IL-2 and myelopoiesis: IL-2 induces blast cell proliferation in some cases of acute myeloid leukaemia

Therapeutic Antibodies for Myeloid Neoplasms-Current Developments and Future Directions

Therapeutic monoclonal antibodies (mAbs) such as antibody-drug conjugates, ligand-receptor antagonists, immune checkpoint inhibitors and bispecific T cell engagers have shown impressive efficacy in the treatment of multiple human cancers. Numerous therapeutic mAbs that have been developed for myeloid neoplasms, including acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS), are currently investigated in clinical trials. Because AML and MDS originate from malignantly transformed hematopoietic stem/progenitor cells-the so-called leukemic stem cells (LSCs) that are highly resistant to most standard drugs-these malignancies frequently relapse and have a high disease-specific mortality. Therefore, combining standard chemotherapy with antileukemic mAbs that specifically target malignant blasts and particularly LSCs or utilizing mAbs that reinforce antileukemic host immunity holds great promise for improving patient outcomes. This review provides an overview of therapeutic mAbs for AML and MDS. Antibody targets, the molecular mechanisms of action, the efficacy in preclinical leukemia models, and the results of clinical trials are discussed. New developments and future studies of therapeutic mAbs in myeloid neoplasms will advance our understanding of the immunobiology of these diseases and enhance current therapeutic strategies.

Prognostic Relevance of Cytokine Receptor Expression in Acute Myeloid Leukemia: Interleukin-2 Receptor α-Chain (CD25) Expression Predicts a Poor Prognosis

A variety of cytokine/cytokine receptor systems affect the biological behavior of acute leukemia cells. However, little is known about the clinical relevance of cytokine receptor expression in acute myeloid leukemia (AML). We quantitatively examined the expression of interleukin-2 receptor α-chain (IL-2Rα, also known as CD25), IL-2Rβ, IL-3Rα, IL-4Rα, IL-5Rα, IL-6Rα, IL-7Rα, the common β-chain (βc), γc, granulocyte-macrophage colony-stimulating factor (GM-CSF)Rα, G-CSFR, c-fms, c-mpl, c-kit, FLT3, and GP130 in leukemia cells from 767 adult patients with AML by flow cytometry and determined their prevalence and clinical significance. All cytokine receptors examined were expressed at varying levels, whereas the levels of IL-3Rα, GM-CSFRα, IL-2Rα, γc, c-kit, and G-CSFR exhibited a wide spectrum of ≥10,000 sites/cell. In terms of their French-American-British classification types, GM-CSFRα and c-fms were preferentially expressed in M4/M5 patients, G-CSF in M3 patients, and IL-2Rα in non-M3 patients. Elevated levels of IL-3Rα, GM-CSFRα, and IL-2Rα correlated with leukocytosis. In patients ≤60 years old, higher levels of these 3 receptors correlated with poor responses to conventional chemotherapy, but only IL-2Rα was associated with a shorter overall survival. By incorporating IL-2Rα status into cytogenetic risk stratification, we could sort out a significantly adverse-risk cohort from the cytogenetically intermediate-risk group. Analyses with various phenotypical risk markers revealed the expression of IL-2Rα as an independent prognostic indicator in patients with intermediate-risk cytogenetics. These findings were not observed in patients >60 years old. Our results indicate that several cytokine receptors were associated with certain cellular and clinical features, but IL-2Rα alone had prognostic value that provides an additional marker to improve current risk evaluation in AML patients ≤60 years old.

Interleukin-2 receptor alpha-chain (CD25) expression on leukaemic blasts is predictive for outcome and level of residual disease in AML

We investigated the role of CD25 as a prognostic marker in acute myeloid leukaemia (AML). Seventy-two newly diagnosed patients < or =60 years were retrospectively analysed by flow cytometry for CD25 positivity of AML blasts. Patients with CD25 expression of >10%, when compared to < or =10%, had a significantly shorter overall survival (OS, p=0.0005) and relapse-free survival (RFS, p=0.005). In multivariate analysis CD25 expression is an independent adverse factor for OS and RFS. High CD25 combined with FLT3-ITD positivity resulted in the poorest OS and RFS (p=0.001 and p=0.003, respectively). CD25 expression remained prognostic within the intermediate cytogenetic risk group. In addition, after the first cycle of chemotherapy, a significantly higher MRD frequency was found in patients expressing CD25 above cut-off (p=0.003). Our results show that CD25 expression is an independent adverse prognostic marker in AML patients < or =60 and correlates with MRD.

