Immunization against Leishmania major infection using LACK- and IL-12-expressing Lactococcus lactis induces delay in footpad swelling

Enhancement of live vaccines by co-delivery of immune modulating proteins

Vaccines are very effective in providing protection against many infectious diseases. However, it has proven difficult to develop highly efficacious vaccines against some pathogens and so there is a continuing need to improve vaccine technologies. The first successful and widely used vaccines were based on attenuated pathogens (e.g., laboratory passaged Pasteurella multocida to vaccinate against fowl cholera) or closely related non-pathogenic organisms (e.g., cowpox to vaccinate against smallpox). Subsequently, live vaccines, either attenuated pathogens or non-pathogenic microorganisms modified to deliver heterologous antigens, have been successfully used to induce protective immune responses against many pathogens. Unlike conventional killed and subunit vaccines, live vaccines can deliver antigens to mucosal surfaces in a similar manner and context as the natural infection and hence can often produce a more appropriate and protective immune response. Despite these advantages, there is still a need to improve the immunogenicity of some live vaccines. The efficacy of injectable killed and subunit vaccines is usually enhanced using adjuvants such mineral salts, oils, and saponin, but such adjuvants cannot be used with live vaccines. Instead, live vaccines can be engineered to produce immunomodulatory molecules that can stimulate the immune system to induce more robust and long-lasting adaptive immune responses. This review focuses on research that has been undertaken to engineer live vaccines to produce immunomodulatory molecules that act as adjuvants to increase immunogenicity. Adjuvant strategies with varying mechanisms of action (inflammatory, antibody-mediated, cell-mediated) and delivery modes (oral, intramuscular, intranasal) have been investigated, with varying degrees of success. The goal of such research is to define adjuvant strategies that can be adapted to enhance live vaccine efficacy by triggering strong innate and adaptive immune responses and produce vaccines against a wider range of pathogens.

Host–Pathogen Interaction in Leishmaniasis: Immune Response and Vaccination Strategies

Leishmaniasis is a zoonotic and vector-borne infectious disease that is caused by the genus Leishmania belonging to the trypanosomatid family. The protozoan parasite has a digenetic life cycle involving a mammalian host and an insect vector. Leishmaniasisis is a worldwide public health problem falling under the neglected tropical disease category, with over 90 endemic countries, and approximately 1 million new cases and 20,000 deaths annually. Leishmania infection can progress toward the development of species–specific pathologic disorders, ranging in severity from self-healing cutaneous lesions to disseminating muco-cutaneous and fatal visceral manifestations. The severity and the outcome of leishmaniasis is determined by the parasite’s antigenic epitope characteristics, the vector physiology, and most importantly, the immune response and immune status of the host. This review examines the nature of host–pathogen interaction in leishmaniasis, innate and adaptive immune responses, and various strategies that have been employed for vaccine development.

Recombinant lactic acid bacteria as promising vectors for mucosal vaccination

Lactic acid bacteria (LAB), a diverse family of gram-positive bacteria, has been proven effective in delivering varieties of therapeutic and prophylactic molecules such as antigens and cytokines. Featuring the properties of acid-resistant, high uptake into Peyer's patches, and superior capacity for inducing secretory IgA antibodies, LAB have good potential to be used as vaccine vectors for mucosal vaccination. Mucosal immunization enables both mucosal and systemic immune responses, which are critical for resisting pathogens that invade the host through the mucosal surfaces. With the development of genetic engineering, LAB strains, primarily Lactococcus and Lactobacillus have been exploited to express a range of heterologous antigens. Numerous studies have demonstrated that LAB mucosal vaccines can stimulate all arms of the immune system to provide adequate protection against pathogen infections. Additionally, several LAB-based human papillomavirus vaccines have entered the clinical trial studies, which suggest the great promise of LAB vaccines for new interventions in mucosal transport diseases. Herein, we will discuss the factors that influence the immunogenicity of LAB vaccines, including LAB strains, the location of antigens, and administration routes, and focus on the current strategies that have been reported for optimizing LAB vaccines.

