Table B.9.

Essentiality of the KERs; WoE analysis

3 Empirical support for KERs	Defining question	High (strong)	Moderate	Low (weak)
	Does the empirical evidence support that a change in the KEup leads to an appropriate change in the KEdown? Does KEup occur at lower doses and earlier time points than KEdown and is the incidence of KEup higher than that for KEdown? Are inconsistencies in empirical support cross taxa, species and stressors that don't align with expected pattern of hypothesised AOP?	Multiple studies showing dependent change in both exposure to a wide range of specific stressors (extensive evidence for temporal, dose–response and incidence concordance) and no or few critical data gaps or conflicting data	Demonstrated dependent change in both events following exposure to a small number of specific stressors and some evidence inconsistent with expected pattern that can be explained by factors such as experimental design, technical considerations, differences among laboratories, etc	Limited or no studies reporting dependent change in both events following exposure to a specific stressor (i.e. endpoints never measured in the same study or not at all); and/or significant inconsistencies in empirical support across taxa and species that don't align with expected pattern for hypothesised AOP
MIE → KE1	Low
KE1 → KE2 Chromosomal translocations lead to differentiation arrest of HSPCs in utero	Strong	Rationale: A transgenic zebrafish model expressing TEL‐AML1‐positive ALL either ubiquitously or in lymphoid progenitors showed B‐cell differentiation arrest. TEL‐AML1 expression in all lineages, but not lymphoid‐restricted expression, led to progenitor cell expansion that evolved into oligoclonal B‐lineage ALL in 3% of the transgenic zebrafisha The strongest evidence comes from experimental models and genome wide association studies
KE2 → KE3 Cooperative mutations and Delayed infections in HSPCs with a differentiation blockage lead to clonal expansion	Moderate	Rationale: In principle, there are a large number of factors and pathways linking the fusion product and differentiation blockage with clonal expansion, recurrent cooperative mutations and delayed infections
KE3 → AO Clonal expansion leads to childhood leukaemia	Moderate	Rationale: The accumulation of recurrent mutations in preleukaemic clones and dysfunction of the immune system following delayed infections have been linked to the development of childhood leukaemia

^aSabaawy HE, Azuma M, Embree LJ, Tsai HJ, Starost MF, Hickstein DD, 2006. TEL‐AML1 transgenic zebrafish model of precursor B cell acute lymphoblastic leukemia. Proceedings of the National Academy of Sciences USA, 103, 15166–15171.