Early development of acute myelogenous leukemia following kidney transplantation: possible role of multiple serum cytokines

We report a patient who at the time of kidney transplantation for polycystic kidney disease was found to have an enlarged inguinal lymph node which later demonstrated evidence of extra medullary granulopoiesis. During the first two weeks following kidney transplantation, a striking leukemoid pattern developed and 2 months after transplant the patient was diagnosed with acute myelogenous leukemia (AML). Retrospective analysis of peripheral blood cytokines over this time revealed elevated levels of GMCSF and gamma IFN at the time of peak peripheral blood WBC with subsequent peaks in IL-4, IL-6 and IL-2 as the peripheral blood WBC fell. A rise in levels of TNF alpha also preceded the peripheral blood WBC rise (although these concentrations were at or below those following uncomplicated kidney transplants). The clinical course of AML in this patient was marked by relentless relapse despite chemotherapy. The possibility of cytokine facilitated tumor growth is discussed.

Relapse of acute myelogenous leukemia during low dose interleukin-2 (IL-2) therapy. Phenotypic evolution associated with strong expression of the IL-2 receptor alpha chain

BACKGROUND

Interleukin-2 (IL-2) has produced remissions in patients with solid tumors, predominantly malignant melanoma and renal cell carcinoma. Recently, clinical trials have assessed the therapeutic benefit of this cytokine in acute myelogenous leukemia (AML). However, little is known about the potential of IL-2 to promote the growth of leukemic cells in vivo.

METHODS

A patient with acute myelocytic leukemia whose leukemic blasts displayed lymphoid (TdT+ and CD4+) and myeloid features (myeloperoxidase [MPO]+ and CD13+) is reported. The IL-2 receptor alpha chain (CD25 antigen) was present on 28.9% of his blasts. After entering complete remission with chemotherapy, he was treated on a protocol using IL-2 maintenance.

RESULTS

Six weeks after beginning low-dose IL-2, his leukocyte count increased to 448,000/microliters with 86% blasts. The phenotype of these blasts was different from that at diagnosis with expression of the CD25 antigen and the CD33 antigen on 75.9% and 74.8 of the blasts, respectively. Furthermore, 30% of the cells were TdT+, whereas MPO was not detectable.

CONCLUSION

The rapid course of relapse, phenotypic evolution, and the high expression of CD25 antigen on the blasts after IL-2 therapy raise the possibility that the cytokine therapy may have promoted the growth of leukemic cells.

Is there a place for immunotherapy with interleukin-2 to prevent relapse after autologous stem cell transplantation for acute leukemia?

Chemotherapy-resistant cells cause disease recurrence in a significant proportion of patients with acute leukemia treated with autologous stem cell transplantation due to the lack of immune-mediated effects which contribute significantly to the prevention of post-treatment disease recurrence. This conclusion is based on the observation that relapse after high dose chemotherapy supported by a stem cell transplant from a twin donor is 3-4 times higher than after transplant from an allogeneic donor. This anti-leukemic mechanism of transplanted donor cells has been termed graft-versus-leukemia (GVL) effect, and efforts are being directed toward utilizing such an immune-mechanism after autologous transplantation. Since interleukin-2 (IL-2) can induce remissions in selected patients with advanced leukemia, it has become a candidate cytokine to be used in attempts to introduce GVL after autologous stem cell transplantation. Here we review the available clinical data with IL-2 and critically evaluate whether IL-2 has a place as adjunct treatment to prevent relapse after autologous transplantation for acute leukemia.

Cytokine receptor expression in leukaemic cells

Cytokines have been postulated to play important roles in tumour biology and in the host response to tumours, and a number of therapeutic modalities involving cytokines have been proposed. If patients are to be treated with cytokines, or cytokine inhibitors, it will be important to determine the potential for direct action of the cytokine on the tumour cells. In this study, a high-sensitivity immunofluorescence technique is used to determine the expression of a number of cytokine receptors on a total of 115 leukaemic samples. The results show that many leukaemic samples express low levels of cytokine receptors, and that malignancies of a particular type are heterogeneous with respect to receptor expression. In vitro culture experiments show, as expected, that receptor expression is a necessary but not sufficient requirement for responsiveness to cytokines. The cytokine receptor phenotype may provide useful additional clinical and prognostic information, and should be determined particularly for patients undergoing treatment with cytokines or cytokine inhibitors.

