Graft-versus-Leukemia Effect Following Hematopoietic Stem Cell Transplantation for Leukemia

Advances in ex vivo expansion of hematopoietic stem and progenitor cells for clinical applications

As caretakers of the hematopoietic system, hematopoietic stem cells assure a lifelong supply of differentiated populations that are responsible for critical bodily functions, including oxygen transport, immunological protection and coagulation. Due to the far-reaching influence of the hematopoietic system, hematological disorders typically have a significant impact on the lives of individuals, even becoming fatal. Hematopoietic cell transplantation was the first effective therapeutic avenue to treat such hematological diseases. Since then, key use and manipulation of hematopoietic stem cells for treatments has been aspired to fully take advantage of such an important cell population. Limited knowledge on hematopoietic stem cell behavior has motivated in-depth research into their biology. Efforts were able to uncover their native environment and characteristics during development and adult stages. Several signaling pathways at a cellular level have been mapped, providing insight into their machinery. Important dynamics of hematopoietic stem cell maintenance were begun to be understood with improved comprehension of their metabolism and progressive aging. These advances have provided a solid platform for the development of innovative strategies for the manipulation of hematopoietic stem cells. Specifically, expansion of the hematopoietic stem cell pool has triggered immense interest, gaining momentum. A wide range of approaches have sprouted, leading to a variety of expansion systems, from simpler small molecule-based strategies to complex biomimetic scaffolds. The recent approval of Omisirge, the first expanded hematopoietic stem and progenitor cell product, whose expansion platform is one of the earliest, is predictive of further successes that might arise soon. In order to guarantee the quality of these ex vivo manipulated cells, robust assays that measure cell function or potency need to be developed. Whether targeting hematopoietic engraftment, immunological differentiation potential or malignancy clearance, hematopoietic stem cells and their derivatives need efficient scaling of their therapeutic potency. In this review, we comprehensively view hematopoietic stem cells as therapeutic assets, going from fundamental to translational.

Dendritic cell vaccination strategy for the treatment of acute myeloid leukemia: a systematic review

BACKGROUND AIMS

Acute myeloid leukemia (AML) is classified as a hematologic malignancy characterized by the proliferation of immature blood cells within the bone marrow (BM), resulting in an aberrant and unregulated cellular growth. The primary therapeutic modalities for AML include chemotherapy and hematopoietic stem cell transplantation. However, it is important to note that these treatments are accompanied by important adverse effects and mortality rates. Therefore, the need for more effective treatment options seems necessary, and dendritic cell (DC) vaccine therapy can be one of these options. In this study, we aim to investigate the effectiveness of DC vaccination therapy for the management of AML.

METHODS

PubMed, Scopus, ProQuest, Web of Science, and Google Scholar databases were searched for this systematic review. The articles were evaluated based on the inclusion criteria of this study and initially compared in terms of titles or abstracts. Finally, the articles related to the topic of this review were obtained in full text. The complete remission and partial remission, survival, correlative immune assays, and health-related metrics were used to evaluate this cellular immunotherapy effectiveness. The quality of the studies was assessed independently using the Cochrane risk-of-bias tools. The compiled data were input into a standard Excel spreadsheet. Each domain was evaluated as having either a "low risk," "high risk," or "unclear risk" of bias.

RESULTS

Among the 3986 studies that were determined, a total of 11 correlated trials were selected for inclusion in this systematic review. DC vaccine therapy was effective in inducing complete and partial remission, and stabilization of the disease. Additionally, it was discovered that the treatment strengthened the immune system as seen by increased levels of CD4+ and CD8+ T cells, Th1 cytokines, WT1-specific T cells, and activated NK cells.

CONCLUSION

We conducted a systematic review that supports the use of DC vaccine therapy as an effective treatment for AML. The therapy demonstrated potentials in achieving remission, enhancing the immune system function, and increasing overall survival. However, more studies are required to improve the methods of preparing and delivering the DC vaccine, and to confirm its long-term safety and effectiveness.

Graft-versus-leukaemia immunity is retained following treatment with post-transplant cyclophosphamide alone or combined with tocilizumab in humanised mice

Objectives

Donor haematopoietic stem cell transplantation treats leukaemia by inducing graft-versus-leukaemia (GVL) immunity. However, this benefit is often mitigated by graft-versus-host disease (GVHD), which is reduced by post-transplant cyclophosphamide (PTCy) alone or combined with tocilizumab (TOC) in humanised mice. This study established a preclinical humanised mouse model of GVL and investigated whether PTCy alone or combined with TOC impacts GVL immunity.

Methods

NOD-scid-IL2Rγnull mice were injected with 2 × 107 human peripheral blood mononuclear cells (hPBMCs) on day 0 and with 1 × 106 THP-1 acute myeloid leukaemia cells on day 14. In subsequent experiments, mice were also injected with PTCy (33 mg kg-1) or Dulbecco's phosphate buffered saline (PBS) on days 3 and 4, alone or combined with TOC or control antibody (25 mg kg-1) twice weekly for 28 days. Clinical signs of disease were monitored until day 42.

Results

Mice with hPBMCs from three different donors and THP-1 cells showed similar survival, clinical score and weight loss. hCD33+ leukaemia cells were minimal in mice reconstituted with hPBMCs from two donors but present in mice with hPBMCs from a third donor, suggesting donor-specific GVL responses. hPBMC-injected mice treated with PTCy alone or combined with TOC (PTCy + TOC) demonstrated prolonged survival compared to control mice. PTCy alone and PTCy + TOC-treated mice with hPBMCs showed minimal hepatic hCD33+ leukaemia cells, indicating sustained GVL immunity. Further, the combination of PTCy + TOC reduced histological damage in the lung and liver.

Conclusion

Collectively, this research demonstrates that PTCy alone or combined with TOC impairs GVHD without compromising GVL immunity.

Metabolic instruction of the graft-versus-leukemia immunity

Allogeneic hematopoietic cell transplantation (allo-HCT) is frequently performed to cure hematological malignancies, such as acute myeloid leukemia (AML), through the graft-versus-leukemia (GVL) effect. In this immunological process, donor immune cells eliminate residual cancer cells in the patient and exert tumor control through immunosurveillance. However, GVL failure and subsequent leukemia relapse are frequent and associated with a dismal prognosis. A better understanding of the mechanisms underlying AML immune evasion is essential for developing novel therapeutic strategies to boost the GVL effect. Cellular metabolism has emerged as an essential regulator of survival and cell fate for both cancer and immune cells. Leukemia and T cells utilize specific metabolic programs, including the orchestrated use of glucose, amino acids, and fatty acids, to support their growth and function. Besides regulating cell-intrinsic processes, metabolism shapes the extracellular environment and plays an important role in cell-cell communication. This review focuses on recent advances in the understanding of how metabolism might affect the anti-leukemia immune response. First, we provide a general overview of the mechanisms of immune escape after allo-HCT and an introduction to leukemia and T cell metabolism. Further, we discuss how leukemia and myeloid cell metabolism contribute to an altered microenvironment that impairs T cell function. Next, we review the literature linking metabolic processes in AML cells with their inhibitory checkpoint ligand expression. Finally, we focus on recent findings concerning the role of systemic metabolism in sustained GVL efficacy. While the majority of evidence in the field still stems from basic and preclinical studies, we discuss translational findings and propose further avenues for bridging the gap between bench and bedside.

Kinetics of Recovery of Naïve and Memory T Cells in Acute Leukemia Patients after Allogeneic Stem Cell Transplantation Depending on Different GVHD Prophylaxis Regimens

Background: Memory T cells are a heterogeneous population of immune cells that provide adaptive immunity. Its full recovery seems essential for graft-versus-tumor reactions that provide an opportunity for biological cure in patients with acute leukemia. The use of mismatched or haploidentical donors has increased, which has become possible because of modifications in graft versus host disease (GVHD) prophylaxis. Materials and Methods: Sixty-five leukemia patients (acute myeloid leukemia - 40, acute lymphoblastic leukemia - 25), median age 33 (17-61) years, underwent allo-HSCT from 2016 to 2019 in the National Research Centre for Hematology. Patients were divided into three groups based on the impact of GVHD prophylaxis on T cell recovery: horse antithymocyte globulin (ATG)-based regimen (n=32), horse ATG combined with posttransplant cyclophosphamide (PT-Cy) (n=18), and ex vivo T cell depletion (n=15). Results: The early period after transplantation (before day +100) was characterized by significantly lower absolute numbers of T naïve, memory stem and T central memory cells in peripheral blood in patients after ATG+PT-Cy-regimen or ex vivo T cell depletion than after ATG-based prophylaxis (p<0.05). Moreover, strong depletion of naïve T and memory stem cells prevents the development of GVHD, and determining the absolute number of CD8+ naïve T and memory stem cells with a cutoff of 1.31 cells per microliter seems to be a perspective in assessing the risks of developing acute GVHD (p=0.008). The dynamics of T cell recovery showed the involvement of either circulating or bone marrow resident T effector cells shortly after allogeneic transplantation in all patients, but the use of manipulated grafts with ex vivo T cell depletion requires the involvement of naïve and memory stem cells. There was no significant effect of T cell recovery on leukemia relapse after allogeneic transplantation. Conclusion: These experimental outcomes contribute to providing the best understanding of immunological events that occur early after transplantation and help in the rational choice of GVHD prophylaxis in patients who will undergo allogeneic transplantation. Our study demonstrated the comparable immunological effects of posttransplant cyclophosphamide and ex vivo T cell depletion and immunological inefficiency of horse ATG for GVHD prevention.

