Defective natural killer (NK) cell-mediated cytotoxicity does not imply clonal involvement of NK cells in myelodysplastic syndromes

Cytolytic function and survival of natural killer cells are severely altered in myelodysplastic syndromes

Natural Killer (NK) cells are critical in host defense against malignant transformation and are potent antileukemic cytotoxic effectors. In the present study, we investigated the peripheral NK function in patients with myelodysplastic syndromes (MDS). We demonstrated that the peripheral NK cell population was quantitatively normal in MDS patients. Furthermore, NK cells displayed an expression of the activating natural cytotoxicity receptors (NCR) NKp46 and NKp30 as well as NKG2D similar to that observed in donors, but exert a highly decreased constitutive cytolytic activity compared to resting normal NK cells. Although activation with IL-2 resulted in the upregulation of NKp46 expression by MDS-NK cells, their cytolytic function remained deeply altered as compared to activated donor NK cells. In addition, MDS NK cells did not proliferate in vitro, and displayed an increased rate of apoptosis in response to IL-2 stimulation although the spontaneous apoptosis was not significantly increased. Interestingly, a proportion of peripheral MDS-NK cells were derived from the MDS clone as the cytogenetic anomaly found in bone marrow karyotype was also detected in 20-50% of circulating NK cells. In conclusion, NK cells' cytolytic function and proliferative capacities in response to activation by cytokines are profoundly altered in MDS.

Increased apoptosis in bone marrow B lymphocytes but not T lymphocytes in myelodysplastic syndrome

The hallmark of myelodysplastic syndrome (MDS) is enhanced apoptosis in myeloid, erythroid, and megakaryocytic cells in the bone marrow leading to ineffective hematopoiesis. Recent studies suggested that immunological and microenvironmental factors play a role in the pathophysiology of this disease. We report a significant increase in apoptosis in bone marrow B lymphocytes in MDS as compared to that found in acute myeloid leukemia and healthy controls. Furthermore, we demonstrate that patients with refractory anemia with excess blasts in transformation (RAEB-T) had apoptosis levels in lymphocytes similar to those seen in other subtypes of MDS. Our findings suggest that the alterations in B lymphocytes in the form of increased apoptosis can be seen in MDS and support the concept that immune modulation plays a role in the pathophysiology of MDS.

Determination of T-cell receptors of clonal CD8-positive T-cells in myelodysplastic syndrome with erythroid hypoplasia

We determined T-cell receptor alpha-chain variable (TCRAV) and T-cell receptor beta-chain variable (TCRBV) region repertoires in peripheral bloods from patients with myelodysplastic syndrome (MDS) with erythroid hypoplasia. T-cells bearing TCR ADV14S1/BV5S2, AV21S1/BV21S4, and AV2S2/BV7S2 segments were markedly increased in three of four MDS patients, respectively. In addition, there was a positive relationship between the increase in the number of CD8-positive T-cells and the expression levels of these TCR transcripts. These findings suggest that CD8-positive T-cells monoclonally or oligoclonally expanded in the peripheral blood. We also determined the nucleotide and amino acid sequences of the complementarity-determining region 3 (CDR3) of TCR alpha- and beta-chains of the expanded T-cells. Unique sequences were detected in a high percentage of the respective CDR3 clones. The gene segment of the variable and joining regions, however, varied among the patients. The deduced amino acid sequences of CDR3 were heterogeneous among the patients, and there was no common motif. These results indicate there is monoclonal or oligoclonal proliferation of CD8-positive T-cells in MDS patients with erythroid hypoplasia, and suggest that these proliferating T-cells are responsible for the pathogenesis of the MDS entity.

Autologous lymphocytes inhibit hemopoiesis in long-term culture in patients with myelodysplastic syndrome

OBJECTIVE

The current therapy of myelodysplastic syndrome (MDS) is unsatisfactory and comprises mainly supportive treatment or antileukemic chemotherapy. Recent studies about successful immunosuppressive therapy suggest an autoimmune mechanism in subtypes of myelodysplastic syndrome.

PATIENTS AND METHODS

To investigate this hypothesis, bone marrow mononuclear cells (MNC) from 15 patients with low-grade MDS, refractory anemia, and refractory anemia with ringed sideroblasts (RA and RARS), and from 7 normal donors were depleted of CD2(+), CD5(+), and CD7(+) lymphocytes using magnetic cell sorting. Depleted and nondepleted MNC were seeded onto irradiated allogeneic bone marrow stroma and the generation of colony-forming-cells (CFC), the clonal origin of hemopoietic progenitor cells in long-term bone marrow culture (LTC), was compared.

