Identification and characterization of epitopes of the receptor for hyaluronic acid-mediated motility (RHAMM/CD168) recognized by CD8+ T cells of HLA-A2-positive patients with acute myeloid leukemia

The receptor for hyaluronic acid-mediated motility (RHAMM/CD168) has been described as a leukemia-associated antigen. To define T-cell epitopes of RHAMM/CD168 toward specific immunotherapies for acute myeloid leukemia (AML), 10 potential HLA-A2-binding RHAMM/CD168 peptides (R1 to R10) were synthesized based on computer algorithms and screened by enzyme-linked immunospot (ELISPOT) analysis using CD8+ T cells isolated from peripheral blood (PB) of patients with AML and healthy donors. We found that CD8+ cells from 7 of 13 (54%) patients with AML presensitized with peptides R3 (ILSLELMKL) or R5 (SLEENIVIL) specifically recognized T2 cells pulsed with R3 (39%) or R5 (15%) peptide. In contrast, only 4 of 21 (19%) healthy volunteers had CD8+ cells reactive with R3- or R5-pulsed T2 cells after presensitization. The presence of R3 peptide-specific effector T cells in the peripheral blood of patients with AML could be confirmed by staining as HLA-A2/R3 peptide tetramer+ CCR7-CD45RA+ cells. In chromium-51 release assays, peptide-primed CD8+ T cells from patients with AML were able to lyse RHAMM/CD168 peptide-pulsed T2 cells, AML blasts, and dendritic cells generated thereof (AML DCs). Transfection of COS7 cells with RHAMM/CD168 cDNA revealed that peptides R3 and R5 are naturally processed epitopes of RHAMM/CD168 that are presented in an HLA-A2-restricted manner. In summary, RHAMM/CD168 is a promising target for immunotherapies in patients with AML, and we have therefore initiated a clinical vaccination trial with R3 peptide. Because RHAMM/CD168 is also expressed in various other hematologic malignancies and solid tumors, vaccines targeting this antigen may have even wider application.     

High-dose RHAMM-R3 peptide vaccination for patients with acute myeloid leukemia, myelodysplastic syndrome and multiple myeloma

Background

Recently, we demonstrated immunological and clinical responses to a RHAMM-R3 peptide vaccine in patients with acute myeloid leukemia, myelodysplastic syndrome and multiple myeloma. To improve the outcome of the vaccine, a second cohort was vaccinated with a higher dose of 1,000 μg peptide.

Design and Methods

Nine patients received four vaccinations subcutaneously at a biweekly interval. Immunomonitoring of cytotoxic CD8⁺ as well as regulatory CD4⁺ T cells was performed by flow cytometry as well as by enzyme-linked immunospot (ELISpot) assays. Parameters of clinical response were assessed.

Results

In 4 of 9 patients (44%) we detected positive immunological responses. These patients showed an increase of CD8⁺RHAMM-R3_tetramer⁺/CD45RA⁺/CCR7⁻/CD27⁻/CD28⁻ effector T cells and an increase of R3-specific CD8+ T cells. Two of these patients showed a significant decrease of regulatory T cells (Tregs). In one patient without response Tregs frequency increased from 5 to 16%. Three patients showed clinical effects: one patient with myelodysplastic syndrome RAEB-1 showed a reduction of leukemic blasts in the bone marrow, another myelodysplastic syndrome patient an improvement of peripheral blood counts and one patient with multiple myeloma a reduction of free light chains. Clinical and immunological reactions were lower in this cohort than in the 300 μg cohort.

