Probiotics and pidotimod face scrutiny for residual immune activation in HIV

A 2026 narrative mini-review concludes that selected probiotics and the synthetic immune modulator pidotimod may warrant further investigation as complementary approaches to residual immune activation and mucosal dysfunction in people with HIV receiving antiretroviral therapy, but it finds no evidence that either strategy should enter routine care. The authors distinguish between probiotics that might act upstream through the intestinal microbial ecosystem and barrier function, and pidotimod, which might influence downstream innate and mucosal immune responses. No clinical trial has established that the two interventions act synergistically, that either reduces non-AIDS disease in treated HIV, or that their biological effects translate into meaningful clinical benefit.

The review was prepared through a focused PubMed/MEDLINE search covering January 2014 through August 25, 2026, with older seminal studies retained for selected concepts. It also consulted NIH and European AIDS Clinical Society guidance and ClinicalTrials.gov. The final narrative synthesis used 41 cited sources, including randomized and controlled trials, observational studies, pilot studies, systematic reviews, mechanistic investigations, consensus documents and registered trials. Because this was a narrative review rather than a systematic review or meta-analysis, the authors did not perform a PRISMA flow analysis, formal risk-of-bias assessment or quantitative pooling. Registered studies without peer-reviewed results were treated as descriptive information, not evidence of efficacy.

The rationale focuses on the incomplete restoration of immune homeostasis that can persist despite suppressive antiretroviral therapy. In treated HIV, gut-associated lymphoid-tissue damage, dysbiosis, impaired epithelial integrity and microbial translocation may coexist with dysregulated systemic immune activation. Markers including IL-6, soluble CD14, D-dimer and high-sensitivity C-reactive protein have been associated with non-AIDS events, but lowering such markers has not been shown to improve clinical outcomes. Current NIH and EACS guidance therefore does not recommend probiotics or pidotimod as standard treatments for residual immune activation. The review presents these approaches as a testable translational hypothesis, not as an established combined therapy.

Probiotics may exert several strain-specific effects, including competition with pathogens for nutrients and adhesion sites, production of organic acids and bacteriocins, strengthening of epithelial tight junctions, increased mucin and IgA production, and modulation of dendritic cells, regulatory T cells and Toll-like receptor signaling. These properties cannot be extrapolated to the probiotic category as a whole. Outcomes depend on the precise microorganisms, dose, formulation, storage conditions, treatment duration, population and endpoint studied. Evidence outside HIV is strongest for preventing antibiotic-associated diarrhea, where a meta-analysis of 42 adult randomized studies found a lower risk, although the magnitude depended on baseline risk, dose and product composition. Selected formulations also have guidance-based roles in preventing Clostridioides difficile infection, while systematic reviews suggest that some products may reduce the number or duration of acute upper respiratory tract infections. These findings do not establish equivalent effects for every commercially available probiotic.

Human evidence in HIV is similarly formulation-specific and limited. A systematic review identified possible signals for diarrhea, CD4 counts, inflammation and microbial translocation, but emphasized substantial heterogeneity and limited certainty. In the phase II VISBIOME ES trial, 93 people receiving antiretroviral therapy were randomized to a multistrain formulation of approximately 1.8 × 10^12 colony-forming units per day or placebo for 24 weeks. The intervention was safe and altered the microbiome, but it did not significantly improve systemic inflammation or gut permeability. In a separate placebo-controlled study of 30 virologically suppressed adults, four weeks of Vivomixx before and after pneumococcal vaccination was associated with greater anti-pneumococcal IgG, salivary IgA, IL-10 and IL-8 responses. That study measured vaccine-response biomarkers and was underpowered to determine whether participants experienced fewer pneumococcal infections. The RECOVER trial in immunologically discordant adults found small changes in the CD4/CD8 ratio and soluble CD14 for a synbiotic group, whereas the probiotic-only group showed no significant immune or fecal-microbiome effect.

Safety is a particular concern in people with profound immune impairment or damaged mucosal barriers. Although probiotics are generally well tolerated, rare Lactobacillus bacteremia and Saccharomyces fungemia have been reported, and inadequately characterized products may carry antimicrobial-resistance determinants. Advanced or uncontrolled HIV, very low CD4 counts, severe barrier impairment, critical illness, central venous catheterization and broad-spectrum antibiotic exposure require individualized assessment. Product evaluation should include strain-level identity, lot traceability, viability and purity testing, manufacturing quality control and evidence against clinically relevant transferable resistance. Next-generation organisms such as Akkermansia muciniphila may require pharmaceutical-grade development as live biotherapeutic products; no Akkermansia-based product has established efficacy for residual immune activation in treated HIV.