RESULTS

The capacity of MNC from 7 healthy donors to generate hemopoiesis remained unchanged in the lymphocyte-depleted LTC. In contrast, cultures initiated with lymphocyte-depleted MNC from patients with RA and RARS exhibited a significantly increased generation of CFC compared with the corresponding nondepleted cultures. Microsatellite analysis in 6 patients revealed that a significantly increased number of CFC grown in lymphocyte-depleted LTC showed no allelic loss, suggesting an outgrowth of normal hemopoietic cells.

CONCLUSION

These results provide a rationale for the recently described successful treatment of MDS with immunosuppressive therapy. We suggest that in certain subtypes of MDS the residual normal hemopoiesis is suppressed by autoimmune mechanisms, eventually allowing the expansion of the abnormal clone.

Effect of thrombopoietin on proliferation of blasts from patients with myelodysplastic syndromes

Thrombopoietin (TPO), a major cytokine involved in megakaryocytopoiesis/thrombopoiesis, may be effective for treatment of the thrombocytopenia associated with myelodysplastic syndromes (MDS). However, it has been unclear whether TPO stimulates proliferation of MDS blasts, as observed in de novo acute myeloid leukemia. This study examined this concern. When marrow cells from 37 MDS cases were cultured with or without recombinant human PEGylated TPO, TPO increased the blast number (stimulation index > or =1.5) in 9 of 16 high-risk MDS cases (refractory anemia with excess blasts [RAEB] and RAEB in transformation) and 4 of 10 cases with MDS transformed to acute leukemia (MDS-AL), but none of 11 cases with low-risk MDS (RA and RA with ringed sideroblasts). When the cell cycle of cultured cells was determined by three-color flow cytometry, TPO activated the cell cycle of MDS cells (causing a decrease in G(0)-phase cells) in most of the cases whose blast number increased in response to TPO. Reverse transcriptase-polymerase chain reaction analysis detected TPO receptor messenger RNA in purified blasts from all six cases examined, irrespective of the response of their blasts to TPO in culture. Analysis of the patients' characteristics identified a high-serum lactate dehydrogenase (LDH) value as being associated with blast proliferation in high-risk MDS cases (p = 0.0036). We conclude that TPO stimulates in vitro proliferation of blasts from a fraction of MDS patients. High-risk MDS patients, especially those who have a high-serum LDH value, and MDS-AL patients should be monitored with particular care in clinical trials of TPO for MDS.

Plasma thrombopoietin (TPO) levels and expression of TPO receptor on platelets in patients with myelodysplastic syndromes

Data on endogenous thrombopoietin (TPO) levels and their regulation in myelodysplastic syndromes (MDS) are sparse. We examined the plasma TPO level of 85 MDS patients by a sensitive enzyme immunoassay and the platelet expression of TPO receptor (TPO-R) protein, which metabolizes endogenous TPO, in 19 MDS patients with an equilibrium binding assay using 125I-TPO. The MDS patients had higher plasma TPO levels (7.0 +/- 9.3 fmol/ml) than 52 normal subjects (P < 0.0001). Refractory anaemia (RA) patients (n = 39) had higher plasma TPO levels than patients (n = 28) with RA with excess blasts (RAEB) or RAEB in transformation (RAEB-t) (P = 0.0002), irrespective of similar platelet counts in these groups. The plasma TPO level correlated inversely with the platelet count in RA patients (P = 0.0027) but not in RAEB and RAEB-t patients (P = 0.7865). These data suggest that the physiological pathway for TPO production and metabolism is conserved, at least partially, in RA, but deranged in RAEB/RAEB-t. The number of TPO-R per platelet was significantly smaller in 19 MDS patients (17.5 +/- 13.3) than in normals (P = 0.0014), but similar between RA patients and patients with RAEB and RAEB-t. Further, the bone marrow megakaryocyte count, determined in 31 MDS patients, was quite similar between RA patients and patients with RAEB or RAEB-t. Thus, in addition to thrombocytopenia, a reduced platelet TPO-R number may contribute to elevated plasma TPO levels in MDS, and a regulatory pathway for circulating TPO other than platelet TPO-R and marrow megakaryocytes, such as blasts expressing TPO-R, may operate in RAEB/RAEB-t.

