CD4 and viral infectious disease: SB-based tools can also contribute to the quick diagnosis, therapy, and prevention of viral infections.26 Wei et al. engineered Lactobacillus jensenii, a commensal bacterium that colonizes the cervicovaginal mucosa, to prevent HIV transmission; the engineered strain secretes two-domain CD4 (2D CD4) proteins,183 which associate with HIV type 1 (HIV-1) gp120 and inhibit HIV-1 invasion.