A multicenter retrospective analysis on therapeutic plasma exchange in immune thrombocytopenic purpura.

Immune Thrombocytopenia (ITP) is an autoimmune disease characterized by thrombocytopenia and skin and mucosal bleeding. In patients with an indication for treatment, corticosteroids, intravenous immunoglobulin (IVIg) and anti-D are recommended as the first line, while splenectomy, thrombopoietin receptor agonists or rituximab are recommended second line options. Approximately 10 % of adult patients with ITP fall into the chronic refractory ITP group. Therapeutic plasma exchange (TPE) has generally been tested in patients with refractory ITP, who have failed to respond to conventional treatments, in case of bleeding or prior to surgical interventions. It has been stated that elimination of the antibodies that are held responsible in the pathogenesis of the disease has an effective role in the treatment. In this article, we present the results of 17 patients, who underwent TPE for refractory ITP, together with the literature data.

Eltrombopag second-line therapy in adult patients with primary immune thrombocytopenia in an attempt to achieve sustained remission off-treatment: results of a phase II, multicentre, prospective study.

Up to 30% immune thrombocytopenia (ITP) patients achieve a sustained remission off-treatment (SROT) after discontinuation of thrombopoietin receptor agonists (TPO-RAs). Factors predictive of response are lacking. Patients aged ≥18 years with newly diagnosed or persistent ITP were treated with eltrombopag for 24 weeks. Primary end-point was SROT: the proportion of responders that were able to taper and discontinue eltrombopag maintaining the response during a period of observation (PO) of six months. Secondary end-points included the association between some immunological parameters (TPO serum levels, cytokines and lymphocyte subsets) and response. Fifty-one patients were evaluable. Primary end-point was achieved in 13/51 (25%) treated patients and 13/34 (38%) patients who started the tapering. Baseline TPO levels were not associated with response at week 24 nor with SROT. Higher baseline levels of IL-10, IL-4, TNF-α and osteopontin were negative factors predictive of response (P = 0·001, 0·008, 0·02 and 0·03 respectively). This study confirms that SROT is feasible for a proportion of ITP patients treated with eltrombopag. Some biological parameters were predictive of response.

Tuning MPL signaling to influence hematopoietic stem cell differentiation and inhibit essential thrombocythemia progenitors.

Thrombopoietin (TPO) and the TPO-receptor (TPO-R, or c-MPL) are essential for hematopoietic stem cell (HSC) maintenance and megakaryocyte differentiation. Agents that can modulate TPO-R signaling are highly desirable for both basic research and clinical utility. We developed a series of surrogate protein ligands for TPO-R, in the form of diabodies (DBs), that homodimerize TPO-R on the cell surface in geometries that are dictated by the DB receptor binding epitope, in effect "tuning" downstream signaling responses. These surrogate ligands exhibit diverse pharmacological properties, inducing graded signaling outputs, from full to partial TPO agonism, thus decoupling the dual functions of TPO/TPO-R. Using single-cell RNA sequencing and HSC self-renewal assays we find that partial agonistic diabodies preserved the stem-like properties of cultured HSCs, but also blocked oncogenic colony formation in essential thrombocythemia (ET) through inverse agonism. Our data suggest that dampening downstream TPO signaling is a powerful approach not only for HSC preservation in culture, but also for inhibiting oncogenic signaling through the TPO-R.

Clinical association between thyroid disease and immune thrombocytopenia.

Immune thrombocytopenia (ITP) can coexist with autoimmune thyroid disease. However, the detailed clinical features remain unknown. We retrospectively reviewed 248 patients with newly diagnosed ITP in our institute for whom we had thyroid function data at diagnosis between 2000 and 2019. Of the 248 patients with ITP, 74 patients also had thyroid disease, including 36 with overt thyroid disease (13 Graves' disease and 23 Hashimoto's thyroiditis) and 38 with subclinical thyroid disease (3 hyperthyroidism and 35 hypothyroidism). ITP and thyroid disease were concurrently diagnosed in 54 patients. Female sex and positivity for antinuclear antibodies (ANA) were significantly associated with thyroid diseases. Platelet-associated immunoglobulin G (PAIgG) levels in patients with Graves' disease were higher than those in patients with Hashimoto's thyroiditis. Platelet counts were similar among euthyroid patients and patients with thyroid disease. Thrombopoietin-receptor agonist was administered more frequently in patients with thyroid disease. The cumulative incidences of thrombosis and bleeding and overall survival did not differ between patients with and without thyroid disease. Treatment for thyroid disease in 22 patients improved thrombocytopenia in 21 patients, especially in 4 patients who were not treated for ITP. This study demonstrated that thyroid diseases were commonly found in patients with ITP. Treatment of the underlying thyroid disease may improve thrombocytopenia.

