphocytes (B1 and B2). Lower infection risk recipients had also a significantly greater percentage of NK cells (22,3%) than high-risk patients (9,3%) p = 0,04.ConclusionOur data do not support the initial hypothesis of accelerated aging in the long term all-HCT recipients with the exception of the recipients lymphocytes (mainly CD8+) which present some molecular features, characteristic for physiological ageing (telomeric shortening, immunophenotype) when compared to their respective donors. However, a history of lower infection numbers in HCT recipients seems to be associated with increased percentage of NK cells. The history of GVHD seems not to affect the rate of ageing. Therefore, it is safe to conclude that the observed subtle differences between recipients’ and donors’ cells result mainly from the proliferative stress in the early period after allo-HCT and the difference between hosts’ and recipients’ microenvironments.

Real-life experiences of letermovir prophylaxis for cytomegalovirus infection in patients after hematopoietic stem cell transplantation: Polish Acute Leukemia Group (PALG) analysis

Introduction: Letermovir (LMV) is a new, cytomegalovirus (CMV)-specific, antiviral drug, approved in 2018 for CMV prophylaxis in patients after allogeneic hematopoietic transplantation. The introduction of letermovir prophylaxis has changed the management of CMV infection: it has reduced the incidence of CMV infections and CMV-related complications, and also improved the overall survival in CMV seropositive patients. However, until recently, due to its high treatment cost, prophylaxis with letermovir has not beeen a standard of care in Poland. Material and methods: To confirm the effectiveness and safety of letermovir prophylaxis, we collected real-life data from eight Polish transplant centers, in which a total of 53 patients were treated with letermovir, including off-label use. Results: LMV is characterized by low toxicity and good tolerability. There were no reports of special adverse events caused by LMV. Conclusions: Our experiences confirm the effectiveness and safety of letermovir prophylaxis, and suggest that this prophylaxis should be started as soon as possible after the infusion of stem cells, preferably no later than day 14. Moreover, our findings indicate that some patients could benefit from extended letermovir prophylaxis beyond 100 days after transplant.

CT-514 Acute Cardiac Tamponade Following Adult Allogeneic Hematopoietic Transplantation

Large pericardial effusions (LPEs) occur in <1% of the adult population. Early onset (<100 days from allogeneic hematopoietic transplantation (allo-SCT)) LPEs are related to cardiac toxicity of conditioning regimen while late LPEs (>100 from allo-SCT) are chronic GvHD related. The major determinant of acute pericardial tamponade (ACT) is the rapidity with which fluid accumulates. We herein document 4 adult patients with early LPEs that led to ACT. Interestingly, 3 of these also manifested idiopathic immune thrombocytopenia (ITP), an association that has not been previously described. Median age of 3 females and 1 male was 46 years (range 19-58). All patients received high-dose cyclophosphamide either as part of conditioning or post-transplant GvHD prevention (conditioning comprised: busulfan, fludarabine and tiotepa and post-transplantation cyclophosphamide =1, cyclophosphamide, total body irradiation and alemtuzumab =2 and cyclophosphamide and antithymocyte globulin =1). Donors comprised: matched unrelated donor =2, matched sibling donor =1 and haploidentical donor =1. Engraftment occurred on days +20, +30, +12, and +21. All four patients developed ACT at <100 days from allo-SCT on days +1, +16, + 22, and +60 after allo-SCT. ACT manifested as acute, new, or worsening shortness of breath. At ACT, all 4 were negative for CMV infection and acute GvHD (aGVHD). Pericardial fluid was serous in 2 and serosanguinous in 2 patients. Laboratory analysis did not support bacterial or viral infections and rheumatologic profile was negative. ACT was managed by cardiologist who performed either pericardiocentesis with pericardial drain or pericardial window. A cumulative total of 1700 ml, 1500 ml, 1500 ml and 300 ml pericardial fluid was removed. LPEs reoccurred in 2 patients; one with ACT physiology required pericardial window. Additionally, 3 patients developed ITP after development of ACT. The median time to ITP was day+30 (30, 30 and 75 days) from engraftment. Bone marrow biopsies in patients who developed ITP revealed adequate megakaryocytes. ITP responded promptly to steroids, thrombopoietin receptor agonists and IVIG. Prompt cardiac evaluation with doppler echocardiogram facilitates lifesaving management of ACT. Early onset LPEs in our patients was not associated with aGVHD; it is more likely to be associated with cardiac toxicity of cyclophosphamide. Association with ITP may reflect shared pathogenesis.

Comparative analysis of humoral responses to BNT162b2 vaccine among patients with hematologic disorders and organ transplant recipients.

