Immunotherapy of AML: future directions

Autologous hematopoietic stem cell transplantation followed by interleukin-2 for adult acute myeloid leukemia patients with favorable or intermediate risk after complete remission

High-dose chemotherapy followed by allogeneic hematopoietic stem cell transplantation (allo-HSCT) is generally the optimal option for patients with acute myeloid leukemia (AML). However, for favorable- and intermediate-risk patients, the regimen remains less understood due to graft versus host disease (GVHD) and increased non-relapsed mortality (NRM) caused by allo-HSCT. Additionally, the benefit of maintenance therapy has not yet been conclusively proven. Here, we conducted a retrospective study on the long-term outcome of AML patients with favorable or intermediate risk who underwent autologous hematopoietic stem cell transplantation (auto-HSCT) followed by interleukin-2 (IL-2) subcutaneous injection as maintenance therapy. A total of 49 patients from 2007 to 2019 were included in our study. They all received a daunorubicin + cytarabine regimen as induction chemotherapy followed by four to six cycles of consolidation therapy with medium- or high-dose cytarabine. Once patients achieved complete remission (CR1), they started receiving auto-HSCT followed by IL-2 injections. The results showed that no patients stopped receiving IL-2 injections on account of adverse side effects, and the 5-year overall survival (OS) and leukemia-free survival (LFS) rates were 85.6 ± 5.0% and 78.5 ± 6.1%, respectively. The multivariate analysis also suggested that age, gender, initial white blood cell (WBC) count, AML subtype, cytogenetic risk, and conditioning regimen did not affect the prognosis. In conclusion, auto-HSCT followed by IL-2 injection is an effective treatment that can improve the prognosis of AML for patients with favorable or intermediate risk.

Targeting CD300f to enhance hematopoietic stem cell transplantation in acute myeloid leukemia

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) significantly reduces the rate of relapse in acute myeloid leukemia (AML) but comes at the cost of significant treatment-related mortality. Despite the reduction in relapse overall, it remains common, especially in high-risk groups. The outcomes for patients who relapse after transplant remains very poor. A large proportion of the morbidity that prevents most patients from accessing allo-HSCT is due to toxic nonspecific conditioning agents that are required to remove recipient hematopoietic stem and progenitor cells (HSPCs), allowing for successful donor engraftment. CD300f is expressed evenly across HSPC subtypes. CD300f has transcription and protein expression equivalent to CD33 on AML. We have developed an anti-CD300f antibody that efficiently internalizes into target cells. We have generated a highly potent anti-CD300f antibody-drug conjugate (ADC) with a pyrrolobenzodiazepine warhead that selectively depletes AML cell lines and colony forming units in vitro. The ADC synergizes with fludarabine, making it a natural combination to use in a minimal toxicity conditioning regimen. Our ADC prolongs the survival of mice engrafted with human cell lines and depletes primary human AML engrafted with a single injection. In a humanized mouse model, a single injection of the ADC depletes CD34+ HSPCs and CD34+CD38-CD90+ hematopoietic stem cells. This work establishes an anti-CD300f ADC as an attractive potential therapeutic that, if validated in transplant models using a larger cohort of primary AML samples, will reduce relapse rate and toxicity for patients with AML undergoing allo-HSCT.

Maintenance Therapy With Interleukin-2 for Childhood AML: Results of ELAM02 Phase III Randomized Trial

Despite significant progress in the treatment of pediatric acute myeloblastic leukemia (AML), relapse remains the commonest cause of death. Randomized ELAM02 trial questioned if maintenance therapy with interleukin-2 (IL2), for 1 year, improves disease-free survival (DFS). Patients aged 0 to 18 years, with newly diagnosed AML (excluding patients with acute promyelocytic leukemia or down syndrome AML) were enrolled. They received 1 course of induction treatment (cytarabine and mitoxantrone) and 3 courses of consolidation treatment (high-dose cytarabine in courses 1 and 3). According to the cytogenetics risk, patients not undergoing hematopoietic stem cell transplantation, still in complete remission (CR) after the third course of consolidation treatment, were eligible for randomization to 1 year of maintenance therapy with monthly courses of IL2 or no maintenance treatment. There were 438 evaluable patients, 154 of whom were randomized to the IL2/no maintenance groups. Relapse occurred in 28 patients from the IL2+ group and 29 patients in the IL2- group. Survival was similar in the 2 groups, with a 4-year DFS of 62% without IL2 and 66% with IL2 (P = 0.75). In the CBF population, 4-year DFS was 55% without IL2 and 78% with IL2 (P = 0.07). No deaths from toxicity or excess of serious adverse events related to IL2 treatment were recorded. Prolonged IL2 for maintenance therapy after intensive chemotherapy is feasible and safe in pediatric AML patients in their first CR. Such treatment did not improve DFS in this study, but a positive trend was observed in favor of IL2 maintenance therapy among core binding factor acute myeloblastic leukemia.

