Single-domain antibody-conjugated lipid nanoparticles for selective mRNA delivery to CD4⁺ T cells and Brec1-mediated excision of HIV-1 proviral DNA

Approaches to curing HIV infection aim to eliminate the latent viral reservoir — long-lived, resting CD4⁺ T cells harboring integrated but transcriptionally silent proviral DNA — which persists despite effective antiretroviral therapy. The HIV-1 LTR-specific designer-recombinase Brec1 can precisely excise integrated proviral DNA from infected cells. However, targeted delivery of therapeutic payloads to HIV reservoir-bearing CD4⁺ T cells remains a major challenge. Here, we present a proof-of-concept study of a modular platform combining CD4-specific single-domain antibody (sdAb)-conjugated lipid nanoparticles (LNPs) with Brec1 mRNA for targeted delivery to CD4⁺ T cells. In primary human PBMCs, sdAb-LNPs achieved 44% transfection efficiency in CD4⁺ T cells with pronounced specificity over CD8⁺ T cells (4:1 ratio) and B cells (9:1 ratio), without compromising cell viability. Brec1 recombinase activity was validated across three reporter cell systems of increasing complexity, confirming efficient translation of delivered Brec1 mRNA into a functional recombinase capable of precise, error-free loxBTR-mediated proviral excision. These findings provide proof of concept for sdAb-LNP-mediated Brec1 mRNA delivery as a candidate strategy for HIV reservoir reduction, with the modular platform design enabling flexible adaptation to other cell-specific therapeutic applications.