Tapering and discontinuation of thrombopoietin receptor agonists in immune thrombocytopenia: Real-world recommendations.

Thrombopoietin receptor agonists (TPO-RAs) are currently indicated for continuous treatment of chronic primary immune thrombocytopenia (ITP). However, there is growing evidence that TPO-RAs can also trigger sustained response in 10-30% of cases after treatment tapering and discontinuation. Therefore, at least for selected responding patients, it might be rational to plan TPO-RA interruption to exploit off-treatment response. Intriguingly, complete or partial responses with TPO-RAs are frequently observed when treatments are initiated early, suggesting that unknown immune-related mechanisms may be involved in this phenomenon. The sustained responses observed after interruption of TPO-RAs may be interpreted as a recovery of immunological tolerance; thus, the re-establishment of immunological equilibrium might be primarily responsible for the observed off-treatment effect. Importantly, these findings may indicate that anticipated TPO-RA usage can lead to improved responses, and that optimized tapering and interruption in selected patients can furthermore improve prognoses. On the base of this rationale, a series of real-life considerations have been generated by a panel of Experts to elucidate possible novel criteria and modalities to identify subgroups of patients who can benefit from tapering and/or discontinuation of TPO-RAs. Towards this aim, the results of a survey of ITP experts are herein reported, reflecting a snapshot of current real-life experience on early discontinuation of TPO-RA-based therapy. The present manuscript also highlights the importance of future translational studies on novel prognostic and predictive biomarkers that can stratify patients and facilitate the clinical choice for second-line treatment of ITP.

An agonist antibody prefers relapsed AML for induction of cells that kill each other.

Previously, we reported an agonist antibody to a cytokine receptor, Thrombopoietin receptor (TPOR) that effectively induces cytotoxic killer cells from precursor tumor cells isolated from newly diagnosed AML patients. Here, we show that the TPOR agonist antibody can induce even relapsed AML cells into killer cells more potently than newly diagnosed AML cells. After stimulation by the agonist antibody, these relapsed leukemic cells enter into a differentiation process of killer cells. The antibody-induced killer cells express, Granzyme B and Perforin that assault and kill other members of the AML cell population. Particularly, the agonist antibody showed potent efficacy on the AML xenograft model in mice using the NOD/LtSz-scid IL2Rγc null (NSG) mice. These results show that the TPOR agonist antibody that induces AML cells to kill each other is effective on both relapsed AML cells and in vivo. Therefore, this study suggests a new strategy for the treatment of cancer relapse after chemotherapy.

Autoantibodies to thrombopoietin and the thrombopoietin receptor in patients with immune thrombocytopenia.

Autoantibodies to thrombopoietin (TPO, also termed THPO) or the TPO receptor (cMpl, also termed MPL) could play a pathological role in immune thrombocytopenia (ITP). In this study, we tested for autoantibodies against TPO, cMpl, or the TPO/cMpl complex in ITP and other thrombocytopenic disorders. Using an inhibition step with excess TPO in fluid-phase to improve binding specificity, the prevalence of anti-TPO autoantibodies was: active ITP: 9/32 (28%); remission ITP: 0/14 (0%); non-immune thrombocytopenias: 1/10 (10%); and healthy controls: 1/11 (9%). Similarly, using an inhibition step with excess cMpl, the prevalence of specific anti-cMpl autoantibodies was: active ITP: 7/32 (22%); remission ITP: 1/14 (7%); non-immune thrombocytopenias: 3/10 (30%); and healthy controls: 0/11 (0%). Two active ITP patients had autoantibodies against the TPO/cMpl complex, but not against TPO or cMpl alone. Anti-TPO or anti-cMpl autoantibodies were found in 44% of ITP patients, and in 40% of patients with other thrombocytopenic disorders. These autoantibodies did not correlate with ITP disease severity or number of ITP treatments received; however, in this cohort, 3 patients failed to respond to TPO receptor agonist medications, and of those, 2 had anti-TPO autoantibodies. This suggests that anti-TPO and anti-cMpl autoantibodies are associated with thrombocytopenia, and may be clinically relevant in a subset of ITP patients.

A critical appraisal of the evidence for the role of splenectomy in adults and children with ITP.

