Late diagnosed HIV-infected subjects show impaired immunological recovery resulting in a greater risk of clinical progression. Gut bacteria metabolism appears to impact immune recovery in HIV-infected subjects, and while nutritional interventions with prebiotics and probiotics seem to exert immunological effects, the clinical implications in this key population remain unknown. This is a pilot multicenter randomized placebo-controlled, double blind clinical trial in HIV-infected ART-naive subjects with <350 CD4 T cells/mm3 or AIDS. Participants will be randomized (1:1) to either the synbiotic nutritional supplement PMT25341 or placebo for 48 weeks, each in combination with first-line ART. Primary outcomes will be safety and immunological recovery. Secondary outcomes will include changes in fecal microbiota structure and plasma inflammatory markers.

Inclusion Criteria:

• HIV-infected ART-naive subjects with <350 CD4 T cells/mm3 or AIDS
• Initiating ART with any first-line regimen recommended in the Spanish GESIDA National Guidelines

Exclusion Criteria:

• Age <18 years
• Pregnancy
• Type 1 or 2 diabetes
• End-stage renal disease
• Lactose intolerance
• Use of immunomodulatory drugs
• Neutrophil count <750cells/uL