Suramin has adjuvant properties and promotes expansion of antigen-specific Th1 and Th2 cells in vivo.

Aluminum hydroxide and incomplete Freund's adjuvant (IFA) are the only adjuvants approved for human use. Both are T helper 2 (Th2) adjuvants, however, T helper 1 (Th1) immunity is induced if microbial products such as mycobacteria, CpG's, or bacterial toxins are included in the adjuvant preparation. The usefulness of bacterial toxins, such as Pertussis toxin (PT) or Cholera toxin (CT), as adjuvants for human vaccination is limited by toxic side effects and high immunogenicity. Hence, we asked whether or not the adjuvant activity of bacterial toxins on Th1 and Th2 immunity could be mimicked by chemical compounds of small molecular weight and less immunogenicity. In the present study, we show that Suramin, a small molecular weight naphthylurea, which mainly acts on G-proteins and on P2X/P2Y receptors, promotes expansion of hen eggwhite lysozyme (HEL)-specific Th1 and Th2 cells upon immunization of BALB/c mice with HEL in aluminum hydroxide (alum). The results indicated that the adjuvant effects of Suramin on T cell responses were mediated by enhancing the expression of MHC class II and costimulatory molecules on antigen presenting cells (APCs), and by increasing their pro-inflammatory cytokine production. Together, the results suggest that small molecular weight compounds such as Suramin could be used as alternative vaccine adjuvants.