Conclusions

High-dose RHAMM-R3 peptide vaccination induced immunological responses and positive clinical effects. Therefore, RHAMM constitutes a promising structure for further targeted immunotherapies in patients with different hematologic malignancies. However, higher doses of peptide did not improve the frequency and intensity of immune responses in this trial. (This study is registered at http://ISRCTN.org as ISRCTN32763606)     

In situ RHAMM protein expression in acute myeloid leukemia blasts suggests poor overall survival

Treatment options for patients with high-risk acute myeloid leukemia (AML) include high-dose chemotherapy regimens in combination with allogeneic hematopoietic stem cell transplantation, which takes advantage of the donor T-cell-mediated graft-versus-leukemia effect. Together with beneficial responses observed in assays targeted at leukemia-associated antigens (LAA), this encouraged research on cancer vaccines and adoptive cellular therapies in AML. The receptor for hyaluronic acid-mediated motility (RHAMM, CD168) was identified as one of the most promising LAA in AML. Thus far, little is known about in situ expression in leukemic bone marrow blasts or the prognostic role of RHAMM and its interaction partners in AML. We immunohistochemically analyzed the expression and prognostic significance of RHAMM on trephine bone marrow biopsies from 71 AML cases that had been evaluated for cytogenetics and presence of FLT3-internal tandem duplications and NPM1 mutations. Fifty-five patients (77%) were treated with curative intent, while 16 (23%) received the most appropriate supportive care. Twenty of 71 (28%) AML cases were considered RHAMM+. Receiver operating characteristic curves showed significant discriminatory power considering overall survival (OS) in AML patients treated curatively for RHAMM (p = 0.015). Multivariable analysis revealed that expression of RHAMM in >5% of leukemic blasts identifies a subgroup of curatively treated cases with adverse OS independent of failures to achieve complete remission. RHAMM not only represents a promising LAA with specific T-cell responses in AML but, if assessed in situ on blasts, also a probable prognostic factor.     

Generation of migratory antigen-specific plasma blasts and mobilization of resident plasma cells in a secondary immune response

Maintenance of protective humoral immunity depends on the generation and survival of antibody-secreting cells. The bone marrow provides niches for long-term survival of plasma cells generated in the course of systemic immune responses in secondary lymphoid organs. Here, we have analyzed migratory human plasma blasts and plasma cells after secondary vaccination with tetanus toxin. On days 6 and 7 after immunization, CD19(+)/CD27(high)/intracellular immunoglobulin G(high) (IgG(high))/HLA-DR(high)/CD38(high)/CD20(-)/CD95(+) tetanus toxin-specific antibody-secreting plasma blasts were released in large numbers from the secondary lymphoid organs into the blood. These cells show chemotactic responsiveness toward ligands for CXCR3 and CXCR4, probably guiding them to the bone marrow or inflamed tissue. At the same time, a population of CD19(+)/CD27(high)/intracellular IgG(high)/HLA-DR(low)/CD38(+)/CD20(-)/CD95(+) cells appeared in the blood in large numbers. These cells, with the phenotype of long-lived plasma cells, secreted antibodies of unknown specificity, not tetanus toxoid. The appearance of these plasma cells in the blood indicates successful competition for survival niches in the bone marrow between newly generated plasma blasts and resident plasma cells as a fundamental mechanism for the establishment of humoral memory and its plasticity.     

Dendritic cells fused with core binding factor-beta positive acute myeloid leukaemia blast cells induce activation of cytotoxic lymphocytes

Several reports have described various strategies of dendritic cell (DC) vaccination to induce specific T-cell responses in patients with acute myeloid leukaemia (AML). About 50-60% of AML cases blasts have chromosomal abnormalities, such as inv(16) or t(8,21), which could encode for leukaemia-specific antigenic peptide sequences, possibly presented in the context of self-major histocompatibility complex (MHC) molecules. As the co-culture of AML blasts with T lymphocytes seldom resulted in T-cell stimulation, we fused AML blasts with autologous DC to enhance this effect. The fusion cells expressed MHC class I and II, CD40, B7-1, B7-2, CD209 and several adhesion molecules. In a mixed lymphocyte hybrid reaction, the fusion cells induced the proliferation of autologous T cells. Moreover, in the special case of fusion cells established from AML blasts with the chromosomal abnormality inv(16), the autologous T lymphocytes could be primed to induce cytotoxicity against up to 70% autologous AML blasts in a effector:target ratio of 20:1. Blocking assays demonstrated that the lysis was chiefly mediated by CD8(+), CCR7(-) T lymphocytes, which could be further expanded in the form of effector memory CD8(+) T cells by repeated co-cultures with the autologous fusion cells.     

