BCR-ABL Activity Is Critical for the Immunogenicity of Chronic Myelogenous Leukemia Cells

Putative COVID-19 therapies imatinib, lopinavir, ritonavir, and ivermectin cause hair cell damage: A targeted screen in the zebrafish lateral line

The biomedical community is rapidly developing COVID-19 drugs to bring much-need therapies to market, with over 900 drugs and drug combinations currently in clinical trials. While this pace of drug development is necessary, the risk of producing therapies with significant side-effects is also increased. One likely side-effect of some COVID-19 drugs is hearing loss, yet hearing is not assessed during preclinical development or clinical trials. We used the zebrafish lateral line, an established model for drug-induced sensory hair cell damage, to assess the ototoxic potential of seven drugs in clinical trials for treatment of COVID-19. We found that ivermectin, lopinavir, imatinib, and ritonavir were significantly toxic to lateral line hair cells. By contrast, the approved COVID-19 therapies dexamethasone and remdesivir did not cause damage. We also did not observe damage from the antibiotic azithromycin. Neither lopinavir nor ritonavir altered the number of pre-synaptic ribbons per surviving hair cell, while there was an increase in ribbons following imatinib or ivermectin exposure. Damage from lopinavir, imatinib, and ivermectin was specific to hair cells, with no overall cytotoxicity noted following TUNEL labeling. Ritonavir may be generally cytotoxic, as determined by an increase in the number of TUNEL-positive non-hair cells following ritonavir exposure. Pharmacological inhibition of the mechanotransduction (MET) channel attenuated damage caused by lopinavir and ritonavir but did not alter imatinib or ivermectin toxicity. These results suggest that lopinavir and ritonavir may enter hair cells through the MET channel, similar to known ototoxins such as aminoglycoside antibiotics. Finally, we asked if ivermectin was ototoxic to rats in vivo. While ivermectin is not recommended by the FDA for treating COVID-19, many people have chosen to take ivermectin without a doctor’s guidance, often with serious side-effects. Rats received daily subcutaneous injections for 10 days with a clinically relevant ivermectin dose (0.2 mg/kg). In contrast to our zebrafish assays, ivermectin did not cause ototoxicity in rats. Our research suggests that some drugs in clinical trials for COVID-19 may be ototoxic. This work can help identify drugs with the fewest side-effects and determine which therapies warrant audiometric monitoring.

Immune modulation by molecular cancer targets and targeted therapies: Rationale for novel combination strategies

Following our recent observation that alterations of the Natural Killer (NK) cell compartment in the presence of BCR-ABL-induced myeloproliferation fail to revert under targeted therapy, we discuss by what mechanisms oncogenic molecular pathways and their pharmacological inhibition may interfere with immune functions. Rational combinations of molecularly targeted and immunological strategies may provide a means for more effective cancer targeting.

Unraveling the regulatory role of endoplasmic-reticulum-associated degradation in tumor immunity

During malignant transformation and cancer progression, tumor cells face both intrinsic and extrinsic stress, endoplasmic reticulum (ER) stress in particular. To survive and proliferate, tumor cells use multiple stress response pathways to mitigate ER stress, promoting disease aggression and treatment resistance. Among the stress response pathways is ER-associated degradation (ERAD), which consists of multiple components and steps working together to ensure protein quality and quantity. In addition to its established role in stress responses and tumor cell survival, ERAD has recently been shown to regulate tumor immunity. Here we summarize current knowledge on how ERAD promotes protein degradation, regulates immune cell development and function, participates in antigen presentation, exerts paradoxical roles on tumorigenesis and immunity, and thus impacts current cancer therapy. Collectively, ERAD is a critical protein homeostasis pathway intertwined with cancer development and tumor immunity. Of particular importance is the need to further unveil ERAD's enigmatic roles in tumor immunity to develop effective targeted and combination therapy for successful treatment of cancer.

Induction of CML-specific immune response through cross-presentation triggered by CTP-mediated BCR-ABL-derived peptides

Although targeted therapy using tyrosine kinase inhibitors (TKIs) has made remarkable progress in treating chronic myeloid leukemia (CML), this disease remains largely incurable, warranting further investigation of new therapeutic strategies. BCR-ABL is a highly specific tumor antigen in CML and provides an attractive opportunity for vaccination therapy. Exogenous antigens must be presented on MHC class I molecules-via a process termed cross-presentation-to activate specific cytotoxic T lymphocyte response. The relative efficiency of cross-presentation is determined in part by the ability of dendritic cells (DCs) to internalize and present antigens. Here, we present a novel tool that uses cytoplasmic transduction peptide (CTP) to facilitate the internalization of antigens by DCs in an endocytosis-independent manner, which greatly enhances the efficiency of antigen presentation, thereby inducing stronger cytotoxic activity to ensure the elimination of CML cells. The data suggest that CTP-fused CML-specific peptides can be applied in vaccination therapies for CML patients.

Unraveling survivin expression in chronic myeloid leukemia: Molecular interactions and clinical implications

Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by the BCR-ABL oncoprotein, known to drive leukemogenesis by orchestrating multiple signaling pathways ultimately involved in cell survival. Despite successful response rates of CML patients to tyrosine kinase inhibitors (TKIs), resistance eventually arises due to BCR-ABL-dependent and independent mechanisms. Survivin is an inhibitor of apoptosis protein acting in the interface between apoptosis deregulation and cell cycle progression. In CML, high levels of survivin have been associated with late stages of disease and therapy resistance. In this review, we provide an overview of important aspects concerning survivin subcellular localization and expression pattern in CML patients and cell lines. Moreover, we highlight the relevance of molecular networks involving survivin for disease progression and treatment resistance. Finally, we discuss the mechanisms accounting for survivin overexpression, as well as novel therapeutic interventions that have been designed to counteract survivin-associated malignancy in CML.