Cytoplasmic expression of a model antigen with M Cell-Targeting moiety in lactic acid bacteria and implication of the mechanism as a mucosal vaccine via oral route

Lactic acid bacteria (LAB) have been widely studied as mucosal vaccine delivery carriers against many infectious diseases for heterologous expression of protein antigens. There are three antigen expression strategies for LAB: cytoplasmic expression (CE), cell surface display (SD), and extracellular secretion (ES). Despite the generally higher protein expression level and many observations of antigen-specific immunogenicity in CE, its application as a mucosal vaccine has been overlooked relative to SD and ES because of the antigens enclosed by the LAB cell wall. We hypothesized that the antigens in CE could be released from the LAB into the intestinal lumen before host bacterial access to gut-associated lymphoid tissue (GALT), which could contribute to antigen-specific immune responses after oral administration. To elucidate this hypothesis, three recombinant Lactobacillus plantarum (LP) strains were constructed to produce a model antigen, BmpB, with or without an M cell-targeting moiety, and their immunogenicities were analyzed comparatively as oral vaccines in mouse model. The data indicated that the recombinant LPs producing BmpBs with different conformations could induce mucosal immunity differentially. This suggests that the cytoplasmic antigens in LAB could be released into the intestinal lumen, subsequently translocated through M cells, and stimulate the GALT to generate antigen-specific immune responses. Therefore, the CE strategy has great potential, especially in the application of oral LAB vaccines as well as SD and ES strategies. This research provides a better understanding of the mechanism for recombinant oral LAB vaccines and gives insight to the future design of LAB vaccines and oral delivery applications for useful therapeutic proteins.

Probiotic-Based Vaccines May Provide Effective Protection against COVID-19 Acute Respiratory Disease

Severe acute respiratory syndrome coronavirus 2 virus (SARS-CoV-2) infection, the causative agent of COVID-19, now represents the sixth Public Health Emergency of International Concern (PHEIC)—as declared by the World Health Organization (WHO) since 2009. Considering that SARS-CoV-2 is mainly transmitted via the mucosal route, a therapy administered by this same route may represent a desirable approach to fight SARS-CoV-2 infection. It is now widely accepted that genetically modified microorganisms, including probiotics, represent attractive vehicles for oral or nasal mucosal delivery of therapeutic molecules. Previous studies have shown that the mucosal administration of therapeutic molecules is able to induce an immune response mediated by specific serum IgG and mucosal IgA antibodies along with mucosal cell-mediated immune responses, which effectively concur to neutralize and eradicate infections. Therefore, advances in the modulation of mucosal immune responses, and in particular the use of probiotics as live delivery vectors, may encourage prospective studies to assess the effectiveness of genetically modified probiotics for SARS-CoV-2 infection. Emerging trends in the ever-progressing field of vaccine development re-emphasize the contribution of adjuvants, along with optimization of codon usage (when designing a synthetic gene), expression level, and inoculation dose to elicit specific and potent protective immune responses. In this review, we will highlight the existing pre-clinical and clinical information on the use of genetically modified microorganisms in control strategies against respiratory and non-respiratory viruses. In addition, we will discuss some controversial aspects of the use of genetically modified probiotics in modulating the cross-talk between mucosal delivery of therapeutics and immune system modulation.

Group II Introns Generate Functional Chimeric Relaxase Enzymes with Modified Specificities through Exon Shuffling at Both the RNA and DNA Level

Group II introns are large self-splicing RNA enzymes with a broad but somewhat irregular phylogenetic distribution. These ancient retromobile elements are the proposed ancestors of approximately half the human genome, including the abundant spliceosomal introns and non-long terminal repeat retrotransposons. In contrast to their eukaryotic derivatives, bacterial group II introns have largely been considered as harmful selfish mobile retroelements that parasitize the genome of their host. As a challenge to this view, we recently uncovered a new intergenic trans-splicing pathway that generates an assortment of mRNA chimeras. The ability of group II introns to combine disparate mRNA fragments was proposed to increase the genetic diversity of the bacterial host by shuffling coding sequences. Here, we show that the Ll.LtrB and Ef.PcfG group II introns from Lactococcus lactis and Enterococcus faecalis respectively can both use the intergenic trans-splicing pathway to catalyze the formation of chimeric relaxase mRNAs and functional proteins. We demonstrated that some of these compound relaxase enzymes yield gain-of-function phenotypes, being significantly more efficient than their precursor wild-type enzymes at supporting bacterial conjugation. We also found that relaxase enzymes with shuffled functional domains are produced in biologically relevant settings under natural expression levels. Finally, we uncovered examples of lactococcal chimeric relaxase genes with junctions exactly at the intron insertion site. Overall, our work demonstrates that the genetic diversity generated by group II introns, at the RNA level by intergenic trans-splicing and at the DNA level by recombination, can yield new functional enzymes with shuffled exons, which can lead to gain-of-function phenotypes.

