Telomeres and telomerase in paediatric patients with T-cell acute lymphoblastic leukaemia (T-ALL)

A Bright Horizon: Immunotherapy for Pediatric T-Cell Malignancies

Immunotherapy has transformed the treatment of hematologic malignancies in the past two decades. The treatment of acute lymphoblastic leukemia (ALL), in particular, has been highly impacted by multiple novel immunotherapies. For pediatric patients with T-cell malignancies, translating immunotherapies has proved more challenging due to the complexities of fratricide, risk of product contamination with malignant cells, and concerns over T-cell aplasia. Despite these hurdles, many creative and promising strategies are on the horizon. We review challenges in the development of immunotherapy for T-cell malignancies, strategies to overcome these challenges, as well as therapies currently being investigated and starting to reach the clinic. Immunotherapy will hopefully successfully treat patients with relapsed and refractory T-cell malignancies and may someday be incorporated in up-front protocols in order to prevent relapses.

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.

Harnessing immunotherapy for pediatric T-cell malignancies

Pediatric T-cell hematologic malignancies are a diverse group of rare cancers. The most common pediatric T-cell malignancies include T-cell acute lymphoblastic leukemia (T-ALL) and anaplastic large cell lymphoma (ALCL). Although the overall survival rates have improved markedly in recent years, children with relapsed T-ALL and ALCL have very low rates of cure and few salvage therapies exist. Current treatment regimens rely on toxic chemotherapies with significant short- and long-term morbidity. Immunotherapies, including antibodies and adoptive cellular therapies, have revolutionized the treatment of B-cell malignancies in pediatrics. The adaptation of these therapies to T-cell malignancies has been slower because of challenges implicit in the design and implementation of immunotherapies for T-cell malignancies, including the potential risks of fratricide, immunosuppression, and graft versus host disease (GVHD). We present a review of current challenges in the development of immunotherapies for T-cell hematologic malignancies, potential solutions and therapies under investigation. We include a particular focus on T-ALL and ALCL. Immunotherapies offer promising strategies to improve outcomes in children with T-cell malignancies, particularly in the setting of relapse. Optimizing efficacy, mitigating toxicity, and safely integrating with conventional therapies are key considerations as immunotherapies are translated into the clinic.

TERT polymorphisms modify the risk of acute lymphoblastic leukemia in Chinese children

Human telomerase reverse transcriptase (TERT) is essential for the maintenance of telomere DNA length, chromosomal stability and cellular immortality. We hypothesized that TERT polymorphisms are associated with risk of childhood acute lymphoblastic leukemia (ALL). We first conducted a case-control study of 570 ALL cases and 673 cancer-free controls of Chinese children, using the tagging single-nucleotide polymorphisms (tSNPs) approach. We then examined the functionality of the important SNPs. We found that TERT promoter region tSNP (rs2735940) and two intron region tSNPs (rs2736100 and rs10069690) were associated with risk of childhood ALL (P = 0.036, 0.011 and 0.022, respectively, in allele comparison). The in vitro luciferase assays in Jurkat cells showed an increased transcriptional activity of rs2735940 T allele compared with the C allele. Additional experiments with ALL bone marrow revealed that the rs2735940 T allele increased levels of the TERT messenger RNA. Notably, TERT intron 2 polymorphism (rs2736100) was associated with lower telomerase activity and longer telomeres. Our findings suggested that TERT promoter rs2735940 polymorphism may affect the TERT activity, and rs2736100 may be associated with telomere function, and thus, it is a potential biomarker for genetic susceptibility to ALL in Chinese children.

Telomere biology in hematopoiesis and stem cell transplantation

Telomeres are long (TTAGGG)(n) nucleotide repeats and an associated protein complex located at the end of the chromosomes. They shorten with every cell division and, thus are markers for cellular aging, senescence, and replicative capacity. Telomere dysfunction is linked to several bone marrow disorders, including dyskeratosis congenita, aplastic anemia, myelodysplastic syndrome, and hematopoietic malignancies. Hematopoietic stem cell transplantation (HSCT) provides an opportunity in which to study telomere dynamics in a high cell proliferative environment. Rapid telomere shortening of donor cells occurs in the recipient shortly after HSCT; the degree of telomere attrition does not appear to differ by graft source. As expected, telomeres are longer in recipients of grafts with longer telomeres (e.g., cord blood). Telomere attrition may play a role in, or be a marker of, long term outcome after HSCT, but these data are limited. In this review, we discuss telomere biology in normal and abnormal hematopoiesis, including HSCT.

Dynamics of telomere's length and telomerase activity in Philadelphia chromosome negative myeloproliferative neoplasms

Telomere exhaustion and increased telomerase activity are associated with the acquisition of aggressive molecular events in a variety of haematological malignancies. In Philadelphia chromosome negative myeloproliferative neoplasms (Ph(neg)MPN's), telomere dynamics during clonal evolution of these diseases have not yet been fully elucidated. Herein we demonstrated that telomere shortening is a global phenomenon in Ph(neg)MPN's, irrespective of disease phenotype, treatment administration and JAK2V617F mutational status but the presence of additional cytogenetic abnormalities further affects them. Consistent with the above finding, TA was upregulated in CD34+ haemopoietic progenitors from almost all Ph(neg)MPN subgroups compared to healthy donors. Moreover, TL below the cut-off value of 27% could predict disease progression in Ph(neg)MPN patients (PFS at 5 years 39% vs 81%). Thus, TL emerges as a new prognostic marker in Ph(neg)MPN, reflecting probably the genetic instability of highly proliferating MPN clones.

The role of telomere biology in bone marrow failure and other disorders

Telomeres, consisting of nucleotide repeats and a protein complex at chromosome ends, are essential in maintaining chromosomal integrity. Dyskeratosis congenita (DC) is the inherited bone marrow failure syndrome (IBMFS) that epitomizes the effects of abnormal telomere biology. Patients with DC have extremely short telomere lengths (<1st percentile) and many have mutations in telomere biology genes. Interpretation of telomere length in other IBMFSs is less straightforward. Abnormal telomere shortening has been reported in patients with apparently acquired hematologic disorders, including aplastic anemia, myeolodysplasia, paroxysmal nocturnal hemoglobinuria, and leukemia. In these disorders, the shortest-lived cells have the shortest telomeres, suggestive of increased hematopoietic stress. Telomeres are also markers of replicative and/or oxidative stress in other complex disease pathways, such as inflammation, stress, and carcinogenesis. The spectrum of related disorders caused by mutations in telomere biology genes extends beyond classical DC to include marrow failure that does not respond to immunosuppression, idiopathic pulmonary fibrosis, and possibly other syndromes. We suggest that such patients be categorized as having an inherited disorder of telomere biology. Longitudinal studies of patients with very short telomeres but without classical DC are necessary to further understand the long-term sequelae, such as malignancy, osteonecrosis/osteoporosis, and pulmonary and liver disease.