Effect of lethal total body irradiation on bone marrow chimerism, acute graft-versus-host disease, and tumor engraftment in mouse models: impact of different radiation techniques using low- and high-energy X-rays

PURPOSE

Effects of X‑ray energy levels used for myeloablative lethal total body irradiation (TBI) delivery prior to bone marrow transplantation (BMT) in preclinical mouse models were examined.

MATERIALS AND METHODS

In mouse models, single-fraction myeloablative TBI at a lethal dose was delivered using two different X‑ray devices, either low (160 kV cabinet irradiator) or high energy (6 MV linear accelerator), before semi-allogeneic hematopoietic stem-cell transplantation (HSCT) to ensure bone marrow (BM) chimerism, graft-versus-host disease (GVHD), and tumor engraftment. Recipient mice were clinically followed for 80 days after bone marrow transplantation (BMT). Flow cytometry was performed to assess donor chimerism and tumor engraftment in recipient mice.

RESULTS

Both X‑ray irradiation techniques delivered a 10 Gy single fraction of TBI, presented a lethal effect, and could allow near-complete early donor chimerism on day 13. However, low-energy irradiation increased T cells' alloreactivity compared to high-energy irradiation, leading to clinical consequences for GVHD and tumor engraftment outcomes. The alloreactive effect differences might be attributed to the distinction in inflammatory status of irradiated recipients at donor cell infusion (D0). Delaying donor cell administration (D1 after lethal TBI) attenuated T cells' alloreactivity and clinical outcomes in GVHD mouse models.

CONCLUSION

Different X‑ray irradiation modalities condition T cell alloreactivity in experimental semi-allogeneic BMT. Low-energy X‑ray irradiator induces a post-TBI inflammatory burst and exacerbates alloreactive reactions. This technical and biological information should be considered in interpreting GVHD/ graft-versus-leukemia effect results in mice experimental models of BMT.

Early immune reconstitution as predictor for outcomes after allogeneic hematopoietic cell transplant; a tri-institutional analysis

BACKGROUND AIMS

CD4 immune reconstitution (IR) after allogeneic hematopoietic cell transplant (allo-HCT) correlates with lower non-relapse mortality (NRM), but its impact on leukemia relapse remains less clear, especially in children. We studied the correlation between IR of lymphocyte subsets and HCT outcomes in a large cohort of children/young adults with hematological malignancies.

METHODS

We retrospectively analyzed CD4, CD8, B-cell and natural killer (NK) cell reconstitution in patients after first allo-HCT for a hematological malignancy at three large academic institutions (n = 503; period 2008-2019). We used Cox proportional hazard and Fine-Gray competing risk models, martingale residual plots and maximally selected log-rank statistics to assess the impact of IR on outcomes.

RESULTS

Achieving CD4 >50 and/or B cells >25 cells/μL before day 100 after allo-HCT was a predictor of lower NRM (CD4 IR: hazard ratio [HR] 0.26, 95% confidence interval [CI] 0.11-0.62, P = 0.002; CD4 and B cell IR: HR 0.06, 95% CI 0.03-0.16, P < 0.001), acute graft-versus-host disease (GVHD) (CD4 and B cell IR: HR 0.02, 95% CI 0.01-0.04, P < 0.001) and chronic GVHD (CD4 and B cell IR: HR 0.16, 95% CI 0.05-0.49, P = 0.001) in the full cohort, and of lower risk of relapse (CD4 and B cell IR: HR 0.24, 95% CI 0.06-0.92, P = 0.038) in the acute myeloid leukemia subgroup. No correlation between CD8 and NK-cell IR and relapse or NRM was found.

CONCLUSIONS

CD4 and B-cell IR was associated with clinically significant lower NRM, GVHD and, in patients with acute myeloid leukemia, disease relapse. CD8 and NK-cell IR was neither associated with relapse nor NRM. If confirmed in other cohorts, these results can be easily implemented for risk stratification and clinical decision making.

The delicate balance of graft versus leukemia and graft versus host disease after allogeneic hematopoietic stem cell transplantation

INTRODUCTION

The curative basis of allogeneic hematopoietic stem cell transplantation (HSCT) relies in part upon the graft versus leukemia (GvL) effect, whereby donor immune cells recognize and eliminate recipient malignant cells. However, alloreactivity of donor cells against recipient tissues may also be deleterious. Chronic graft versus host disease (cGvHD) is an immunologic phenomenon wherein alloreactive donor T cells aberrantly react against host tissues, leading to damaging inflammatory symptoms.

AREAS COVERED

Here, we discuss biological insights into GvL and cGvHD and strategies to balance the prevention of GvHD with maintenance of GvL in modern HSCT.

EXPERT OPINION/COMMENTARY

Relapse remains the leading cause of mortality after HSCT with rates as high as 40% for some diseases. GvHD is a major cause of morbidity after HSCT, occurring in up to half of patients and responsible for 15-20% of deaths after HSCT. Intriguingly, the development of chronic GvHD may be linked to lower relapse rates after HSCT, suggesting that GvL and GvHD may be complementary sides of the immunologic foundation of HSCT. The ability to fine tune the balance of GvL and GvHD will lead to improvements in survival, relapse rates, and quality of life for patients undergoing HSCT.

Donor Lymphocyte Infusion and Molecular Monitoring for Relapsed Myelofibrosis After Hematopoietic Cell Transplantation

Hematopoietic cell transplantation (HCT) is a curative approach for myelofibrosis patients, but relapse is a major cause of treatment failure. We investigated the effect of donor lymphocyte infusion (DLI) in 37 patients with molecular (n = 17) or hematological relapse (n = 20) after HCT. Patients received median of 2 (range, 1-5) cumulative DLI (total of 91 infusions). Median starting dose was 1 × 10⁶ cells/kg, escalated by half-log ≥6 weeks if no response nor graft-versus-host disease (GvHD) occurred. Median time to first DLI was 40 weeks for molecular relapse versus 145 weeks for hematological relapse. Overall molecular complete response (mCR) at any time was 73% (n = 27) and was significantly higher for initial molecular relapse (88%) versus hematological relapse (60%; P = 0.05). The 6-year overall survival was 77% versus 32% (P = 0.03). Acute GvHD 2-4 occurred in 22% and half of the patients achieved mCR without any GvHD. All patients who relapsed from mCR achieved after first DLI could be salvaged with subsequent DLI, showing long-term survival. No second HCT was needed for molecular relapse versus 6 for hematological relapse. This comprehensive and largest study to date suggests molecular monitoring together with DLI as standard of care and a crucial approach to achieve excellent outcomes in relapsed myelofibrosis.

Leukemia relapse via genetic immune escape after allogeneic hematopoietic cell transplantation

Graft-versus-leukemia (GvL) reactions are responsible for the effectiveness of allogeneic hematopoietic cell transplantation as a treatment modality for myeloid neoplasia, whereby donor T- effector cells recognize leukemia neoantigens. However, a substantial fraction of patients experiences relapses because of the failure of the immunological responses to control leukemic outgrowth. Here, through a broad immunogenetic study, we demonstrate that germline and somatic reduction of human leucocyte antigen (HLA) heterogeneity enhances the risk of leukemic recurrence. We show that preexistent germline-encoded low evolutionary divergence of class II HLA genotypes constitutes an independent factor associated with disease relapse and that acquisition of clonal somatic defects in HLA alleles may lead to escape from GvL control. Both class I and II HLA genes are targeted by somatic mutations as clonal selection factors potentially impairing cellular immune responses and response to immunomodulatory strategies. These findings define key molecular modes of post-transplant leukemia escape contributing to relapse.

Leukemia relapse via genetic immune escape after allogeneic hematopoietic cell transplantation

Graft-versus-leukemia (GvL) reactions are responsible for the effectiveness of allogeneic hematopoietic cell transplantation as a treatment modality for myeloid neoplasia, whereby donor T- effector cells recognize leukemia neoantigens. However, a substantial fraction of patients experience relapses because of the failure of the immunological responses to control leukemic outgrowth. Here, through a broad immunogenetic study, we demonstrate that germline and somatic reduction of human leucocyte antigen (HLA) heterogeneity enhances the risk of leukemic recurrence. We show that preexistent germline-encoded low evolutionary divergence of class II HLA genotypes constitutes an independent factor associated with disease relapse and that acquisition of clonal somatic defects in HLA alleles may lead to escape from GvL control. Both class I and II HLA genes are targeted by somatic mutations as clonal selection factors potentially impairing cellular immune reactions and response to immunomodulatory strategies. These findings define key molecular modes of post-transplant leukemia escape contributing to relapse.