Immunotherapeutic strategies for relapse control in acute myeloid leukemia

Despite that the initial phases of chemotherapy induce disappearance of leukemic cells in many patients with acute myeloid leukemia (AML), the prevention of life-threatening relapses in the post-remission phase remains a significant clinical challenge. Allogeneic bone marrow transplantation, which is available for a minority of patients, efficiently prevents recurrences of leukemia by inducing immune-mediated elimination of leukemic cells, and over the past decades, numerous immunotherapeutic protocols have been developed aiming to mimic the graft-versus-leukemia reaction for the prevention of relapse. Here we review past and present strategies for relapse control with focus on overcoming leukemia-related immunosuppression in AML. We envisage future treatment protocols, in which systemic immune activators, such as vaccines, dendritic cell-based therapies, engineered variants of IL-2, or IL-15, are combined with agents that counter immunosuppression mediated by, e.g., the PD/PDL interaction, CTLA-4, CD200, reactive oxygen species, IDO expression, CXCR4, or the KIR/class I interaction, based on characteristics of the prevailing malignant clone. This combinatorial approach may pave the way for individualized immunotherapy in AML.

Remission maintenance in acute myeloid leukemia: impact of functional histamine H2 receptors expressed by leukemic cells

Post-consolidation immunotherapy with histamine dihydrochloride and interleukin-2 has been shown to improve leukemia-free survival in acute myeloid leukemia in a phase III trial. For this study, treatment efficacy was determined among 145 trial patients with morphological forms of acute myeloid leukemia as defined by the French-American-British classification. Leukemia-free survival was strongly improved in M4/M5 (myelomonocytic/monocytic) leukemia but not in M2 (myeloblastic) leukemia. We also analyzed histamine H(2) receptor expression by leukemic cells recovered from 26 newly diagnosed patients. H(2) receptors were typically absent from M2 cells but frequently expressed by M4/M5 cells. M4/M5 cells, but not M2 cells, produced reactive oxygen species that triggered apoptosis in adjacent natural killer cells. These events were significantly inhibited by histamine dihydrochloride. Our data demonstrate the presence of functional histamine H(2) receptors on human AML cells and suggest that expression of these receptors by leukemic cells may impact on the effectiveness of histamine-based immunotherapy.

Cell therapy: promise fulfilled?

Cellular immunotherapy has been widely accepted as a new powerful modality of cancer treatment. The last 2 decades have seen impressive results in its application against haemato-oncologic malignancies, melanomas and prostate carcinoma. Cellular immunotherapy has since found applicability beyond cancer into autoimmunity and continues to expand in its clinical applicability. The discovery that stem cells have the ability to differentiate into more mature cell types, like neurones and myocardium, has focused research on using exogenous cells to repair damaged tissues. This led to numerous clinical trials using stem cells in myocardial infarction, cardiomyopathy and spinal cord damage. Results have ranged from modest to significant clinical outcomes with continuing debate on the exact process of regeneration achieved. The intertwining between cell therapy and transfusion medicine now includes research on progenitor cells for the production of mature red cells. It is also clear that cell therapy has enabled an improved understanding of the pathogenesis and clinical course of many diseases, while perhaps its role in regenerative medicine is most enticing. However, the critical role of manufacturing in terms of cost, complexity, reproducibility, and regulatory matters remains a central issue in the consideration of whether cell therapy has met all of its promise.

Interleukin-15 supports generation of highly potent clinical-grade natural killer cells in long-term cultures for targeting hematological malignancies

OBJECTIVE

Interleukin (IL)-15 is a promising novel cytokine for natural killer (NK) cell activation and survival. We studied the effects of IL-15 compared to IL-2 on NK cells in long-term cultures for clinical translation.

MATERIALS AND METHODS

CD56(+)CD3(-) NK cells were expanded with IL-2 or IL-15 for 2 to 4 weeks within lymphokine-activated killer (LAK) cell cultures (LAK-NK) in serum-enriched AIM V or CellGro Stem Cell Growth Medium (SCGM). Cell growth, viability, and NK cell content were monitored and cytotoxicity assessed in a flow cytometric cytotoxicity assay.

RESULTS

IL-15 (100-1000 U/mL) could replace IL-2 (1000 U/mL) in AIM V cultures to achieve efficient LAK cell expansion. However, IL-15-stimulated LAK cells exceeded cytotoxicity of IL-2-stimulated LAK cells against K562, notably at later culture points. In the powerful CellGro SCGM, LAK cells expanded over 28 days an average of 905-fold ± 320-fold standard error of the mean (SEM) for IL-2 (500 U/mL) and 484-fold ± 98-fold SEM for IL-15 (500 U/mL), and NK cells within such LAK cultures expanded an average of 2320-fold ± 975-fold SEM for IL-2 and 1084-fold ± 309-fold SEM for IL-15. Importantly, such IL-15-activated LAK-NK cells retained enhanced cytotoxicity at later culture points against K562 as well. IL-15-stimulated effectors were also highly cytotoxic against hematological targets MOLT-4 and KU812 and nontoxic against autologous nonmalignant cells. Interestingly, IL-15-LAK-NK cells showed overall significant upregulation of the main activating and inhibitory NK cell receptors after long-term cytokine stimulation.

