Impact of SARS on development of childhood acute lymphoblastic leukaemia

The role of microenvironment in the initiation and evolution of B-cell precursor acute lymphoblastic leukemia

B cell precursor acute lymphoblastic leukemia (BCP-ALL) is a malignant disorder of immature B lineage immune progenitors and is the commonest cancer in children. Despite treatment advances it remains a leading cause of death in childhood and response rates in adults remain poor. A preleukemic state predisposing children to BCP-ALL frequently arises in utero, with an incidence far higher than that of transformed leukemia, offering the potential for early intervention to prevent disease. Understanding the natural history of this disease requires an appreciation of how cell-extrinsic pressures, including microenvironment, immune surveillance and chemotherapy direct cell-intrinsic genetic and epigenetic evolution. In this review, we outline how microenvironmental factors interact with BCP-ALL at different stages of tumorigenesis and highlight emerging therapeutic avenues.

In Utero Development and Immunosurveillance of B Cell Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is the most frequent type of pediatric cancer with a peak incidence at 2–5 years of age. ALL frequently begins in utero with the emergence of clinically silent, preleukemic cells. Underlying leukemia-predisposing germline and acquired somatic mutations define distinct ALL subtypes that vary dramatically in treatment outcomes. In addition to genetic predisposition, a second hit, which usually occurs postnatally, is required for development of overt leukemia in most ALL subtypes. An untrained, dysregulated immune response, possibly due to an abnormal response to infection, may be an important co-factor triggering the onset of leukemia. Furthermore, the involvement of natural killer (NK) cells and T helper (Th) cells in controlling the preleukemic cells has been discussed. Identifying the cell of origin of the preleukemia-initiating event might give additional insights into potential options for prevention. Modulation of the immune system to achieve prolonged immunosurveillance of the preleukemic clone that eventually dies out in later years might present a future directive. Herein, we review the concepts of prenatal origin as well as potential preventive approaches to pediatric B cell precursor (BCP) ALL.

Childhood B-Cell Acute Lymphoblastic Leukemia Following SARS CoV-2 Infection: A Potential Second "Hit" in Leukemogenesis

The Coronavirus Disease 2019 (COVID-19) pandemic has become the worst pandemic in modern history. The lack of prior immunity to the virus has resulted in a high mortality rate, though children have fared better than adults, overall. We present a case of a child who developed B-cell acute lymphoblastic leukemia 1 week following a symptomatic COVID-19 infection. It is possible that this viral infection provided the "second hit" posited to occur in pediatric leukemogenesis as proposed by Dr Greaves, with his initial viral exposure occurring several weeks earlier.

Toward prevention of childhood ALL by early-life immune training

B-cell precursor acute lymphoblastic leukemia (BCP-ALL) is the most common form of childhood cancer. Chemotherapy is associated with life-long health sequelae and fails in ∼20% of cases. Thus, prevention of leukemia would be preferable to treatment. Childhood leukemia frequently starts before birth, during fetal hematopoiesis. A first genetic hit (eg, the ETV6-RUNX1 gene fusion) leads to the expansion of preleukemic B-cell clones, which are detectable in healthy newborn cord blood (up to 5%). These preleukemic clones give rise to clinically overt leukemia in only ∼0.2% of carriers. Experimental evidence suggests that a major driver of conversion from the preleukemic to the leukemic state is exposure to immune challenges. Novel insights have shed light on immune host responses and how they shape the complex interplay between (1) inherited or acquired genetic predispositions, (2) exposure to infection, and (3) abnormal cytokine release from immunologically untrained cells. Here, we integrate the recently emerging concept of "trained immunity" into existing models of childhood BCP-ALL and suggest future avenues toward leukemia prevention.

Leukaemia and lockdown: The delayed infection model of childhood acute lymphoblastic leukaemia and the COVID-19 pandemic

Acute lymphoblastic leukaemia (ALL) is the most common type of leukaemia diagnosed in children. The prevailing hypothesis regarding pathogenesis of childhood ALL was developed by Greaves, and states that ALL is caused by an abnormal immune response to a common infection. The response arises either due to naivety of the immune system caused by a lack of common childhood infections, or genetic susceptibility due to specific alleles. The former explanation is known as the delayed infection hypothesis. COVID-19 is a new infection that no children in the UK were exposed to prior to 2020. Furthermore, the lockdown measures designed to prevent spread of this virus have also greatly reduced spread of other common infections. It is therefore important to examine the evidence for this hypothesis, and to consider it in the context of the pandemic to determine what effect lockdown measures may have on incidence of ALL in children.