A novel RIPK1 inhibitor reduces GVHD in mice via a nonimmunosuppressive mechanism that restores intestinal homeostasis

Intestinal epithelial cells (IECs) are implicated in the propagation of T-cell-mediated inflammatory diseases, including graft-versus-host disease (GVHD), but the underlying mechanism remains poorly defined. Here, we report that IECs require receptor-interacting protein kinase-3 (RIPK3) to drive both gastrointestinal (GI) tract and systemic GVHD after allogeneic hematopoietic stem cell transplantation. Selectively inhibiting RIPK3 in IECs markedly reduces GVHD in murine intestine and liver. IEC RIPK3 cooperates with RIPK1 to trigger mixed lineage kinase domain-like protein-independent production of T-cell-recruiting chemokines and major histocompatibility complex (MHC) class II molecules, which amplify and sustain alloreactive T-cell responses. Alloreactive T-cell-produced interferon gamma enhances this RIPK1/RIPK3 action in IECs through a JAK/STAT1-dependent mechanism, creating a feed-forward inflammatory cascade. RIPK1/RIPK3 forms a complex with JAK1 to promote STAT1 activation in IECs. The RIPK1/RIPK3-mediated inflammatory cascade of alloreactive T-cell responses results in intestinal tissue damage, converting the local inflammation into a systemic syndrome. Human patients with severe GVHD showed highly activated RIPK1 in the colon epithelium. Finally, we discover a selective and potent RIPK1 inhibitor (Zharp1-211) that significantly reduces JAK/STAT1-mediated expression of chemokines and MHC class II molecules in IECs, restores intestinal homeostasis, and arrests GVHD without compromising the graft-versus-leukemia (GVL) effect. Thus, targeting RIPK1/RIPK3 in IECs represents an effective nonimmunosuppressive strategy for GVHD treatment and potentially for other diseases involving GI tract inflammation.

Peripheral blood persistence and expansion of transferred non-genetically modified Natural Killer cells might not be necessary for clinical activity

Natural killer (NK) cells are innate lymphocytes that react without previous exposition to virus infected or malignant cells and stimulate adaptive immune response to build a long-lasting immunity against it. To that end, tissue resident NK cells are predominantly regulatory as opposed to cytotoxic. In the hematopoietic stem cell transplant (HSCT) setting, which curative potential relies on the graft versus leukemia effect, NK cells are known to play a significant role. This knowledge has paved the way to the active investigation on its anti-tumor effect outside the stem cell transplant scenario. Based on the relevant literature on the adoptive transfer of non-genetically modified NK cells for the treatment of relapsed/refractory acute leukemia and on our own experience, we discuss the role of donor cell peripheral blood persistence and expansion and its lack of correlation with anti-leukemia activity.

Role of NK cells in cord blood transplantation and their enhancement by the missing ligand effect of the killer-immunoglobulin like receptor

Natural killer (NK) cells are the first lymphocytes reconstituted after allogenic hematopoietic stem cell transplantation (HSCT). Especially, in cord blood transplantation (CBT), the increase in the number of NK cells is sustained for a long period. Although there are conflicting results, many studies show that early reconstitution of NK cells is associated with favorable CBT outcomes, suggesting that maximizing NK cell functions could improve the CBT outcome. Killer immunoglobulin-like receptors (KIRs) include inhibitory and stimulatory receptors, which can regulate NK-cell activity. Because some of the KIRs have HLA class I as their ligand, the KIR—ligand interaction on NK cells can be lost in some cases of CBT, which results in the activation of NK cells and alters HSCT outcome. Thus, effects of KIR–ligand mismatch under various conditions have been widely examined; however, the results have been controversial. Among such studies, those using the largest number of CBTs showed that HLA—C2 (KIR2DL1—ligand) mismatches have a favorable effect on the relapse rate and overall survival only when the CBT used methotrexate for graft-versus-host disease prophylaxis. Another study suggested that KIR—ligand mismatch is involved in reducing the relapse of acute myeloid leukemia, mediated by reactivation of cytomegalovirus. These results indicate that activation of NK cells by KIR—ligand mismatch may have favorable effects on CBT outcomes and could help enhance the NK-cell function.

Spectral flow cytometry cluster analysis of therapeutic donor lymphocyte infusions identifies T cell subsets associated with outcome in patients with AML relapse

Identification of immune phenotypes linked to durable graft-versus-leukemia (GVL) response following donor lymphocyte infusions (DLI) is of high clinical relevance. In this prospective observational study of 13 AML relapse patients receiving therapeutic DLI, we longitudinally investigated changes in differentiation stages and exhaustion markers of T cell subsets using cluster analysis of 30-color spectral flow cytometry during 24 months follow-up. DLI cell products and patient samples after DLI were analyzed and correlated to the clinical outcome. Analysis of DLI cell products revealed heterogeneity in the proportions of naïve and antigen experienced T cells. Cell products containing lower levels of effector memory (eff/m) cells and higher amounts of naïve CD4⁺ and CD8⁺ T cells were associated with long-term remission. Furthermore, investigation of patient blood samples early after DLI showed that patients relapsing during the study period, had higher levels of CD4⁺ eff/m T cells and expressed a mosaic of surface molecules implying an exhausted functional state. Of note, this observation preceded the clinical diagnosis of relapse by five months. On the other hand, patients with continuous remission retained lower levels of exhausted CD4⁺ eff/m T cells more than four months post DLI. Moreover, lower frequencies of exhausted CD8⁺ eff/m T cells as well as higher amounts of CD4⁺temra CD45RO⁺ T cells were present in this group. These results imply the formation of functional long-term memory pool of T cells. Finally, unbiased sample analysis showed that DLI cell products with low levels of eff/m cells both in CD4⁺ and CD8⁺ T cell subpopulations associate with a lower relapse incidence. Additionally, competing risk analysis of patient samples taken early after DLI revealed that patients with high amounts of exhausted CD4⁺ eff/m T cells in their blood exhibited significantly higher rates of relapse. In conclusion, differentially activated T cell clusters, both in the DLI product and in patients post infusion, were associated with AML relapse after DLI. Our study suggests that differences in DLI cell product composition might influence GVL. In-depth monitoring of T cell dynamics post DLI might increase safety and efficacy of this immunotherapy, while further studies are needed to assess the functionality of T cells found in the DLI.

Insights into mechanisms of graft-versus-host disease through humanised mouse models

Graft-versus-host disease (GVHD) is a major complication that occurs following allogeneic haematopoietic stem cell transplantation (HSCT) for the treatment of haematological cancers and other blood-related disorders. GVHD is an inflammatory disorder, where the transplanted donor immune cells can mediate an immune response against the recipient and attack host tissues. Despite over 60 years of research, broad-range immune suppression is still used to prevent or treat GVHD, leading to an increased risk of cancer relapse and infection. Therefore, further insights into the disease mechanisms and development of predictive and prognostic biomarkers are key to improving outcomes and reducing GVHD development following allogeneic HSCT. An important preclinical tool to examine the pathophysiology of GVHD and to understand the key mechanisms that lead to GVHD development are preclinical humanised mouse models. Such models of GVHD are now well-established and can provide valuable insights into disease development. This review will focus on models where human peripheral blood mononuclear cells are injected into immune-deficient non-obese diabetic (NOD)-scid-interleukin-2(IL-2)Rγ mutant (NOD-scid-IL2Rγ^null) mice. Humanised mouse models of GVHD can mimic the clinical setting for GVHD development, with disease progression and tissues impacted like that observed in humans. This review will highlight key findings from preclinical humanised mouse models regarding the role of donor human immune cells, the function of cytokines and cell signalling molecules and their impact on specific target tissues and GVHD development. Further, specific therapeutic strategies tested in these preclinical models reveal key molecular pathways important in reducing the burden of GVHD following allogeneic HSCT.

Allogeneic MHC-matched T-cell receptor α/β-depleted bone marrow transplants in SHIV-infected, ART-suppressed Mauritian cynomolgus macaques

Allogeneic hematopoietic stem cell transplants (allo-HSCTs) dramatically reduce HIV reservoirs in antiretroviral therapy (ART) suppressed individuals. However, the mechanism(s) responsible for these post-transplant viral reservoir declines are not fully understood. Therefore, we modeled allo-HSCT in ART-suppressed simian-human immunodeficiency virus (SHIV)-infected Mauritian cynomolgus macaques (MCMs) to illuminate factors contributing to transplant-induced viral reservoir decay. Thus, we infected four MCMs with CCR5-tropic SHIV162P3 and started them on ART 6-16 weeks post-infection (p.i.), maintaining continuous ART during myeloablative conditioning. To prevent graft-versus-host disease (GvHD), we transplanted allogeneic MHC-matched α/β T cell-depleted bone marrow cells and prophylactically treated the MCMs with cyclophosphamide and tacrolimus. The transplants produced ~ 85% whole blood donor chimerism without causing high-grade GvHD. Consequently, three MCMs had undetectable SHIV DNA in their blood post-transplant. However, SHIV-harboring cells persisted in various tissues, with detectable viral DNA in lymph nodes and tissues between 38 and 62 days post-transplant. Further, removing one MCM from ART at 63 days post-transplant resulted in SHIV rapidly rebounding within 7 days of treatment withdrawal. In conclusion, transplanting SHIV-infected MCMs with allogeneic MHC-matched α/β T cell-depleted bone marrow cells prevented high-grade GvHD and decreased SHIV-harboring cells in the blood post-transplant but did not eliminate viral reservoirs in tissues.