Effects of interleukin 2 on myelodysplastic syndromes

To evaluate the clinical usefulness of interleukin 2 (IL-2) on myelodysplastic syndromes (MDS), the serum IL-2 level, the effect of IL-2 on the proliferation of blasts, and the cell-mediated cytotoxic effect of IL-2 on blasts were examined in MDS patients. Of 18 patients, 2 patients had an increased serum IL-2 level. Although the proliferation of blasts in most cases, including the two patients having a high serum IL-2 level, was not stimulated by IL-2, the blasts of one case apparently proliferated in response to IL-2. It was also clearly shown that IL-2-stimulated normal peripheral blood mononuclear cells (PBMNC) showed cytotoxicity against MDS blasts, whereas the PBMNC of the advanced stages of MDS were usually defective in regard to this IL-2-dependent cytotoxicity. The therapeutic usefulness of IL-2 or lymphokine-activated killer cells for MDS was not established by the present study.

Interleukin-2 receptor alpha chain on acute myelocytic leukemia cells is involved in cell-to-cell interactions

Leukemic cells from 21 to 197 adult patients with de novo acute myelocytic leukemia (AML) were positive for IL-2R alpha chain (IL-2R alpha), whereas IL-2R beta chain (IL-2R beta), which is responsible for IL-2 signal transduction, was not found on leukemic cells from any of these cases tested. The expression of IL-2R alpha was closely associated with that of adhesion molecules CD4, CD11b and CD22, and endopeptidase CD10. None of the IL-2R alpha (+) AML cells responded to recombinant human IL-2. These data suggest that IL-2R alpha on AML cells may not be involved in cellular proliferation as one of growth factor receptors but may have a role in the control of cell-to-cell interactions.

Detection of cytokine receptors by high-sensitivity immunofluorescence/flow cytometry

Cytokines have profound effects on cells, and act through receptors which need only be at low concentrations (around 100 copies per cell) to transmit activation signals. The detection of such low concentrations is possible using monoclonal antibodies and fluorescence/flow cytometry, but only by using specialized techniques. The best results so far have been obtained using biotinylated second antibody followed by phycoerythrin-streptavidin, and batches of these reagents have to be carefully selected. Analysis of the fluorescence is best done using 546 nm excitation from a mercury arc lamp, but 512 nm excitation from an argon-ion laser can also be used. With appropriate alignment, instruments with 488 nm fixed-wavelength lasers can give sensitivity almost as good as the 546 nm system. Working at high sensitivity, background levels also increase, particularly for B lymphocytes. Background staining can be reduced to acceptable levels by blocking the two major mechanisms for non-specific binding. Applications of these methods to the detection of cytokine receptors on normal and malignant cells are reviewed.

Diagnostic and clinical importance of interleukin-2 receptor alpha chain expression on non-T-cell acute leukaemia cells

The expression of interleukin-2 receptors (IL-2R) was examined in 328 adult patients with non-T-cell (non-T) acute leukaemia and blast crisis of chronic myelocytic leukaemia (CML.BC) using two monoclonal antibodies, anti-Tac for IL-2R alpha chain (IL-2R alpha) and Mik beta 1 for IL-2R beta chain (IL-2R beta). Leukaemic cells in the following cases were positive for anti-Tac; 28/192 of acute myelocytic leukaemia (AML), 24/44 CML-BC, 4/28 CD19(+)CD10(-) acute lymphoblastic leukaemia (ALL), and 20/64 common ALL (c-ALL). IL-2R beta was not detected on leukaemic cells of any case examined. Eleven of IL-2R alpha(+) AML were derived from myelodysplastic syndrome. None of the IL-2R alpha positive leukaemic cells responded to exogenous recombinant human IL-2 (rhIL-2) in culture. In addition, IL-2R alpha expression on non-T leukaemic cells was closely correlated with coexpressing different lineage markers and the presence of the Philadelphia abnormality. Marked increase of serum soluble IL-2R alpha was demonstrated in the IL-2R alpha(+) patients examined. Clinically, the IL-2R alpha(+) patients showed significantly lower response to chemotherapy and poorer prognosis than IL-2R alpha(-) patients. Our results clearly indicate the diagnostic importance of IL-2R alpha expression in non-T acute leukaemia with a close relation to the particular cellular characteristics and the prognosis.

IL-2 abolishes fibroblast proliferation in long-term bone marrow culture by inhibition of an accessory cell

Addition of interleukin-2 (IL-2 (greater than 250 U/ml) during the first 3 d of long-term bone marrow culture (LTBMC) permanently abolished the fibroblast component of the stromal layer, even when IL-2 was removed after the 3 d culture period. When IL-2 was added at more than 72 h after initiation of culture, no effect was observed. Stromal growth in IL-2-treated culture was restored by addition of irradiated bone marrow, indicating that the IL-2 inhibited an accessory cell rather than the fibroblast directly. Accessory cells were shown to be necessary for fibroblast proliferation at low cell densities and were also inhibited by IL-2. The accessory cell effect could not be replaced by LTBMC supernatants or extracellular matrix. It is suggested that these observations are relevant to the suppression of haemopoiesis observed in patients receiving IL-2.

