Immune escape from a graft-versus-leukemia effect may play a role in the relapse of myeloid leukemias following allogeneic bone marrow transplantation

EZH2-driven immune evasion defines high-risk pediatric AML with t(16;21) FUS::ERG gene fusion

Minimal improvement in outcomes for high-risk pediatric acute myeloid leukemia (pAML) patients has been made in the past decades. Nowhere is this more evident than in patients carrying a t(16;21)(p11;q22) FUS::ERG translocation; quick time to relapse and universal failure of hematopoietic stem cell transplant contribute to one of the lowest survival rates in childhood leukemia. Here, we have identified a unique, defining immune-evasion phenotype in FUS::ERG pAML driven by EZH2 and characterized by loss of MHC class I and II molecules and immune co-stimulatory receptors. This loss of immune engagement, present at diagnosis, allows pervasiveness of blasts that prove resistant to standard treatment. We demonstrate that treatment with the FDA-approved EZH2 inhibitor tazemetostat, in combination with IFN-γ, reverses the phenotype, re-expresses MHC receptor expression, and reduces blast viability. EZH2 inhibitors provide a novel therapeutic option for this high-risk population and may prove a beneficial supplemental treatment for FUS::ERG pAML.

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.

High-expression of the innate-immune related gene UNC93B1 predicts inferior outcomes in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous hematological malignancy with dismal prognosis. Identification of better biomarkers remained a priority to improve established stratification and guide therapeutic decisions. Therefore, we extracted the RNA sequence data and clinical characteristics of AML from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression database (GTEx) to identify the key factors for prognosis. We found UNC93B1 was highly expressed in AML patients and significantly linked to poor clinical features (p < 0.05). We further validated the high expression of UNC93B1 in another independent AML cohort from GEO datasets (p < 0.001) and performed quantitative PCR of patient samples to confirm the overexpression of UNC93B1 in AML (p < 0.005). Moreover, we discovered high level of UNC93B1 was an independent prognostic factor for poorer outcome both in univariate analysis and multivariate regression (p < 0.001). Then we built a nomogram model based on UNC93B1 expression, age, FAB subtype and cytogenetic risk, the concordance index of which for predicting overall survival was 0.729 (p < 0.001). Time-dependent ROC analysis for predicting survival outcome at different time points by UNC93B1 showed the cumulative 2-year survival rate was 43.7%, and 5-year survival rate was 21.9%. The differentially expressed genes (DEGs) between two groups divided by UNC93B1 expression level were enriched in innate immune signaling and metabolic process pathway. Protein-protein interaction (PPI) network indicated four hub genes (S100A9, CCR1, MRC1 and CD1C) interacted with UNC93B1, three of which were also significantly linked to inferior outcome. Furthermore, we discovered high UNC93B1 tended to be infiltrated by innate immune cells, including Macrophages, Dendritic cells, Neutrophils, Eosinophils, and NK CD56dim cells. We also found UNC93B1 had a significantly positive correlation with CD14, CD68 and almost all Toll-like receptors. Finally, we revealed negatively correlated expression of UNC93B1 and BCL2 in AML and conjectured that high-UNC93B1 monocytic AML is more resistant to venetoclax. And we found high MCL-1 expression compensated for BCL-2 loss, thus, we proposed MCL-1 inhibitor might overcome the resistance of venetoclax in AML. Altogether, our findings demonstrated the utility of UNC93B1 as a powerful poor prognostic predictor and alternative therapeutic target.

Transcriptional Plasticity Drives Leukemia Immune Escape

Relapse of acute myeloid leukemia (AML) after allogeneic bone marrow transplantation has been linked to immune evasion due to reduced expression of major histocompatibility complex class II (MHCII) genes through unknown mechanisms. In this work, we developed CORENODE, a computational algorithm for genome-wide transcription network decomposition that identified a transcription factor (TF) tetrad consisting of IRF8, MYB, MEF2C, and MEIS1, regulating MHCII expression in AML cells. We show that reduced MHCII expression at relapse is transcriptionally driven by combinatorial changes in the expression of these TFs, where MYB and IRF8 play major opposing roles, acting independently of the IFNγ/CIITA pathway. Beyond the MHCII genes, MYB and IRF8 antagonistically regulate a broad genetic program responsible for cytokine signaling and T-cell stimulation that displays reduced expression at relapse. A small number of cells with altered TF abundance and silenced MHCII expression are present at the time of initial leukemia diagnosis, likely contributing to eventual relapse.

SIGNIFICANCE

Our findings point to an adaptive transcriptional mechanism of AML evolution after allogeneic transplantation whereby combinatorial fluctuations of TF expression under immune pressure result in the selection of cells with a silenced T-cell stimulation program. This article is highlighted in the In This Issue feature, p. 369.

Azacitidine maintenance therapy post-allogeneic stem cell transplantation in poor-risk acute myeloid leukemia

OBJECTIVE/BACKGROUND

Allogeneic hematopoietic stem cell transplant (HSCT) is the potential curative modality for poor-risk acute myeloid leukemia (AML), relapse remains the main reason for transplant failure. Early-phase studies showed azacitidine is safe for post-transplant maintenance therapy in AML.

METHODS

We performed a single institutional prospective cohort study to evaluate the benefit of azacitidine maintenance therapy following allogeneic HSCT in poor-risk AML. The main objective of this study is to generate a hypothesis aiming to optimize post-transplantation outcomes in poor-risk AML. Forty-nine adults with poor-risk AML who underwent allogeneic HSCT were evaluated in a nonrandomized prospective cohort fashion. Thirty-one participants received post-transplant azacitidine (32 mg/m²) on Days 1-5 for a 28-day treatment cycle beginning approximately 40 days after transplantation. The study was controlled using 18 matched individuals who were on a noninterventional surveillance protocol.