Challenges in Cell Fate Acquisition to Scid-Repopulating Activity from Hemogenic Endothelium of hiPSCs Derived from AML Patients Using Forced Transcription Factor Expression

The generation of human hematopoietic stem cells (HSCs) from human pluripotent stem cells (hPSCs) represents a major goal in regenerative medicine and is believed would follow principles of early development. HSCs arise from a type of endothelial cell called a “hemogenic endothelium” (HE), and human HSCs are experimentally detected by transplantation into SCID or other immune-deficient mouse recipients, termed SCID-Repopulating Cells (SRC). Recently, SRCs were detected by forced expression of seven transcription factors (TF) (ERG, HOXA5, HOXA9, HOXA10, LCOR, RUNX1, and SPI1) in hPSC-derived HE, suggesting these factors are deficient in hPSC differentiation to HEs required to generate HSCs. Here we derived PECAM-1-, Flk-1-, and VE-cadherin-positive endothelial cells that also lack CD45 expression (PFV^CD45−) which are solely responsible for hematopoietic output from iPSC lines reprogrammed from AML patients. Using HEs derived from AML patient iPSCs devoid of somatic leukemic aberrations, we sought to generate putative SRCs by the forced expression of 7TFs to model autologous HSC transplantation. The expression of 7TFs in hPSC-derived HE cells from an enhanced hematopoietic progenitor capacity was present in vitro, but failed to acquire SRC activity in vivo. Our findings emphasize the benefits of forced TF expression, along with the continued challenges in developing HSCs for autologous-based therapies from hPSC sources.

An Overview of Autophagy in Hematopoietic Stem Cell Transplantation

Autophagy is a fundamental homeostatic process crucial for cellular adaptation in response to metabolic stress. Autophagy exerts its effect through degrading intracellular components and recycling them to produce macromolecular precursors and energy. This physiological process contributes to cellular development, maintenance of cellular/tissue homeostasis, immune system regulation, and human disease. Allogeneic hematopoietic stem cell transplantation (HSCT) is the only preferred therapy for most bone marrow-derived cancers. Unfortunately, HSCT can result in several serious and sometimes untreatable conditions due to graft-versus-host disease (GVHD), graft failure, and infection. These are the major cause of morbidity and mortality in patients receiving the transplant. During the last decade, autophagy has gained a considerable understanding of its role in various diseases and cellular processes. In light of recent research, it has been confirmed that autophagy plays a crucial role in the survival and function of hematopoietic stem cells (HSCs), T-cell differentiation, antigen presentation, and responsiveness to cytokine stimulation. Despite the importance of these events to HSCT, the role of autophagy in HSCT as a whole remains relatively ambiguous. As a result of the growing use of autophagy-modulating agents in the clinic, it is imperative to understand how autophagy functions in allogeneic HSCT. The purpose of this literature review is to elucidate the established and implicated roles of autophagy in HSCT, identifying this pathway as a potential therapeutic target for improving transplant outcomes.

Genetic Engineering and Enrichment of Human NK Cells for CAR-Enhanced Immunotherapy of Hematological Malignancies

The great clinical success of chimeric antigen receptor (CAR) T cells has unlocked new levels of immunotherapy for hematological malignancies. Genetically modifying natural killer (NK) cells as alternative CAR immune effector cells is also highly promising, as NK cells can be transplanted across HLA barriers without causing graft-versus-host disease. Therefore, off-the-shelf usage of CAR NK cell products might allow to widely expand the clinical indications and to limit the costs of treatment per patient. However, in contrast to T cells, manufacturing suitable CAR NK cell products is challenging, as standard techniques for genetically engineering NK cells are still being defined. In this study, we have established optimal lentiviral transduction of primary human NK cells by systematically testing different internal promoters for lentiviral CAR vectors and comparing lentiviral pseudotypes and viral entry enhancers. We have additionally modified CAR constructs recognizing standard target antigens for acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) therapy—CD19, CD33, and CD123—to harbor a CD34-derived hinge region that allows efficient detection of transduced NK cells in vitro and in vivo and also facilitates CD34 microbead-assisted selection of CAR NK cell products to >95% purity for potential clinical usage. Importantly, as most leukemic blasts are a priori immunogenic for activated primary human NK cells, we developed an in vitro system that blocks the activating receptors NKG2D, DNAM-1, NKp30, NKp44, NKp46, and NKp80 on these cells and therefore allows systematic testing of the specific killing of CAR NK cells against ALL and AML cell lines and primary AML blasts. Finally, we evaluated in an ALL xenotransplantation model in NOD/SCID-gamma (NSG) mice whether human CD19 CAR NK cells directed against the CD19+ blasts are relying on soluble or membrane-bound IL15 production for NK cell persistence and also in vivo leukemia control. Hence, our study provides important insights into the generation of pure and highly active allogeneic CAR NK cells, thereby advancing adoptive cellular immunotherapy with CAR NK cells for human malignancies further.

MicroRNA serum profiles and chronic graft versus host disease

Chronic graft versus host disease (cGVHD) is the most common long-term complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). During the last decade, the interest of micro RNAs (miRNAs) in the pathophysiological process of cGVHD has increased. The objectives of this study were to investigate a wide range of serum miRNAs in allografted patients and identify associations between miRNAs and cGVHD. The study included 79 allotransplanted adults, where serum samples were obtained one year after the allo-HSCT, and miRNA profiling analysis in serum was performed. 50 of the 79 patients (63%) had signs of cGVHD at the one-year post-allo-HSCT control. miRNA-sequencing analysis revealed 1380 different miRNAs detected for at least one patient, while 233 miRNAs (17%) were detected in more than 70 patients. We identified ten miRNAs that differed significantly between patients with and without cGVHD (p <0.005, false discovery rate (FDR) <0.1), and all or these miRNAs were detected for >75 of the patients. Furthermore, five distinct miRNAs; miR-365-3p, miR-148-3p, miR-122-5p, miR-378-3p, and miR-192-5p, were found to be particularly associated with cGVHD in our analysis and validated by receiver operating characteristics (ROC) analysis. Based on only three miRNAs, miR-365-3p, miR-148-3p, and miR-378-3p, we developed a miRNA signature which by bioinformatic approaches and linear regression model utterly improved our potential diagnostic biomarker model for cGVHD. We conclude that miRNAs are differently expressed among patients with and without cGVHD, although further and larger studies are needed to validate our present findings.

Class I/Class II HLA Evolutionary Divergence Ratio Is an Independent Marker Associated With Disease-Free and Overall Survival After Allogeneic Hematopoietic Stem Cell Transplantation for Acute Myeloid Leukemia

Class I Human Leukocyte Antigen (HLA) evolutionary divergence (HED) is a metric which reflects immunopeptidome diversity and has been associated with immune checkpoint inhibitor responses in solid tumors. Its impact and interest in allogeneic hematopoietic stem cell transplantation (HCT) have not yet been thoroughly studied. This study analyzed the clinical and immune impact of class I and II HED in 492 acute myeloid leukemia (AML) recipients undergoing HCT. The overall cohort was divided into a training (n=338) and a testing (n=132) set. Univariate cox screening found a positive impact of a high class I HED and a negative impact of a high class II HED on both disease-free (DFS) and overall survival (OS). These results were combined in a unique marker, class I/class II HED ratio, and assessed in the testing cohort. The final multivariate cox model confirmed the positive impact of a high versus low class I/class II HED ratio on both DFS (Hazard Ratio (HR) 0.41 [95% CI 0.2-0.83]; p=0.01) and OS (HR 0.34 [0.19-0.59]; p<0.001), independently of HLA matching and other HCT parameters. No significant association was found between the ratio and graft-versus-host disease (GvHD) nor with neutrophil and platelet recovery. A high class I HED was associated with a tendency for an increase in NK, CD8 T-cell, and B cell recovery at 12 months. These results introduce HED as an original and independent prognosis marker reflecting immunopeptidome diversity and alloreactivity after HCT.

Targeting an alternate Wilms' tumor antigen 1 peptide bypasses immunoproteasome dependency

Designing effective antileukemic immunotherapy will require understanding mechanisms underlying tumor control or resistance. Here, we report a mechanism of escape from immunologic targeting in an acute myeloid leukemia (AML) patient, who relapsed 1 year after immunotherapy with engineered T cells expressing a human leukocyte antigen A*02 (HLA-A2)-restricted T cell receptor (TCR) specific for a Wilms' tumor antigen 1 epitope, WT1_126-134 (T_TCR-C4). Resistance occurred despite persistence of functional therapeutic T cells and continuous expression of WT1 and HLA-A2 by the patient's AML cells. Analysis of the recurrent AML revealed expression of the standard proteasome, but limited expression of the immunoproteasome, specifically the beta subunit 1i (β1i), which is required for presentation of WT1_126-134. An analysis of a second patient treated with T_TCR-C4 demonstrated specific loss of AML cells coexpressing β1i and WT1. To determine whether the WT1 protein continued to be processed and presented in the absence of immunoproteasome processing, we identified and tested a TCR targeting an alternative, HLA-A2-restricted WT1_37-45 epitope that was generated by immunoproteasome-deficient cells, including WT1-expressing solid tumor lines. T cells expressing this TCR (T_TCR37-45) killed the first patients' relapsed AML resistant to WT1_126-134 targeting, as well as other primary AML, in vitro. T_TCR37-45 controlled solid tumor lines lacking immunoproteasome subunits both in vitro and in an NSG mouse model. As proteasome composition can vary in AML, defining and preferentially targeting these proteasome-independent epitopes may maximize therapeutic efficacy and potentially circumvent AML immune evasion by proteasome-related immunoediting.

