Silibinin‐driven microbial and metabolic reprogramming restores CD4⁺ T cell immunity in HIV immunological nonresponders

Despite the effectiveness of combination antiretroviral therapy (cART) in suppressing viral replication, 10%–40% of HIV‐infected individuals, characterized as immunological nonresponders (INRs), exhibit insufficient CD4⁺ T cell recovery and persistent chronic inflammation. This study investigated whether silibinin (SIL), a natural flavonoid, could reverse the nicotinamide adenine dinucleotide (NAD⁺) metabolic dysfunction through gut microbiota modulation to correct immune dysfunction in INRs. SIL treatment significantly increased CD4⁺ T cell counts and reduced T cell activation (HLA‐DR⁺) and pro‐inflammatory cytokines (CXCL11 and IL‐8) in INRs. 16S rDNA profiling revealed that SIL treatment selectively expanded Blautia, which was associated with CD4⁺ T cell recovery, and PICRUSt2 functional prediction indicated marked vitamin B3 pathway enrichment. LC‐MS/MS and enzyme‐linked immunosorbent assay (ELISA) corroborated the unique “nicotinamide (NAM) accumulation–NAD⁺ depletion” signature of INRs (NAM: INR > IR > HC; NAMPT: IR > HC > INR; NAD⁺: INR < IR < HC), and revealed that SIL markedly restored NAM‐NMN‐NAD⁺‐nicotinamide adenine dinucleotide reduced form (NADH) pool and re‐activated nicotinamide phosphoribosyltransferase (NAMPT). Metagenomic analysis confirmed that enriched Blautia wexlerae harbors functional NAMPT domains, and its growth was significantly suppressed by the NAMPT inhibitor FK866 in vitro. Furthermore, NAD⁺ supplementation restored mitochondrial membrane potential, ATP production, and cell viability of T cells in vitro. In vivo, specific pathogen‐free (SPF) mice cleared oral NAM faster and up‐regulated colonic NAMPT expression than germ‐free (GF) mice, underscoring microbiota‐dependent NAD⁺ homeostasis. Together, these findings identify a microbiota–metabolic–immune axis in which SIL‐associated Blautia enrichment is correlated with NAD⁺ salvage pathway restoration replenishes NAD⁺, and attenuates T‐cell exhaustion in INRs.