Targeting Telomere Biology in Acute Lymphoblastic Leukemia.

Increased cell proliferation is a hallmark of acute lymphoblastic leukemia (ALL), and genetic alterations driving clonal proliferation have been identified as prognostic factors. To evaluate replicative history and its potential prognostic value, we determined telomere length (TL) in lymphoblasts, B-, and T-lymphocytes, and measured telomerase activity (TA) in leukocytes of patients with ALL. In addition, we evaluated the potential to suppress the in vitro growth of B-ALL cells by the telomerase inhibitor imetelstat. We found a significantly lower TL in lymphoblasts (4.3 kb in pediatric and 2.3 kb in adult patients with ALL) compared to B- and T-lymphocytes (8.0 kb and 8.2 kb in pediatric, and 6.4 kb and 5.5 kb in adult patients with ALL). TA in leukocytes was 3.2 TA/C for pediatric and 0.7 TA/C for adult patients. Notably, patients with high-risk pediatric ALL had a significantly higher TA of 6.6 TA/C compared to non-high-risk patients with 2.2 TA/C. The inhibition of telomerase with imetelstat ex vivo led to significant dose-dependent apoptosis of B-ALL cells. These results suggest that TL reflects clonal expansion and indicate that elevated TA correlates with high-risk pediatric ALL. In addition, telomerase inhibition induces apoptosis of B-ALL cells cultured in vitro. TL and TA might complement established markers for the identification of patients with high-risk ALL. Moreover, TA seems to be an effective therapeutic target; hence, telomerase inhibitors, such as imetelstat, may augment standard ALL treatment.

Serologic response to meningococcal vaccination in patients with paroxysmal nocturnal hemoglobinuria (PNH) chronically treated with the terminal complement inhibitor eculizumab.

Eculizumab is indicated for the therapy of patients with symptomatic paroxysmal nocturnal hemoglobinuria (PNH). Due to inhibition of terminal complement cascade, patients on eculizumab are susceptible to Neisseria meningitidis infections. The two mainstays to reduce the risk of infection are vaccination and antibiotic prophylaxis. In this retrospective study, serologic response was analyzed after vaccination with a meningococcal vaccine in 23 PNH patients (median age 36 years; range 25 - 88 years; 15 males, 8 females) by measuring serum bactericidal assay (SBA) using rabbit complement (rSBA) titers against meningococcal serogroups A, C, W, and Y. Serologic protection was defined by an rSBA titer ≥1:8. Forty-three percent (10/23) were vaccinated more than once due to chronic eculizumab treatment. Overall serologic response for the meningococcal serogroups was A: 78% (18/23), C: 87% (20/23), W: 48% (11/23), and Y: 70% (16/23). No meningococcal infections have been observed. As immunological response to vaccines varies, the use of serologic response analyses is warranted. Re-vaccination with a tetravalent conjugate vaccine under eculizumab therapy every 3 years is essential or should be based on response rates. If meningococcal infection is suspected, standby therapy with ciprofloxacin and immediate medical evaluation are recommended. The novel vaccines covering serogroup B may even further reduce the risk for infection.