These findings define an immunometabolic link between peroxisomal lipid metabolism and T cell differentiation and highlight the 25-HC-LXR-Blimp-1 axis as a mechanistic link regulating CD4<sup>+</sup> T-cell polarization, with potential relevance to X-ALD-associated neuroinflammation. The gene discussed is CD4; the disease is X-linked adrenoleukodystrophy.