Exisulind induces apoptosis in advanced myelodysplastic syndrome (MDS) and acute myeloid leukaemia/MDS

The influence of Exisulind on the viability and apoptosis of CD34(+) stem cells from patients with advanced myelodysplastic syndrome (MDS) and acute myeloid leukaemia (AML)/MDS was investigated. In eight out of 10 patient samples Exisulind reduced the fraction of viable cells by inducing apoptosis. We found evidence that Exisulind-mediated apoptosis depends on c-Jun NH(2)-terminal kinase (JNK) activation. Addition of a specific JNK-inhibitor to Exisulind-treated advanced MDS and AML/MDS cells partly abrogated apoptosis. We propose that Exisulind is tested in clinical phase I/II trials for the treatment of advanced MDS and AML/MDS.     

Overexpression of IL-3Rα on CD34+CD38- stem cells defines leukemia-initiating cells in Fanconi anemia AML

Patients with Fanconi anemia (FA) have a high risk of developing acute myeloid leukemia (AML). In this study, we attempted to identify cell-surface markers for leukemia-initiating cells in FA-AML patients. We found that the IL-3 receptor-α (IL-3Rα) is a promising candidate as an leukemia-initiating cell-specific antigen for FA-AML. Whereas IL-3Rα expression is undetectable on normal CD34(+)CD38(-) HSCs, it is overexpressed on CD34(+)CD38(-) cells from FA patients with AML. We examined the leukemia-initiating cell activity of IL-3Rα-positive FA-AML cells in a "humanized" FA xenotransplant model in which we separated AML cells into IL-3Rα-positive and IL-3Rα-negative CD34 fractions and transplanted them into irradiated recipient mice. In all 3 FA-AML samples, only IL-3Rα-positive cells showed significant levels of engraftment and developed leukemia in the recipient mice. The FA CD34(+)IL-3Rα(+) blasts isolated from leukemic mice exhibited hypersensitivity to IL-3 deprivation and JAK2-STAT5 overactivation after IL-3 treatment. Finally, treatment of FA CD34(+)IL-3Rα(+) blasts with an IL-3Rα-neutralizing antibody inhibited IL-3-mediated proliferation and STAT5 activation. These results demonstrate that IL-3Rα is a cell-surface marker present on FA-AML leukemia-initiating cells and may be a valuable therapeutic target.     

Mutated regions of nucleophosmin 1 elicit both CD4(+) and CD8(+) T-cell responses in patients with acute myeloid leukemia

Mutations in the nucleophosmin gene (NPM1(mut)) are one of the most frequent molecular alterations in acute myeloid leukemia (AML), and immune responses may contribute to the favorable prognosis of AML patients with NPM1(mut). In the present study, we were able to demonstrate both CD4(+) and CD8(+) T-cell responses against NPM1(mut). Ten peptides derived from wild-type NPM1 and NPM1(mut) were subjected to ELISPOT analysis in 33 healthy volunteers and 27 AML patients. Tetramer assays against the most interesting epitopes were performed and Cr(51)-release assays were used to show the cytotoxicity of peptide-specific T cells. Moreover, HLA-DR-binding epitopes were used to test the role of CD4(+) T cells in NPM1 immunogenicity. Two epitopes (epitopes #1 and #3) derived from NPM1(mut) induced CD8(+) T-cell responses. A total of 33% of the NPM1(mut) AML patients showed immune responses against epitope #1 and 44% against epitope #3. Specific lysis of leukemic blasts was detected. To obtain robust immune responses against tumor cells, the activation of CD4(+) T cells is crucial. Therefore, overlapping (OL) peptides were analyzed in ELISPOT assays and OL8 was able to activate both CD8(+) and CD4(+) T cells. The results of the present study show that NPM1(mut) induces specific T-cell responses of CD4(+) and CD8(+) T cells and therefore is a promising target for specific immunotherapies in AML.     