CONCLUSIONS

Our results demonstrate the potential for IL-15 to support large-scale expansion of clinical-grade LAK-NK effectors, which could retain enhanced longer-term potency and preserve activation receptors in therapy of hematological malignancies. Protocols are readily clinically translatable.

Individual patient data meta-analysis of randomized trials evaluating IL-2 monotherapy as remission maintenance therapy in acute myeloid leukemia

IL-2 is a natural, T cell-derived cytokine that stimulates the cytotoxic functions of T and natural killer cells. IL-2 monotherapy has been evaluated in several randomized clinical trials (RCTs) for remission maintenance in patients with acute myeloid leukemia (AML) in first complete remission (CR1), and none demonstrated a significant benefit of IL-2 monotherapy. The objective of this meta-analysis was to reliably determine IL-2 efficacy by combining all available individual patient data (IPD) from 5 RCTs (N = 905) and summary data from a sixth RCT (N = 550). Hazard ratios (HRs) were estimated using Cox regression models stratified by trial, with HR < 1 indicating treatment benefit. Combined IPD showed no benefit of IL-2 over no treatment in terms of leukemia-free survival (HR = 0.97; P = .74) or overall survival (HR = 1.08; P = .39). Analyses including the sixth RCT yielded qualitatively identical results (leukemia-free survival HR = 0.96, P = .52; overall survival HR = 1.06; P = .46). No significant heterogeneity was found between the trials. Prespecified subset analyses showed no interaction between the lack of IL-2 effect and any factor, including age, sex, baseline performance status, karyotype, AML subtype, and time from achievement of CR1 to initiation of maintenance therapy. We conclude that IL-2 alone is not an effective remission maintenance therapy for AML patients in CR1.

Emerging natural killer cell immunotherapies: large-scale ex vivo production of highly potent anticancer effectors

Natural killer (NK) cell therapies are emerging worldwide as promising anticancer treatments, exploiting the fast cytolytic action of NK effectors and their potentially broad applicability against a wide range of malignancies. Until recently, clinical protocols have mainly involved freshly isolated NK cells or short- term activated NK cells or lymphokine-activated killer (LAK) cells. However, overall effector numbers and their anticancer potencies remained restricted, which poses a limiting factor to clinical efficacy. Recent developments in the field aim to improve clinical trial designs by increasing effector to target cell ratios in vivo and by application of superior cytotoxic NK effectors. Large-scale production of clinical grade NK cells through long-term activation in ex vivo cultures are another novel means in achieving these goals. However, such procedures require compliance with the strict Good Manufacturing Practice (GMP) regulations to ensure quality and safety of the NK cell product. Although the overall number of new protocols still remains comparably low, some of the protocols are already translated into clinical use. Also striking is the diversity of the different protocols proposed. We highlight in this review the most recent developments in the NK cell field with a focus on long-term NK cell expansion. Critical issues relating to this novel and promising type of therapy are highlighted and discussed.

Interferon-α in acute myeloid leukemia: an old drug revisited

Interferon-α (IFN-α), a type I IFN, is a well-known antitumoral agent. The investigation of its clinical properties in acute myeloid leukemia (AML) has been prompted by its pleiotropic antiproliferative and immune effects. So far, integration of IFN-α in the therapeutic arsenal against AML has been modest in view of the divergent results of clinical trials. Recent insights into the key pharmacokinetic determinants of the clinical efficacy of IFN along with advances in its pharmaceutical formulation, have sparked renewed interest in its use. This paper reviews the possible applicability of IFN-α in the treatment of AML and provides a rational basis to re-explore its efficacy in clinical trials.

Immunotherapy in multiple myeloma - possibility or probability?

In a small number of patients with multiple myeloma (MM), long-term disease-free survival has been achieved by harnessing the immune phenomenon, 'graft-versus-tumour' effect, induced by allogeneic haemopoietic stem cell transplantation. This has prompted many investigators to examine ways in which a patient's own immune system can be more effectively directed against their disease, with the ultimate aim of tumour eradication. In this review we assess the current understanding of immunobiology in MM, and how the different components of the immune system, such as dendritic cells, T cells and natural killer cells, may be harnessed using in-vitro and in-vivo priming techniques. We look at the clinical immunotherapy trials reported to date and whether, in light of the current information, immunotherapy for MM is an achievable goal.