RESULTS

The relapse rate was significantly higher in the control cohort (66.67%) versus (25.81%) in the azacitidine maintenance cohort (p < .005). Time to relapse was significantly prolonged by azacitidine maintenance, not reached versus 4.1 months in the control arm (p < .0001). In addition, median overall survival was lower in the control cohort at 7.6 versus 27.4 months in the interventional cohort (p < .0001). At a median follow-up of 24 months, incidence of graft-versus-host disease (GVHD) did not differ between study groups (p = .325). In both cohorts, minimal residual disease was correlated with higher hazard of relapse (95% confidence interval, 2.31-13.74; p < .001).

CONCLUSION

We conclude that low dose azacitidine maintenance following allogeneic HSCT in poor-risk AML, decreased relapse rate, and increased both the time to relapse and overall survival without increased risk of GVHD.

Post-transplantation cyclophosphamide reduces the incidence of acute graft-versus-host disease in patients with acute myeloid leukemia/myelodysplastic syndromes who receive immune checkpoint inhibitors after allogeneic hematopoietic stem cell transplantation

Background

Immune checkpoint inhibitors (ICIs) are being used after allogeneic hematopoietic stem cell transplantation (alloHCT) to reverse immune dysfunction. However, a major concern for the use of ICIs after alloHCT is the increased risk of graft-versus-host disease (GVHD). We analyzed the association between GVHD prophylaxis and frequency of GVHD in patients who had received ICI therapy after alloHCT.

Methods

A retrospective study was performed in 21 patients with acute myeloid leukemia (n=16) or myelodysplastic syndromes (n=5) who were treated with antiprogrammed cell death protein 1 (16 patients) or anticytotoxic T lymphocyte-associated antigen 4 (5 patients) therapy for disease relapse after alloHCT. Associations between the type of GVHD prophylaxis and incidence of GVHD were analyzed.

Results

Four patients (19%) developed acute GVHD. The incidence of acute GVHD was associated only with the type of post-transplantation GVHD prophylaxis; none of the other variables included (stem cell source, donor type, age at alloHCT, conditioning regimen and prior history of GVHD) were associated with the frequency of acute GVHD. Twelve patients received post-transplantation cyclophosphamide (PTCy) for GVHD prophylaxis. Patients who received PTCy had a significantly shorter median time to initiation of ICI therapy after alloHCT compared with patients who did not receive PTCy (median 5.1 months compared with 26.6 months). Despite early ICI therapy initiation, patients who received PTCy had a lower observed cumulative incidence of grades 2–4 acute GVHD compared with patients who did not receive PTCy (16% compared with 22%; p=0.7). After controlling for comorbidities and time from alloHCT to ICI therapy initiation, the analysis showed that PTCy was associated with a 90% reduced risk of acute GVHD (HR 0.1, 95% CI 0.02 to 0.6, p=0.01).

Conclusions

ICI therapy for relapsed acute myeloid leukemia/myelodysplastic syndromes after alloHCT may be a safe and feasible option. PTCy appears to decrease the incidence of acute GVHD in this cohort of patients.

Identification of an Immune-Related Gene Signature Based on Immunogenomic Landscape Analysis to Predict the Prognosis of Adult Acute Myeloid Leukemia Patients

Acute myeloid leukemia (AML) is a hematopoietic malignancy characterized by highly heterogeneous molecular lesions and cytogenetic abnormalities. Immune disorders in AML and impaired immune cell function have been found to be associated with abnormal karyotypes in AML patients. Immunotherapy has become an alternative therapeutic method that can improve the outcomes of AML patients. For solid tumors, the expression patterns of genes associated with the immune microenvironment provide valuable prognostic information. However, the prognostic roles of immune genes in AML have not been studied as yet. In this study, we identified 136 immune-related genes associated with overall survival in AML patients through a univariate Cox regression analysis using data from TCGA-AML and GTEx datasets. Next, we selected 24 hub genes from among the 136 genes based on the PPI network analysis. The 24 immune-related hub genes further underwent multivariate Cox regression analysis and LASSO regression analysis. Finally, a 6 immune-related gene signature was constructed to predict the prognosis of AML patients. The function of the hub IRGs and the relationships between hub IRGs and transcriptional factors were investigated. We found that higher levels of expression of CSK, MMP7, PSMA7, PDCD1, IKBKG, and ISG15 were associated with an unfavorable prognosis of AML patients. Meanwhile, patients in the TCGA-AML datasets were divided into a high risk score group and a low risk score group, based on the median risk score value. Patients in the high risk group tended to show poorer prognosis [P = 0.00019, HR = 1.89 (1.26–2.83)]. The area under the curve (AUC) was 0.6643. Multivariate Cox Regression assay confirmed that the 6 IRG signature was an independent prognostic factor for AML. The prognostic role of the immune related-gene signature was further validated using an independent AML dataset, GSE37642. In addition, patients in the high risk score group in the TCGA dataset were found to be of an advanced age, IDH mutation, and M5 FAB category. These results suggested that the proposed immune related-gene signature may serve as a potential prognostic tool for AML patients.

Recurrent genetic HLA loss in AML relapsed after matched unrelated allogeneic hematopoietic cell transplantation

Immune evasion is a hallmark of cancer and a central mechanism underlying acquired resistance to immune therapy. In allogeneic hematopoietic cell transplantation (alloHCT), late relapses can arise after prolonged alloreactive T-cell control, but the molecular mechanisms of immune escape remain unclear. To identify mechanisms of immune evasion, we performed a genetic analysis of serial samples from 25 patients with myeloid malignancies who relapsed ≥1 year after alloHCT. Using targeted sequencing and microarray analysis to determine HLA allele-specific copy number, we identified copy-neutral loss of heterozygosity events and focal deletions spanning class 1 HLA genes in 2 of 12 recipients of matched unrelated-donor HCT and in 1 of 4 recipients of mismatched unrelated-donor HCT. Relapsed clones, although highly related to their antecedent pretransplantation malignancies, frequently acquired additional mutations in transcription factors and mitogenic signaling genes. Previously, the study of relapse after haploidentical HCT established the paradigm of immune evasion via loss of mismatched HLA. Here, in the context of matched unrelated-donor HCT, HLA loss provides genetic evidence that allogeneic immune recognition may be mediated by minor histocompatibility antigens and suggests opportunities for novel immunologic approaches for relapse prevention.