Primitive acute myeloid leukemia cells with long-term proliferative ability in vitro and in vivo lack surface expression of c-kit (CD117)

A hierarchy of progenitor cells is thought to exist in human acute myeloid leukemia (AML), with only the most primitive cells capable of proliferating to maintain the malignant clone. To further characterize this AML cell hierarchy, we evaluated the coexpression of CD34 and c-kit (CD117) on cells that are capable of long-term proliferation in vitro and in vivo.AML cells were sorted for coexpression of CD34 and c-kit (CD117) using two c-kit monoclonal antibodies (mAbs), clones 95C3 and 104D2. Sorted subfractions were evaluated for the ability to produce colony-forming units (CFU) for up to 8 weeks in suspension culture (SC) and for the capacity to repopulate NOD/SCID mice.When expression of c-kit on blood cells from 19 AML patients at diagnosis was compared using both mAbs, expression defined by 104D2 (34% +/- 6% c-kit(+)) was somewhat higher than that defined using 95C3 (18% +/- 4%). AML cells were sorted for coexpression of CD34 and c-kit using both c-kit mAbs, and the subfractions were assayed in vitro and in vivo. Whereas the majority of AML blast cells lacked expression of CD34, most AML cells capable of proliferating to produce CFU after 4 to 8 weeks in SC were CD34(+)/c-kit(-). Cultures of sorted CD34(+)/c-kit(-) cells, supplemented with steel factor, were composed of a large proportion (18% to 87%) of CD34(+)/c-kit(+) cells after 1 week, suggesting that either c-kit expression was upregulated or CD34(+)/c-kit(+) cells were produced. Moreover, the CD34(+)/c-kit(-) subfraction was found to be capable of responding to steel factor alone to produce CFU after 4 weeks in SC. In most AML patients tested (11/15), the only sorted subfraction capable of engrafting NOD/SCID mice was CD34(+)/c-kit(-). The CD34(+)/c-kit(+) subfraction from only 2 of the 15 patients and CD34(-) cells from 3 patients also engrafted the NOD/SCIDs. Only the CD34(+)/c-kit(+) subfraction of normal bone marrow engrafted.These studies suggest that primitive AML cells capable of long-term proliferation in vitro and NOD/SCID repopulation differ from primitive normal progenitor cells in their lack of surface expression of c-kit.     

Expression profiling reveals fundamental biological differences in acute myeloid leukemia with isolated trisomy 8 and normal cytogenetics

Acute myeloid leukemia (AML) is a heterogeneous group of diseases. Normal cytogenetics (CN) constitutes the single largest group, while trisomy 8 (+8) as a sole abnormality is the most frequent trisomy. How trisomy contributes to tumorigenesis is unknown. We used oligonucleotide-based DNA microarrays to study global gene expression in AML+8 patients with +8 as the sole chromosomal abnormality and AML-CN patients. CD34(+) cells purified from normal bone marrow (BM) were also analyzed as a representative heterogeneous population of stem and progenitor cells. Expression patterns of AML patients were clearly distinct from those of CD34(+) cells of normal individuals. We show that AML+8 blasts overexpress genes on chromosome 8, estimated at 32% on average, suggesting gene-dosage effects underlying AML+8. Systematic analysis by cellular function indicated up-regulation of genes involved in cell adhesion in both groups of AML compared with CD34(+) blasts from normal individuals. Perhaps most interestingly, apoptosis-regulating genes were significantly down-regulated in AML+8 compared with AML-CN. We conclude that the clinical and cytogenetic heterogeneity of AML is due to fundamental biological differences.     

Cancer vaccines for patients with acute myeloid leukemia--definition of leukemia-associated antigens and current clinical protocols targeting these antigens