Twenty years of research on HPV vaccines based on genetically modified lactic acid bacteria: an overview on the gut-vagina axis

Most cervical cancer (CxCa) are related to persistent infection with high-risk human papillomavirus (HR-HPV) in the cervical mucosa, suggesting that an induction of mucosal cell-mediated immunity against HR-HPV oncoproteins can be a promising strategy to fight HPV-associated CxCa. From this perspective, many pre-clinical and clinical trials have proved the potential of lactic acid bacteria (LAB) genetically modified to deliver recombinant antigens to induce mucosal, humoral and cellular immunity in the host. Altogether, the outcomes of these studies suggest that there are several key factors to consider that may offer guidance on improvement protein yield and improving immune response. Overall, these findings showed that oral LAB-based mucosal HPV vaccines expressing inducible surface-anchored antigens display a higher potential to induce particularly specific systemic and mucosal cytotoxic cellular immune responses. In this review, we describe all LAB-based HPV vaccine investigations by reviewing databases from international studies between 2000 and 2020. Our aim is to promote the therapeutic HPV vaccines knowledge and to complete the gaps in this field to empower scientists worldwide to make proper decisions regarding the best strategies for the development of therapeutic HPV vaccines.

Evaluation of a new live recombinant vaccine against cutaneous leishmaniasis in BALB/c mice

Background

Leishmaniasis is a serious health problem in some parts of the world. In spite of the many known leishmaniasis control measures, the disease has continued to increase in endemic areas, and no effective vaccine has been discovered.

Methods

In this study, Leishmania tarentulae was used as a living factory for the production of two LACK and KMP11 immunogenic antigens in the mice body, and safety profiles were investigated. The sequences of the KMP11 and LACK L. major antigens were synthesized in the pLEXSY-neo 2.1 plasmid and cloned into E. coli strain Top10, and after being linearized with the SwaI enzyme, they were transfected into the genome of L. tarentolae. The L. tarentolae-LACK/KMP11/EGFP in the stationary phase with CpG ODN as an adjuvant was used for vaccination in BALB/c mice. Vaccination was performed into the left footpad. Three weeks later, the booster was injected in the same manner. To examine the effectiveness of the injected vaccine, pathogenic L. major (MRHO/IR/75/ER) was injected into the right footpad of all mice three weeks following the booster vaccination. In order to assess humoral immunity, the levels of IgG1, and IgG2a antibodies before and 6 weeks after the challenge were studied in the groups. In addition, in order to investigate cellular immunity in the groups, the study measured IFN-γ, IL-5, TNF-α, IL-6 and IL-17 cytokines before, 3 weeks and 8 weeks after the challenge, and also the parasite load in the lymph node with real-time PCR.

Results

The lowest level of the parasitic load was observed in the G1 group (mice vaccinated with L. tarentolae-LACK/KMP11/EGFP with CpG) in comparison with other groups (L. tarentolae-LACK/KMP11/EGFP +non-CpG (G2); L. tarentolae-EGFP + CpG (G3, control); L. tarentolae-EGFP + non-CpG (G4, control); and mice injected with PBS (G5, control). Moreover, the evaluation of immune response showed a delayed-type hypersensitivity towards Th1.

Conclusions

According to the results of this study, the live recombinant vaccine of L. tarentolae-LACK/KMP11/EGFP with the CpG adjuvant reduced the parasitic load and footpad induration in infected mice. The long-term effects of this vaccine can be evaluated in volunteers as a clinical trial in future planning.

Lactococcus lactis expressing sand fly PpSP15 salivary protein confers long-term protection against Leishmania major in BALB/c mice