Immune Escape after Hematopoietic Stem Cell Transplantation (HSCT): From Mechanisms to Novel Therapies

Acute myeloid leukemia (AML) is the most common type of acute leukemia in adults. Recent advances in understanding its molecular basis have opened the way to new therapeutic strategies, including targeted therapies. However, despite an improvement in prognosis it has been documented in recent years (especially in younger patients) that allogenic hematopoietic stem cell transplantation (allo-HSCT) remains the only curative treatment in AML and the first therapeutic option for high-risk patients. After allo-HSCT, relapse is still a major complication, and is observed in about 50% of patients. Current evidence suggests that relapse is not due to clonal evolution, but instead to the ability of the AML cell population to escape immune control by a variety of mechanisms including the altered expression of HLA-molecules, production of anti-inflammatory cytokines, relevant metabolic changes and expression of immune checkpoint (ICP) inhibitors capable of “switching-off” the immune response against leukemic cells. Here, we review the main mechanisms of immune escape and identify potential strategies to overcome these mechanisms.

Checkpoint inhibitors in AML: are we there yet?

Immunotherapy is distinct from traditional chemotherapy in that it acts on immune cells rather than cancer cells themselves. Monoclonal antibodies targeting immune checkpoints on T cells - CTLA-4 and PD-1 - and PD-L1 on the cells of immune microenvironment are now approved for clinical use in several solid tumors and hematological malignancies. This article provides a general overview of the use of checkpoint inhibitors in hematologic malignancies with a special focus in acute myeloid leukemia.

Clonal evolution and immune evasion in posttransplantation relapses

Despite the considerable improvements witnessed over the last few decades in the feasibility and safety of allogeneic hematopoietic cell transplantation (allo-HCT) for hematological malignancies, disease relapse continues to represent a frequent occurrence, with largely unsatisfactory salvage options. Recent studies have shed new light on the biology of posttransplantation relapses, demonstrating that they can frequently be explained using an evolutionary perspective: The changes in disease clonal structure and immunogenicity that are often documented at relapse may in fact represent the end results of a process of selection, allowing the outgrowth of variants that are more capable of resisting the therapeutic control of allo-HCT. This review provides an overview of the mechanisms forming the basis of relapse, including clonal evolution, gain of tropism for privileged sites, genomic and nongenomic changes in the HLA asset, and enforcement of immune checkpoints. Finally, this review discusses how these mechanisms may combine in complex patterns and how understanding and untangling these interactions may provide key knowledge for the selection of personalized therapeutic approaches.

The role of checkpoint blockade after allogeneic stem cell transplantation in diseases other than Hodgkin's Lymphoma

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only curative treatment option for many malignant high-risk hematological diseases. The Graft-vs.-Tumor (GvT) effect is the major hallmark of this treatment approach. However, disease relapse remains a major limitation. Boosting the GvT effect by checkpoint inhibitors (CI) is an attractive option in this desperate situation although potentially triggering Graft-vs.-Host Disease (GvHD). Early reports in patients with Hodgkin's lymphoma support the idea that CI therapy after HSCT is feasible and effective. We have retrospectively analyzed CI therapy for treatment of disease recurrence after allo-HSCT other than Hodgkin's lymphoma including 21 patients from eight German transplant centers. The median follow-up was 59 days. The overall response rate (ORR) was 43%. Patients receiving donor lymphocyte infusion (DLI) in combination with CI had superior response (ORR 80%). Severe acute GvHD grade III-IV and moderate to severe chronic GvHD were observed in 29% of all patients. Taken together, CI therapy in relapsed patients after HSCT, especially in combination with DLI, is effective but induces severe GvHD in a considerable proportion of patients. Thus, prospective trials or EBMT registry-based validation of different dosing and application schedules including immunosuppressive regimens in those patients are urgently needed.

Immune Escape of Relapsed AML Cells after Allogeneic Transplantation

BACKGROUND

As consolidation therapy for acute myeloid leukemia (AML), allogeneic hematopoietic stem-cell transplantation provides a benefit in part by means of an immune-mediated graft-versus-leukemia effect. We hypothesized that the immune-mediated selective pressure imposed by allogeneic transplantation may cause distinct patterns of tumor evolution in relapsed disease.

METHODS

We performed enhanced exome sequencing on paired samples obtained at initial presentation with AML and at relapse from 15 patients who had a relapse after hematopoietic stem-cell transplantation (with transplants from an HLA-matched sibling, HLA-matched unrelated donor, or HLA-mismatched unrelated donor) and from 20 patients who had a relapse after chemotherapy. We performed RNA sequencing and flow cytometry on a subgroup of these samples and on additional samples for validation.

RESULTS

On exome sequencing, the spectrum of gained and lost mutations observed with relapse after transplantation was similar to the spectrum observed with relapse after chemotherapy. Specifically, relapse after transplantation was not associated with the acquisition of previously unknown AML-specific mutations or structural variations in immune-related genes. In contrast, RNA sequencing of samples obtained at relapse after transplantation revealed dysregulation of pathways involved in adaptive and innate immunity, including down-regulation of major histocompatibility complex (MHC) class II genes ( HLA-DPA1, HLA-DPB1, HLA-DQB1, and HLA-DRB1) to levels that were 3 to 12 times lower than the levels seen in paired samples obtained at presentation. Flow cytometry and immunohistochemical analysis confirmed decreased expression of MHC class II at relapse in 17 of 34 patients who had a relapse after transplantation. Evidence suggested that interferon-γ treatment could rapidly reverse this phenotype in AML blasts in vitro.

CONCLUSIONS

AML relapse after transplantation was not associated with the acquisition of relapse-specific mutations in immune-related genes. However, it was associated with dysregulation of pathways that may influence immune function, including down-regulation of MHC class II genes, which are involved in antigen presentation. These epigenetic changes may be reversible with appropriate therapy. (Funded by the National Cancer Institute and others.).