Targeted immunotherapies require the identification and characterization of appropriate antigen structures. Initially, T-cell based cancer vaccines were designed for patients with solid tumors after the definition of suitable tumor-associated antigens. Several immunological and even clinical responses prompted researchers and clinicians to extend the spectrum of cancer vaccines towards hematologic malignancies such as acute myeloid leukemia (AML). Only 20-40% of all patients with AML achieve a disease-free survival of more than 5 years. The graft-versus-leukemia (GVL) effect observed after allogeneic stem cell transplantation and donor lymphocyte infusions strongly suggests that T lymphocytes play a major role in the rejection of leukemic cells. Therefore, immunotherapy directed against leukemia-associated antigens might elicit specific immune responses that could eliminate minimal residual disease after chemotherapy, or enhance the GVL effect after hematopoietic stem cell transplantation. This review summarizes hitherto identified and characterized LAA as targets for T-cell-based immunotherapies. Current clinical peptide vaccination trials targeting different epitopes of the Wilms' tumor gene 1 (WT1), the proteinase-3 derived epitope peptide (PR1) and the receptor for hyaluronic acid mediated motility (RHAMM/CD168)-derived epitope R3 are reviewed, and perspectives but also limitations of immunotherapeutic approaches for AML patients are discussed.     

Clinical significance of phenotypic features of blasts in patients with myelodysplastic syndrome

Knowledge of the blast phenotype in myelodysplastic syndrome (MDS) would be valuable, as in other malignancies, but remains sparse. This is mainly because MDS blasts are a minor population in clinical samples, making analysis difficult. Thus, for this blast phenotype study, we prepared blast-rich specimens (using a new density centrifugation reagent for harvesting blasts) from blood and marrow samples of 95 patients with various MDS subtypes and 21 patients with acute leukemia transformed from MDS (AL-MDS). Flow cytometry revealed that a high proportion of the enriched blast cells (EBCs) from almost all patients showed an immunophenotype of committed myeloid precursors (CD34(+)CD38(+)HLA-DR(+)CD13(+)CD33(+)), regardless of the disease subtype. The cytochemical reaction for myeloperoxidase was negative in 58% of the cases. Thus, the EBC phenotype is more immature in MDS than in de novo acute myeloid leukemia. MDS EBCs often coexpressed stem cell antigens and late-stage myeloid antigens asynchronously, but rarely expressed T- and B-lymphoid cell-specific antigens. Markers for myeloid cell maturation (CD10 and CD15) were more prevalent on EBCs from low-risk MDS (refractory anemia [RA] and RA with ringed sideroblasts), whereas markers for myeloid cell immaturity (CD7 and CD117) were more prevalent on EBCs from high-risk MDS (chronic myelomonocytic leukemia, RA with excess blasts [RAEB], and RAEB in transformation) and AL-MDS. A shift to a more immature phenotype of EBCs, accompanying disease progression, was also documented by sequential phenotyping of the same patients. Further, CD7 positivity of EBCs was an independent variable for a poor prognosis in MDS. These data represent new, valuable information regarding MDS.     

Chronic myeloid leukemia cells express tumor-associated antigens eliciting specific CD8+ T-cell responses and are lacking costimulatory molecules

Specific immunotherapies for patients with chronic myeloid leukemia (CML) might eliminate residual CML cells after therapy with imatinib or chemotherapy and might enhance a specific graft-versus-leukemia effect after allogeneic stem cell transplantation. Here, we investigated the mRNA expression and T-cell recognition of tumor-associated antigens or leukemia-associated antigens (LAAs) in 34 patients with CML. Several LAAs are expressed in CML and therefore are candidate structures for specific immunotherapies: bcr-abl (100%), G250 (24%), hTERT (53%), MPP11 (91%), NEWREN60 (94%), PRAME (62%), Proteinase3 (71%), RHAMM/CD168 (83%), and WT1 (53%), but not BAGE, MAGE-A1, SSX2, or NY-ESO-1. The frequency of mRNA expression of RHAMM/CD168, Proteinase3, and PRAME was higher in acceleration phase and blast crisis. In flow cytometry, CD34+ progenitor cells typed positive for HLA molecules but were deficient for CD40, CD80, CD83, and CD86. However, RHAMM/CD168 R3-peptide (ILSLELMKL)-specific T-cell responses in CML patients were demonstrated by ELISPOT analysis and specific lysis of RHAMM/CD168 R3-pulsed T2 cells and CD34+ CML cells in chromium-51 release assays. RHAMM-R3-specific T cells could be phenotyped as CD8+R3*tetramer+CD45RA+CCR7-CD27- early effector T cells by tetramer staining. Therefore, vaccination strategies inducing such RHAMM-R3-directed effector T cells might be a promising approach to enhance specific immune responses against CML cells.     