Cutaneous leishmaniasisis a vector-borne disease transmitted by Leishmania infected sand flies. PpSP15 is an immunogenic salivary protein from the sand fly Phlebotomus papatasi. Immunization with PpSP15 was shown to protect against Leishmania major infection. Lactococcus lactis is a safe non-pathogenic delivery system that can be used to express antigens in situ. Here, the codon-optimized Ppsp15-egfp gene was cloned in pNZ8121 vector downstream of the PrtP signal peptide that is responsible for expression and secretion of the protein on the cell wall. Expression of PpSP15-EGFP recombinant protein was monitored by immunofluorescence, flow cytometry and Western blot. Also, expression of protein in cell wall compartment was verified using whole cell ELISA, Western blot and TEM microscopy. BALB/c mice were immunized three times with recombinant L. lactis-PpSP15-EGFPcwa, and the immune responses were followed up, at short-term (ST, 2 weeks) and long-term (LT, 6 months) periods. BALB/c mice were challenged with L. major plus P. papatasi Salivary Gland Homogenate. Evaluation of footpad thickness and parasite burden showed a delay in the development of the disease and significantly decreased parasite numbers in PpSP15 vaccinated animals as compared to control group. In addition, immunized mice showed Th1 type immune responses. Importantly, immunization with L. lactis-PpSP15-EGFPcwa stimulated the long-term memory in mice which lasted for at least 6 months.

Adjuvant Strategies for Lactic Acid Bacterial Mucosal Vaccines

Lactic acid bacteria (LAB) are Gram-positive, acid-tolerant bacteria that have long been used in food fermentation and are generally recognized as safe (GRAS). LAB are a part of a normal microbiome and act as probiotics, improving the gastrointestinal microbiome and health when consumed. An increasing body of research has shown the importance of the microbiome on both mucosal immune heath and immune response to pathogens and oral vaccines. Currently, there are few approved mucosal vaccines, and most are attenuated viruses or bacteria, which necessitates cold chain, carries the risk of reversion to virulence, and can have limited efficacy in individuals with poor mucosal health. On account of these limitations, new types of mucosal vaccine vectors are necessary. There has been increasing interest and success in developing recombinant LAB as next generation mucosal vaccine vectors due to their natural acid and bile resistance, stability at room temperature, endogenous activation of innate and adaptive immune responses, and the development of molecular techniques that allow for manipulation of their genomes. To enhance the immunogenicity of these LAB vaccines, numerous adjuvant strategies have been successfully employed. Here, we review these adjuvant strategies and their mechanisms of action which include: Toll-like receptor ligands, secretion of bacterial toxins, secretion of cytokines, direct delivery to antigen presenting cells, and enterocyte targeting. The ability to increase the immune response to LAB vaccines gives them the potential to be powerful mucosal vaccine vectors against mucosal pathogens.

Subcutaneous Immunization with Recombinant Lactococcus lactis Expressing F1S1 Fusion Protein Induces Systemic and Mucosal Immune Responses in BALB/C Mice

BACKGROUND

Lactic acid bacteria such as Lactococcus (L.) lactis are powerful tools that can function as live delivery vectors and heterologous protein expression hosts in development of novel vaccines. Pertussis toxin (PT) and filamentous hemagglutinin (FHA) are important virulence factors of Bordetella (B.) pertussis and constitute the major components of commercially available acellular pertussis (aP) vaccines. The purpose of the present study was to express F1S1 fusion protein, consisted of the N-terminal region of S1 subunit from PT and FHA type 1 immunodominant domain by L. lactis and to evaluate its immunogenicity.

METHODS

The fusion gene composed of sequences encoding the F1S1 and the signal peptide of usp45 fragments (SECF1S1) was codon optimized for protein production in L. lactis and was synthesized and inserted in-frame inside pNZ8149 plasmid. The resulting pNZ8149-SECF1S1 construct was introduced by electroporation into L. lactis cells (LL-F1S1). BALB/c mice were subcutaneously immunized with LL-F1S1 or commercial DTaP vaccine. The immune responses were investigated.

RESULTS

The LL-F1S1-immunized mice produced significant levels of specific IFN-g compared to their respective controls and DTaP-immunized mice. The F1S1- specific IgG antibody response was lower in LL-F1S1-immunized mice while the IgG2a/IgG1 ratio was higher in this group compared to the DTaP-immunized mice. Moreover, anti-F1S1 IgA antibodies were only detected in the lung homogenates of the LL-F1S1-immunized mice, suggesting the induction of a mucosal immune response.

CONCLUSION

These results indicate the feasibility of expression of F1S1 fusion protein in L. lactis. This recombinant bacterium could induce mucosal and Th1-type systemic immune responses following subcutaneous administration.