Alloantigen expression on malignant cells and healthy host tissue influences graft-versus-tumor reactions after allogeneic hematopoietic stem cell transplantation

Durable remissions of hematological malignancies regularly observed following allogeneic hematopoietic stem cell transplantation (aHSCT) are due to the conditioning regimen, as well as an immunological phenomenon called graft-versus-leukemia (GVL) or graft-versus-tumor (GVT) effect. The development of GVL is closely linked to graft-versus-host disease (GVHD), the main side effect associated with aHSCT. Both, GVHD and GVL are mediated by donor T cells that are initially activated by antigen-presenting cells that present recipient-derived alloantigens in the context of either matched or mismatched MHC class I molecules. Using murine models of aHSCT we show that ubiquitously expressed minor histocompatibility alloantigens (mHAg) are no relevant target for GVT effects. Interestingly, certain ubiquitously expressed MHC alloantigens augmented GVT effects early after transplantation, while others did not. The magnitude of GVT effects correlated with tumor infiltration by CD8+ cytotoxic T cells and tumor cell apoptosis. Furthermore, the immune response underlying GVHD and GVT was oligoclonal, highlighting that immunodominance is an important factor during alloimmune responses. These results emphasize that alloantigen expression on non-hematopoietic tissues can influence GVT effects in a previously unrecognized fashion. These findings bear significance for harnessing optimal GVL effects in patients receiving aHSCT.

Three relapses after a haploidentical transplantation in a pediatric patient: Cure with no further transplantation

Isolated extramedullary relapse (EMR) after hematopoietic stem cell transplantation (HSCT) is a highly fatal condition that creates uncertainty regarding treatment options. Although certain approaches such as repeat HSCT and donor lymphocyte infusion are recommended, we report a patient with acute lymphoblastic leukemia who had three isolated EMRs after HSCT at different locations and at different times that were responsive to local and systemic therapies, without the need for a second transplantation.

Isolated Breast Relapse of Acute Lymphoblastic Leukemia After Allogeneic Hematopoietic Stem Cell Transplantation

Isolated breast relapse after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is less often seen. Chronic graft-versus-host disease (cGVHD) is effective in preventing marrow relapse, but cGVHD seems not to be effective extramedullary relapse (EMR). We report the case of isolated breast relapse after first allo-HSCT for acute lymphoblastic leukemia (ALL). A 47-year-old female was diagnosed with ALL achieved complete remission with salvage chemotherapy and underwent allo-HSCT from an HLA-matched sibling male donor. At 17 months post-transplant, she presented with a bilateral breast masses that confirmed the diagnosis lymphoblast involvement. She had no evidence of leukemia in her marrow that determined 100 % full-donor chimerism when she was relapsed in her both breasts.

Patient-individualized CD8⁺ cytolytic T-cell therapy effectively combats minimal residual leukemia in immunodeficient mice

Adoptive transfer of donor-derived cytolytic T-lymphocytes (CTL) has evolved as a promising strategy to improve graft-versus-leukemia (GvL) effects in allogeneic hematopoietic stem-cell transplantation. However, durable clinical responses are often hampered by limited capability of transferred T cells to establish effective and sustained antitumor immunity in vivo. We therefore analyzed GvL responses of acute myeloid leukemia (AML)-reactive CD8(+) CTL with central and effector memory phenotype in a new allogeneic donor-patient specific humanized mouse model. CTL lines and clones obtained upon stimulation of naive CD45RA(+) donor CD8(+) T cells with either single HLA antigen-mismatched or HLA-matched primary AML blasts, respectively, elicited strong leukemia reactivity during cytokine-optimized short to intermediate (i.e., 2-8 weeks) culture periods. Single doses of CTL were intravenously infused into NOD/scidIL2Rcg(null) mice when engraftment with patient AML reached bone marrow infiltration of 1-5%, clinically defining minimal residual disease status. This treatment resulted in complete regression of HLA-mismatched and strong reduction of HLA-matched AML infiltration, respectively. Most importantly, mice receiving AML-reactive CTL showed significantly prolonged survival. Transferred CTL were detectable in murine bone marrow and spleen and demonstrated sustained AML-reactivity ex vivo. Moreover, injections with human IL-15 clearly promoted CTL persistence. In summary, we show that naive donor-derived CD8(+) CTL effectively combat patient AML blasts in immunodeficient mice. The donor-patient specific humanized mouse model appears suitable to evaluate therapeutic efficacy of AML-reactive CTL before adoptive transfer into patients. It may further help to identify powerful leukemia rejection antigens and T-cell receptors for redirecting immunity to leukemias even in a patient-individualized manner.

Strategies to reduce relapse after allogeneic hematopoietic cell transplantation in acute myeloid leukemia

The incidence of acute myeloid leukemia (AML) is expected to increase in conjunction with our ageing population. Although it is proving to be a heterogeneous disease process, the only treatment with proven survival benefit for poor risk AML remains allogeneic hematopoietic cell transplant. Although this is presumed to be a curative strategy, many patients relapse after transplant, prompting us to examine various ways that we can improve outcomes. These efforts involve every step of AML diagnostics and therapy, including the intricate processes of conditioning, graft manipulation and immunomodulation. The hope is that improvement in these steps will ultimately improve survival and decrease relapse rates for AML patients after transplant.

A two-step approach to allogeneic haploidentical hematopoietic stem cell transplantation

Strategies that exploit natural killer (NK) cell alloreactivity or attenuate rather than deplete T cells have resulted in improved outcomes after haploidentical hematopoietic stem cell transplantation (HSCT). However, no approach has consistently produced the triad of optimal immune reconstitution, avoidance of significant graft-versus-host disease (GVHD), and durable control of malignancy. We developed a two-step approach to haploidentical HSCT in which the lymphoid and myeloid portions of the graft are given in two separate steps in order to control and optimize T-cell dosing. The initial results from these trials have included robust immune reconstitution, low rates of toxicity and significant GVHD, and durable disease control in good-risk patients, as well as insights regarding a threshold for T-cell dosing above which graft-versus-tumor (GVT) effects might be expected. Patients who were not in remission at the time of HSCT had higher rates of relapse requiring efforts to further strengthen GVT effects. Second-generation trials are underway to further exploit changes in the dosing and timing of administration of T cells and to optimize donor selection in an effort to decrease relapse rates in high-risk patients.