SARS-CoV-2 Infection During Induction Chemotherapy in a Child With High-risk T-Cell Acute Lymphoblastic Leukemia

The clinical course of SARS-CoV-2 infection (COVID-19) in children with hematologic malignancies is unclear. We describe the diagnosis, treatment and outcome of a 4-year-old boy with high-risk acute lymphoblastic leukemia and COVID-19. Regardless of immunosuppressive induction chemotherapy his symptoms remained moderate. He received only supportive treatment. Seroconversion occurred in a similar period as in immunocompetent adults. Despite prolonged myelosuppression he did neither acquire secondary infections nor did the treatment delay caused by the infection have a measurable negative impact on the residual disease of acute lymphoblastic leukemia. Intriguingly, residual leukemia even decreased even though he did not receive any antileukemic therapy.

Etiology of Acute Leukemia: A Review

Simple Summary

Acute leukemias are some of the most common cancers affecting all age groups. Despite a significant improvement made in the treatment of acute leukemias, their cause remains unknown. A number of genetic and environmental factors for the development of acute leukemias have been proposed, but none have been proven. Undoubtedly, genetics have a major role in the development of these diseases. The effects of a variety of environmental factors, occupations and hobbies have been explored. A recent “two-hit” theory” for the development of acute lymphoblastic leukemia has been proposed. This combines genetic factors and exposure to infections for the development of this disease. Several genetic factors are suggested. Most recently, for the infection portion, exposure to a virus containing Aspergillus Flavus has been proposed. This review summarizes what is currently known about the factors that are proposed for the development of acute leukemias.

Abstract

Acute leukemias constitute some of the most common malignant disorders. Despite significant progress made in the treatment of these disorders, their etiology remains unknown. A large and diverse group of genetic and environmental variables have been proposed. The role of a variety of factors, including pre-existing and acquired genetic mutations, exposure to radiation and various chemicals during preconception, pregnancy and throughout life, have been explored. The effects of inherited genetic variations and disorders, pre-existing diseases, infectious agents, hobbies, occupations, prior treatments, and a host of other factors have been proposed, but none is universally applicable to all cases. Variation in the incidence and prognosis based on the age, sex, race, type of the disease, geographic area of residence and other factors are intriguing but remain unexplained. Advances in genomic profiling, including genome-wide gene expression, DNA copy number and single nucleotide polymorphism (SNP) genotype, may shed some light on the role of genetics in these disparities. Separate two-hit hypotheses for the development of acute myeloblastic and lymphoblastic leukemia have been proposed. The latter combines genetics and infection factors resulting in leukemogenesis. A number of pre- and post-natal environmental conditions and exposure to infections, including a mycovirus infected Aspergillus flavus, have been suggested. The exact nature, timing, sequence of the events and mechanisms resulting in the occurrence of leukemia requires further investigations. This review summarizes some of the above factors in acute lymphoblastic and myeloblastic leukemias and the direction for future research on the etiology of these disorders.

Cancer Patients Have a Higher Risk Regarding COVID-19 - and Vice Versa?

The world is currently suffering from a pandemic which has claimed the lives of over 230,000 people to date. The responsible virus is called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and causes the coronavirus disease 2019 (COVID-19), which is mainly characterized by fever, cough and shortness of breath. In severe cases, the disease can lead to respiratory distress syndrome and septic shock, which are mostly fatal for the patient. The severity of disease progression was hypothesized to be related to an overshooting immune response and was correlated with age and comorbidities, including cancer. A lot of research has lately been focused on the pathogenesis and acute consequences of COVID-19. However, the possibility of long-term consequences caused by viral infections which has been shown for other viruses are not to be neglected. In this regard, this opinion discusses the interplay of SARS-CoV-2 infection and cancer with special focus on the inflammatory immune response and tissue damage caused by infection. We summarize the available literature on COVID-19 suggesting an increased risk for severe disease progression in cancer patients, and we discuss the possibility that SARS-CoV-2 could contribute to cancer development. We offer lines of thought to provide ideas for urgently needed studies on the potential long-term effects of SARS-CoV-2 infection.