Oral immunization with recombinant Lactococcus lactis NZ9000 expressing human papillomavirus type 16 E7 antigen and evaluation of its immune effects in female C57BL/6 mice

The ORFs of both native and codon-optimized E7 genes were successfully fused to SPusp45 signal peptide and expressed by a nisin-controlled gene expression system in the NZ9000 strains of Lactococcus lactis. Recombinant strains were confirmed by Western blot analysis. To measure immune responses against the E7 antigen, specific-pathogen-free C57BL/6 mice were inoculated with L lactis harboring pNZ8123-rE7 by oral gavage. Then, specific antibodies and cytokines were measured by enzyme-linked immunosorbent assay and enzyme-linked immunospot assay, respectively. Oral administration of L lactis strains expressing rE7 elicited the highest levels of E7-specific antibody and greatest numbers of E7-specific CD4⁺ T helper and CD8⁺ T cell precursors. Our outcomes indicated that the HPV-16 E7 specific IL-2- and IFN-γ-secreting T cells in antigen-stimulated splenocytes and intestinal mucosal lymphocytes were significantly higher than the control groups. Our data also demonstrated that mice vaccinated with recombinant L lactis were able to generate potent protective effects against challenge with the E7-expressing tumor cell line (TC-1). Moreover, L lactis containing pNZ8123-HPV16-optiE7 showed strong therapeutic antitumor effects against established tumors in vivo. These findings demonstrate that recombinant L lactis induce both humoral and cellular immune responses in mice and are therefore recommended for therapeutic treatments in humans after oral administration.

Live bacterial vaccine vector and delivery strategies of heterologous antigen: A review

Live bacteria, including attenuated bacteria and probiotics, can be engineered to deliver target antigen to excite the host immune system. The preponderance of these live bacterial vaccine vectors is that they can stimulate durable humoral and cellular immunity. Moreover, delivery strategies of heterologous antigen in live bacterial promote the applications of new vaccine development. Genetic technologies are evolving, which potentiate the developing of heterologous antigen delivery systems, including bacterial surface display system, bacterial secretion system and balanced lethal vector system. Although the live bacterial vaccine vector is a powerful adjuvant, certain disadvantages, such as safety risk, must also be taken into account. In this review, we compare the development of representative live bacterial vectors, and summarize the main characterizations of the various delivery strategies of heterologous antigen in live vector vaccines.

Protein Secretion in Gram-Positive Bacteria: From Multiple Pathways to Biotechnology

A number of Gram-positive bacteria are important players in industry as producers of a diverse array of economically interesting metabolites and proteins. As discussed in this overview, several Gram-positive bacteria are valuable hosts for the production of heterologous proteins. In contrast to Gram-negative bacteria, proteins secreted by Gram-positive bacteria are released into the culture medium where conditions for correct folding are more appropriate, thus facilitating the isolation and purification of active proteins. Although seven different protein secretion pathways have been identified in Gram-positive bacteria, the majority of heterologous proteins are produced via the general secretion or Sec pathway. Not all proteins are equally well secreted, because heterologous protein production often faces bottlenecks including hampered secretion, susceptibility to proteases, secretion stress, and metabolic burden. These bottlenecks are associated with reduced yields leading to non-marketable products. In this chapter, besides a general overview of the different protein secretion pathways, possible hurdles that may hinder efficient protein secretion are described and attempts to improve yield are discussed including modification of components of the Sec pathway. Attention is also paid to omics-based approaches that may offer a more rational approach to optimize production of heterologous proteins.

Recombinant Invasive Lactococcus lactis Carrying a DNA Vaccine Coding the Ag85A Antigen Increases INF-γ, IL-6, and TNF-α Cytokines after Intranasal Immunization

Tuberculosis (TB) remains a major threat throughout the world and in 2015 it caused the death of 1.4 million people. The Bacillus Calmette-Guérin is the only existing vaccine against this ancient disease; however, it does not provide complete protection in adults. New vaccines against TB are eminently a global priority. The use of bacteria as vehicles for delivery of vaccine plasmids is a promising vaccination strategy. In this study, we evaluated the use of, an engineered invasive Lactococcus lactis (expressing Fibronectin-Binding Protein A from Staphylococcus aureus) for the delivery of DNA plasmid to host cells, especially to the mucosal site as a new DNA vaccine against tuberculosis. One of the major antigens documented that offers protective responses against Mycobacterium tuberculosis is the Ag85A. L. lactis FnBPA⁺ (pValac:Ag85A) which was obtained and used for intranasal immunization of C57BL/6 mice and the immune response profile was evaluated. In this study we observed that this strain was able to produce significant increases in the amount of pro-inflammatory cytokines (IFN-γ, TNF-α, and IL-6) in the stimulated spleen cell supernatants, showing a systemic T helper 1 (Th1) cell response. Antibody production (IgG and sIgA anti-Ag85A) was also significantly increased in bronchoalveolar lavage, as well as in the serum of mice. In summary, these findings open new perspectives in the area of mucosal DNA vaccine, against specific pathogens using a Lactic Acid Bacteria such as L. lactis.