Vaccination against SARS-COV-2 is considered the most promising approach to curbing the pandemic. Patients with an immunocompromised state, such as those with hematological malignancies and organ transplantation recipients, are considered more susceptible to infection, but these at-risk patients were underrepresented in early clinical trials for vaccination. Although a growing body of studies suggests that the humoral response to COVID-19 vaccination in each of these at-risk groups of patients may be suboptimal in comparison to healthy controls, a clinical and strategic information for the further comparative analysis among these groups is not fully described. The humoral responses after two doses of BNT162b2 vaccination were evaluated in a total of 187 patients either with allogeneic hematopoietic transplantation, with renal transplantation, with anti-CD20 antibody therapy, or with anti-CD38 antibody therapy, and in 66 healthy controls. The early response at one to three months after vaccination was significantly inferior among patients with renal transplantation, patients with anti-CD20 antibody therapy, and patients with anti-CD38 antibody therapy in comparison to healthy control. But the patients with allogeneic hematopoietic transplantation showed early humoral response comparable to healthy control. The late response at 6 months after vaccination was still suboptimal among patients with renal transplantation and patients with anti-CD20 therapy. Among our patient group, renal transplant recipients had the lowest antibody titers after vaccination regardless of timing of vaccination. Patients who had received allogeneic hematopoietic transplantation attained a comparable serological response to the control group especially if they are vaccinated >300 days after transplantation, but the response was suboptimal if the vaccination was within 300 days after transplantation. Our results may provide policy makers with critical information for the further stratification of at-risk groups, helping contribute to a better allocation of resources, including additional booster vaccination.

Long-term transplant outcomes after allogeneic hematopoietic transplant in pediatric patients with hematological malignancies are influenced by severe chronic graft vs. host disease and immune reconstitution.

Long-term follow-up studies are crucial to ensure surveillance and intervention for late complications after allogeneic stem cell transplantation, but they are scarce on the pediatric population. This study aims to analyze risk factors for long-term transplant outcomes. We report a landmark analysis of 162 pediatric patients who underwent allogeneic transplantation between 1991 and 2016, and survived for at least 12 months after the transplant. With a median follow-up time of 10 years for the survivors, the probability of disease-free survival (DFS) and overall survival (OS) is 81 ± 3 and 88 ± 2%, respectively. Variables that influenced DFS in the univariate analysis were: disease phase (early phase 87 ± 3% vs. advanced phase 74 ± 5%; p = 0.04), acute graft vs. host disease (aGvHD; yes 73 ± 5% vs. no 87 ± 3%; p = 0.038), severe chronic GvHD (cGvHD; yes 41 ± 13% vs. no 85 ± 3%; p = 0.0001), and CD4+ lymphocytes 2 years after the transplant (above the median of 837/μl 98 ± 2% vs. below the median 82 ± 6%, p = 0.026). However, in the multivariate analysis, the only variable that influenced DFS was presence of severe chronic GvHD (yes vs. no, HR 6.25; 95% CI, 1.35–34.48; p = 0.02). Transplant strategies should aim to reduce the risk of severe cGvHD. Immune reconstitution surveillance may help clinicians to better deal with late transplant complications.