FLT3 internal tandem duplication in CD34+/CD33- precursors predicts poor outcome in acute myeloid leukemia

Acute myeloid leukemia (AML) is a clonal disease characterized by heterogeneous involvement of hematopoietic stem cell/progenitor cell populations. Using FLT3 internal tandem duplication (FLT3/ITD) as a molecular marker, we tested the hypothesis that clinical outcome in AML correlates with disease involvement of CD34(+)/CD33(-) precursors. Diagnostic specimens from 24 children with FLT3/ITD-positive AML were sorted by fluorescence-activated cell sorting (FACS), and resultant CD34(+)/CD33(-) and CD34(+)/CD33(+) progenitors were analyzed directly and after colony-forming cell (CFC) assay for the presence of FLT3/ITD. FLT3/ITD was present in all CD34(+)/CD33(+) patient samples. In contrast, FLT3/ITD was detected in CD34(+)/CD33(-) progenitors in only 19 of 24 samples. A bipotent progenitor was affected in a subset of patients, as evidenced by the presence of FLT3/ITD in both granulocyte-macrophage colony-forming unit (CFU-GM) and erythroid burst-forming unit (BFU-E) colonies. Those patients in whom CD34(+)/CD33(-) precursors harbored the FLT3/ITD had worse clinical outcome; actuarial event-free survival (EFS) at 4 years from study entry for those patients with and without FLT3/ITD detection in CD34(+)/CD33(-) progenitors was 11% +/- 14% versus 100% +/- 0%, respectively (P = .002). This study suggests that FLT3/ITD involvement in CD34(+)/CD33(-) precursors is heterogeneous and that detection of the mutation in the less-mature progenitor population may be associated with disease resistance.     

Clinical grade expansion of CD45RA, CD45RO, and CD62L-positive T-cell lines from HLA-compatible donors: high cytotoxic potential against AML and ALL cells

OBJECTIVE: Identification of a clinical grade method for the ex vivo generation of donor-derived T cells cytotoxic against both myeloid and lymphoblastic cells still remains elusive. We investigated rapid generation and expansion of donor derived-allogeneic T-cell lines cytotoxic against patient leukemic cells. MATERIALS AND METHODS: Acute myelogenous leukemia (AML) and acute lymphoblastic leukemia (ALL) blasts were cultured 5 days in Stem Span, granulocyte macrophage colony-stimulating factor, interleukin-4, and calcium ionophore. All B-precursor ALL (N22) and AML (N13), but not T-cell ALL (N3), differentiated into mature leukemia-derived antigen-presenting cells (LD-APC). All but one LD-APC generated cytotoxic T lymphocyte (CTL) from adult human leukocyte antigen (HLA)-identical (N8) or unrelated donors (N2). RESULTS: Upon in vitro culture, donor-derived CTL acquired a memory T phenotype, showing concomitant high CD45RA, CD45RO, CD62L expression. CD8(+) cells, but not CD4(+) cells, were granzyme, perforine, and interferon-gamma-positive. Pooled CD4(+) and CD8(+) cells were cytotoxic against leukemic blasts (32%, 30:1 E:T ratio), but not against autologous or patient-derived phytohemagglutinin blasts. LD-APC from five ALL patients were used to generate CTL from cord blood. A mixed population of CD4(+) and CD8(+) cells was documented in 54% of wells. T cells acquired classical effector memory phenotype and showed a higher cytotoxicity against leukemia blasts (47%, 1:1 E:T ratio). Adult and cord blood CTL showed a skewing from a complete T-cell receptor repertoire to an oligo-clonal/clonal pattern. CONCLUSIONS: Availability of these cells should allow clinical trials for salvage treatment of leukemia patients relapsing after allogeneic stem cell transplantation.     