Characterization of the protective immune response to Yersinia pseudotuberculosis infection in mice vaccinated with an LcrV-secreting strain of Lactococcus lactis

BACKGROUND

Pseudotuberculosis is an infection caused by the bacterial enteropathogen Yersinia pseudotuberculosis and is considered to be a significant problem in veterinary medicine. We previously found that intranasal administration of a recombinant Lactococcus lactis strain that secretes the low-calcium response V (LcrV) antigen from Y. pseudotuberculosis (Ll-LcrV) confers protection against a lethal Y. pseudotuberculosis infection. Here, we aimed at characterizing the immunological basis of this LcrV-elicited protective response and at determining the duration of vaccine-induced immunity.

METHODS

Splenocytes from BALB/c mice intranasally immunized with Ll-LcrV or Ll as control were immunostained then analyzed by flow cytometry. Protection against a lethal intravenous injection of Y. pseudotuberculosis was also determined (i) in immunized BALB/c mice depleted or not of CD4⁺, CD8⁺ or CD25⁺ cells and (ii) in naïve BALB/c mice receiving serum from immunized mice by counting the number of bacteria in liver and spleen. Lastly, survival rate of immunized BALB/c mice following a lethal intravenous injection of Y. pseudotuberculosis was followed up to 9-months.

RESULTS

We found that T and B lymphocytes but not non-conventional lymphoid cells were affected by Ll-LcrV immunization. We also observed that depletion of CD4⁺ and CD25⁺ but not CD8⁺ cells in immunized mice eradicated protection against a lethal systemic Y. pseudotuberculosis infection, suggesting that activated CD4⁺ T lymphocytes are required for vaccine-induced protection. Adoptive transfer of LcrV-specific antibodies from Ll-LcrV-immunized animals significantly reduced the bacterial counts in the liver compared to non-vaccinated mice. Lastly, the protective immunity conferred by Ll-LcrV decreased slightly over time; nevertheless almost 60% of the mice survived a lethal bacterial challenge at 9months post-vaccination.

CONCLUSION

Mucosal vaccination of mice with Ll-LcrV induced cell- and antibody-mediated protective immunity against Y. pseudotuberculosis infection in the mouse and the protection is long-lasting.

Display of recombinant proteins at the surface of lactic acid bacteria: strategies and applications

Lactic acid bacteria (LAB) are promising vectors of choice to deliver active molecules to mucosal tissues. They are recognized as safe by the World Health Organization and some strains have probiotic properties. The wide range of potential applications of LAB-driven mucosal delivery includes control of inflammatory bowel disease, vaccine delivery, and management of auto-immune diseases. Because of this potential, strategies for the display of proteins at the surface of LAB are gaining interest. To display a protein at the surface of LAB, a signal peptide and an anchor domain are necessary. The recombinant protein can be attached to the membrane layer, using a transmembrane anchor or a lipoprotein-anchor, or to the cell wall, by a covalent link using sortase mediated anchoring via the LPXTG motif, or by non-covalent liaisons employing binding domains such as LysM or WxL. Both the stability and functionality of the displayed proteins will be affected by the kind of anchor used. The most commonly surfaced exposed recombinant proteins produced in LAB are antigens and antibodies and the most commonly used LAB are lactococci and lactobacilli. Although it is not necessarily so that surface-display is the preferred localization in all cases, it has been shown that for certain applications, such as delivery of the human papillomavirus E7 antigen, surface-display elicits better biological responses, compared to cytosolic expression or secretion. Recent developments include the display of peptides and proteins targeting host cell receptors, for the purpose of enhancing the interactions between LAB and host. Surface-display technologies have other potential applications, such as degradation of biomass, which is of importance for some potential industrial applications of LAB.

