PDCD1 and neoplasm: This process primes CD8 + T cells for more effective antitumor immunity.239 Furthermore, indole-3-lactic acid modulates the cholesterol metabolism of CD8 + T cells by altering chromatin accessibility, leading to enhanced T cell function and improved responses against tumor growth.239 Additionally, supplementation with Lactobacillus johnsonii or the tryptophan-derived metabolite indole-3-propionic acid (IPA) has been shown to increase the efficacy of anti-PD-1 immunotherapy.