Immunological weapons against acute myeloid leukaemia

A better understanding of the biology of malignant cells and of the host immune system together with dramatic advances in technology have led to the design of innovative immune-mediated approaches to control neoplastic clones, including various haematological malignancies. One of the major problems with conventional cancer therapies is their inability to eradicate residual cancer cells that are resistant to therapy, hence immune intervention might improve the clinical outcome of patients. This mini-review will focus mainly on immunological approaches to the therapy of acute myeloid leukaemia (AML), a subset of a much larger family of leukaemias. Immune-mediated approaches ranging from allogeneic lymphocyte transplants to cytokine therapy, immune-gene therapy and vaccination by dendritic-cell-based vaccines will be discussed.

Acute myelogenous leukemia: advances and limitations of treatment

Acute myelogenous leukemia (AML) describes a group of related hematologic malignancies that are being approached therapeutically from several perspectives. Conventional chemotherapeutic agents, such as anthracyclines and cytosine arabinoside (Ara-C), are useful in treating AML but now appear to have reached their maximum potential. Newer therapeutic approaches to AML have recently focused on immune-based therapy through monoclonal antibodies that target and destroy malignant cells via specific cell receptors. One such agent is gemtuzumab (CMA-676), an agent that targets the CD33 antigen on malignant myeloid cells. Initial studies have shown significant anticancer activity. We will discuss traditional and newer therapeutic approaches to AML and review the role of monoclonal antibody based therapies for patients with AML. A case of a 30-year-old man with refractory AML who was treated with gemtuzumab will be mentioned, highlighting potential applications and possible limitations to this novel therapy. Despite the effective reduction in the number of malignant cells in bone marrow, gemtuzumab ineffectively treated extramedullary leukemic gingival infiltrate. Regardless of limitations, monoclonal-based therapy offers an exciting and potentially safer adjunctive therapy for patients with AML.

Treatment of relapse after allogeneic bone marrow transplantation with reduced intensity conditioning (FLAG +/- Ida) and second allogeneic stem cell transplant

Acute leukaemias in relapse after allogeneic stem cell transplantation (SCT) respond poorly to donor leucocyte infusions (DLI) compared with chronic myeloid leukaemia (CML), at least in part because of faster disease kinetics. Fludarabine-containing 'non-myeloablative' chemotherapy followed by further allo SCT may offer more rapid and effective disease control. We report 14 patients with relapse after allo SCT for acute leukaemia [seven acute myeloid leukaemia (AML), five acute lymphoblastic leukaemia (ALL)] or refractory anaemia with excess blasts in transformation (RAEB-t, n = 2) treated with fludarabine, high-dose cytosine arabinoside (ara-C) and granulocyte colony-simulating factor (G-CSF) with (n = 10) or without (n = 2) idarubicin (FLAG +/- Ida) or DaunoXome (FLAG-X) (n = 2) and second allo SCT from the original donor. Donors were fully human leucocyte antigen (HLA) -matched in 13 cases with a single class A mismatch in one. Actuarial overall survival was 60% and disease-free survival was 26% at 58 months. Remissions after the second SCT were longer than those after the first bone marrow transplantation (BMT) in eight of the 13 assessable patients to date. Haematopoietic recovery was rapid. Transplants were well tolerated with no treatment-related deaths. The major complication was graft-versus-host disease (GvHD, acute >/= grade II-2 cases, chronic - eight cases, two limited, six extensive) although there have been no deaths attributable to this. FLAG +/- Ida and second allo SCT is a safe and useful approach and may be more effective than DLI in the treatment of acute leukaemias relapsing after conventional allo SCT.

Hepatosplenic Candidiasis, its Treatment and Effect on Remission Status in Patients with Acute Leukaemia-a Report of Five Cases

Hepatosplenic candidiasis is an increasingly encountered complication of treatment of patients with acute leukaemia [[1] Clin. Infect. Dis. 24 (1997) 375]. Management is difficult as delay in further chemotherapy may allow relapse of the leukaemia while the infection may progress if chemotherapy is continued [[2] Anticancer Res. 19 (1999) 757]. We report five cases of suspected hepatosplenic candidiasis in a single haematology unit over a 30-month period. All patients were treated with oral fluconazole following intravenous amphotericin or liposomal amphotericin B lipid complex. Chemotherapy was withheld during treatment of infection. Two patients remain in haematological remission despite suboptimal therapy for their leukaemia. One patient died from progressive fungal infection, 1 patient of cardiac disease and 1 patient has had recent relapse of their leukaemia. We demonstrate that hepatosplenic candidiasis may be treated with oral fluconazole while chemotherapy is discontinued and also suggest that this infection or its treatment may have had a beneficial immunomodulatory affect on the leukaemic process in the surviving patients.