New Approaches and Treatment Combinations for the Management of Chronic Myeloid Leukemia

Current treatment of chronic myeloid leukemia (CML) with tyrosine kinase inhibitors (TKI) is effective in many patients, but is not curative and frequently limited by intolerance or resistance. Also, treatment free remission is a novel option for CML patients and requires reaching a deep molecular remission, which is not consistently achieved with TKI monotherapy. Together, multiple unmet clinical needs remain and therefore the continued need to explore novel treatment strategies. With increasing understanding of CML biology, many options have been explored and are under investigation. This includes the use asciminib as first in class inhibitor targeting the myristoyl pocket of BCR-ABL, combination treatments with established non-TKI drugs such as interferon and drugs with novel targets relevant to CML biology such as gliptins and thiazolidinediones. Together, an overview is provided of treatment strategies in development for CML beyond current TKI monotherapy.

Association of HLA class I type with prevalence and outcome of patients with acute myeloid leukemia and mutated nucleophosmin

Acute myeloid leukemia with mutated nucleophosmin (NPMc+ AML) forms a distinct AML subgroup with better prognosis which can potentially be associated with immune response against the mutated nucleophosmin (NPM). As the T-cell-mediated immunity involves antigen presentation on HLA class I molecules, we hypothesized that individuals with suitable HLA type could be less prone to develop NPMc+ AML. We compared HLA class I distribution in NPMc+ AML patient cohort (398 patients from 5 centers) with the HLA allele frequencies of the healthy population and found HLA-A*02, B*07, B*40 and C*07 underrepresented in the NPMc+ AML group. Presence of B*07 or C*07:01 antigen was associated with better survival in patients without concomitant FLT3 internal tandem duplication. Candidate NPM-derived immunopeptides were found for B*40 and B*07 using prediction software tools. Our findings suggest that a T-cell-mediated immune response could actually explain better prognosis of NPMc+ patients and provide a rationale for attempts to explore the importance of immunosuppressive mechanisms in this AML subgroup.

Cytokine Syntheses by T-Cell Subsets From Chronic Myeloid Leukemia Patients: Relationship Between Pre-Treatment Levels and Response to Imatinib Therapy

Background

Although T-cell cytokine's role in the long-term control of chronic myeloid leukemia (CML) is well established, previous studies showed contradicting results regarding imatinib (IM) effect on the endogenous T-cell function by IM. The purpose of this study was to determine the relation between the endogenous T-cell function prior to therapy and the degree of response to IM therapy in CP CML. In addition, modulation of the endogenous T-cell function during IM therapy was studied.

Methods

We evaluated Th1 (gamma interferon (IFN-γ)), Th2 (interleukin (IL-4)) and tumor necrosis factor (TNF)-α cytokine synthesis by activated T-cell subsets in 20 patients with newly diagnosed CML in chronic phase (CP CML) using flow cytometry before and during IM therapy compared to patients with IM resistance (IM Res) and healthy donors.

Results

Patients with optimal response (CML OR) to IM demonstrated a lower pre-treatment Th1 cytokine compared to that of healthy donors, and a higher percentage of Th2 and TNF-α producing T cells compared to that of healthy donors, non-optimal responders (CML nOR) and those with IM Res. A shift from Th2 profile to Th1 profile and initial decline of TNF-α producing T cells was detected early during therapy in optimal responders which was coinciding with complete hematological remission with a significant increase in the percentages of CD4+ve/IFN-γ+ve cells (P = 0.01) and a significant drop of in CD8+ve/IL-4+ve T cells (P = 0.04).

Conclusion

We believe that pre-treatment levels of IL-4 and/or TNF-α may have a role in identifying CP CML patients who may respond to IM therapy; however, further investigation is needed.

Cancer immune therapy for myeloid malignancies: present and future

The myelodysplastic syndromes, the chronic myeloproliferative neoplasms, and the acute myeloid leukemia are malignancies of the myeloid hematopoietic stem cells of the bone marrow. The diseases are characterized by a dysregulation of the immune system as both the cytokine milieu, immune phenotype, immune regulation, and expression of genes related to immune cell functions are deregulated. Several treatment strategies try to circumvent this deregulation, and several clinical and preclinical trials have shown promising results, albeit not in the same scale as chimeric antigen receptor T cells have had in the treatment of refractory lymphoid malignancies. The use of immune checkpoint blocking antibodies especially in combination with hypomethylating agents has had some success-a success that will likely be enhanced by therapeutic cancer vaccination with tumor-specific antigens. In the chronic myeloproliferative neoplasms, the recent identification of immune responses against the Januskinase-2 and calreticulin exon 9 driver mutations could also be used in the vaccination setting to enhance the anti-tumor immune response. This immune response could probably be enhanced by the concurrent use of immune checkpoint inhibitors or by vaccination with epitopes from immune regulatory proteins such as arginase-1 and programmed death ligand-1. Herein, we provide an overview of current cancer immune therapeutic treatment strategies as well as potential future cancer immune therapeutic treatment options for the myeloid malignancies.