Graft versus leukaemia effects after marrow transplantation in man

A graft versus leukaemia (GvL) effect makes a significant contribution to the lower risk of relapse seen in patients after BMT compared with patients receiving chemotherapy alone. Both T cell-dependent and T cell-independent effectors of GvL exist, and both may play an important role in the elimination of minimal residual disease after BMT. There is evidence that GvL activity may be separable from GvHD either by identifying T cell clones recognizing specific leukaemia antigens or by using immunomodulatory drugs or cytokines to enhance T cell-independent GvL mechanisms which operate without alloreactivity and therefore without concomitant exacerbation of GvHD. These approaches should improve survival after both autologous and allogeneic BMT.

Growth of certain myeloid leukemic cells can be stimulated by interleukin-2

The effect of recombinant interleukin-2 (IL-2) on the proliferation of T-cell depleted leukemic blasts was evaluated in 23 patients with acute myelogenous leukemia (AML). For this purpose, the effect of IL-2 on cell growth, [3H]-thymidine incorporation into the blasts and the expression of IL-2 receptors on cell surface using T-cell depleted blasts were studied. The results showed that IL-2 stimulated [3H]-thymidine incorporation significantly in blasts of 8 out of 23 cases of AML. An IL-2 induced increase in cell number was directly demonstrated in seven out of eight IL-2 responsive patients studied. IL-2 stimulated the proliferation of blasts in monocytic lineage (M4 and M5), but not all M4/M5 leukemics responded to rIL-2. Stimulation of the growth of leukemic cells was not correlated with the expression of Tac antigen on the cell surface, but it was significantly correlated with the expression of IL-2 receptor (IL-2R) beta chain on the cell surface. These results indicate that IL-2 is an active growth factor in certain myeloid leukemia cells, especially of monocytic type.

Acute myeloid leukaemia relapsing following interleukin-2 treatment expresses the alpha chain of the interleukin-2 receptor

Immunotherapy with recombinant human Interleukin-2 (rhIL-2) was given to nine patients in first complete remission from acute myeloid leukaemia (AML). Five patients relapsed. The median time to relapse after commencing rhIL-2 was 26 weeks (range 2-44). Four patients were studied at relapse. The morphological and cytochemical features at relapse and presentation were similar. Cytogenetic analysis at relapse in patients 1 and 3 showed a normal karyotype. At relapse, patient 4 had the abnormality 46,XY, t(2;3). Patient 2 had the chromosomal abnormality t(8;21) at presentation and relapse. Patients 3 and 4 with M5 AML relapsed rapidly at 2 and 9 weeks after starting rhIL-2 treatment. Relapse leukaemia cells had features normally associated with lymphoid development. Patient 3 was TdT positive, with rearranged immunoglobulin genes, and a proportion of cells expressing the CD7 antigen; patient 4 also expressed the CD7 antigen. Relapse leukaemic cells from three of four patients expressed the alpha chain of the IL-2 receptor as assessed by flow cytometry. After overnight incubation and removal of T-lymphocytes the proportion of cells from these patients expressing the alpha chain increased from 15% to 61% (P less than 0.01). Using tritiated thymidine uptake to assess cell proliferation, two of three patients who expressed the IL-2 receptor alpha chain proliferated in response to 1000 u/ml of rhIL-2 in vitro, with a stimulation index greater than 1.95 (P less than 0.05). Following rhIL-2 immunotherapy for AML, relapse cells may express an inducible form of the alpha chain of the IL-2 receptor, which can mediate a proliferative response. It is possible that rhIL-2 when administered to AML patients in remission, may induce relapse. This may be a particular risk in patients with the M5 subtype.

Lymphocyte activation in patients with acute myeloid leukaemia. Evidence for the presence of myeloblast antigen?

A group of 27 patients with acute myeloid leukaemia (AML), 15 with active disease and 12 in complete remission, were investigated for evidence of T cell activation. The parameters of T cell activation measured were the serum levels of soluble interleukin-2 receptor (sIL-2R), soluble CD4 (sCD4) and soluble CD8 (sCD8) molecules and the proportions of T cells expressing the cytotoxicity-linked cytoplasmic serine esterase. All patients studied with active disease had elevated sIL-2R and sCD8 molecules and an elevated proportion of T cells expressing serine esterase. Patients studied in complete remission also had elevated sIL-2R. sCD8 and serine-esterase-positive T cells, but values were lower than those studied in active disease. These patients were all studied in the absence of any ongoing or recent infection or exposure to homologous blood products, either of which could potentially affect these parameters. In the absence of any obvious alternative cause, we suggest these data indicate that AML leukaemia blast cells may be immunogenic and lead to the activation of cytotoxic T cells.