Relationship between leukaemic stem cells and hematopoietic stem cells and their clinical application

The world is aging and with it an associated increase in malignancies. Haematological malignancies especially Acute Myeloid Leukemia (AML) are no exception to this trend. With scientific advances, development of new AML treatments has improved patient mortality. One future research interest would be Leukeamic Stem Cells (LSC). This review aims to briefly highlight main LSC characteristics and their relationship with hematopoietic stem cells. Key LSC characteristics include dysregulated apoptosis, capacity for self-renewal, genomic instability, dysregulated energetics, immune privilege and an altered tumor microenvironment. Similar characteristics are also found in HSCs though in a regulated form. Classifying these characteristics will aid in the development of clinical biomarkers for LSC which is a potential clinical application of LSC biology. LSC biomarkers might prove to be critical in future AML management through improving accuracy of AML diagnosis, providing targeted treatment to minimize side effects, refinement of prognosis and relapse risk for earlier intervention.

An Update on Immune Based Therapies in Acute Myeloid Leukemia: 2021 and Beyond!

Despite advances in the treatment of acute myeloid leukemia (AML), relapse is still widely observed and represents the major cause of death among patients with AML. Treatment options in the relapse setting are limited, still relying predominantly on allogeneic hematopoietic stem cell transplantation (allo-HSCT) and cytotoxic chemotherapy, with poor outcomes. Novel targeted and venetoclax-based combinations are being investigated and have shown encouraging results. Immune checkpoint inhibitors in combination with low-intensity chemotherapy demonstrated encouraging response rates and survival among patients with relapsed and/or refractory (R/R) AML, especially in the pre- and post-allo-HSCT setting. Blocking the CD47/SIRPα pathway is another strategy that showed robust anti-leukemic activity, with a response rate of around 70% and an encouraging median overall survival in patients with newly diagnosed, higher-risk myelodysplastic syndrome and patients with AML with a TP53 mutation. One approach that was proven to be very effective in the relapsed setting of lymphoid malignancies is chimeric antigen receptor (CAR) T cells. It relies on the infusion of genetically engineered T cells capable of recognizing specific epitopes on the surface of leukemia cells. In AML, different CAR constructs with different target antigens have been evaluated and demonstrated safety and feasibility in the R/R setting. However, the difficulty of potently targeting leukemic blasts in AML while sparing normal cells represents a major limitation to their use, and strategies are being tested to overcome this obstacle. A different approach is based on endogenously redirecting the patient's system cells to target and destroy leukemic cells via bispecific T-cell engagers (BiTEs) or dual antigen receptor targeting (DARTs). Early results have demonstrated the safety and feasibility of these agents, and research is ongoing to develop BiTEs with longer half-life, allowing for less frequent administration schedules and developing them in earlier and lower disease burden settings.

Newly Found Peacekeeper: Potential of CD8+ Tregs for Graft-Versus-Host Disease

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains the most effective and potentially curative treatment for a variety of hematologic malignancies. However, graft-versus-host disease (GVHD) is a major obstacle that limits wide application of allo-HSCT, despite the development of prophylactic strategies. Owing to experimental and clinical advances in the field, GVHD is characterized by disruption of the balance between effector and regulatory immune cells, resulting in higher inflammatory cytokine levels. A reduction in regulatory T cells (Tregs) has been associated with limiting recalibration of inflammatory overaction and maintaining immune tolerance. Moreover, accumulating evidence suggests that immunoregulation may be useful for preventing GVHD. As opposed to CD4⁺ Tregs, the CD8⁺ Tregs population, which constitutes an important proportion of all Tregs, efficiently attenuates GVHD while sparing graft-versus-leukemic (GVL) effects. CD8⁺ Tregs may provide another form of cellular therapy for preventing GVHD and preserving GVL effects, and understanding the underlying mechanisms that different from those of CD4⁺ Tregs is significant. In this review, we summarize preclinical experiments that have demonstrated the role of CD8⁺ Tregs during GVHD and attempted to obtain optimized CD8⁺ Tregs. Notably, although optimized CD8⁺ Tregs have obvious advantages, more exploration is needed to determine how to apply them in the clinic.

Clonal expansion of CD8+ T cells reflects graft-versus-leukemia activity and precedes durable remission following DLI

GVL activity in patients receiving DLI for relapse after allogeneic hematopoietic stem cell transplantation is associated with clonal expansion of CD8⁺ T cells.

Absence of clonal expansion of the CD8⁺TRB repertoire after DLI predicts relapse at a median time of 11.2 months before clinical diagnosis.

Donor lymphocyte infusion (DLI) is a standard of care for relapse of acute myeloid leukemia after allogeneic hematopoietic stem cell transplantation. Currently it is poorly understood how and when CD8⁺ αβ T cells exert graft-versus-leukemia (GVL) activity after DLI. Also, there is no reliable biomarker to monitor GVL activity of the infused CD8⁺ T cells. Therefore, we analyzed the dynamics of CD8⁺ αβ T-cell clones in patients with DLI. In this prospective clinical study of 29 patients, we performed deep T-cell receptor β (TRB ) sequencing of sorted CD8⁺ αβ T cells to track patients’ repertoire changes in response to DLI. Upon first occurrence of GVL, longitudinal analyses revealed a preferential expansion of distinct CD8⁺TRB clones (n = 14). This did not occur in samples of patients without signs of GVL (n = 11). Importantly, early repertoire changes 15 days after DLI predicted durable remission for the 36-month study follow-up. Furthermore, absence of clonal outgrowth of the CD8⁺TRB repertoire after DLI was an early biomarker that predicted relapse at a median time of 11.2 months ahead of actual diagnosis. Additionally, unbiased sample analysis regardless of the clinical outcome revealed that patients with decreasing CD8⁺TRB diversity at day 15 after DLI (n = 13) had a lower relapse incidence (P = .0040) compared with patients without clonal expansion (n = 6). In conclusion, CD8⁺TRB analysis may provide a reliable tool for predicting the efficacy of DLI and holds the potential to identify patients at risk for progression and relapse after DLI.

Innate Immune Mechanisms and Immunotherapy of Myeloid Malignancies

Similar to other cancers, myeloid malignancies are thought to subvert the immune system during their development. This subversion occurs via both malignant cell-autonomous and non-autonomous mechanisms and involves manipulation of the innate and adaptive immune systems. Multiple strategies are being studied to rejuvenate, redirect, or re-enforce the immune system in order to fight off myeloid malignancies. So far, the most successful strategies include interferon treatment and antibody-based therapies, though chimeric antigen receptor (CAR) cells and immune checkpoint inhibitors are also promising therapies. In this review, we discuss the inherent immune mechanisms of defense against myeloid malignancies, currently-approved agents, and agents under investigation. Overall, we evaluate the efficacy and potential of immuno-oncology in the treatment of myeloid malignancies.

Antibody-drug conjugates plus Janus kinase inhibitors enable MHC-mismatched allogeneic hematopoietic stem cell transplantation

Despite the curative potential of hematopoietic stem cell transplantation (HSCT), conditioning-associated toxicities preclude broader clinical application. Antibody-drug conjugates (ADC) provide an attractive approach to HSCT conditioning that minimizes toxicity while retaining efficacy. Initial studies of ADC conditioning have largely focused on syngeneic HSCT. However, to treat acute leukemias or induce tolerance for solid organ transplantation, this approach must be expanded to allogeneic HSCT (allo-HSCT). Using murine allo-HSCT models, we show that pharmacologic Janus kinase 1/2 (JAK1/2) inhibition combined with CD45- or cKit-targeted ADCs enables robust multilineage alloengraftment. Strikingly, myeloid lineage donor chimerism exceeding 99% was achievable in fully MHC-mismatched HSCT using this approach. Mechanistic studies using the JAK1/2 inhibitor baricitinib revealed marked impairment of T and NK cell survival, proliferation and effector function. NK cells were exquisitely sensitive to JAK1/2 inhibition due to interference with IL-15 signaling. Unlike irradiated mice, ADC-conditioned mice did not develop pathogenic graft-versus-host alloreactivity when challenged with mismatched T cells. Finally, the combination of ADCs and baricitinib balanced graft-versus-host disease and graft-versus-leukemia responses in delayed donor lymphocyte infusion models. Our allo-HSCT conditioning strategy exemplifies the promise of immunotherapy to improve the safety of HSCT for treating hematologic diseases.

Immunometabolic Therapeutic Targets of Graft-versus-Host Disease (GvHD)

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative option in the treatment of aggressive malignant and non-malignant blood disorders. However, the benefits of allo-HSCT can be compromised by graft-versus-host disease (GvHD), a prevalent and morbid complication of allo-HSCT. GvHD occurs when donor immune cells mount an alloreactive response against host antigens due to histocompatibility differences between the donor and host, which may result in extensive tissue injury. The reprogramming of cellular metabolism is a feature of GvHD that is associated with the differentiation of donor CD4+ cells into the pathogenic Th1 and Th17 subsets along with the dysfunction of the immune-suppressive protective T regulatory cells (Tregs). The activation of glycolysis and glutaminolysis with concomitant changes in fatty acid oxidation metabolism fuel the anabolic activities of the proliferative alloreactive microenvironment characteristic of GvHD. Thus, metabolic therapies such as glycolytic enzyme inhibitors and fatty acid metabolism modulators are a promising therapeutic strategy for GvHD. We comprehensively review the role of cellular metabolism in GvHD pathogenesis, identify candidate therapeutic targets, and describe potential strategies for augmenting immunometabolism to ameliorate GvHD.