Cellular and Molecular Networks in Chronic Myeloid Leukemia: The Leukemic Stem, Progenitor and Stromal Cell Interplay

The use of imatinib, second and third generation ABL tyrosine kinase inhibitors (TKI) (i.e. dasatinib, nilotinib, bosutinib and ponatinib) made CML a clinically manageable and, in a small percentage of cases, a cured disease. TKI therapy also turned CML blastic transformation into a rare event; however, disease progression still occurs in those patients who are refractory, not compliant with TKI therapy or develop resistance to multiple TKIs. In the past few years, it became clear that the BCRABL1 oncogene does not operate alone to drive disease emergence, maintenance and progression. Indeed, it seems that bone marrow (BM) microenvironment-generated signals and cell autonomous BCRABL1 kinase-independent genetic and epigenetic alterations all contribute to: i. persistence of a quiescent leukemic stem cell (LSC) reservoir, ii. innate or acquired resistance to TKIs, and iii. progression into the fatal blast crisis stage. Herein, we review the intricate leukemic network in which aberrant, but finely tuned, survival, mitogenic and self-renewal signals are generated by leukemic progenitors, stromal cells, immune cells and metabolic microenvironmental conditions (e.g. hypoxia) to promote LSC maintenance and blastic transformation.

The BCR-ABL1 transcript type influences response and outcome in Philadelphia chromosome-positive chronic myeloid leukemia patients treated frontline with imatinib

The most frequent BCR-ABL1 fusion transcripts in chronic myeloid leukemia (CML) are the e13a2 (b2a2) and the e14a2 (b3a2) ones. In the imatinib era few studies addressing the prognostic significance of the BCR-ABL1 transcript type in early chronic phase CML have been published. Overall, these studies suggest that in e14a2 patients the response to imatinib is faster and deeper. To evaluate if the BCR-ABL1 transcript type (e13a2 compared to e14a2) affect the response to imatinib and the clinical outcome in newly diagnosed adult CML patients, 559 patients enrolled in 3 prospective studies (NCT00514488, NCT00510926, observational study CML/023) were analyzed. A qualitative PCR was performed at baseline: 52% patients had a e14a2 transcript, 37% a e13a2 transcript, 11% co-expressed both transcripts and 1% had other rare transcripts. The median follow-up was 76 months (95% of the patients had at least a 5-year observation). The complete cytogenetic response rates were comparable in e14a2 and e13a2 patients. The median time to MR^3.0 (6 and 12 months) and MR^4.0 (41 and 61 months) was significantly shorter for e14a2 patients compared to e13a2 patients, with a higher cumulative probability of MR^3.0 (88% and 83%, P < .001) and MR^4.0 (67% and 52%, P = .001). The 7-year overall survival (90% and 83%, P = .017), progression-free survival (89% and 81%, P = .005) and failure-free survival (71% and 54%, P < .001) were significantly better in patients with e14a2 transcript. In conclusion, patients with e13a2 transcript had a slower molecular response with inferior response rates to imatinib and a poorer long-term outcome.

A novel mutation of SETBP1 in atypical chronic myeloid leukemia transformed from acute myelomonocytic leukemia

To investigate an oncogenic mutation of SETBP1 in the evolution from acute myelomonocytic leukemia (M4) to secondary aCML. Clinical data and molecular studies were analyzed of paired aCML and 'normal'DNA from a case with M4. We identified a mutation in SETBP1 (encoding a p.Asp868Ala alteration). The analysis of paired sample indicated that SETBP1 mutation was acquired during leukemic evolution.

Immunological status of chronic myelogenous leukemia patients with complete cytogenetic response after treatment

BACKGROUND

The aim of this study was to compare the T lymphocyte subsets of chronic myelogenous leukemia (CML) patients who had a complete cytogenetic response (CCyR) after treatment with imatinib (IM) or homoharringtonine (HHT).

METHODS

T and Th lymphocyte subsets in CCyR patients treated with HHT (n = 15) or IM (n = 16) were assayed with flow cytometry.

RESULTS

It was found that there were no differences in T lymphocyte subset proportions at the time of achieving CCyR0 and also no difference in the CD8+T cell proportions at the 12th month after CCyR (CCyR12), between the 2 groups. The values of CD3+T, CD4+T, CD8+T, CD4+T/CD8+T, Th1 and Th2 cells were 54.21% ± 6.12% vs. 44.32% ± 4.85%, 29.83% ± 5.53% vs. 22.27% ± 3.22%, 24.66 ± 4.91 vs. 25.41% ± 5.72% , 1.11 ± 0.23 vs. 0.92 ± 0.19, 10.23% ± 4.24% vs. 8.34% ± 3.45% and 11.12% ± 3.91% vs. 13.67% ± 4.78%, respectively in the HHT group and IM group at CCyR12, which meant that the proportions of CD3+T, CD4+T and Th1 cells and the ratio of CD4+T to CD8+T cells were higher and the CD8+T and Th2 cell proportions were lower in the HHT group than in the IM group.

CONCLUSIONS

HHT has a weaker immunodepression effect on T lymphocyte subsets compared with IM.

Immunology of chronic myeloid leukemia: current concepts and future goals

Although chronic myeloid leukemia is a rare malignancy, it has developed into a model system for the study of a variety of aspects of cancer biology and immunology. The introduction of tyrosine kinase inhibitors has resulted in a significant prolongation of the survival rates of chronic myeloid leukemia patients but has not resulted in a cure. There is a growing conviction that this aim can be achieved through immunotherapy. For this concept to be successful, a considerable increase in the present understanding of chronic myeloid leukemia immunology is required. The authors attempt to review and evaluate the current findings that demonstrate a number of immunological aberrations in patients prior to the start of any therapy and their normalization after achieving remission. They also discuss the recent clinical trials with experimental therapeutic vaccines and then present their own strategy on how to address the problem.

