To evaluate the effect of OR-S1 and valemetostat on cytokine production, we measured the concentrations of the pro-inflammatory cytokines IFN-γ, TNF-α, and IL-6 and the anti-inflammatory cytokine IL-10 in the culture supernatants of PBMCs of patients with HAM (n = 8) on day 12 after culture, in the presence or absence of each drug. Here, IL10 is linked to tropical spastic paraparesis.