Relapse after allogeneic stem cell transplantation

Since allogeneic stem cell transplantation (SCT) represents an intensive curative treatment for high-risk malignancies, its failure to prevent relapse leaves few options for successful salvage treatment. While many patients have a high early mortality from relapse, some respond and have sustained remissions, and a minority has a second chance of cure with appropriate therapy. The prognosis for relapsed hematological malignancies after SCT depends on four factors: the time elapsed from SCT to relapse (with relapses occurring within 6 months having the worst prognosis), the disease type (with chronic leukemias and some lymphomas having a second possibility of cure with further treatment), the disease burden and site of relapse (with better treatment success if disease is treated early), and the conditions of the first transplant (with superior outcome for patients where there is an opportunity to increase either the alloimmune effect, the specificity of the antileukemia effect with targeted agents or the intensity of the conditioning in a second transplant). These features direct treatments toward either modified second transplants, chemotherapy, targeted antileukemia therapy, immunotherapy or palliative care.

Wilms' tumor 1 as a novel target for immunotherapy of leukemia

Wilms' tumor 1 (WT1) is a leukemia associated antigen (LAA) differentially expressed by leukemic blasts. Thus, WT1 may constitute a target for therapies such as those mediated by adoptive-specific T lymphocytes. Serological and cellular immune responses have been elicited by WT1 in patients with leukemia. Specific CD8+ T cells able to recognize this antigen can be selected by streptamers and then infused into leukemia patients. Potentially, these T cells could lyse leukemic blasts expressing WT1. The only good manufacturing practice-certified technology is streptamers, which are available for antigen-specific T-cell sorting. Immunocompromised patients may have their antigen-specific immune responses restored through the transfer of adoptive T cells specific for this LAA.

Current immunotherapy for solid tumors

Explorative knowledge of cellular and molecular mechanisms of immune function and regulation has provided optimism in developing cancer immunotherapy. However, three decades of experimental and clinical investigations to offer powerful immunotherapeutic strategies against solid tumors, with the possible exception of monoclonal antibody-targeted therapies, have not succeeded in significantly prolonging patient survival. Nonspecific immune approaches, including cytokine-based therapies and allogeneic hematopoietic stem cell transplantation, have so far produced consistent, although limited, results. In this review, we present the developments of cell transfer-based strategies that, in preclinical studies, have demonstrated potential efficacy, but have only established tumor regression in limited numbers of patients. The key to success demands creative combinations of tumor antigens, adjuvance, gene modification and various administration strategies in the development of cell-based therapies together with other cancer-treatment principles, often in a stepwise 'space-rocket-type' approach. Combined efforts of several scientific disciplines, such as tumor biology and immunology, as well as cell and gene research in transplantation, will open new venues. New regulation for clinical trials with advanced therapy medicine products to ensure patient safety will be highlighted.

NCI First International Workshop on The Biology, Prevention and Treatment of Relapse after Allogeneic Hematopoietic Cell Transplantation: report from the committee on prevention of relapse following allogeneic cell transplantation for hematologic malignancies

Prevention of relapse after allogeneic hematopoietic stem cell transplantation is the most likely approach to improve survival of patients treated for hematologic malignancies. Herein we review the limits of currently available transplant therapies and the innovative strategies being developed to overcome resistance to therapy or to fill therapeutic modalities not currently available. These novel strategies include nonimmunologic therapies, such as targeted preparative regimens and posttransplant drug therapy, as well as immunologic interventions, including graft engineering, donor lymphocyte infusions, T cell engineering, vaccination, and dendritic cell-based approaches. Several aspects of the biology of the malignant cells as well as the host have been identified that obviate success of even these newer strategies. To maximize the potential for success, we recommend pursuing research to develop additional targeted therapies to be used in the preparative regimen or as maintenance posttransplant, better characterize the T cell and dendritic cells subsets involved in graft-versus-host disease and the graft-versus-leukemia/tumor effect, identify strategies for timing immunologic or nonimmunologic therapies to eliminate the noncycling cancer stem cell, identify more targets for immunotherapies, develop new vaccines that will not be limited by HLA, and develop methods to identify populations at very high risk for relapse to accelerate clinical development and avoid toxicity in patients not at risk for relapse.

Immunotherapy prospects for acute myeloid leukaemia

While chemotherapy is successful at inducing remission of acute myeloid leukaemia (AML), the disease has a high probability of relapse. Strategies to prevent relapse involve consolidation chemotherapy, stem cell transplantation and immunotherapy. Evidence for immunosurveillance of AML and susceptibility of leukaemia cells to both T cell and natural killer (NK) cell attack and justifies the application of immune strategies to control residual AML persisting after remission induction. Immune therapy for AML includes allogeneic stem cell transplantation, adoptive transfer of allogeneic or autologous T cells or NK cells, vaccination with leukaemia cells, dendritic cells, cell lysates, peptides and DNA vaccines and treatment with cytokines, antibodies and immunomodulatory agents. Here we describe what is known about the immunological features of AML at presentation and in remission, the current status of immunotherapy and strategies combining treatment approaches with a view to achieving leukaemia cure.