H2AX phosphorylation regulated by p38 is involved in Bim expression and apoptosis in chronic myelogenous leukemia cells induced by imatinib

Increasing evidence suggests that histone H2AX plays a critical role in regulation of tumor cell apoptosis and acts as a novel human tumor suppressor protein. However, the action of H2AX in chronic myelogenous leukemia (CML) cells is unknown. The detailed mechanism and epigenetic regulation by H2AX remain elusive in cancer cells. Here, we report that H2AX was involved in apoptosis of CML cells. Overexpression of H2AX increased apoptotic sensitivity of CML cells (K562) induced by imatinib. However, overexpression of Ser139-mutated H2AX (blocking phosphorylation) decreased sensitivity of K562 cells to apoptosis. Similarly, knockdown of H2AX made K562 cells resistant to apoptotic induction. These results revealed that the function of H2AX involved in apoptosis is strictly related to its phosphorylation (Ser139). Our data further indicated that imatinib may stimulate mitogen-activated protein kinase (MAPK) family member p38, and H2AX phosphorylation followed a similar time course, suggesting a parallel response. H2AX phosphorylation can be blocked by p38 siRNA or its inhibitor. These data demonstrated that H2AX phosphorylation was regulated by p38 MAPK pathway in K562 cells. However, the p38 MAPK downstream, mitogen- and stress-activated protein kinase-1 and -2, which phosphorylated histone H3, were not required for H2AX phosphorylation during apoptosis. Finally, we provided epigenetic evidence that H2AX phosphorylation regulated apoptosis-related gene Bim expression. Blocking of H2AX phosphorylation inhibited Bim gene expression. Taken together, these data demonstrated that H2AX phosphorylation regulated by p38 is involved in Bim expression and apoptosis in CML cells induced by imatinib.

SEA antagonizes the imatinib-meditated inhibitory effects on T cell activation via the TCR signaling pathway

The BCR-ABL kinase inhibitor imatinib is highly effective in the treatment of chronic myeloid leukemia (CML). However, long-term imatinib treatment induces immunosuppression, which is mainly due to T cell dysfunction. Imatinib can reduce TCR-triggered T cell activation by inhibiting the phosphorylation of tyrosine kinases such as Lck, ZAP70, LAT, and PLCγ1 early in the TCR signaling pathway. The purpose of this study was to investigate whether the superantigen SEA, a potent T cell stimulator, can block the immunosuppressive effects of imatinib on T cells. Our data show that the exposure of primary human T cells and Jurkat cells to SEA for 24 h leads to the upregulation of the Lck and ZAP70 proteins in a dose-dependent manner. T cells treated with SEA prior to TCR binding had increased the tyrosine phosphorylation of Lck, ZAP70, and PLCγ1. Pretreatment with SEA prevents the inhibitory effects of imatinib on TCR signaling, which leads to T cell proliferation and IL-2 production. It is conceivable that SEA antagonizes the imatinib-mediated inhibition of T cell activation and proliferation through the TCR signaling pathway.

Peptide vaccines for hematological malignancies: a missed promise?

Despite the crucial aid that newly developed target therapies are providing to chemotherapy and stem cell transplant, the cure for many hematological malignancies is still an unmet need. Although available therapies are able to induce an effective debulking of the tumor, most of the time, an insidious minimal residual disease survives current treatments and it is responsible for an immediate or delayed relapse. Peptide-derived antitumor vaccines have been developed with the idea that an artificially "educated" immune system may exert an active specific antitumor response able to control and ultimately eradicate underlying post-treatment residual disease. This review will summarize current knowledge of peptide vaccines for hematological malignancies, trying to analyze promises and pitfalls of a safe and intelligent tool that after many years from its first appearance has not yet established its potential role as alternative immune mediated therapeutic approach for hematopoietic tumors.

Imatinib mesylate and nilotinib affect MHC-class I presentation by modulating the proteasomal processing of antigenic peptides

Imatinib (IM) has been described to modulate the function of dendritic cells and T lymphocytes and to affect the expression of antigen in CML cells. In our study, we investigated the effect of the tyrosine kinase inhibitors IM and nilotinib (NI) on antigen presentation and processing by analyzing the proteasomal activity in CML cell lines and patient samples. We used a biotinylated active site-directed probe, which covalently binds to the proteasomally active beta-subunits in an activity-dependent fashion. Additionally, we analyzed the cleavage and processing of HLA-A3/11- and HLA-B8-binding peptides derived from BCR-ABL by IM- or NI-treated isolated 20S immunoproteasomes using mass spectrometry. We found that IM treatment leads to a reduction in MHC-class I expression which is in line with the inhibition of proteasomal activity. This process is independent of BCR-ABL or apoptosis induction. In vitro digestion experiments using purified proteasomes showed that generation of epitope-precursor peptides was significantly altered in the presence of NI and IM. Treatment of the immunoproteasome with these compounds resulted in an almost complete reduction in the generation of long precursor peptides for the HLA-A3/A11 and -B8 epitopes while processing of the short peptide sequences increased. Treatment of isolated 20S proteasomes with serine-/threonine- and tyrosine-specific phosphatases induced a significant downregulation of the proteasomal activity further indicating that phosphorylation of the proteasome regulates its function and antigen processing. Our results demonstrate that IM and NI can affect the immunogenicity of malignant cells by modulating proteasomal degradation and the repertoire of processed T cell epitopes.

