ITP: Tregs come to the rescue

Long-term treatment with romiplostim and treatment-free platelet responses in children with chronic immune thrombocytopenia

Children with immune thrombocytopenia for ≥6 months completing a romiplostim study received weekly subcutaneous romiplostim (1-10 μg/kg targeting platelet counts of 50-200×10⁹/L) in this extension to examine romiplostim’s long-term safety and efficacy. Sixty-five children received romiplostim for a median of 2.6 years (range: 0.1-7.0 years). Median baseline age was 11 years (range: 3-18 years) and platelet count was 28×10⁹/L (range: 2-458×10⁹/L). No patient discontinued treatment for an adverse event. Median average weekly dose was 4.8 mg/kg (range: 0.1-10 mg/kg); median platelet counts remained >50×10⁹/L, starting at week 2. Nearly all patients (94%) had ≥1 platelet response (≥50×10⁹/L, no rescue medication in the previous 4 weeks), 72% had responded at ≥75% of visits, and 58% had responded at ≥90% of visits. Treatment-free response (platelets ≥50×10⁹/L ≥24 weeks without immune thrombocytopenia treatment) was seen in 15 of 65 patients while withholding romiplostim doses. At onset of treatment-free response, the nine girls and six boys had a median immune thrombocytopenia duration of four years (range: 1-12 years) and had received romiplostim for two years (range: 1-6 years). At last observation, treatment-free responses lasted for a median of one year (range: 0.4-2.1 years), with 14 of 15 patients still in treatment-free response. Younger age at first dose and platelet count >200×10⁹/L in the first four weeks were associated with treatment-free responses. In this 7-year open-label extension, three-quarters of the patients responded ≥75% of the time, and romiplostim was well tolerated, with no substantial treatment-related adverse events. Importantly, 23% of children maintained treatment-free platelet responses while withholding romiplostim and all other immune thrombocytopenia medications for ≥6 months. (Registered at clinicaltrials.gov identifier: 01071954)

Case study of remission in adults with immune thrombocytopenia following cessation of treatment with the thrombopoietin mimetic romiplostim

OBJECTIVES

In adults, immune thrombocytopenia (ITP), characterized by platelet counts <100 × 10(9)/l, is typically chronic, with remission reported infrequently ≥3 years post-diagnosis. The thrombopoietin mimetic romiplostim increases platelet counts and reduces use of concomitant ITP medications in chronic ITP. While often perceived as a long-term treatment, dose-adjustment rules allow romiplostim to be discontinued when hemostatic platelet counts are reached, as reported in Amgen trials.

METHODS

Eight romiplostim trials were examined for remission, defined as ≥26 consecutive weeks of platelets ≥50 × 10(9)/l without treatment.

RESULTS

Remission was identified in 27 patients; median (quartile 1 [Q1], quartile 3 [Q3]) ITP duration of 2.1 (0.5, 4.2) years, 17/27 (63%) having ITP for >1 year, mean baseline platelets 20.9 × 10(9)/l, median preremission maximum dose 3.0 µg/kg, 12/27 (44%) were splenectomized at baseline, and there were 40-276 cumulative weeks of romiplostim with median time to remission 7.1 months.

DISCUSSION/CONCLUSION

No clear-cut predictors of remission were apparent; however, a number of patients had ITP for <1 year and received romiplostim for <1 year.

B-cell depletion in immune thrombocytopenia

B cells play an important role in the immune response and can lead to the development of autoimmune diseases and particularly immune thrombocytopenia (ITP). A rational approach to ITP treatment could involve B-cell depletion such as with rituximab. Rituximab is a chimeric monoclonal antibody directed against CD20 molecule. It has direct effects on antibody production and indirect effects on cellular immunity. Rituximab demonstrated an overall response rate of 62.5% that lasted from 2-48 months. The ability of rituximab as an effective splenectomy-avoiding option was recently confirmed in a meta-analysis of randomized clinical trials and observational studies including 368 patients with an overall response rate of 57%. However, the estimated 5- year response is only 21% in adults. Rituximab appears to be well tolerated, but we lack studies of long-term tolerance. The optimal time to administer rituximab for ITP remains unclear. There is consensus to administer corticosteroids or intravenous immunoglobulin (IVIg) as first-line therapy in ITP. A panel of experts was unable to formulate a clear strategy for the respective place of splenectomy, thrombopoietin-receptor agonists, and rituximab as second-line treatment. Among new-generation CD20-targeted therapy, only veltuzumab has been tested for ITP. Preliminary study suggests that it could have similar efficacy to rituximab. Options other than anti-CD20 treatment may modulate and/or inhibit the B-cell compartment. Several monoclonal antibodies (MoAbs) directed against different B-lymphocyte receptors or structures implicated in the cooperation between B and T lymphocytes have been successfully tested in various autoimmune diseases. Testing these options in ITP will be an exciting challenge.

CD4+CD25highFoxP3+ regulatory T-cells in hematologic diseases

BACKGROUND

CD4+CD25+ regulatory T-cells (Tregs) play a critical role in immune responses. We explored the status of Tregs in neoplastic and autoimmune hematologic diseases. We also evaluated the technical aspects of Treg measurement in terms of sample type and detection markers.

METHODS

A total of 68 subjects were enrolled: 11 with AML, 8 with MDS, 10 with autoimmune diseases, and 39 controls. Tregs were analyzed in peripheral blood (PB) and bone marrow (BM) samples from each subject. Flow cytometry and the Human Regulatory T cell Staining Kit (eBioscience, USA) for CD4, CD25, and FoxP3 (forkhead box P3) were used.

RESULTS

The CD4+CD25(high)/CD4 and CD4+CD25(high)FoxP3+/CD4 populations were significantly correlated (P<0.0001). The AML and high-risk MDS groups had significantly larger CD4+CD25(high)/CD4 and CD4+CD25(high)FoxP3+/CD4 populations in PB than the autoimmune (P=0.007 and 0.012, respectively) and control groups (P=0.004 and 0.006, respectively). Comparable findings were observed in BM. The CD4+CD25(high)FoxP3+/CD4 population was significantly larger in PB than in BM (P=0.0003).

CONCLUSIONS

This study provides comparison data for Tregs in AML, MDS, and autoimmune hematologic diseases, and would be helpful for understanding the different immunologic bases of various hematologic diseases. Treg measurement using CD4, CD25, and/or FoxP3 in PB rather than in BM seems to be practical for routine hematologic purposes. Large-scale analysis of the diagnostic role of Treg measurement is needed.