Lytic activity against primary AML cells is stimulated in vitro by an autologous whole cell vaccine expressing IL-2 and CD80

Despite being of the myeloid lineage, acute myeloid leukaemia (AML) blasts are of low immunogenicity, probably because they lack the costimulatory molecule CD80 and secrete immunosuppressive factors. We have previously shown that in vitro stimulation of autologous peripheral blood mononuclear cells (PBMCs) with primary AML cells modified to express CD80 and IL-2 promotes proliferation, secretion of Th1 cytokines and expansion of activated CD8(+) T cells. In this study, we show that allogeneic effector cells (from a healthy donor or AML patients) when stimulated with IL-2/CD80 modified AML blasts were able to induce the lysis of unmodified AML blasts. Effector cells stimulated with IL-2/CD80AML blasts had higher lytic activity than cells stimulated with AML cells expressing CD80 or IL-2 alone. Similarly, AML patient PBMCs primed with autologous IL-2/CD80 AML cells had a higher frequency of IFN-gamma secreting cells and show cytotoxicity against autologous, unmodified blasts. Crucially, the response appears to be leukaemia specific, since stimulated patient PBMCs show higher frequencies of IFN-gamma secreting effector cells in response to AML blasts than to remission bone marrow cells from the same patients. Although studied in a small number of heterogeneous patient samples, the data are encouraging and support the continuing development of vaccination for poor prognosis AML patients with autologous cells genetically modified to express IL-2/CD80.

Myeloid leukemic progenitor cells can be specifically targeted by minor histocompatibility antigen LRH-1–reactive cytotoxic T cells

CD8+ T cells recognizing minor histocompatibility antigens (MiHAs) on leukemic stem and progenitor cells play a pivotal role in effective graft-versus-leukemia reactivity after allogeneic stem cell transplantation (SCT). Previously, we identified a hematopoiesis-restricted MiHA, designated LRH-1, which is presented by HLA-B7 and encoded by the P2X5 purinergic receptor gene. We found that P2X5 is significantly expressed in CD34+ leukemic subpopulations from chronic myeloid leukemia (CML) and acute myeloid leukemia (AML) patients. Here, we demonstrate that LRH-1–specific CD8+ T-cell responses are frequently induced in myeloid leukemia patients following donor lymphocyte infusions. Patients with high percentages of circulating LRH-1–specific CD8+ T cells had no or only mild graft-versus-host disease. Functional analysis showed that LRH-1–specific cytotoxic T lymphocytes (CTLs) isolated from 2 different patients efficiently target LRH-1–positive leukemic CD34+ progenitor cells from both CML and AML patients, whereas mature CML cells are only marginally lysed due to down-regulation of P2X5. Furthermore, we observed that relative resistance to LRH-1 CTL-mediated cell death due to elevated levels of antiapoptotic XIAP could be overcome by IFN-γ prestimulation and increased CTL-target ratios. These findings provide a rationale for use of LRH-1 as immunotherapeutic target antigen to treat residual or persisting myeloid malignancies after allogeneic SCT.

Graft-versus-leukemia effects of transplantation and donor lymphocytes

Allogeneic transplantation of hematopoietic cells is an effective treatment of leukemia, even in advanced stages. Allogeneic lymphocytes produce a strong graft-versus-leukemia (GVL) effect, but the beneficial effect is limited by graft-versus-host disease (GVHD). Depletion of T cells abrogates GVHD and GVL effects. Delayed transfusion of donor lymphocytes into chimeras after T cell-depleted stem cell transplantation produces a GVL effect without necessarily producing GVHD. Chimerism and tolerance provide a platform for immunotherapy using donor lymphocytes. The allogeneic GVL effects vary from one disease to another, the stage of the disease, donor histocompatibility, the degree of chimerism, and additional treatment. Immunosuppressive therapy before donor lymphocyte transfusions may augment the effect as well as concomitant cytokine treatment. Possible target antigens are histocompatibility antigens and tumor-associated antigens. Immune escape of tumor cells and changes in the reactivity of T cells are to be considered. Durable responses may be the result of the elimination of leukemia stem cells or the establishment of a durable immune control on their progeny. Recently, we have learned from adoptive immunotherapy of viral diseases and HLA-haploidentical stem cell transplantation that T-cell memory may be essential for the effective treatment of leukemia and other malignancies.

The Wilms' tumor antigen is a novel target for human CD4+ regulatory T cells: implications for immunotherapy

Compelling evidences indicate a key role for regulatory T cells (T(reg)) on the host response to cancer. The Wilms' tumor antigen (WT1) is overexpressed in several human leukemias and thus considered as promising target for development of leukemia vaccine. However, recent studies indicated that the generation of effective WT1-specific cytotoxic T cells can be largely affected by the presence of T(regs). We have generated T-cell lines and clones that specifically recognized a WT1-84 (RYFKLSHLQMHSRKH) peptide in an HLA-DRB1*0402-restricted manner. Importantly, they recognized HLA-DRB1*04-matched fresh leukemic cells expressing the WT1 antigen. These clones exerted a T helper 2 cytokine profile, had a CD4(+)CD25(+)Foxp3(+)GITR(+)CD127(-) T(reg) phenotype, and significantly inhibited the proliferative activity of allogeneic T cells independently of cell contact. Priming of alloreactive T cells in the presence of T(regs) strongly inhibited the expansion of natural killer (NK), NK T, and CD8(+) T cells and had an inhibitory effect on NK/NK T cytotoxic activity but not on CD8(+) T cells. Furthermore, priming of T cells with the WT1-126 HLA-A0201-restricted peptide in the presence of T(regs) strongly inhibited the induction of anti-WT1-126 CD8(+) CTL responses as evidenced by both very low cytotoxic activity and IFN-gamma production. Moreover, these T(reg) clones specifically produced granzyme B and selectively induced apoptosis in WT1-84-pulsed autologous antigen-presenting cells but not in apoptotic-resistant DR4-matched leukemic cells. Importantly, we have also detected anti-WT1-84 interleukin-5(+)/granzyme B(+)/Foxp3(+) CD4(+) T(regs) in five of eight HLA-DR4(+) acute myeloid leukemia patients. Collectively, our in vitro and in vivo findings strongly suggest important implications for the clinical manipulation of T(regs) in cancer patients.