Imatinib induces H2AX phosphorylation and apoptosis in chronic myelogenous leukemia cells in vitro via caspase-3/Mst1 pathway

AIM

Histone H2AX is a novel tumor suppressor and its phosphorylation at the C terminus (Ser139 and Tyr142) is required for tumor cell apoptosis. The aim of the present study was to elucidate the mechanisms underlying imatinib-induced C-terminal phosphorylation of H2AX in chronic myelogenous leukemia cells in vitro.

METHODS

BCR-ABL-positive K562 cells were used. Microscopy, Western blotting and flow cytometry were used to study the signaling pathways that regulate imatinib-induced H2AX phosphorylation and the apoptotic mechanisms.

RESULTS

Treatment of K562 cells with imatinib (1-8 μmol/L) induced phosphorylation of H2AX at Ser139 and Tyr142 in time- and dose-dependent manners. In contrast, imatinib at the same concentrations did not affect H2AX acetylation at Lys 5, and the acetylated H2AX maintained a higher level in the cells. Meanwhile, imatinib (1-8 μmol/L) activated caspase-3 and its downstream mammalian STE20-like kinase 1 (Mst1), and induced apoptosis of K562 cells. The caspase-3 inhibitor Z-VAD (40 μmol/L) reduced imatinib-induced H2AX phosphorylation at Ser139 and Tyr142 and blocked imatinib-induced apoptosis of K562 cells. Imatinib (4 μmol/L) induced expression of Williams-Beuren syndrome transcription factor (WSTF), but not wild-type p53-induced phosphatase 1 (Wip1) in K562 cells.

CONCLUSION

The caspase-3/Mst1 pathway is required for H2AX C-terminal phosphorylation at Ser139 and Tyr142 and subsequent apoptosis in Bcr-Abl-positive K562 cells induced by imatinib.

Efficient RNA interference in patients' acute lymphoblastic leukemia cells amplified as xenografts in mice

Background

Signaling studies in cell lines are hampered by non-physiological alterations obtained in vitro. Physiologic primary tumor cells from patients with leukemia require passaging through immune-compromised mice for amplification. The aim was to enable molecular work in patients' ALL cells by establishing siRNA transfection into cells amplified in mice.

Results

We established delivering siRNA into these cells without affecting cell viability. Knockdown of single or multiple genes reduced constitutive or induced protein expression accompanied by marked signaling alterations.

Conclusion

Our novel technique allows using patient-derived tumor cells instead of cell lines for signaling studies in leukemia.

The immune inhibitory receptor osteoactivin is upregulated in monocyte-derived dendritic cells by BCR-ABL tyrosine kinase inhibitors

Multiple approaches presently aim to combine targeted therapies using tyrosine kinase inhibitors with immunotherapy. Ex vivo-generated dendritic cells are frequently used in such strategies due to their unique ability to initiate primary T-cell immune responses. Besides governing tumor cell growth, many kinases targeted by tyrosine kinase inhibitors are involved in the development and function of dendritic cells and thus tyrosine kinase inhibitor therapy may cause immunoinhibitory side effects. We here report that exposure of developing human monocyte-derived dendritic cells to the BCR-ABL inhibitors imatinib, dasatinib, and nilotinib results in profound upregulation of the transmembrane glycoprotein osteoactivin that has recently been characterized as a negative regulator of T-cell activation. Thus, in line with osteoactivin upregulation, exposure to tyrosine kinase inhibitors resulted in significantly reduced stimulatory capacity of dendritic cells in mixed lymphocyte reactions that could be restored by the addition of blocking anti-osteoactivin antibody. Our data demonstrate that tyrosine kinase inhibitor-mediated inhibition of dendritic cell function is, at least in great part, mediated by upregulation of the immune inhibitory molecule osteoactivin.

Antigens in chronic myeloid leukemia: implications for vaccine development

Treatment with imatinib mesylate and other tyrosine kinase inhibitors (TKI) revolutionized the therapy of chronic myeloid leukemia (CML). However, it alone does not cure this disease. Moreover, some patients develop resistance or adverse effects to this therapy. As successful treatment of a portion of CML patients by hematopoietic stem cell transplantation (HSCT) suggests the importance of immune mechanisms in the elimination of leukemic cells, including leukemia stem cells, TKI administration or HSCT might be combined with vaccination to cure CML patients. However, antigens implicated in the immune responses have not yet been sufficiently identified. Therefore, in this report, we compiled and characterized a list of 165 antigens associated with CML (CML-Ag165) and analyzed the expression of the corresponding genes in CML phases, subpopulations of leukemic cells, and CML-derived cell lines using available datasets from microarray transcriptional-profiling studies. From the CML-Ag165 list, we selected antigens most suitable for vaccine development and evaluated their appropriate characteristics.

Approaches to relapse after allogeneic stem cell transplantation

PURPOSE OF REVIEW

Relapse has become the leading cause of death following allogeneic hematopoietic stem cell transplantation (HSCT). Despite improved understanding of the biology that underlies the graft-versus-leukemia/tumor effect the relapse rate did not decrease over the past 20 years. In general, prognosis is poor for patients who relapsed to an allograft since effective treatment options are limited. Here, we review the available and upcoming treatment approaches for relapse.