Flash survey on severe acute respiratory syndrome coronavirus-2 infections in paediatric patients on anticancer treatment

INTRODUCTION

Since the beginning of COVID-19 pandemic, it is known that the severe course of the disease occurs mostly among the elderly, whereas it is rare among children and young adults. Comorbidities, in particular, diabetes and hypertension, clearly associated with age, besides obesity and smoke, are strongly associated with the need for intensive treatment and a dismal outcome. A weaker immunity of the elderly has been proposed as a possible explanation of this uneven age distribution. Thus, there is concern that children treated for cancer may allso be at risk for an unfavourable course of infection. Along the same line, anecdotal information from Wuhan, China, mentioned a severe course of COVID-19 in a child treated for leukaemia.

AIM AND METHODS

We made a flash survey on COVID-19 incidence and severity among children on anticancer treatment. Respondents were asked by email to fill in a short Web-based survey.

RESULTS

We received reports from 25 countries, where approximately 10,000 patients at risk are followed up. At the time of the survey, more than 200 of these children were tested, nine of whom were positive for COVID-19. Eight of the nine cases had asymptomatic to mild disease, and one was just diagnosed with COVID-19. We also discuss preventive measures that are in place or should be taken and treatment options in immunocompromised children with COVID-19.

CONCLUSION

Thus, even children receiving anticancer chemotherapy may have a mild or asymptomatic course of COVID-19. While we should not underestimate the risk of developing a more severe course of COVID-19 than that observed here, the intensity of preventive measures should not cause delays or obstructions in oncological treatment.

Flash survey on severe acute respiratory syndrome coronavirus-2 infections in paediatric patients on anticancer treatment

INTRODUCTION

Since the beginning of COVID-19 pandemic, it is known that the severe course of the disease occurs mostly among the elderly, whereas it is rare among children and young adults. Comorbidities, in particular, diabetes and hypertension, clearly associated with age, besides obesity and smoke, are strongly associated with the need for intensive treatment and a dismal outcome. A weaker immunity of the elderly has been proposed as a possible explanation of this uneven age distribution. Thus, there is concern that children treated for cancer may allso be at risk for an unfavourable course of infection. Along the same line, anecdotal information from Wuhan, China, mentioned a severe course of COVID-19 in a child treated for leukaemia.

AIM AND METHODS

We made a flash survey on COVID-19 incidence and severity among children on anticancer treatment. Respondents were asked by email to fill in a short Web-based survey.

RESULTS

We received reports from 25 countries, where approximately 10,000 patients at risk are followed up. At the time of the survey, more than 200 of these children were tested, nine of whom were positive for COVID-19. Eight of the nine cases had asymptomatic to mild disease, and one was just diagnosed with COVID-19. We also discuss preventive measures that are in place or should be taken and treatment options in immunocompromised children with COVID-19.

CONCLUSION

Thus, even children receiving anticancer chemotherapy may have a mild or asymptomatic course of COVID-19. While we should not underestimate the risk of developing a more severe course of COVID-19 than that observed here, the intensity of preventive measures should not cause delays or obstructions in oncological treatment.

The ‘delayed infection’ (aka ‘hygiene’) hypothesis for childhood leukaemia

The common variant of childhood acute lymphoblastic leukaemia (cALL) is the most frequent paediatric cancer subtype. Its incidence rate appears to have increased substantially in Western societies during the mid-20th century and continues to increase at ∼1%/year. Worldwide cALL appears to track with affluence of societies. The ‘delayed infection’ hypothesis, first formulated in 1988, parallels the hygiene hypothesis and has an evolutionary foundation in the concept of a mismatch between prior genetic selection and programming (of the immune system) and contemporary social circumstances. In essence, the hypothesis predicts that ALL is triggered by an abnormal immune response to one or more common microbial infections and that the abnormality arises for two reasons: (i) infectious exposures being delayed beyond the immunologically anticipated period of infancy; (ii) some degree of inherited genetic susceptibility via, for example, allelic variation in genes involved in the MHC and/or immune response network. The hypothesis also has a framework in the underlying cell and molecular biology of ALL and its natural history. Epidemiological studies of social contacts in infancy (as a proxy for common infections) and risk of ALL provide indirect but strong support for the hypothesis. The idea still requires mechanistic and genetic endorsement and the appropriate studies are in progress.