Isolated extramedullary relapse presenting as autologous lymphocyte response

Isolated EMR in the CNS is a relatively rare form of recurrent leukemia. We report here a case of a 38-year-old man with inv(16) acute myeloid leukemia (AML, M2) who suffered a central nervous system (CNS) relapse after allogeneic bone marrow transplantation (BMT) from a human leukocyte antigen (HLA)-matched sibling donor. After complete remission was achieved by chemotherapy, he received allogeneic BMT from his HLA-matched sister. His leukemia relapsed in the CNS 2.5 years after the allogeneic BMT. Lumbar puncture revealed 780/muL white blood cells with 67.3% leukemia cells and 32.7% mature lymphocytes. Fluorescent in situ hybridization (FISH) using a probe for the Y chromosome demonstrated that both leukemia cells and lymphocytes in the cerebrospinal fluid (CSF) were derived from the recipient, although the bone marrow cells were from the donor. No leukemia cells with inv(16) were detected by FISH in the bone marrow. This is the first report to clarify the chimerism of lymphocytes in the CSF of patients with isolated EMR in the CNS after allogeneic SCT, in which analysis revealed that autologous immunologic cells rather than donor lymphocytes responded to the recurrent isolated leukemic cells in CNS. This observation suggests that the CNS is a "sanctuary" site not only from chemotherapy but also from the graft-versus-leukemia effect. The present case contributes to our understanding of the possibility of immunological escape phenomenon of recurrent leukemia cells in extramedullary sites.

Dynamics in chimerism of T cells and dendritic cells in relapsed CML patients and the influence on the induction of alloreactivity following donor lymphocyte infusion

Donor lymphocyte infusion (DLI) after allogeneic SCT induces complete remissions in approximately 80% of patients with relapsed CML in chronic phase, but some patients do not respond to DLI. We studied absolute numbers of dendritic cell (DC) subsets and chimerism in T cells and two subsets of blood DCs (myeloid DCs (MDCs) and plasmacytoid DCs (PDCs)) in relation to DLI-induced alloreactivity. Based on T cell and DC chimerism, we identified three groups. Four patients were completely donor chimeric in T cells and DC subsets. These patients had an early stage of relapse, and three of the four patients attained complete molecular remission (CMolR) without significant GVHD. Six patients were completely donor in T cells and mixed chimeric in DC subsets. All patients entered CMolR, but this was associated with GVHD in four and cytopenia in three patients. Five patients had mixed chimerism in T cells and complete recipient chimerism in MDC; only two patients entered CMolR. Our data suggest that the combination of donor T cells and mixed chimerism in DC subsets induces a potent graft-versus-leukemia (GVL) effect in association with GVHD. DLI in patients with an early relapse and donor chimerism in both T cells and DC subsets results in GVL reactivity without GVHD.

The B7-H1 (PD-L1) T lymphocyte-inhibitory molecule is expressed in breast cancer patients with infiltrating ductal carcinoma: correlation with important high-risk prognostic factors

B7-H1 molecule increases the apoptosis of tumor-reactive T lymphocytes and reduces their immunogenicity. Breast cancer is the second most common cause of mortality after lung cancer. Direct evidence linking B7-H1 with cancer has been shown in several malignancies; however, its expression in breast cancer has not been investigated. We used immunohistochemistry to investigate the expression of the B7-H1 molecule in 44 breast cancer specimens and to study its correlation with patients' clinicopathological parameters. The expression of B7-H1 was shown in 22 of 44 patients and was not restricted to the tumor epithelium (15 of 44, 34% in tumor cells), but was also expressed by tumor-infiltrating lymphocytes (TIL; 18 of 44, 41%). Interestingly, intratumor expression of B7-H1 was significantly associated with histologic grade III-negative (P = .012), estrogen receptor-negative (P = .036), and progesterone receptor-negative (P = .040) patients. In addition, the expression of B7-H1 in TIL was associated with large tumor size (P = .042), histologic grade III (P = .015), positivity of Her2/neu status (P = .019), and severe tumor lymphocyte infiltration (P = .001). Taken together, these data suggest that B7-H1 may be an important risk factor in breast cancer patients and may represent a potential immunotherapeutic target using monoclonal antibody against the B7-H1 molecule.

T cell-mediated graft-versus-leukemia reactions after allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation represents the only curative approach for many hematological malignancies. During the last years the impact of the conditioning regimen has been re-assessed. With the advent of reduced-intensity conditioning the paradigm has changed from cytoreduction executed by high-dose radio-chemotherapy to immunological surveillance of leukemia by donor cells. Distinct subsets of T cells and NK cells contribute to graft-versus-leukemia reactions. So far, cytotoxic T lymphocytes are the mainstay of allogeneic immunotherapy. Here, we summarise the current knowledge of T cell-mediated graft-versus-leukemia reactions and present results from pre-clinical and clinical studies of T cell-based adoptive immunotherapy. We address the issues of feasibility and specificity of adoptive immunotransfer from a clinical point of view and discuss the prerequisites for successful clinical applications. Finally, the prospects for immunological research that have evolved with the increasing use of reduced-intensity conditioning and allogeneic stem cell transplantation are highlighted.

Immune evasion strategies of pediatric precursor-B acute lymphoblastic leukemia after allogeneic bone marrow transplantation—a case study

Bone marrow transplantation (BMT) is the primary curative option for refractory/relapsed pediatric acute lymphoblastic leukemia. Although post-transplantation relapse remains a frequent cause of transplantation failure, the mechanisms underlying this are poorly understood. In this study, we compared allogeneic T cell stimulation induced by sequentially obtained precursor-B acute lymphoblastic leukemia (ALL) samples from a single patient with overt graft versus leukemia (GVL) activity. We observed a loss of T cell stimulatory capacity by post-transplantation relapse samples and changes in expression of MHC and the costimulatory molecule CD137 ligand. This study suggests that escape from immune mechanisms after withdrawal of immune suppression is important to ALL progression.