Myelodysplastic syndrome is not merely "preleukemia"

Myelodysplastic syndrome (MDS) is a disease characterized by ineffective hematopoiesis. There are significant biologic and clinical differences between MDS and acute myeloid leukemia (AML). We studied a cohort of 802 patients, 279 (35%) with newly diagnosed MDS and 523 (65%) with newly diagnosed AML, and compared clinical and biologic characteristics of the 2 groups. Complete clinical and cytogenetic data were available on all patients, and a subgroup of patients was studied for apoptosis, angiogenesis, proliferation, and growth factors. Our results demonstrate that MDS is a discrete entity that is different from AML and is characterized primarily by increased apoptosis in early and mature hematopoietic cells. Using cell sorting and loss of heterozygosity, we demonstrate that the leukemic cells from MDS patients are capable of differentiation into mature myeloid cells and monocytes. We also demonstrate that there is a significant overlap between AML and MDS when MDS is defined on the basis of an arbitrary percentage of blasts of 20% or 30%. These data suggest that despite similarities between AML and MDS in their responses to treatment and outcomes, MDS is biologically and clinically different from AML and should not be considered an early phase of AML. The data indicate that MDS must be better defined on the basis of its biology rather than the percentage of blasts; further, the data suggest that there is a need to develop therapeutic approaches that specifically address the biologic abnormalities of MDS.     

Expression of CD86 in acute myelogenous leukemia is a marker of dendritic/monocytic lineage

OBJECTIVE: The aim of this study was to determine whether expression of the CD86 costimulatory molecule in acute myeloid leukemia (AML) can identify blast cells committed to the monocytic/dendritic lineage. MATERIAL AND METHODS: One hundred ten consecutive AML patients observed at diagnosis were studied by flow cytometry. In selected experiments, in vitro cultures with CD34(+)CD86(+) or CD34(-)CD86(+) blasts were performed in the presence of granulocyte-macrophage colony-stimulating actor (GM-CSF) with or without tumor necrosis factor-alpha (TNF-alpha) or GM-CSF + interleukin-4 (IL-4), respectively, to induce a dendritic differentiation, documented by morphologic and immunophenotypic assays. T-cell alloreactivity to CD86(+) AML cells and leukemic dendritic cells (AML-DC) was tested in mixed leukocyte cultures and anti-leukemic cytotoxic assays. RESULTS: CD86 was expressed in 54% AML, whereas CD80 and CD1a were only occasionally positive. CD86(+) AML samples included M5 and M4, but also 47% M0-M1 FAB types, and were more frequently CD14(+) (p < 0.00001) and CD34(-) (p = 0.00005) than CD86(-)AML. Six different patterns of CD86(+) AML were identified, according to CD34 or CD14 total or partial coexpression. Four samples enriched in CD34(+)CD86(+) AML cells differentiated into AML-DC CD86(+), CD80(+), CD40(+), CD11c(+), HLA-DR(++), CD14(+/-) that also were CD1a(+) or CD83(+), after 6 days of in vitro culture with GM-CSF +/- TNF-alpha. CD34(-)CD86(+) AML cells differentiated into AML-DC after 3 to 5 days (n = 5 experiments), and trisomy 8 was found in two AML and AML-DC samples by fluorescence in situ hybridization analysis. Finally, AML-DC induced more potent allo-T-cell proliferation, cytokine release, and anti-leukemic cytotoxicity than CD86(+) blasts. CONCLUSIONS: In AML, CD86 is a marker of monocytic/dendritic lineage. Because CD86(+) blasts may differentiate into DC rapidly, CD86(+)AML patients could be optimal candidates for immunotherapy studies, both in autologous and allogeneic settings.     

Erythropoietin-dependent transformation of myelodysplastic syndrome to acute monoblastic leukemia.

Acute monoblastic leukemia (acute myeloid leukemia [AML], French-American-British type M5a) with leukemia cutis developed in a patient 6 weeks after the initiation of erythropoietin (EPO) therapy for refractory anemia with ringed sideroblasts. AML disappeared from both marrow and skin after the discontinuation of EPO. Multiparameter flow cytometric analysis of bone marrow cells demonstrated coexpression of the EPO receptor with CD45 and CD13 on the surface of blasts. The incubation of marrow cells with EPO, compared to without, resulted in 1.3- and 1.6-fold increases, respectively, in tritiated thymidine incorporation and bromodeoxyuridine incorporation into CD13(+) cells. Clinical and laboratory findings were consistent with the EPO-dependent transformation of myelodysplastic syndrome (MDS) to AML. It is concluded that leukemic transformation in patients with MDS treated with EPO may be EPO-dependent and that management should consist of the discontinuation of EPO followed by observation, if clinically feasible.     

