Immunotherapy for pediatric leukemia

Novel agents for the treatment of childhood leukemia: an update

Achieving lower morbidity and higher survival rates in the treatment of childhood leukemia has been a paradigm of success in modern oncology. However, serious long-term health complications occur in very large populations of childhood leukemia survivors, in the case of both acute lymphoid leukemia and acute myeloid leukemia (AML). Additionally, 15% of acute lymphoid leukemia patients have treatment failures, and rates are even higher in childhood AML. In the last few decades, as a result of well-tested experiments that statistically analyzed treatment cohorts, new agents have emerged as alternatives or supplements to established treatments, in which high survival and/or less morbidity were observed. This review provides an overview of better practice in the treatment of childhood leukemia.

NK cell-based immunotherapies in Pediatric Oncology

The past decade has seen several anticancer immunotherapeutic strategies transition from "promising preclinical models" to treatments with proven clinical activity or benefit. In 2013, the journal Science selected the field of Cancer Immunotherapy as the overall number-1 breakthrough for the year in all of scientific research. In the setting of cancer immunotherapy for adult malignancies, many of these immunotherapy strategies have relied on the cancer patient's endogenous antitumor T-cell response. Although much promising research in pediatric oncology is similarly focused on T-cell reactivity, several pediatric malignancies themselves, or the chemo-radiotherapy used to achieve initial responses, can be associated with profound immune suppression, particularly of the T-cell system. A separate component of the immune system, also able to mediate antitumor effects and less suppressed by conventional cancer treatment, is the NK-cell system. In recent years, several distinct immunotherapeutic approaches that rely on the activity of NK cells have moved from preclinical development into clinical testing, and some have shown clear antitumor benefit. This review provides an overview of NK cell-based immunotherapy efforts that are directed toward childhood malignancies, with an emphasis on protocols that are already in clinical testing.

Expression of RKIP in chronic myelogenous leukemia K562 cell and inhibits cell proliferation by regulating the ERK/MAPK pathway

RAF kinase inhibitor protein (RKIP) is a negative regulator of the RAS-mitogen-activated protein kinase/extracellular signal-regulated kinase signaling cascade. We investigated the expression of RKIP in chronic myelogenous leukemia (CML) K562 cells and the effects of RKIP on the characteristics of K562 cells. The recombinant plasmid pcDNA3.1-RKIP was established and transfected into K562 cells with the help of Lipofectamine 2000. At the same time, the RKIP-siRNA was transfected into K562 cells in another group. The expressions of RKIP in all groups were assayed by Western blot after 48 h. MTT (3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was used to analyze the cell viability. Flow cytometry (FCM) was used to examine the cell cycle and cell apoptosis. Colony forming unit (CFU) assay was used to analyze the effect of RKIP on the clonogenic growth of CML cells. Western blot or luciferase reporter assay was used to detect the effect of RKIP on the level of phospho-ERK1/2 or the transcriptional activity of NF-κB. Western blot analysis showed that the plasmid pcDNA3.1-RKIP or RKIP-siRNA significantly enhanced or decreased RKIP expression (p < 0.01), respectively. In addition, MTT, FCM, and CFU assay indicated that the overexpression of RKIP significantly lowered the cell viability, cell proliferation and the clonogenic growth (p < 0.05), but improved cell apoptosis (p < 0.01). Western blot analysis or luciferase reporter assay showed that the level of phospho-ERK1/2 or the transcriptional activity of NF-κB was strongly inhibited by overexpression of RKIP. All these results could bring us a new perspective for biological therapy in myelogenous leukemia in the future.

Cytotoxicity of CD56-positive lymphocytes against autologous B-cell precursor acute lymphoblastic leukemia cells

Precursor B-lineage acute lymphoblastic leukemia (pre-B ALL) affects hematopoietic development and therefore is associated with immune deficiencies that can be further exacerbated by chemotherapy. It is unclear if and when monoclonal antibodies (mAbs) that stimulate antibody-mediated cellular cytotoxicity (ADCC) can be used for treatment because this depends on the presence of functional effector cells. Here, we used flow cytometry to determine that patient samples at diagnosis, post-induction and relapse contain detectable numbers of CD56+ cells. We were able to selectively expand CD56+ immune effector cells from bone marrow and peripheral blood samples at diagnosis and at various stages of treatment by co-culture with artificial antigen-presenting K562 clone 9.mbIL-21 cells. Amplified CD56+CD3- cells had spontaneous and anti-BAFF-R mAb-stimulated ADCC activity against autologous ALL cells, which could be further enhanced by IL15. Importantly, matched CD56+ effector cells also killed autologous ALL cells grown out from leukemia samples of the same patient, through both spontaneous as well as antibody-dependent cellular cytotoxicity. Since autologous cell therapy will not be complicated by graft-versus-host disease, our results show that expanded CD56+ cells could be applied for treatment of pre-B-ALL without transplantation, or for purging of bone marrow in the setting of autologous bone marrow transplants.