RECENT FINDINGS

Treatment of relapse after allogeneic HSCT has been rarely investigated systematically and results differ substantially from diseases. Withdrawal of immunosuppressive medication, donor lymphocyte infusions with or without chemotherapy and/or second allogeneic HSCT are the most used options. New specific cellular approaches such as disease-specific T-cells, alloreactive natural killer cells or vaccination strategies are under investigation. Novel agents such as tyrosine-kinase inhibitors, hypomethylating agents, monoclonal antibodies, immunomodulating drugs, or proteasome-inhibitors either alone or in combination with adoptive immunotherapy are upcoming promising options, but valid data are lacking so far.

SUMMARY

With some exceptions (chronic myeloid leukemia), treatment options for patients who relapse are limited. The results are poor and the majority of patients ultimately die of their disease. More effort and research is needed to prevent and treat relapse after allogeneic HSCT.

Intradermal vaccinations with RNA coding for TAA generate CD8+ and CD4+ immune responses and induce clinical benefit in vaccinated patients

The aim of this phase I/II nonrandomized trial was to assess feasibility, safety as well as immunological and clinical responses of a mRNA-based vaccination in patients with stage IV renal cell cancer using granulocyte-macrophage colony stimulating factor (GM-CSF) as adjuvant. Intradermal injections of in vitro transcribed naked mRNA, which was generated using plasmids coding for the tumor-associated antigens mucin 1(MUC1), carcinoembryonic (CEA), human epidermal growth factor receptor 2 (Her-2/neu), telomerase, survivin, and melanoma-associated antigen 1 (MAGE-A1) were performed in 30 enrolled patients. In the first 14 patients (cohort A) vaccinations were administered on days 0, 14, 28, and 42 (20 µg/antigen) while in the consecutive 16 patients (cohort B) an intensified protocol consisting of injections at days 0-3, 7-10, 28, and 42 (50 µg/antigen) was used. In both cohorts, after this induction period, vaccinations were repeated monthly until tumor progression analyzed by Response Evaluation Criteria In Solid Tumors criteria (RECIST). Vaccinations were well tolerated with no severe side effects and induced clinical responses [six stable diseases (SD) and one partial response in cohort A and nine SD in cohort B]. In cohort A, 35.7% survived 4 years (median survival 24 months) compared to 31.25% in cohort B (median survival 29 months). Induction of CD4(+) and CD8(+) T cell responses was shown for several tumor-associated antigens (TAA) using interferon-γ (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) and Cr-release assays.

Immunotherapy of chronic myeloid leukemia: present state and future prospects

In spite of the considerable successes that have been achieved in the treatment of chronic myeloid leukemia (CML), cure for the disease can only be obtained by the present means in a rather small minority of patients. During the past decade, considerable progress has been made in the understanding of the immunology of CML, which has raised hopes that this disease may be curable by supplementing the current targeted chemotherapy with immunotherapeutic approaches. More than ten small-scale clinical trials have been carried out with experimental vaccines predominantly based on the p210bcr-abl fusion protein. Their results suggested beneficial effects in some patients. Recent data obtained in human patients as well as in animal models indicate that the p210bcr-abl protein does not carry the immunodominant epitope(s). These observations, combined with the recognition of an ever increasing number of other immunogenic proteins in CML cells, strongly support the concept that gene-modified, cell-based vaccines containing the full spectrum of tumor antigens might be the most effective immunotherapeutic approach. Recently created mathematical models have provided important leads for the timing of the combination of targeted drug therapy with vaccine administration. A strategy of how targeted drug therapy might be combined with vaccination is outlined.

NCI First International Workshop on the Biology, Prevention, and Treatment of Relapse after Allogeneic Hematopoietic Stem Cell Transplantation: Report from the Committee on Treatment of Relapse after Allogeneic Hematopoietic Stem Cell Transplantation

Relapse is a major cause of treatment failure after allogeneic hematopoietic stem cell transplantation (alloHSCT). Treatment options for relapse have been inadequate, and the majority of patients ultimately die of their disease. There is no standard approach to treating relapse after alloHSCT. Withdrawal of immune suppression and donor lymphocyte infusions are commonly used for all diseases; although these interventions are remarkably effective for relapsed chronic myelogenous leukemia, they have limited efficacy in other hematologic malignancies. Conventional and novel chemotherapy, monoclonal antibody therapy, targeted therapies, and second transplants have been utilized in a variety of relapsed diseases, but reports on these therapies are generally anecdotal and retrospective. As such, there is an immediate need for well-designed, disease-specific trials for treatment of relapse after alloHSCT. This report summarizes current treatment options under investigation for relapse after alloHSCT in a disease-specific manner. In addition, recommendations are provided for specific areas of research necessary in the treatment of relapse after alloHSCT.

Gene-modified T cells as immunotherapy for multiple myeloma and acute myeloid leukemia expressing the Lewis Y antigen

We have evaluated the carbohydrate antigen Lewis(Y) (Le(Y)) as a potential target for T-cell immunotherapy of hematological neoplasias. Analysis of 81 primary bone marrow samples revealed moderate Le(Y) expression on plasma cells of myeloma patients and myeloblasts of patients with acute myeloid leukemia (AML) (52 and 46% of cases, respectively). We developed a retroviral vector construct encoding a chimeric T-cell receptor that recognizes the Le(Y) antigen in a major histocompatibility complex-independent manner and delivers co-stimulatory signals to achieve T-cell activation. We have shown efficient transduction of peripheral blood-derived T cells with this construct, resulting in antigen-restricted interferon-gamma secretion and cell lysis of Le(Y)-expressing tumor cells. In vivo activity of gene-modified T cells was demonstrated in the delayed growth of myeloma xenografts in NOD/SCID mice, which prolonged survival. Therefore, targeting Le(Y)-positive malignant cells with T cells expressing a chimeric receptor recognizing Le(Y) was effective both in vitro and in a myeloma mouse model. Consequently, we plan to use T cells manufactured under Good Manufacturing Practice conditions in a phase I immunotherapy study for patients with Le(Y)-positive myeloma or AML.