Beware clonal haematopoiesis following chronic lymphocytic leukaemia treatment

Clonal myeloid haematopoiesis co-existing with chronic lymphocytic leukaemia (CLL) is not rare and is associated with high risks for development of therapy-related myeloid neoplasms (t-MNs) after cytotoxic chemotherapy. This has serious implications for the use of these therapies in newly diagnosed CLL patients. Therapy-related myeloid neoplasms are devastating conditions. Their development following cytotoxic chemotherapy for various neoplasms often ultimately leads to treatment-refractory acute myeloid leukaemia and is usually lethal for afflicted patients. These neoplasms often develop following exposure to alkylating agents or anthracyclines,1 but they have been reported following single-agent fludarabine.2 T-MNs typically present after prior cytotoxic therapy given in an adjuvant context or for relatively indolent neoplasms, and thus their development is particularly distressing for many otherwise cancer-free or cancer-controlled patients. Effective long-term control of t-MNs is difficult to achieve, and at present always requires allogeneic haematopoietic transplant. The paper by Voso et al.3 regarding clonal haematopoiesis of indeterminant potential (CHIP) as a risk factor for t-MNs following chemotherapy for CLL is thus timely and worthy of attention from all physicians who manage CLL. CHIP has (unsurprisingly) been associated with increased risks of t-MN. The current report is, however, the first reported study of t-MN following therapy for CLL. It is worth noting that this experience is based upon 15 patients who were selected only for the availability of pretreatment genomic material. Amongst the relevant 13 patients whose t-MN followed the use of cytotoxic therapy, a prior mutation consistent with myeloid CHIP was present in 10, or 77%. Mutations compatible with CHIP were found in 34 of 285 cases of CLL not developing t-MN. The authors thus appropriately conclude that CHIP seems to be a significant risk factor for the development of t-MN following cytotoxic therapy for CLL. This work presents a detailed description of the mutations found in prechemotherapy haematopoietic material. The authors are conservative in terms of attributing these mutations to the CLL or the myeloid elements found in the available pretreatment cells. They correctly observe that mutations of TP53 and SF3B1 could in principle arise either from clonal CLL cells or from a myeloid CHIP clone, and thus cannot be firmly identified as having driven the development of the t-MN. Data found in their table S4, however, show that in two patients (#6 and #8), mutations in TP53 (two cases) and in SF3B1 (one case), were identical in pretreatment samples of CLL containing cells and in the t-MN material. The same mutated sequences were found in these two paired samples in both cases and for both genes. Thus, although we cannot be completely certain, it seems very likely that in fact the pretreatment mutation was found in myeloid cells that were subsequently transformed in response to the exposure to cytotoxic agents, leading to the t-MN. These findings have important implications for the management of CLL and other neoplasms. First, CHIP is reasonably common in patients who are candidates to receive cytotoxic agents. Pre-existing CHIP clearly poses very significant risks for the development of t-MN and most of these secondary neoplasms will prove to be lethal for affected patients. Thus, particularly in older patients with higher risks of CHIP, it seems reasonable to consider screening patients for myeloid clonal states prior to offering cytotoxic therapy for management. Notably, there are now alternative systemic therapies available for CLL (and many other neoplasms) which do not involve cytotoxic therapy and thus should not pose the same risk of potential secondary neoplasm. Another and potentially provocative conclusion is that mutations of TP53 or SF3B1 found in pretreatment blood or other tissues from CLL patients may not necessarily represent changes in the CLL clone but may be situated in associated myeloid cells. This issue in it itself may affect decisions concerning CLL management, as TP53 mutations are associated with poor prognosis and as this finding in a CLL patient may potentially increase the desire for aggressive therapy. Finally, in such patients the use of cytotoxic chemotherapy in disease management might have disastrous downstream consequences, leading to a lethal t-MN. The development of effective systemic targeted therapies for CLL not employing cytotoxic or mutagenic agents has revolutionized the therapy of CLL. The application of these agents has already greatly reduced the use of potentially leukaemogenic therapies. Recently, however, it has been asserted that “In fit patients with immunoglobulin heavy chain mutation, it is still acceptable to use the chemotherapy regimen with fludarabine, cyclophosphamide, and rituximab (FCR) and, in those who [are] not fit or are not IgVH-mutated, bendamustine-rituximab regimen”.4 Given the availability of effective non-cytotoxic agents for management of essentially all CLL patients, haematologists and oncologists managing this group of highly treatable but fragile patients should take pause, and note the findings described by Voso et al.

The long and winding road: homeostatic and disordered haematopoietic microenvironmental niches: a narrative review.

ABSTRACTHaematopoietic microenvironmental niches have been described as the ‘gatekeepers’ for the blood and immune systems. These niches change during ontogeny, with the bone marrow becoming the predominant site of haematopoiesis in post-natal life under steady state conditions. To determine the structure and function of different haematopoietic microenvironmental niches, it is essential to clearly define specific haematopoietic stem and progenitor cell subsets during ontogeny and to understand their temporal appearance and anatomical positioning. A variety of haematopoietic and non-haematopoietic cells contribute to haematopoietic stem and progenitor cell niches. The latter is reported to include endothelial cells and mesenchymal stromal cells (MSCs), skeletal stem cells and/or C-X-C motif chemokine ligand 12-abundant-reticular cell populations, which form crucial components of these microenvironments under homeostatic conditions. Dysregulation or deterioration of such cells contributes to significant clinical disorders and diseases worldwide and is associated with the ageing process. A critical appraisal of these issues and of the roles of MSC/C-X-C motif chemokine ligand 12-abundant-reticular cells and the more recently identified skeletal stem cell subsets in bone marrow haematopoietic niche function under homeostatic conditions and during ageing will form the basis of this research review. In the context of haematopoiesis, clinical translation will deal with lessons learned from the vast experience garnered from the development and use of MSC therapies to treat graft versus host disease in the context of allogeneic haematopoietic transplants, the recent application of these MSC therapies to treating emerging and severe coronavirus disease 2019 (COVID-19) infections, and, given that skeletal stem cell ageing is one proposed driver for haematopoietic ageing, the potential contributions of these stem cells to haematopoiesis in healthy bone marrow and the benefits and challenges of using this knowledge for rejuvenating the age-compromised bone marrow haematopoietic niches and restoring haematopoiesis.