Reservoir differences across HIV-1 subtypes: a systematic review to guide cure research.

Introduction: Despite effective antiretroviral therapy, HIV-1 persists as a viral reservoir and remains a major barrier to a durable cure. Reservoir size and dynamics are central determinants of the success of cure strategies. Efforts to characterize and target the HIV-1 reservoir have primarily focused on people with HIV-1 subtype B in Western Europe and North America. This emphasis has limited our understanding of reservoir size and dynamics in individuals with non-B subtypes, which account for most infections globally, particularly in high-burden regions such as sub-Saharan Africa. This systematic review synthesizes evidence on HIV-1 reservoir size in individuals with non-B subtypes and compiles reported reservoir outcomes alongside demographic and clinical metadata. Methods: PubMed and EMBASE were searched for studies quantifying the HIV-1 reservoir in peripheral blood from individuals with non-B subtypes. Eligible studies quantified reservoir size in at least three non-B samples stratified by subtype or directly compared measurements between subtypes. Data were extracted on subtype, reservoir size, statistical comparisons thereof, and key demographic and clinical data. Study quality was assessed using a pre-defined, custom set of criteria. Data were synthesized by organizing within-study statistical comparisons by subtype in a schematic overview to indicate the direction of effect. Results: Of 1589 unique records, 40 studies quantifying HIV-1 reservoir size in individuals with non-B subtypes were included. Records excluded at full-text screening commonly lacked viral subtype determination and/or subtype-stratified outcomes. Comparisons between subtype B and pooled non-B subtypes suggest a larger reservoir for subtype B. Substantial differences in study design, (meta)data reporting, and comparability limited direct comparison across studies. Conclusion: Strengthening knowledge on the HIV-1 subtype-specific reservoir is essential for the development of effective and globally relevant cure strategies. The available data point toward possible differences in reservoir size between subtype B and non-B subtypes. To improve further assessment, we developed recommendations urging studies to use standardized subtyping methods, report viral subtype according to Los Alamos guidelines, and provide detailed individual-level outcomes and metadata, including disease stage at treatment initiation, ART duration, and viral suppression status. Furthermore, we strongly recommend using multi-subtype reservoir assays that are cross-validated to enhance comparability across studies. Systematic Review Registration: https://www.crd.york.ac.uk/PROSPERO/view/CRD420251074799, identifier CRD420251074799.