Plasma soluble interleukin-2 receptors in patients with myelodysplastic syndromes

We examined the plasma soluble interleukin-2 receptor (sIL-2R) level in 80 subjects with myelodysplastic syndromes (MDS) and analyzed its correlation with hematologic/immunologic parameters and the subsequent clinical course. Compared with low-risk MDS (refractory anemia (RA) and RA with ringed sideroblasts) and normal individuals, the plasma sIL-2R level was significantly elevated in high-risk MDS (three other MDS subtypes and acute leukemia following MDS) patients. There was a significant negative correlation between the plasma sIL-2R level and the absolute counts of T and natural killer cells. Furthermore, the plasma sIL-2R level showed a significant positive correlation with the total cell mass and blast mass in particular, in the marrow, but not with the absolute count of IL-2Ralpha-chain-positive lymphocytes in the circulation. Fourteen of our 40 low-risk MDS subjects developed at least one of the following events during the follow-up period: erythrocyte transfusion dependence, infections requiring hospitalization, disease progression or MDS-related death. The plasma sIL-2R level was significantly higher in these patients than in event-free low-risk cases. By logistic regression analysis of various parameters in the 40 low-risk subjects, the plasma sIL-2R level was identified as a valuable independent parameter for predicting the development of events. Based on these findings, we hypothesize that the sIL-2R plays a role in the development of morbidity and mortality in MDS by inducing immunologic dysfunction.

Effects of interleukin-12 on natural killer cell cytotoxicity and the production of interferon-gamma and tumour necrosis factor-alpha in patients with myelodysplastic syndromes

The effects of interleukin 12 (IL-12) on natural killer (NK) cell cytotoxicity and on the production of interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) were examined in 15 patients with myelodysplastic syndromes (MDS), which are well known to have immunologic defects, and in 11 normal subjects. The NK cell cytotoxicity of all of the normal subjects was augmented by incubation with IL-12 alone, and co-incubation with interleukin 2 (IL-2) further augmented it (type A response). The MDS patients showed varied responses to IL-12/IL-2. Seven patients showed the type A response, resulting in augmented NK cell cytotoxicity which was similar to that in the normal subjects. In five other patients the cytotoxicity was not increased by IL-12 alone, but the combination of IL-12 and IL-2 did augment the cytotoxicity (type B response). The augmented cytotoxicity in these type B patients was lower than that in the normal subjects. In the final three MDS patients the cytotoxicity was low and not affected by IL-12 and/or IL-2 (type C response). All patients with refractory anaemia with excess blasts (RAEB) and patients with RAEB in transformation showed a type B or C response. Conversely, six of eight refractory anaemia patients showed a type A response. In MDS patients there was a positive correlation between the percentage of CD3- CD56+ cells in pre-incubated cells and the cytotoxicity of cells incubated with IL-12/IL-2. The combination of IL-12 and IL-2 augmented IFN-gamma and TNF-alpha production by nonadherent mononuclear cells in a synergistic or cumulative manner, respectively, in most patients. These results suggest that IL-12, alone or with IL-2, may modulate these important immunologic functions in most MDS patients.

Elevated plasma soluble interleukin 2 receptor level correlates with defective natural killer and CD8+ T-cells in myelodysplastic syndromes

The plasma soluble interleukin 2 receptor (sIL-2R) level and its relationships with haematologic and immunologic data were examined in 40 patients with myelodysplastic syndromes (MDS). The plasma sIL-2R level was significantly higher in the high-risk MDS group (refractory anaemia with excess blasts (RAEB), RAEB in transformation and chronic myelomonocytic leukaemia) than in the low-risk MDS group (refractory anaemia (RA) and RA with ringed sideroblasts) or in normal subjects, although there was considerable variation in the plasma sIL-2R level within each MDS group. The plasma sIL-2R level correlated positively with the bone marrow cellularity and bone marrow blast mass, but not with the absolute number of CD25+ lymphocytes. This may support the idea that plasma sIL-2R is derived from malignant MDS cells in the bone marrow. The plasma sIL-2R level correlated negatively with the absolute numbers of the CD8+, CD3-CD16+, and CD3-CD56+ cell populations in freshly isolated lymphocytes, the percentage of CD3-CD56+ cells in lymphokine (interleukin 2)-activated killer (LAK) cells, and the cytotoxicity of LAK cells. We conclude that MDS patients having a high plasma sIL-2R level often have a defect in natural killer and CD8+ T-cells.