Some pneumococcal surface proteins are serotype-independent and represent a promising alternative for the design of a vaccine [4–6]. Adjuvants are necessary for protein administration by the mucosal route and cholera toxin or heat-labile enterotoxin has been used. However, the

combination of proteins with these kinds of co-adjuvants may not be clinically safe [7]; this is the reason why new vaccines that are safe and inexpensive for global application Roxadustat clinical trial to populations at risk are necessary, especially in developing countries. In this sense, probiotic microorganisms emerge as a valuable alternative, as they have important immunomodulatory effects and multiple applications that include the prevention of allergies [8,9] and infectious diseases [10,11], anti-carcinogenic

activity [12] and the improvement of intestinal bowel disease symptoms [13], among other beneficial effects on the health of humans and animals. In addition, Hydroxychloroquine order the generally regarded as safe (GRAS) condition of lactic acid bacteria (LAB), together with their effects on the immune system of the host, make them good candidates for their use as antigen vehicles. In previous work we have demonstrated that non-recombinant Lactoccocus lactis administered orally and nasally has intrinsic adjuvant properties and stimulates both innate and specific immunity [14,15]. It also improves protection against a respiratory infection with S.

pneumoniae. On the basis of these results, and in order to potentiate the protective effect of L. lactis, we designed a recombinant L. lactis able to express pneumococcal protective protein A (PppA) on its surface: L. lactis-PppA+[16]. Pneumococcal protective protein A (PppA) is a small protein conserved antigenically among different serotype strains of S. pneumoniae (3, 5, 9, 14, 19 and 23). It has been reported that nasal immunization of adult mice with PppA administered with mucosal adjuvants elicits antibodies that are effective in reducing pneumococcal nasal colonization [17]. The recombinant strain L. lactis-PppA+ Immune system administered nasally showed effectiveness in the induction of protective antibodies against systemic and respiratory pneumoccocal infection in both young and adult mice [16]. The results obtained with recombinant bacteria that express different pneumococcal antigens constitute an important advance in the fight against the pathogen. However, the potential application of a live recombinant strain by the nasal route in humans still presents aspects that need to be resolved, such as the elimination of the antibiotic resistance genes used in its selection. Hanniffy et al. evaluated the induction of protective antibodies by a dead recombinant lactococcus in a pneumococal infection model [18].