Pidotimod is a synthetic dipeptide developed for prevention and adjunctive treatment of respiratory infections. Experimental and translational studies report effects on dendritic-cell maturation, CD80 and CD86 expression, Toll-like receptor signaling, natural killer-cell activity and mucosal responses, whereas human studies have chiefly assessed circulating or mucosal biomarkers in small cohorts. Calling pidotimod a physiological immunomodulator is therefore a proposed pharmacological characterization rather than a clinically validated distinction from broader immunostimulation. Trained immunity serves only as a theoretical framework for future work: pidotimod has not been shown to produce the epigenetic, transcriptomic, metabolic and functional-rechallenge changes required to establish trained innate immune memory.

Adult respiratory studies provide biological signals but remain limited by small samples, heterogeneous populations, inconsistent treatments and a lack of large independently replicated randomized trials. In a randomized study of 16 hospitalized adults with community-acquired pneumonia, pidotimod at 800 mg twice daily was added to levofloxacin. The combination was associated with changes in immune proteins, TLR2 and TLR4 expression, CD80 and CD86, and TNF-α-producing cells, but the sample was far too small to determine clinical efficacy. A non-randomized Italian study of 184 adults with mild-to-moderate COVID-19 reported fewer emergency-department visits or hospitalizations, shorter illness and less rescue corticosteroid use in the pidotimod group. Non-random allocation, differences in concurrent care and residual confounding prevent a causal interpretation, and these outcomes do not establish antiviral efficacy. Another study of 16 hospitalized patients with COVID-19 pneumonia reported changes in neutrophil-to-lymphocyte ratio, interferon-gamma and Toll-like receptor expression; these were exploratory biomarkers rather than validated clinical endpoints.

The only HIV-specific pidotimod evidence highlighted in the review is a 2021 controlled pilot involving 40 people receiving antiretroviral therapy, with 30 assigned to pidotimod and 10 to control. The intervention was associated with altered cytokine profiles, a sustained increase in salivary IgA, and reductions in cystatin C and microalbuminuria over four weeks plus four weeks of follow-up. These shifts do not demonstrate improved glomerular filtration, prevention of chronic kidney disease, fewer infections or other clinically meaningful benefits. The study had a 3:1 group imbalance, restricted statistical power, multiple biomarkers, no hard clinical endpoint and no independent replication. Pidotimod was generally well tolerated in the available adult studies, but their size and follow-up cannot establish the frequency of uncommon adverse events, and formal antiretroviral interaction studies remain limited.

The review proposes a staged research pathway rather than immediate clinical adoption. A multicenter, randomized, double-blind, placebo-controlled phase II trial could test a single prespecified biological endpoint, such as change in soluble CD14 or IL-6 over 12 to 24 weeks, to determine target engagement, durability and safety. Such a result would not establish prevention of non-AIDS events. A larger subsequent trial would be needed to assess clinically documented infections or morbidity, while CD4/CD8 recovery could be evaluated in a prespecified subgroup of immunological non-responders. D-dimer, high-sensitivity C-reactive protein, salivary IgA, intestinal permeability measures, cystatin C, albuminuria and microbiome or metabolome analyses should remain exploratory unless validated as outcomes. The authors argue that pitavastatin offers a more instructive comparator: the REPRIEVE trial linked it to fewer major adverse cardiovascular events in people with HIV at low-to-moderate predicted risk, demonstrating the evidentiary value of a hard endpoint that probiotics and pidotimod have not yet achieved.

Subject of Research: Evaluation of probiotics and pidotimod for residual immune activation and mucosal dysfunction in treated HIV

Article Title: Complementary strategies to target residual immune activation and mucosal dysfunction in treated HIV: role of probiotics and pidotimod

Article References: Falasca, K., Ferri, R., & Vecchiet, J. (2026). Complementary strategies to target residual immune activation and mucosal dysfunction in treated HIV: role of probiotics and pidotimod. Frontiers in Cellular and Infection Microbiology, 16, 1985254. https://doi.org/10.3389/fcimb.2026.1985254

Image Credits: AI Generated

DOI: 10.3389/fcimb.2026.1985254

Keywords: HIV, residual immune activation, antiretroviral therapy, probiotics, pidotimod, mucosal immunity, microbiota, microbial translocation, immunomodulation, Complementary, strategies, target