New frontiers in pediatric Allo-SCT: novel approaches for children and adolescents with ALL

Although most children with ALL can be cured by chemotherapy approaches, allogeneic hematopoietic cell transplant (HCT) therapy offers a better chance of cure to selected high-risk patients in first remission and most children who relapse. Although transplant-related mortality has decreased significantly in the past decade, relapse remains high after HCT for ALL; developing strategies to decrease relapse and improve survival are vital. Recent studies have shown that relapse risk can be accurately defined using measurements of minimal residual disease (MRD) both pre- and post-HCT and by knowing whether patients get GVHD in the first 2 months after transplant. With these risk definitions in hand, investigators are now applying novel agents and immunotherapeutic methods in attempt to lower MRD before transplant and modulate the GVL effect after transplant. With powerful new immunological approaches coming on line, the transplant process itself will likely expand to include pre and/or post-HCT interventions aimed at reducing relapse.

Effector-mediated eradication of precursor B acute lymphoblastic leukemia with a novel Fc-engineered monoclonal antibody targeting the BAFF-R

B-cell activating factor receptor (BAFF-R) is expressed on precursor B acute lymphoblastic leukemia (pre-B ALL) cells, but not on their pre-B normal counterparts. Thus, selective killing of ALL cells is possible by targeting this receptor. Here, we have further examined therapeutic targeting of pre-B ALL based on the presence of the BAFF-R. Mouse pre-B ALL cells lacking BAFF-R function had comparable viability and proliferation to wild-type cells, but were more sensitive to drug treatment in vitro. Viability of human pre-B ALL cells was further reduced when antibodies to the BAFF-R were combined with other drugs, even in the presence of stromal protection. This indicates that inhibition of BAFF-R function reduces fitness of stressed pre-B ALL cells. We tested a novel humanized anti-BAFF-R monoclonal antibody optimalized for FcRγIII-mediated, antibody-dependent cell killing by effector cells. Antibody binding to human ALL cells was inhibitable, in a dose-dependent manner, by recombinant human BAFF. There was no evidence for internalization of the antibodies. The antibodies significantly stimulated natural killer cell-mediated killing of different human patient-derived ALL cells. Moreover, incubation of such ALL cells with these antibodies stimulated phagocytosis by macrophages. When this was tested in an immunodeficient transplant model, mice that were treated with the antibody had a significantly decreased leukemia burden in bone marrow and spleen. In view of the restricted expression of the BAFF-R on normal cells and the multiple anti-pre-B ALL activities stimulated by this antibody, a further examination of its use for treatment of pre-B ALL is warranted.

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

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

Molecular therapeutic approaches for pediatric acute myeloid leukemia

Approximately two-thirds of children with acute myeloid leukemia (AML) are cured with intensive multi-agent chemotherapy. However, refractory and relapsed AML remains a significant source of childhood cancer mortality, highlighting the need for new therapies. Further therapy intensification with traditional cytotoxic chemotherapy in pediatric AML is not feasible given the risks of both short-term and long-term organ dysfunction. Substantial emphasis has been placed upon the development of molecularly targeted therapeutic approaches for adults and children with high-risk subtypes of AML with the goal of improving remission induction and minimizing relapse. Several promising agents are currently in clinical testing or late preclinical development for AML, including monoclonal antibodies against leukemia cell surface proteins, kinase inhibitors, proteasome inhibitors, epigenetic agents, and chimeric antigen receptor engineered T cell immunotherapies. Many of these therapies have been specifically tested in children with relapsed/refractory AML in Phase 1 and 2 trials with a smaller number of new agents under Phase 3 evaluation for children with de novo AML. Although successful identification and implementation of new drugs for children with AML remain a formidable challenge, enthusiasm for novel molecular therapeutic approaches is great given the potential for significant clinical benefit for children who do not have other curative options.