Sustained molecular response with interferon alfa maintenance after induction therapy with imatinib plus interferon alfa in patients with chronic myeloid leukemia

PURPOSE

Imatinib induces sustained remissions in patients with chronic myelogenous leukemia (CML), but fails to eradicate CML stem cells. This is of major concern regarding the issues of cure, long-term imatinib tolerability, and imatinib resistance. We therefore asked whether interferon alfa-2a (IFN) alone could maintain molecular remissions achieved by a prior combination therapy with imatinib and IFN.

PATIENTS AND METHODS

Imatinib therapy was stopped in 20 patients who had concomitantly been pretreated with imatinib and IFN for a median of 2.4 years (range, 0.2 to 4.8 years) and 2.5 years (range, 0.2 to 4.9 years), respectively. After imatinib discontinuation, remission status was monitored monthly by quantitative analysis of the peripheral-blood BCR-ABL mRNA levels using real-time polymerase chain reaction. Proteinase-3 expression and proteinase-3-specific cytotoxic T cells (CTLs) were longitudinally measured to assess putative markers of IFN response.

RESULTS

With a median time of 2.4 years after imatinib withdrawal (range, 0.5 to 4.0 years), 15 (75%) of 20 patients remained in remission. The number of patients in complete molecular remission increased under IFN from two patients at baseline to five patients after 2 years. Relapses occurred in five patients within 0.4 years (range, 0.2 to 0.8 years), but patients underwent rescue treatment with imatinib, re-establishing molecular remission. IFN therapy was associated with an increase in the expression of leukemia-associated antigen proteinase 3 and induction of proteinase-3-specific CTLs.

CONCLUSION

Treatment with IFN enables discontinuation of imatinib in most patients after prior imatinib/IFN combination therapy and may result in improved molecular response. Induction of a proteinase-3-specific CTL response by IFN may contribute to this effect.

Efficacious immune therapy in chronic myelogenous leukemia (CML) recognizes antigens that are expressed on CML progenitor cells

Curative effects of graft-versus-leukemia-based therapies such as donor lymphocyte infusion (DLI) for chronic myelogenous leukemia (CML) may result from immunologic ablation of self-renewing CML progenitor cells. Patients who achieved durable remissions after DLI developed a significant B-cell lymphocytosis after treatment, which did not occur in patients who were unresponsive to DLI. In this study, we identified antigen targets of this B-cell response by probing two immunoproteomic platforms with plasma immunoglobulins from seven CML patients with clinically apparent graft-versus-leukemia responses after DLI. In total, 62 antigens elicited greater reactivity from post-DLI versus pre-DLI plasma. Microarray analysis revealed that >70% of the antigens were expressed in CML CD34(+) cells, suggesting that expression in malignant progenitor cells is a feature common to antibody targets of DLI. We confirmed elevated expression of three target antigens (RAB38, TBCE, and DUSP12) in CML that together consistently elicited antibody responses in 18 of 21 of an additional cohort of CML patients with therapeutic responses, but not in normal donors and rarely in non-CML patients. In summary, immunologic targets of curative DLI responses include multiple antigens on CML progenitor cells, identifying them as potential immunogens for vaccination and/or monitoring of immunotherapeutics designed to eliminate myeloid leukemia stem cells.

Contribution of BCR-ABL-independent activation of ERK1/2 to acquired imatinib resistance in K562 chronic myeloid leukemia cells

BCR-ABL tyrosine kinase, generated from the reciprocal chromosomal translocation t(9;22), causes chronic myeloid leukemia (CML). BCR-ABL is inhibited by imatinib; however, several mechanisms of imatinib resistance have been proposed that account for loss of imatinib efficacy in patients with CML. Previously, we showed that overexpression of the efflux drug transporter P-glycoprotein partially contributed to imatinib resistance in imatinib-resistant K562 CML cells having no BCR-ABL mutations. To explain an additional mechanism of drug resistance, we established a subclone (K562/R) of the cells and examined the BCR-ABL signaling pathway in these and wild-type K562 (K562/W) cells. We found the K562/R cells were 15 times more resistant to imatinib than their wild-type counterparts. In both cell lines, BCR-ABL and its downstream signaling molecules, such as ERK1/2, ERK5, STAT5, and AKT, were phosphorylated in the absence of imatinib. In both cell lines, imatinib effectively reduced the phosphorylation of all the above, except ERK1/2, whose phosphorylation was, interestingly, only inhibited in the wild-type cells. We then observed that phospho-ERK1/2 levels decreased in the presence of siRNA targeting BCR-ABL, again, only in the K562/W cells. However, using an ERK1/2 inhibitor, U0126, we found that we could reduce phospho-ERK1/2 levels in K562/R cells and restore their sensitivity to imatinib. Taken together, we conclude that the BCR-ABL-independent activation of ERK1/2 contributes to imatinib resistance in K562/R cells, and that ERK1/2 could be a target for the treatment of CML patients whose imatinib resistance is due to this mechanism.