In primary chronic immune thrombocytopenia, long-term response to splenectomy, with 60% of patients enjoying a treatment-free life, is higher when compared with rituximab and similar to that with continuous thrombopoietin-receptor agonists (TPO-RA) administration. Splenectomy should continue to be offered to patients failing initial treatments in the absence of increased surgery-related risks. The higher lifelong safety concerns with splenectomy (increased risk of infection, shared in part with rituximab, and of thrombosis, in common with TPO-RA) and a mortality <1-2%, justify postponing surgery to the chronic phase, when spontaneous remissions are rarer. Patients failing initial treatment with corticosteroids/intravenous immunoglobulin may use TPO-RA (or rituximab in selected cases) as a bridge to surgery if they prefer to reconsider splenectomy later on, in case of no response, adverse effects or if sustained response after stopping TPO-RA is not attained. Special considerations apply in children aged ≤5 years, with splenectomy playing a marginal role. The recent approval of TPO-RA in children may represent a major advancement.

Affinity maturation of an TpoR targeting antibody in full-length IgG form for enhanced agonist activity.

It has been observed that converting scFv formatted antibodies to full-length IgG often associates with loss of affinity. We aim to address this issue in this paper by establishing an integrated affinity maturation method applying yeast display technology platform. To demonstrate that, we employed a human thrombopoietin receptor targeting antibody named 3D9 which was identified previously from a combinational antibody library in scFv-Fc fusion protein form. We have observed that significant potency loss happened when 3D9 was transformed to full-length IgG form. In this study, we tested whether the potency of the full-length IgG can be improved by affinity maturation of 3D9 using a modified Fab yeast display platform. An efficient CDR3 targeted mutagenesis strategy was designed for Fab library with pre-designed CDR diversity. Next generation sequencing was also used for evaluation of the enrichment process and investigation of sequence-function relationship of the antibody. A variant with improved affinity and higher potency was identified. The study demonstrates that the strategy we used here are efficient for optimizing affinity and activity of full-length IgGs.

Acquired amegakaryocytic thrombocytopenia previously diagnosed as idiopathic thrombocytopenic purpura in a patient with hepatitis C virus infection.

We report the first case of a patient with hepatitis C virus (HCV) infection and idiopathic thrombocytopenic purpura (ITP), who later developed acquired amegakaryocytic thrombocytopenia (AAMT), with autoantibodies to the thrombopoietin (TPO) receptor (c-Mpl). A 64-year-old woman, with chronic hepatitis C, developed severe thrombocytopenia and was diagnosed with ITP. She died of liver failure. Autopsy revealed cirrhosis and liver carcinoma. In the bone marrow, a marked reduction in the number of megakaryocytes was observed, while other cell lineages were preserved. Therefore, she was diagnosed with AAMT. Additionally, autoantibodies to c-Mpl were detected in her serum. Autoantibodies to c-Mpl are one of the causes of AAMT, acting through inhibition of TPO function, megakaryocytic maturation, and platelet formation. HCV infection induces several autoantibodies. HCV infection might also induce autoantibodies to c-Mpl, resulting in the development of AAMT. This mechanism may be one of the causes of thrombocytopenia in patients with HCV infection.

Biological Response Modifier in Cancer Immunotherapy.

Biological response modifiers (BRMs) emerge as a lay of new compounds or approaches used in improving cancer immunotherapy. Evidences highlight that cytokines, Toll-like receptor (TLR) signaling, and noncoding RNAs are of crucial roles in modulating antitumor immune response and cancer-related chronic inflammation, and BRMs based on them have been explored. In particular, besides some cytokines like IFN-α and IL-2, several Toll-like receptor (TLR) agonists like BCG, MPL, and imiquimod are also licensed to be used in patients with several malignancies nowadays, and the first artificial small noncoding RNA (microRNA) mimic, MXR34, has entered phase I clinical study against liver cancer, implying their potential application in cancer therapy. According to amounts of original data, this chapter will review the regulatory roles of TLR signaling, some noncoding RNAs, and several key cytokines in cancer and cancer-related immune response, as well as the clinical cases in cancer therapy based on them.

Monoclonal antibody 1.6.1 against human MPL receptor allows HSC enrichment of CB and BM CD34(+)CD38(-) populations.

