The discovery and development of small molecule immune potentiators (SMIPs) as next-generation vaccine adjuvants, the creation of AS37

Aluminum salts remain the most widely used adjuvants in licensed vaccines, but their tendency to favor Th2-dominant humoral responses limits their usefulness when robust Th1, T follicular helper (Tfh), and cellular responses are required. Small-molecule immune potentiators (SMIPs) targeting Toll-like receptor 7 (TLR7) offer a rational way to complement aluminum, provided systemic exposure is tightly controlled. This review re-examines the discovery and development of AS37, a phosphonate-modified benzonaphthyridine TLR7 agonist that is stably adsorbed onto aluminum hydroxide through ligand exchange. We discuss why a TLR7-focused approach was selected, how the adsorption chemistry was validated, and how alum-TLR7 compares with alum alone, MF59, other prominent adjuvants, and related alum-bound TLR7/8 platforms such as Algel-IMDG/Alhydroxiquim-II. Across preclinical studies, AS37 and related alum-TLR7 formulations enhance antibody magnitude and quality, bias CD4+ responses toward Th1 immunity, and promote Tfh- and germinal-center-associated biology. Mechanistic benchmarking in nonhuman primates (NHP) shows increased recruitment and activation of antigen-presenting cells, particularly plasmacytoid dendritic cells, restricted antigen delivery to draining lymph nodes, and a type I interferon-associated program not seen with alum alone. Early human data from a meningococcal C conjugate vaccine show acceptable reactogenicity at lower and intermediate doses together with a transient dose-dependent interferon signature, expanded Tfh responses, and increased memory B cells, but the clinical evidence base remains limited to early-phase studies. AS37 should therefore be viewed as a distinct TLR7-focused, phosphonate-enabled implementation within a broader class of alum-combination innate immune potentiators, with remaining uncertainties around optimal dose, intracellular delivery mechanisms, and comparative clinical performance.