Not reported in the public reviews. Reviewers summarise selectively, so this usually means it wasn't discussed publicly, not that it wasn't studied.
NOAEL / key findings
NOAEL not stated; dose-related WBC increases persisting through recovery, elevated reticulocytes, marked spleen weight increases in monkeys
“Common and reproducible effects of natalizumab in cynomolgus monkeys were: • dose related, significantly increased counts of WBC even at the end of recovery periods • elevated reticulocyte counts • severe increases in spleen weights”