Tumour antigen-targeted immunotherapy for chronic myeloid leukaemia: is it still viable?

In haematological cancers, malignant cells circulate in the blood and lymphatic system. This may make leukaemic cells easier to target by immunotherapy than in other types of cancer. Various immunotherapy strategies have been trialled in several leukaemias including chronic myeloid leukaemia (CML) and in general, these have been aimed at targeting tumour-associated antigens (TAA). There are numerous TAA expressed by CML patients including WT1, proteinase 3, BCR-ABL and HAGE amongst others. The immunogenicity of the CML-specific tumour antigen, BCR-ABL, has been the subject of much debate and its role in the development of the disease and its unique sequence spanning the breakpoint region make it an ideal target for immunotherapy. However, there are a limited number of immunogenic epitopes across the junctional region, which are restricted to only a few HLA types, namely A2, A3 and B7 (Clark et al. in Blood 98:2887-2893, 2001). The second CML-associated antigen is the helicase antigen HAGE, a cancer-testis antigen found to be over-expressed in more than 50% of myeloid leukaemias (Adams et al. in Leukaemia 16:2238-2242, 2002). Very little is known about the function of this antigen and its significance to CML. However, its membership of the DEAD-box family of ATP-dependent RNA helicases and the involvement of other members of this family in tumour cell proliferation (Eberle et al. in Br J Cancer 86:1957-1962, 2002; Yang et al. in Cell Signal 17:1495-504, 2005) suggest a crucial role in the RNA metabolism of tumour cells. For these reasons, HAGE also seems to be a good target for immunotherapy as it would be applicable for the majority of patients with CML. This review aims to discuss the potential of immunotherapy for the treatment of leukaemia, in particular CML, and the prospect of targeting three CML associated antigens: BCR, ABL and HAGE. During his career, Prof. Tony Dodi made a significant contribution in this area of leukaemia research, confirming the identity of immunogenic HLA-A3 and B7-restricted peptides as targets for CTL. Published, as a highlighted paper in Clark et al. (Blood 98:2887-2893, 2001), this study demonstrated the expression of MHC-peptide complexes on the surface of CML cells and the presence of tetramer-positive CTL activity in CML patients positive for these two HLA alleles. His drive and dedication for research excellence will be remembered by all who knew and worked with him.

The biological basis for immunotherapy in patients with chronic myelogenous leukemia

BACKGROUND

Chronic myelogenous leukemia (CML) has long been recognized as an entity responsive to immunotherapeutic interventions. Despite the success of the tyrosine kinase inhibitors (TKIs) in this disease, CML remains incurable. Only allogeneic bone marrow transplantation can provide long-term eradication of CML.

METHODS

This review summarizes the recent advances in the field of immunology in CML, specifically in tumor antigen discovery, that have been incorporated into the design of new clinical trials.

RESULTS

Multiple vaccine approaches are currently under clinical investigation. Recent laboratory and clinical data also point to a unique interaction of TKIs with the immune system.

CONCLUSIONS

A better understanding of these interactions combined with advances in the field of immunotherapy will likely lead to incorporation of TKIs in future therapeutic interventions to develop a cure for this disease.

Immunomodulatory effects of imatinib and second-generation tyrosine kinase inhibitors on T cells and dendritic cells: an update

The discovery of new drugs has occasionally led to a better understanding of biologic processes and unforeseen therapeutic applications. One such example is the new group of tyrosine kinase inhibitors, exemplified by the Bcr-Abl inhibitor imatinib (Glivec). In the last 10 years, these so-called 'small molecules' have started to enter the clinic with the promise of cancer treatments targeted at the underlying molecular changes that are responsible for specific malignant phenotypes. The aim of these small molecules has been to avoid the side-effects of systemic chemotherapies and the high morbidity/mortality risks associated with hematopoietic stem cell transplantation. Concurrently, however, increasing evidence has emerged to indicate that these drugs exert profound immunomodulatory effects on T cells and antigen-presenting cells, such as dendritic cells, which play major roles in immune tumor surveillance and the outcome of hematopoietic stem cell transplantation. Targeted tyrosine kinase inhibitor therapy may thus control cancer cell growth both directly and indirectly by changing the immunologic microenvironment. Furthermore, such molecules might help to unravel the complexities of the human immune system and could find therapeutic application in conditions as diverse as autoimmune diseases and certain infectious processes. In this brief review, we discuss recent developments in this fast evolving field.

Development and dynamics of robust T-cell responses to CML under imatinib treatment

Novel molecular targeted therapies, such as imatinib for chronic myelogenous leukemia (CML), represent the first agents that inhibit cancer cells more than other dividing cells, such as immune cells. We hypothesize that imatinib may create a window in which the immune response is partially restored while apoptotic leukemic cells are present, thus rendering leukemic cells immunogenic as patients enter remission. To detect and quantify antileukemia immune responses in an antigen-unbiased way, we used cryopreserved autologous pretreatment blood samples (representing predominantly leukemic cells) as stimulators to detect antileukemia T-cell responses in CML patients in remission on imatinib. We studied patients over time to address the dynamics of such responses. Our data show that antileukemia T-cell responses develop in the majority of CML patients (9 of 14) in remission and that CD4(+) T cells producing tumor necrosis factor-alpha (median 17.6%) represent the major response over interferon-gamma. This confirms the immune system's ability to respond to leukemia under certain conditions. Such responses may be further amplified as a potential therapy that synergizes with imatinib for improved control of CML.