From Immune Dysregulations to Therapeutic Perspectives in Myelodysplastic Syndromes: A Review

The pathophysiology of myelodysplastic syndromes (MDSs) is complex and often includes immune dysregulation of both the innate and adaptive immune systems. Whereas clonal selection mainly involves smoldering inflammation, a cellular immunity dysfunction leads to increased apoptosis and blast proliferation. Addressing immune dysregulations in MDS is a recent concept that has allowed the identification of new therapeutic targets. Several approaches targeting the different actors of the immune system have therefore been developed. However, the results are very heterogeneous, indicating the need to improve our understanding of the disease and interactions between chronic inflammation, adaptive dysfunction, and somatic mutations. This review highlights current knowledge of the role of immune dysregulation in MDS pathophysiology and the field of new drugs.

Immunotherapy for Acute Myeloid Leukemia: Allogeneic hematopoietic cell transplantation is here to stay

Acute Myeloid Leukemia (AML) represents 1 % of all new cancer diagnosis made annually in the US and has a five-year survival of 30 %. Traditional treatment includes aggressive induction therapy followed by consolidation therapy that may include a hematopoietic stem cell transplant (HSCT). Thus far, HSCT remains the only potentially curative therapy for many patients with AML owing to the graft-versus-leukemia effect elicited by this treatment. The use of novel therapies, specifically immunotherapy, in the treatment of AML has been limited by the lack of appropriate target antigens, therapy associated toxicities and variable success with treatment. Antigenic variability on leukemia cells and the sharing of antigens by malignant and non-malignant cells makes the identification of appropriate antigens problematic. While studies with immunotherapeutic agents are underway, prior investigations have demonstrated a mixed response with some studies prematurely discontinued due to associated toxicities. This review presents a discussion of the envisioned role of immunotherapy in the treatment of AML in the setting of mixed therapeutic success and potentially lethal toxicities.

Adoptive immunotherapy with double-bright (CD56bright /CD16bright ) expanded natural killer cells in patients with relapsed or refractory acute myeloid leukaemia: a proof-of-concept study

Patients with acute myeloid leukaemia (AML) have a five-year survival rate of 28·7%. Natural killer (NK)-cell have anti-leukaemic activity. Here, we report on a series of 13 patients with high-risk R/R AML, treated with repeated infusions of double-bright (CD56^bright /CD16^bright ) expanded NK cells at an academic centre in Brazil. NK cells from HLA-haploidentical donors were expanded using K562 feeder cells, modified to express membrane-bound interleukin-21. Patients received FLAG, after which cryopreserved NK cells were thawed and infused thrice weekly for six infusions in three dose cohorts (10⁶ -10⁷ cells/kg/infusion). Primary objectives were safety and feasibility. Secondary endpoints included overall response (OR) and complete response (CR) rates at 28-30 days after the first infusion. Patients received a median of five prior lines of therapy, seven with intermediate or adverse cytogenetics, three with concurrent central nervous system (CNS) leukaemia, and one with concurrent CNS mycetoma. No dose-limiting toxicities, infusion-related fever, or cytokine release syndrome were observed. An OR of 78·6% and CR of 50·0% were observed, including responses in three patients with CNS disease and clearance of a CNS mycetoma. Multiple infusions of expanded, cryopreserved NK cells were safely administered after intensive chemotherapy in high-risk patients with R/R AML and demonstrated encouraging outcomes.

Donor lymphocyte infusions after first allogeneic hematopoietic stem-cell transplantation in adults with acute myeloid leukemia: a single-center landmark analysis

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is potentially curative for acute myeloid leukemia (AML). The inherent graft-versus-leukemia activity (GvL) may be optimized by donor lymphocyte infusions (DLI). Here we present our single-center experience of DLI use patterns and effectiveness, based on 342 consecutive adult patients receiving a first allo-HSCT for AML between 2009 and 2017. The median age at transplantation was 57 years (range 19-79), and the pre-transplant status was active disease in 58% and complete remission (CR) in 42% of cases. In a combined landmark analysis, patients in CR on day +30 and alive on day +100 were included. In this cohort (n=292), 93 patients received cryopreserved aliquots of peripheral blood-derived grafts for DLI (32%) and median survival was 55.7 months (2-year/5-year probability: 62%/49%). Median survival for patients receiving a first dose of DLI "preemptively," in the absence of relapse and guided by risk marker monitoring (preDLI; n=42), or only after hematological relapse (relDLI; n=51) was 40.9 months (2-year/5-year: 64%/43%) vs 10.4 months (2-year/5-year: 26%/10%), respectively. Survival was inferior when preDLI was initiated at a time of genetic risk marker detection vs mixed chimerism or clinical risk only. Time to first-dose preDLI vs time to first-dose relDLI was similar, suggesting that early warning and intrinsically lower dynamics of AML recurrence may contribute to effectiveness of preDLI-modified GvL activity. Future refinements of the preemptive DLI concept will benefit from collaborative efforts to diagnose measurable residual disease more reliably across the heterogeneous genomic spectrum of AML.

Epigenetic Modification of Death Receptor Genes for TRAIL and TRAIL Resistance in Childhood B-Cell Precursor Acute Lymphoblastic Leukemia

Immunotherapies specific for B-cell precursor acute lymphoblastic leukemia (BCP-ALL), such as anti-CD19 chimeric antigen receptor (CAR) T-cells and blinatumomab, have dramatically improved the therapeutic outcome in refractory cases. In the anti-leukemic activity of those immunotherapies, TNF-related apoptosis-inducing ligand (TRAIL) on cytotoxic T-cells plays an essential role by inducing apoptosis of the target leukemia cells through its death receptors (DR4 and DR5). Since there are CpG islands in the promoter regions, hypermethylation of the DR4 and DR5 genes may be involved in resistance of leukemia cells to immunotherapies due to TRAIL-resistance. We analyzed the DR4 and DR5 methylation status in 32 BCP-ALL cell lines by sequencing their bisulfite PCR products with a next-generation sequencer. The DR4 and DR5 methylation status was significantly associated with the gene and cell-surface expression levels and the TRAIL-sensitivities. In the clinical samples at diagnosis (459 cases in the NOPHO study), both DR4 and DR5 genes were unmethylated in the majority of cases, whereas methylated in several cases with dic(9;20), MLL-rearrangement, and hypodiploidy, suggesting that evaluation of methylation status of the DR4 and DR5 genes might be clinically informative to predict efficacy of immunotherapy in certain cases with such unfavorable karyotypes. These observations provide an epigenetic rational for clinical efficacy of immunotherapy in the vast majority of BCP-ALL cases.

The Potential Role of the Intestinal Micromilieu and Individual Microbes in the Immunobiology of Chimeric Antigen Receptor T-Cell Therapy

Cellular immunotherapy with chimeric antigen receptor (CAR)-T cells (CARTs) represents a breakthrough in the treatment of hematologic malignancies. CARTs are genetically engineered hybrid receptors that combine antigen-specificity of monoclonal antibodies with T cell function to direct patient-derived T cells to kill malignant cells expressing the target (tumor) antigen. CARTs have been introduced into clinical medicine as CD19-targeted CARTs for refractory and relapsed B cell malignancies. Despite high initial response rates, current CART therapies are limited by a long-term loss of antitumor efficacy, the occurrence of toxicities, and the lack of biomarkers for predicting therapy and toxicity outcomes. In the past decade, the gut microbiome of mammals has been extensively studied and evidence is accumulating that human health, apart from our own genome, largely depends on microbes that are living in and on the human body. The microbiome encompasses more than 1000 bacterial species who collectively encode a metagenome that guides multifaceted, bidirectional host-microbiome interactions, primarily through the action of microbial metabolites. Increasing knowledge has been accumulated on the role of the gut microbiome in T cell-driven anticancer immunotherapy. It has been shown that antibiotics, dietary components and gut microbes reciprocally affect the efficacy and toxicity of allogeneic hematopoietic cell transplantation (allo HCT) as the prototype of T cell-based immunotherapy for hematologic malignancies, and that microbiome diversity metrics can predict clinical outcomes of allo HCTs. In this review, we will provide a comprehensive overview of the principles of CD19-CART immunotherapy and major aspects of the gut microbiome and its modulators that impact antitumor T cell transfer therapies. We will outline i) the extrinsic and intrinsic variables that can contribute to the complex interaction of the gut microbiome and host in CART immunotherapy, including ii) antibiotic administration affecting loss of colonization resistance, expansion of pathobionts and disturbed mucosal and immunological homeostasis, and ii) the role of specific gut commensals and their microbial virulence factors in host immunity and inflammation. Although the role of the gut microbiome in CART immunotherapy has only been marginally explored so far, this review may open a new chapter and views on putative connections and mechanisms.