Interleukin-1 and interleukin-2 control granulocyte- and granulocyte-macrophage colony-stimulating factor gene expression and cell proliferation in cultured acute myeloblastic leukemia

In vitro proliferation of leukemic cells purified from 10 cases of acute myeloblastic leukemia (AML) was analyzed in basal conditions or in the presence of exogenous recombinant (r) Interleukin (IL) 1. In parallel, blasts from 5 of these patients were studied for granulocyte-macrophage colony-stimulating factor (GM-CSF) or granulocyte-CSF (G-CSF) mRNA. IL-1 augmented the spontaneous AML cell proliferation in all cases and induced de novo expression or increased amounts of GM-CSF and/or G-CSF transcripts in 4 of the 5 cases evaluated. IL-1-induced AML cell proliferation was modulated by neutralizing anti-GM-CSF or anti-G-CSF antibodies in those cases in which CSF mRNAs were induced or increased by exogenous cytokine. In the same cases, biosynthetic labelling and immunoprecipitation studies using monospecific anti-GM-CSF antibodies showed that IL-1 also increased the levels of GM-CSF protein synthesis. Addition of neutralizing anti-IL-1 antibodies to AML cell cultures completely abolished ongoing GM-CSF synthesis, suggesting that endogenous IL-1 is needed to maintain autocrine production of CSFs. The effects of rIL-2 were investigated in a larger series of 21 patients. The cytokine reduced spontaneous AML cell proliferation in 8 cases. It caused complete disappearance of GM-CSF mRNA in 1 case, and marked reduction of G-CSF mRNA in 2 cases. Increased AML cell proliferation was observed in 2 of 21 cases. These findings suggest that expression of CSF genes and cell proliferation in AML are under the control of different cytokines acting in autocrine or paracrine fashion.

Interleukin 2 does not promote the in vitro and in vivo proliferation and growth of human acute leukaemia cells of myeloid and lymphoid origin

The effect of recombinant interleukin 2 (IL2) on the in vitro and in vivo proliferation and growth of human acute leukaemia cells of both myeloid and lymphoid origin was investigated. In none of the 25 primary samples tested could a continuously in vitro growing cell line be obtained by adding IL2 to the culture medium. Although IL2 induced a proliferative signal in three of the 31 acute leukaemias analysed, the overall 3H-thymidine uptake of the neoplastic cells was significantly reduced (P less than 0.05) in the presence of IL2. The unlikelihood of an important proliferative signal triggered by IL2 was confirmed in a semisolid clonogenic assay, which failed to document an increased colony growth in the 26 samples studied. Furthermore, using a colorimetric assay as a test for cell proliferation and survival, in seven of the 11 fresh acute leukaemia samples tested a 22-40% reduction in viability was observed in the presence of IL2, while in the remaining four, IL2 was ineffective. In order to investigate the effect of IL2 in an in vivo setting, an experimental model in heavily immunosuppressed nu/nu mice was established. In no case did IL2 promote the in vivo proliferation and growth of human myeloid and lymphoid acute leukaemia cells injected in the mice. On the contrary, with seven of the eight leukaemic cell lines which gave rise spontaneously to leukaemic masses, this could be prevented when the mice received locally 300 U of IL2 three times daily for 90 d. IL2 also blocked the growth in vivo of three fresh acute leukaemia samples (two myeloid and one lymphoid). Co-culture experiments using leukaemic cell lines and increasing numbers of normal lymphocytes suggest that the inhibitory effect of IL2 is probably exerted via an indirect mechanism. These findings, coupled to the well-documented ability of IL2 to generate lymphokine activated killer cells cytolytic against leukaemic blasts, further point to the potential role of immunotherapy with IL2 in the management of patients with haematological malignancies.

Recombinant interleukin 2 for acute myeloid leukaemia in first complete remission: a pilot study

We treated nine patients in first remission from AML with rhIL-2. The toxic effects of rhIL-2 infusion were, malaise, pyrexia, and hypotension, which resolved rapidly on cessation of rhIL-2 infusion. No patient required transfer to an intensive care unit. Following rhIL-2 infusions patients developed eosinophilia, and a modest lymphocytosis, involving both NK cells, and T lymphocytes. Relapse occurred in six patients at a median of 39 weeks from remission. A particular concern was rapid relapse in the two patients with AML FAB type M5. There was no survival advantage from rhIL-2 treatment when compared to a similar group of chemotherapy only treated AML patients from this institution.