T‐cell numbers, particularly of CD8+ T cells, are raised in the post‐mortem CNS tissue of AD, ALS and PD patients (Togo et al., 2002) and altered T‐cell levels or subsets in the cerebrospinal fluid and peripheral blood of AD, PD and ALS patients (Gate et al., 2020). This evidence concerns the gene CD8A and amyotrophic lateral sclerosis.