Thrombopoietin (TPO) and its receptor Mpl (CD110) play a crucial role in the regulation of hematopoietic stem cells (HSCs). Functional study of Mpl-expressing HSCs has, however, been hampered by the lack of efficient monoclonal antibodies, explaining the very few data available on Mpl(+) HSCs during human embryonic development and after birth. Investigating the main monoclonal antibodies used so far to sort CD110(+) cells from cord blood (CB) and adult bone marrow (BM), we found that only the recent monoclonal antibody 1.6.1 engineered by Immunex Corporation was specific. Using in vitro functional assays, we found that this antibody can be used to sort a CD34(+)CD38(-)CD110(+) population enriched in hematopoietic progenitor stem cells, both in CB and in adult BM. In vivo injection into NSG mice further indicated that the CB CD34(+)CD38(-)CD110(+) population is highly enriched in HSCs compared with both CD34(+)CD38(-)CD110(-) and CD34(+)CD38(-) populations. Together our results validate MAb1.6.1 as an important tool, which has so far been lacking, in the HSC field.

Long-term follow-up of essential thrombocythemia patients treated with anagrelide: subgroup analysis according to JAK2/CALR/MPL mutational status.

BACKGROUND: Anagrelide represents a treatment option for essential thrombocythemia, although its place in therapy remains controversial. AIM: To assess the impact of mutational status in response rates and development of adverse events during long-term use of anagrelide. METHODS: We retrospectively evaluated 67 patients with essential thrombocythemia treated with anagrelide during 68 (4-176) months. RESULTS: Mutational frequencies were 46.3%, 28.3%, and 1.5% for JAK2V617F, CALR and MPL mutations. Anagrelide yielded a high rate of hematologic responses, which were complete in 49.25% and partial in 46.25%, without differences among molecular subsets. The rate of thrombosis during treatment was one per 100 patient-years, without excess bleeding. Anemia was the major adverse event, 30.3% at 5-yr follow-up, being more frequent in CALR(+) (P < 0.05). Myelofibrotic transformation developed in 14.9% (12.9%, 21%, and 12.5% in JAK2V617F(+), CALR(+), and triple-negative patients, respectively, P = NS) and those treated >60 months were at higher risk, OR (95% CI) 9.32 (1.1-78.5), P < 0.01, indicating the need for bone marrow monitoring during prolonged treatment. CONCLUSION: Although CALR(+) patients were at higher risk of developing anemia, anagrelide proved effective among all molecular subsets, indicating that mutational status does not seem to represent a major determinant of choice of cytoreductive treatment among essential thrombocythemia therapies.

Top-down motif engineering of a cytokine receptor for directing ex vivo expansion of hematopoietic stem cells.

The technique to expand hematopoietic stem cells (HSCs) ex vivo is eagerly anticipated to secure an enough amount of HSCs for clinical applications. Previously we developed a scFv-thrombopoietin receptor (c-Mpl) chimera, named S-Mpl, which can transduce a proliferation signal in HSCs in response to a cognate antigen. However, a remaining concern of the S-Mpl chimera may be the magnitude of the cellular expansion level driven by this molecule, which was significantly less than that mediated by endogenous wild-type c-Mpl. In this study, we engineered a tyrosine motif located in the intracellular domain of S-Mpl based on a top-down approach in order to change the signaling properties of the chimera. The truncated mutant (trunc.) and an amino-acid substitution mutant (Q to L) of S-Mpl were constructed to investigate the ability of these mutants to expand HSCs. The result showed that the truncated and Q to L mutants gave higher and considerably lower number of the cells than unmodified S-Mpl, respectively. The proliferation level through the truncated mutant was even higher than that of non-transduced HSCs with the stimulation of a native cytokine, thrombopoietin. Moreover, we analyzed the signaling properties of the S-Mpl mutants in detail using a pro-B cell line Ba/F3. The data indicated that the STAT3 and STAT5 activation levels through the truncated mutant increased, whereas activation of the Q to L mutant was inhibited by a negative regulator of intracellular signaling, SHP-1. This is the first demonstration that a non-natural artificial mutant of a cytokine receptor is effective for ex vivo expansion of hematopoietic cells compared with a native cytokine receptor.

Requirement of TPO/c-mpl for IL-17A-induced granulopoiesis and megakaryopoiesis.

IL-17A is a critical, proinflammatory cytokine essential to host defense and is induced in response to microbial invasion. It stimulates granulopoiesis, leading to neutrophilia, neutrophil activation, and mobilization. TPO synergizes with other cytokines in stimulating and expanding hematopoietic progenitors, also leading to granulopoiesis and megakaryopoiesis, and is required for thrombocytopoiesis. We investigated the effects of in vivo expression of IL-17A on granulopoiesis and megakaryopoiesis in TPO receptor c-mpl-/- mice. IL-17A expression expanded megakaryocytes by 2.5-fold in normal mice but had no such effect in c-mpl-/- mice. The megakaryocyte expansion did not result in increased peripheral platelet counts. IL-17A expression did not impact bone marrow precursors in c-mpl-/- mice; however, it expanded splenic precursors, although to a lesser extent compared with normal controls (CFU-HPP). No peripheral neutrophil expansion was observed in c-mpl-/- mice. Moreover, in c-mpl-/- mice, release of IL-17A downstream cytokines was reduced significantly (KC, MIP-2, GM-CSF). The data suggest that IL-17A requires the presence of functional TPO/c-mpl to exert its effects on granulopoiesis and megakaryopoiesis. Furthermore, IL-17A and its downstream cytokines are important regulators and synergistic factors for the physiologic function of TPO/c-mpl on hematopoiesis.

