Increased inflammatory cytokine levels and decreased regulatory T-cell levels are associated with the development of toxicities while on idelalisib. (A) Serum CCL-3 and (B) CCL-4 levels in subjects at various time points on idelalisib therapy. Baseline values indicated in red are subjects who experienced toxicity at day ∼28, and blue represents subjects who did not experience early hepatotoxicity. Open symbols represent levels drawn when subjects have held idelalisib for 3 to 9 days due to toxicity; closed symbols represent samples drawn while subjects remain on idelalisib. (C) Percentage of CD4⁺ T cells that are FoxP3⁺CD25^hi regulatory T cells in subjects on idelalisib. (D) Percentage of CD4⁺ T cells that are CD3⁺CD4⁺ FoxP3⁺CD25^hi regulatory T cells in subjects on idelalisib, stratified by toxicity. At baseline, values indicated in red are subjects who experienced toxicity at day ∼28, blue symbols are subjects who did not experience toxicity, and purple symbols are subjects who experienced delayed toxicity and thus contributed data points to the no toxicity group at day ∼28 and the toxicity group at day ∼130.