Streptococcal emm55 protein (Emm55)

Streptococcal emm55 protein is a specific serotype of the M protein, a major surface-anchored virulence factor of Group A Streptococcus (Streptococcus pyogenes). Its native biological function involves aiding bacterial colonization and evading the host immune response by inhibiting phagocytosis and interfering with complement activation [16, 20]. In clinical oncology, the emm55 protein is exploited as a potent immunogenic priming antigen. Therapeutic strategies, such as the plasmid DNA vaccine IFx-Hu2.0 (pAc/emm55), involve the intralesional delivery of the emm55 gene into tumor cells [1, 6]. Once expressed on the tumor cell surface, the emm55 protein serves as a highly visible signal that triggers an influx of CD4+ and CD8+ T cells, effectively overcoming local immune evasion and promoting a systemic anti-tumor immune response [1, 4]. This approach is particularly relevant for treating refractory solid tumors like Merkel cell carcinoma and melanoma, where it is often evaluated in combination with immune checkpoint inhibitors to enhance efficacy [3, 5].

Other names

M55 proteinStreptococcal M55 proteinemm55 gene productStreptococcus pyogenes M protein type 55

Intralesional delivery of a plasmid DNA vaccine encoding the emm55 gene leads to the surface expression of the highly antigenic bacterial Emm55 protein on cancer cells; this acts as a foreign priming antigen that stimulates a systemic, T-cell-mediated anti-tumor immune response [1, 6].