Novel anti-c-Mpl monoclonal antibodies identified multiple differentially glycosylated human c-Mpl proteins in megakaryocytic cells but not in human solid tumors.

Thrombopoietin and its cognate receptor, c-Mpl, are the primary molecular regulators of megakaryocytopoiesis and platelet production. To date the pattern of c-Mpl expression in human solid tumors and the distribution and biochemical properties of c-Mpl proteins in hematopoietic tissues are largely unknown. We have recently developed highly specific mouse monoclonal antibodies (MAb) against human c-Mpl. In this study we used these antibodies to demonstrate the presence of full-length and truncated human c-Mpl proteins in various megakaryocytic cell types, and their absence in over 100 solid tumor cell lines and in the 12 most common primary human tumor types. Quantitative assays showed a cell context-dependent distribution of full-length and truncated c-Mpl proteins. All forms of human c-Mpl protein were found to be modified with extensive N-linked glycosylation but different degrees of sialylation and O-linked glycosylation. Of note, different variants of full-length c-Mpl protein exhibiting differential glycosylation were expressed in erythromegakaryocytic leukemic cell lines and in platelets from healthy human donors. This work provides a comprehensive analysis of human c-Mpl mRNA and protein expression on normal and malignant hematopoietic and non-hematopoietic cells and demonstrates the multiple applications of several novel anti-c-Mpl antibodies.

Thrombopoietin receptor agonists in primary immune thrombocytopenia.

Thrombopoietin (TPO) regulates thrombopoiesis through activation of TPO receptors on the megakaryocyte cell surface, resulting in increased platelet production. The TPO receptor agonists are novel treatments for patients with chronic ITP aimed at increasing platelet production through interactions with the TPO receptor on megakaryocytes. Two TPO receptor agonists, romiplostim and eltrombopag, have received regulatory approval. In patients with chronic ITP who remain at risk of bleeding following treatment with first-line therapies, these agents have been shown to increase platelet counts, decrease bleeding events, and reduce the need for adjunctive or rescue treatments. The TPO receptor agonists are well-tolerated, though uncertainty remains regarding the risk of thromboembolism and bone marrow fibrosis. Comparative clinical trial data addressing the efficacy, safety, cost-effectiveness, and impact on health-related quality of life of TPO receptor agonists relative to other second-line treatment options are needed to guide treatment decisions in chronic ITP patients who fail first-line therapies.

[Role of anti c-mpl antibody in systemic lupus erythematosus with thrombocytopenia].

OBJECTIVE: To determine whether anti-thrompoietin receptor (TPO-R, c-mpl) antibody contributes to thrombocytopenia in systemic lupus erytematosus (SLE) and explore the pathogenic role of this antibody. METHODS: Sera from 24 SLE patients with thrombocytopenia, 27 SLE patients having normal platelet counts with a history of thrombocytopenia, 18 SLE patients with neither thrombocytopenia nor post thrombocytopenia and 18 healthy controls were collected. Anti c-mpl antibodies were detected by an indirected ELISA assay. The serum TPO levels were measured by an ELISA assay. Clinical findings, autoantibody profiles, and SLEDAI were evaluated. RESULTS: Serum anti c-mpl antibodies were detected in 18.8% of the SLE patientis. The frequency of this antibody in SLE with thrombocytopenia, SLE with a history of thrombocytopenia and SLE without thrombocytopenia were of no difference (P=0.600). In the patients with anti c-mpl antibodies, their platelet counts were decreased(P=0.025) and serum TPO levels elevated(P=0.038) than those in the patients without, while there were no differences between the two groups in C3, C4, ESR, CRP level, the frequency of ANA, dsDNA, ANCA and SLEDAI. CONCLUSION: Anti c-mpl antibody contributes to SLE-associated thrombocytopenia by functionally blocking an interaction between thrombopoietin and c-mpl, which might inhibit TPO-dependent megakaryocyte proliferation and differentiation.