Parametric Imaging of Contrast-Enhanced Ultrasound (CEUS) for the Evaluation of Acute Gastrointestinal Graft-Versus-Host Disease

In recent years contrast-enhanced ultrasound (CEUS) has been an emerging diagnostic modality for the detection of acute gastrointestinal (GI) graft-versus-host disease (GvHD) in patients after allogeneic stem cell transplantation. However, broad clinical usage has been partially limited by its high dependence on the expertise of an experienced examiner. Thus, the aim of this study was to facilitate detection of acute GI GvHD by implementing false color-coded parametric imaging of CEUS. As such, two inexperienced examiners with basic knowledge in abdominal and vascular ultrasound analyzed parametric images obtained from patients with clinical suspicion for acute GvHD in a blinded fashion. As diagnostic gold standard, histopathological GvHD severity score on intestinal biopsies obtained from lower GI tract endoscopy was performed. The evaluation of parametric images by the two inexperienced ultrasound examiners in patients with histological confirmation of acute GI GvHD was successful in 17 out of 19 patients (89%) as opposed to analysis of combined B-mode ultrasound, strain elastography, and CEUS by an experienced examiner, which was successful in 18 out of 19 of the patients (95%). Therefore, CEUS with parametric imaging of the intestine was technically feasible and has the potential to become a valuable diagnostic tool for rapid and widely accessible detection of acute GvHD in clinical practice.

State-of-Art of Cellular Therapy for Acute Leukemia

With recent clinical breakthroughs, immunotherapy has become the fourth pillar of cancer treatment. Particularly, immune cell-based therapies have been envisioned as a promising treatment option with curative potential for leukemia patients. Hence, an increasing number of preclinical and clinical studies focus on various approaches of immune cell-based therapy for treatment of acute leukemia (AL). However, the use of different immune cell lineages and subsets against different types of leukemia and patient disease statuses challenge the interpretation of the clinical applicability and outcome of immune cell-based therapies. This review aims to provide an overview on recent approaches using various immune cell-based therapies against acute B-, T-, and myeloid leukemias. Further, the apparent limitations observed and potential approaches to overcome these limitations are discussed.

Chimerism, the Microenvironment and Control of Leukemia

Transplantation of allogeneic hematopoietic cells faces two barriers: failure of engraftment due to a host versus graft reaction, and the attack of donor cells against the patient, the graft versus host (GVH) reaction. This reaction may lead to GVH disease (GVHD), but in patients transplanted due to leukemia or other malignant disorders, this may also convey the benefit of a graft versus leukemia (GVL) effect. The interplay of transplant conditioning with donor and host cells and the environment in the patient is complex. The microbiome, particularly in the intestinal tract, profoundly affects these interactions, directly and via soluble mediators, which also reach other host organs. The microenvironment is further altered by the modifying effect of malignant cells on marrow niches, favoring the propagation of the malignant cells. The development of stable mixed donor/host chimerism has the potential of GVHD prevention without necessarily increasing the risk of relapse. There has been remarkable progress with novel conditioning regimens and selective T-cell manipulation aimed at securing engraftment while preventing GVHD without ablating the GVL effect. Interventions to alter the microenvironment and change the composition of the microbiome and its metabolic products may modify graft/host interactions, thereby further reducing GVHD, while enhancing the GVL effect. The result should be improved transplant outcome.

Oral health-related quality of life of patients with oral chronic graft-versus-host disease

Purpose

Symptoms of oral chronic graft-versus-host-disease (cGVHD) may significantly affect the oral health–related quality of life (OHRQoL). This study aimed to assess the OHRQoL in patients with oral cGVHD and to examine whether oral cGVHD symptoms, mucosal cGVHD, and salivary gland function correlated with OHRQoL.

Methods

Patients referred to the oral cGVHD outpatient clinic were included. Severity of oral mucosal cGVHD, oral cGVHD symptoms, and OHRQoL was assessed by the NIH OMS, NIH OSS, and OHIP-14, respectively. Unstimulated and stimulated whole salivary flow rates were determined and categorized into “hyposalivation,” “normal salivary flow,” and “hypersalivation.”

Results

Of 56 included patients, 80% had mild, moderate, or severe oral mucosal cGVHD. Mean total score of OHRQoL was 16.5 (±11.7), negatively affected by functional problems. Patients reported highest scores regarding oral sensitivity and xerostomia. Significant correlations were found between severity of oral pain and OHRQoL and between oral sensitivity and OHRQoL. No correlation was found between oral mucosal cGVHD and OHRQoL. Patients with hyposalivation, normal salivary flow, and hypersalivation reported equal levels of OHRQoL.

Conclusion

Results demonstrate that the OHRQoL was mostly negatively affected by complaints of oral pain and oral sensitivity and less by the severity of oral mucosal cGVHD assessed by the NIH OMS score. Special attention of (oral) health care professionals for patients with oral cGVHD is mandatory to alleviate their symptoms and improve OHRQoL.

STING and transplantation: can targeting this pathway improve outcomes?

Stimulator of interferon genes (STING) is an innate immune sensor of cytoplasmic dsDNA originating from microorganisms and host cells. STING plays an important role in the regulation of murine graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and may be similarly activated during other transplantation modalities. In this review, we discuss STING in allo-HSCT and its prospective involvement in autologous HSCT (auto-HSCT) and solid organ transplantation (SOT), highlighting its unique role in nonhematopoietic, hematopoietic, and malignant cell types.

Conversion of AML-blasts to leukemia-derived dendritic cells (DCleu) in 'DC-culture-media' shifts correlations of released chemokines with antileukemic T-cell reactions

Dendritic cells (DC) and T-cells are mediators of CTL-responses. Autologous (from patients with acute myeloid leukaemia (AML) or myelodysplasia (MDS)) or allogeneic (donor)-T-cells stimulated by DC_leu, gain an efficient lysis of naive blasts, although not in every case. CXCL8, -9, -10, CCL2, -5 and Interleukin (IL-12) were quantified by Cytometric Bead Array (CBA) in supernatants from 5 DC-generating methods and correlated with AML-/MDS-patients' serum-values, DC-/T-cell-interactions/antileukemic T-cell-reactions after mixed lymphocyte culture (MLC) and patients' clinical course. The blast-lytic activity of T-cells stimulated with DC or mononuclear cells (MNC) was quantified in a cytotoxicity assay. Despite great variations of chemokine-levels, correlations with post-stimulation (after stimulating T-cells with DC in MLC) improved antileukemic T-cell activity were seen: higher released chemokine-values correlated with improved T-cells' antileukemic activity (compared to stimulation with blast-containing MNC) - whereas with respect to the corresponding serum values higher CXCL8-, -9-, and -10- but lower CCL5- and -2-release correlated with improved antileukemic activity of DC-stimulated (vs. blast-stimulated) T-cells. In DC-culture supernatants higher chemokine-values correlated with post-stimulation improved antileukemic T-cell reactivity, whereas higher serum-values of CXCL8, -9, and -10 but lower serum-values of CCL5 and -2 correlated with post-stimulation improved antileukemic T-cell-reactivity. In a context of 'DC'-stimulation (vs serum) this might point to a change of (CCL5 and -2-associated) functionality from a more 'inflammatory' or 'tumor-promoting' to a more 'antitumor'-reactive functionality. This knowledge could contribute to develop immune-modifying strategies that promote antileukemic (adaptive) immune-responses.

Granulocyte Colony-Stimulating Factor Effectively Mobilizes TCR γδ and NK Cells Providing an Allograft Potentially Enhanced for the Graft-Versus-Leukemia Effect for Allogeneic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potential cure for patients with hematological malignancies but substantial risks of recurrence of the malignant disease remain. TCR γδ and NK cells are perceived as potent innate effector cells in HSCT and have been associated with post-transplant protection from relapse in clinical studies. Immunocompetent cells from the donor are crucial for patient outcomes and peripheral blood stem cells (PBSC) are being increasingly applied as graft source. G-CSF is the preferential mobilizing agent in healthy donors for PBSC grafts, yet effects of G-CSF on TCR γδ and NK cells are scarcely uncovered and could influence the graft composition and potency of these cells. Therefore, we analyzed T and NK cell subsets and activation markers in peripheral blood samples of 49 donors before and after G-CSF mobilization and—for a subset of donors—also in the corresponding graft samples using multicolor flowcytometry with staining for CD3, CD4, CD8, TCRαβ, TCRγδ, Vδ1, Vδ2, HLA-DR, CD45RA, CD197, CD45RO, HLA-DR, CD16, CD56, and CD314. We found that TCR γδ cells were mobilized and harvested with an efficiency corresponding that of TCR αβ cells. For TCR γδ as well as for TCR αβ cells, G-CSF preferentially mobilized naïve and terminally differentiated effector (TEMRA) cells over memory cells. In the TCR γδ cell compartment, G-CSF preferentially mobilized cells of the nonVδ2 types and increased the fraction of HLA-DR positive TCR γδ cells. For NK cells, mobilization by G-CSF was increased compared to that of T cells, yet NK cells appeared to be less efficiently harvested than T cells. In the NK cell compartment, G-CSF-stimulation preserved the proportion of CD56dim NK effector cells which have been associated with relapse protection. The expression of the activating receptor NKG2D implied in anti-leukemic responses, was significantly increased in both CD56dim and CD56bright NK cells after G-CSF stimulation. These results indicate differentiated mobilization and altering properties of G-CSF which could improve the effects of donor TCR γδ and NK cells in the processes of graft-versus-leukemia for relapse prevention after HSCT.