Parameters for predicting allogeneic PBSCT outcome of acute myeloid leukemia: cytogenetics at presentation versus disease status at transplantation

In addition to the clinical disease status at transplantation, the cytogenetic risk at presentation also provides critical information for predicting the prognosis or deciding the future therapeutic strategy. As such, the current study examined various parameters, including the cytogenetics at presentation and clinical disease status at transplantation, regarding their effect on the transplant outcomes of acute myeloid leukemia (AML) patients in an allogeneic peripheral blood stem cell transplantation (PBSCT) setting. A total of 36 patients receiving an allogeneic PBSCT from matched sibling donors were included in a state of first complete remission (CR) (n=22, 61%) or beyond the first CR (n=14, 39%). The cytogenetic risk was classified according to Medical Research Council (MRC) 10 criteria: favorable, 7 patients (20%); intermediate, 21 patients (58%); unfavorable eight patients (22%). The 3-year overall survival rates were 80% for the favorable, 63% for the intermediate, and 0% for the unfavorable cytogenetic risk groups (p=0.0002), and 62% for the patients in a state of first CR and 35% for those beyond the first CR (p=0.0524). Multivariate analysis revealed that higher CD34+ cell doses, favorable cytogenetics at presentation, and a lower marrow blast percentage at transplantation were all strongly associated with favorable transplant outcomes, including overall survival (OS), progression-free survival (PFS), and the probability of progression. The cytogenetic risk at presentation was found to be a useful parameter in predicting the transplant outcomes for patients with AML, regardless of the clinical disease status. However, an additive innovative therapeutic strategy is still needed to overcome an unfavorable cytogenetic risk with refractory AML after allogeneic PBSCT.

Graft-versus-leukemia reactions in allogeneic chimeras

There is a strong graft-versus-leukemia (GVL) effect of allogeneic stem cell transplantation (SCT) due to elimination of tumor cells by alloimmune effector lymphocytes. When leukemia relapses after allogeneic SCT, donor lymphocyte transfusions (DLTs) can induce sustained remissions in some patients. This review summarizes the current status on clinical use of DLT, the basis of GVL reactions, problems associated with this therapy, and new strategies to improve DLT. Several multicenter surveys demonstrated that the GVL effect of DLT is most effective in chronic myelogenous leukemia (CML), whereas it is less pronounced in acute leukemia and myeloma. Cytokine stimulation to induce differentiation of myeloid progenitor cells or to up-regulate costimulatory molecules on tumor cells may improve the efficacy of DLT. Infections and graft-versus-host disease (GVHD) are major complications of DLT. Control of GVHD may be improved using suicide gene-modified T cells for DLT, allowing T-cell elimination if severe GVHD develops. Hopefully, in the future, GVL effect can be separated from GVHD through adoptive transfer of selected T cells that recognize leukemia-specific antigens or minor histocompatibility antigens, which are expressed predominantly on hematopoietic cells, thereby precluding attack of normal tissues. In patients with leukemia and lymphomas with fast progression, tumor growth may outpace development of effector T cells. Here it may be preferable to select stem cell transplant donors with HLA-mismatches that allow alloreactive natural killer cells, which appear early after transplantation, to retain their cytolytic function. New approaches for adoptive immune therapy of leukemia, which promise a better prognosis for these patients, are being developed.

Localized lymphoid relapse in the pancreas following allogeneic hematopoietic stem cell transplant for chronic myelogenous leukemia

The incidence of isolated extramedullary disease (EMD) following allogeneic hematopoietic stem cell transplant (allo-HSCT) for chronic myelogenous leukemia (CML) is not fully known. One review found the incidence of isolated myeloid EMD, or granulocytic sarcoma (GS), in an allo-HSCT treated CML/myelodysplastic subgroup to be just 0.22%. The incidence of lymphoid EMD in similar patients is extremely rare with only two cases reported in the literature. While the etiology of EMD in the post-transplant setting is not entirely clear, there may be inefficacy of immune surveillance function outside of the bone marrow cavity. Isolated CML GS following allo-HSCT carries a median interval to bone marrow relapse between 7 and 10 months and a median survival of 12 months. Less is known about lymphoid EMD. The treatment in these cases is ill defined with modalities ranging from involved field radiation to second allo-HSCT. We present a case of isolated pancreatic lymphoid EMD diagnosed 15 months after allo-HSCT for CML. Our patient was also treated with withdrawal of his immunosuppressive regimen. Unfortunately, at just over 4 months following pancreatic resection, he developed systemic relapse and died. While EMD can occur anywhere in the body, CML associated pancreatic EMD is not previously reported.

The clinical implications of mixed lymphocyte reaction with leukemic cells

To evaluate the clinical implications of a mixed lymphocyte reaction between leukemic cells and lymphocytes from HLA-matched sibling donors, we attempted to generate donor-derived, graft-versus-leukemia-effective cells and to define their characteristics. We studied 8 patients with chronic myelogenous leukemia (CML), including 5 patients in the chronic phase (CP), 3 patients in the accelerated phase (AP), and 2 patients with acute myelogenous leukemia (AML) in their first complete remission. Cells from these patients were used as stimulators in a mixed lymphocyte reaction.The effects of natural killer (NK) cells and cytotoxic T-lymphocytes (CTLs) were separated by observing tests for cytotoxicity to target cells, including K562 cells, the patient's leukemic cells, and phytohemagglutinin (PHA) blasts. Donor-derived antileukemic CTLs againstthe patient's own leukemic cells are productive in vitro. The efficacy of generating CTLs against leukemic target cells was (in decreasing order) AML, CML-CP, and CML-AP. Cytotoxic activity against leukemic targets was prominent in 4 cases--2 CML-CP and the 2 AML cases. On the contrary, the 3 cases of CML-AP showed low CTL activity. In cases showing 1 positive result among 3 targets (K562 cells, the patient's leukemic cells, and PHA blasts), the relapse rate was significantly lower (P = .022) on follow-up (median, 33 months; 7-40 months) after hematopoietic stem cell transplantation. By a combined analysis of the cytotoxicity effects for all 3 target cells, we were able to demonstrate a correlation between leukemic relapse and the variable degree of the cytotoxicity test results. Although the total sample numbers for this study were low, we speculate that these results may come from differences in the individual characteristics of the leukemic cells that are in line with their clinical disease status.