RHAMM/HMMR (CD168) is not an ideal target antigen for immunotherapy of acute myeloid leukemia

Background

Criteria for good candidate antigens for immunotherapy of acute myeloid leukemia are high expression on leukemic stem cells in the majority of patients with acute myeloid leukemia and low or no expression in vital tissues. It was shown in vaccination trials that Receptor for Hyaluronic Acid Mediated Motility (RHAMM/HMMR) generates cellular immune responses in patients with acute myeloid leukemia and that these responses correlate with clinical benefit. It is not clear however whether this response actually targets the leukemic stem cell, especially since it was reported that RHAMM is expressed maximally during the G2/M phase of the cell cycle. In addition, tumor specificity of RHAMM expression remains relatively unexplored.

Design and Methods

Blood, leukapheresis and bone marrow samples were collected from both acute myeloid leukemia patients and healthy controls. RHAMM expression was assessed at protein and mRNA levels on various sorted populations, either fresh or after manipulation.

Results

High levels of RHAMM were expressed by CD34⁺CD38⁺ and CD34^- acute myeloid leukemia blasts. However, only baseline expression of RHAMM was measured in CD34⁺CD38^- leukemic stem cells, and was not different from that in CD34⁺CD38^- hematopoietic stem cells from healthy controls. RHAMM was significantly up-regulated in CD34⁺ cells from healthy donors during in vitro expansion and during in vivo engraftment. Finally, we demonstrated an explicit increase in the expression level of RHAMM after in vitro activation of T cells.

Conclusions

RHAMM does not fulfill the criteria of an ideal target antigen for immunotherapy of acute myeloid leukemia. RHAMM expression in leukemic stem cells does not differ significantly from the expression in hematopoietic stem cells from healthy controls. RHAMM expression in proliferating CD34+ cells of healthy donors and activated T cells further compromises RHAMM-specific T-cell-mediated immunotherapy.Key words: leukemic stem cell, acute myeloid leukemia, cell therapy and immunotherapy, HMMR, RHAMM     

Acute myeloid leukemia with T-lymphoid features: a distinct biologic and clinical entity

We studied the clinical and biologic features of 10 cases of acute leukemia that met standard French-American-British (FAB) criteria for acute myeloid leukemia (AML) but in which the blast cells also expressed the T-cell-associated CD2 surface antigen. All cases had greater than 3% myeloperoxidase and Sudan black B-positive leukemic blasts, and blasts from seven cases contained Auer rods. Reactivity of the cells with a panel of monoclonal antibodies (MAbs) indicated that leukemic cells in all cases expressed myeloid-associated (CD11b, CD13) surface antigens, further supporting the diagnosis of AML. However, blasts from every patient coexpressed the T-cell-associated surface CD2 and CD7 as well as cytoplasmic CD3 antigens. Blasts from five patients expressed surface CD25, whereas blasts from only one expressed surface CD3. Five patients had rearranged T-cell receptor beta-chain genes, whereas only three had rearranged T-cell receptor gamma-chain genes. This pattern of lineage-related gene expression appears to define a distinct subtype of AML with T-lymphoid features (CD2+ AML) and could reflect either aberrant gene expression in leukemic blasts or transformation of a pluripotent stem cell having a flexible pattern of gene expression. Clinically, these 10 patients presented at an older age with a higher leukocyte count and a higher frequency of lymphadenopathy than did children whose blast cells were characteristic of myeloid leukemia. Patients with CD2+ AML also had poorer responses to remission induction therapy (50% v 80% entered complete remission, P = .05). However, each of the five children who failed induction chemotherapy on AML protocols had a striking response to drug combinations usually reserved for lymphoid leukemia. We conclude that this leukemia with mixed lymphoid and myeloid characteristics is a distinct biologic and clinical entity.