High proportion of terminally differentiated regulatory T cells after allogeneic hematopoietic stem cell transplantation

It is now well-established that regulatory T cells (Treg) represent a heterogeneous group of CD4⁺ T cells. Previous studies have demonstrated that Treg homeostasis was impacted by allogeneic hematopoietic cell transplantation (allo-HCT) and particularly so in patients with chronic graft-versus-host disease (GVHD). Here, we first assessed the ability of various Treg subsets to phosphorylate STAT5 in response to IL-2 or IL-7 stimulation in vitro. We then compared the frequencies of different Treg subtypes in healthy controls as well as in allo-HCT patients with or without chronic GVHD. The highest phosphorylated STAT5 (pSTAT5) signal in response to IL-2 was observed in the CD45RO⁺CD26^-CD39⁺HLA-DR⁺ Treg fraction. In contrast, naive Treg were mostly less susceptible to IL-2 stimulation in vitro. Following IL-7 stimulation, most Treg subpopulations upregulated pSTAT5 expression but to a lesser extent than conventional T cells. Compared to healthy controls, allo-HCT patients had lower frequencies of the naive CD45RA^brightCD26⁺ Treg subpopulation but higher frequencies of the most differentiated memory CD45RO⁺CD26^-CD39⁺ Treg subpopulations. Further, unbiased analysis revealed that six Treg clusters characterized by high expression of CD25, HLA-DR, and ICOS were significantly more frequent in patients with no or with limited chronic GVHD than in those with moderate/severe chronic GVHD.

MyD88 Costimulation in Donor CD8+ T Cells Enhances the Graft-versus-Tumor Effect in Murine Hematopoietic Cell Transplantation

Donor-derived lymphocytes from allogeneic hematopoietic cell transplantation (allo-HCT) or donor lymphocyte infusion can mediate eradication of host tumor cells in a process labeled the graft-versus-tumor (GVT) effect. Unfortunately, these treatments have produced limited results in various types of leukemia because of an insufficient GVT effect. In this context, molecular engineering of donor lymphocytes to increase the GVT effect may benefit cancer patients. Activating MyD88 signaling in CD8+ T cells via TLR enhances T cell activation and cytotoxicity. However, systemic administration of TLR ligands to stimulate MyD88 could induce hyperinflammation or elicit protumor effects. To circumvent this problem, we devised a synthetic molecule consisting of MyD88 linked to the ectopic domain of CD8a (CD8α:MyD88). We used this construct to test the hypothesis that MyD88 costimulation in donor CD8+ T cells increases tumor control following allo-HCT in mice by increasing T cell activation, function, and direct tumor cytotoxicity. Indeed, an increase in both in vitro and in vivo tumor control was observed with CD8α:MyD88 T cells. This increase in the GVT response was associated with increased T cell expansion, increased functional capacity, and an increase in direct cytotoxic killing of the tumor cells. However, MyD88 costimulation in donor CD8+ T cells was linked to increased yet nonlethal graft-versus-host disease in mice treated with these engineered CD8+ T cells. Given these observations, synthetic CD8α:MyD88 donor T cells may represent a unique and versatile approach to enhance the GVT response that merits further refinement to improve the effectiveness of allo-HCT.

Evaluation of the performance of a prior tacrolimus population pharmacokinetic kidney transplant model among adult allogeneic hematopoietic stem cell transplant patients

Abstract

Tacrolimus is a calcineurin inhibitor used to prevent acute graft versus host disease in adult patients receiving allogeneic hematopoietic stem cell transplantation (HCT). Previous population pharmacokinetic (PK) models have been developed in solid organ transplant, yet none exists for patients receiving HCT. The primary objectives of this study were to (1) use a previously published population PK model in adult patients who underwent kidney transplant and apply it to allogeneic HCT; (2) evaluate model‐predicted tacrolimus steady‐state trough concentrations and simulations in patients receiving HCT; and (3) evaluate covariates that affect tacrolimus PK in allogeneic HCT. A total of 252 adult patients receiving allogeneic HCT were included in the study. They received oral tacrolimus twice daily (0.03 mg/kg) starting 3 days prior to transplant. Data for these analyses included baseline clinical and demographic data, genotype data for single nucleotide polymorphisms in CYP3A4/5 and ABCB1, and the first tacrolimus steady‐state trough concentration. A dosing simulation strategy based on observed trough concentrations (rather than model‐based predictions) resulted in 12% more patients successfully achieving tacrolimus trough concentrations within the institutional target range (5–10 ng/ml). Stepwise covariate analyses identified HLA match and conditioning regimen (myeloablative vs. reduced intensity) as significant covariates. Ultimately, a previously published tacrolimus population PK model in kidney transplant provided a platform to help establish a model‐based dose adjustment strategy in patients receiving allogenic HCT, and identified HCT‐specific covariates to be considered for future prospective studies.

Dendritic Cells of Leukemic Origin: Specialized Antigen-Presenting Cells as Potential Treatment Tools for Patients with Myeloid Leukemia

The prognosis of elderly patients with acute myeloid leukemia (AML) and high-grade myelodysplastic syndrome (MDS) is limited due to the lack of therapy options and high relapse rates. Dendritic cell (DC)-based immunotherapy seems to be a promising treatment tool. DC are potent antigen-presenting cells and play a pivotal role on the interface of the innate and the adaptive immune system. Myeloid leukemia blasts can be converted to DC of leukemic origin (DC_leu), expressing costimulatory molecules along with the whole leukemic antigen repertoire of individual patients. These generated DC_leu are potent stimulators of various immune reactive cells and increase antileukemic immunity ex vivo. Here we review the generating process of DC/DC_leu from leukemic peripheral blood mononuclear cells as well as directly from leukemic whole blood with "minimized" Kits to simulate physiological conditions ex vivo. The purpose of adoptive cell transfer of DC/DC_leu as a vaccination strategy is discussed. A new potential therapy option with Kits for patients with myeloid leukemia, which would render an adoptive DC/DC_leu transfer unnecessary, is presented. In summary, DC/DC_leu-based therapies seem to be promising treatment tools for patients with AML or MDS but ongoing research including trials in animals and humans have to be performed.

A deep dive into UV-based phototherapy: Mechanisms of action and emerging molecular targets in inflammation and cancer

UV-based phototherapy (including psoralen plus UVA (PUVA), UVB and UVA1) has a long, successful history in the management of numerous cutaneous disorders. Photoresponsive diseases are etiologically diverse, but most involve disturbances in local (and occasionally systemic) inflammatory cells and/or abnormalities in keratinocytes that trigger inflammation. UV-based phototherapy works by regulating the inflammatory component and inducing apoptosis of pathogenic cells. This results in a fascinating and complex network of simultaneous events-immediate transcriptional changes in keratinocytes, immune cells, and pigment cells; the emergence of apoptotic bodies; and the trafficking of antigen-presenting cells in skin-that quickly transform the microenvironment of UV-exposed skin. Molecular elements in this system of UV recognition and response include chromophores, metabolic byproducts, innate immune receptors, neurotransmitters and mediators such as chemokines and cytokines, antimicrobial peptides, and platelet activating factor (PAF) and PAF-like molecules that simultaneously shape the immunomodulatory effects of UV and their interplay with the microbiota of the skin and beyond. Phototherapy's key effects-proapoptotic, immunomodulatory, antipruritic, antifibrotic, propigmentary, and pro-prebiotic-promote clinical improvement in various skin diseases such as psoriasis, atopic dermatitis (AD), graft-versus-host disease (GvHD), vitiligo, scleroderma, and cutaneous T-cell lymphoma (CTCL) as well as prevention of polymorphic light eruption (PLE). As understanding of phototherapy improves, new therapies (UV- and non-UV-based) are being developed that will modify regulatory T-cells (Treg), interact with (resident) memory T-cells and /or utilize agonists and antagonists as well as antibodies targeting soluble molecules such as cytokines and chemokines, transcription factors, and a variety of membrane-associated receptors.

Cutaneous manifestations of acute and chronic graft-versus-host disease

Graft-versus-host disease (GvHD) is a commonly occurring immunological reaction and frequent complication following allogeneic hematopoietic stem cell transplantation. Its highly diverse manifestations including skin involvement as the most common appearance of GvHD, can dramatically influence patient's quality of life, in particular in the chronic stage, in addition to patient's decreased survival outcome. Hence, the role of the dermatologist has become very crucial in an interdisciplinary setting, particularly since appearances of GvHD in the skin can be multifaceted and challenging. Clinical manifestation of the acute GvHD (aGvHD) is limited to erythematous maculopapular rash and oral mucosal lesions while the chronic form manifests in a wider range in a localized area or disseminated including involvement of nail, scalp and genital area. This article aims to provide a comprehensive overview on the variable cutaneous presentations of acute and chronic GvHD for a proper and early diagnosis on the one hand, and to discuss updated therapeutic options for both acute and chronic GvHD on the other hand, to initiate an adequate treatment to obtain the most beneficial clinical outcome.