Cutaneous Leishmaniasis Vaccination: A Matter of Quality

There have been exhaustive efforts to develop an efficient vaccine against leishmaniasis. Factors like host and parasite genetic characteristics, virulence, epidemiological scenarios, and, mainly, diverse immune responses triggered by Leishmania species make the achievement of this aim a complex task. It is already clear that the induction of a Th1, pro-inflammatory response, is important in the protection against Leishmania infection. However, many questions must still be answered to fully understand Leishmania immunopathology, especially regarding Leishmania-specific Th1 response induction, regulation, and persistence. A large number of Leishmania antigens able to induce pro-inflammatory response have been selected so far, but none of them demonstrated efficiency in protection assays. A possible explanation is that CD4 T cells display marked heterogeneity at a single-cell level especially regarding the production of Th1-defining cytokines and multifunctionality. It has been established in the literature that Th1 cells undergo a differentiation process, which can generate cells with diverse phenotypes and survival capabilities. Despite that, only a few studies evaluate this heterogenic response and the amount of multifunctional CD4 T cells induced by Leishmania vaccine candidates, missing what can be a crucial point in defining a correlate of protection after vaccination. Moreover, most of the knowledge involving the development of cutaneous leishmaniasis (CL) vaccines comes from the mouse model of infection with Leishmania major, which cannot be fully applied to New World Leishmaniasis. For this reason, the immune response triggered by infection with New World Leishmania species, as well as vaccine candidates, need further studies. In this review, we will reinforce the importance of evaluating the quality of immune response against Leishmania, using a multiparametric analysis in order to understand better this complex host-parasite interaction, discussing the differences in the responses triggered by different New World Leishmania species, as well as the impact on the development of an effective vaccine against CL.

Advances in Studies Related to Interleukin-12 Family and Infectious Diseases

Interleukin (IL)-12 family is a group of cytokines composed of heterogeneous molecules and whose members include IL-12, IL-23, IL-27, and IL-35. IL-12 family bridges natural and adaptive immune responses and especially plays a significant role in classical adaptive immune process participated by TH1, TH17, and Treg cells. Members of IL-12 family participate in adaptive immune responses via the Janus kinase-signal transducers and activators of transcription signaling pathway by sharing some subunits and receptors. IL-12 features an extremely complex regulatory network. During resistance of microbial infection, IL-12 and IL-23 mainly show inflammatory effects, whereas IL-27 and IL-35 commonly show antiinflammatory effects. This study reviews advances in studies related to IL-12 family members and infectious diseases and provides references to further reveal functions of IL-12 family members in occurrence and development of infectious diseases.

Lactic acid bacteria--20 years exploring their potential as live vectors for mucosal vaccination

Lactic acid bacteria (LAB) are a diverse group of Gram-positive, nonsporulating, low G + C content bacteria. Many of them have been given generally regarded as safe status. Over the past two decades, intensive genetic and molecular research carried out on LAB, mainly Lactococcus lactis and some species of the Lactobacillus genus, has revealed new, potential biomedical LAB applications, including the use of LAB as adjuvants, immunostimulators, or therapeutic drug delivery systems, or as factories to produce therapeutic molecules. LAB enable immunization via the mucosal route, which increases effectiveness against pathogens that use the mucosa as the major route of entry into the human body. In this review, we concentrate on the encouraging application of Lactococcus and Lactobacillus genera for the development of live mucosal vaccines. First, we present the progress that has recently been made in the field of developing tools for LAB genetic manipulations, which has resulted in the successful expression of many bacterial, parasitic, and viral antigens in LAB strains. Next, we discuss the factors influencing the efficacy of the constructed vaccine prototypes that have been tested in various animal models. Apart from the research focused on an application of live LABs as carriers of foreign antigens, a lot of work has been recently done on the potential usage of nonliving, nonrecombinant L. lactis designated as Gram-positive enhancer matrix (GEM), as a delivery system for mucosal vaccination. The advantages and disadvantages of both strategies are also presented.

An overview on Leishmania vaccines: A narrative review article

Leishmaniasis is one of the major health problems and categorized as a class I disease (emerging and uncontrolled) by World Health Organization (WHO), causing highly significant morbidity and mortality. Indeed, more than 350 million individuals are at risk of Leishmania infection, and about 1.6 million new cases occur causing more than 50 thousands death annually. Because of the severe toxicity and drug resistance, present chemotherapy regimen against diverse forms of Leishmania infections is not totally worthwhile. However, sound immunity due to natural infection, implies that vigor cellular immunity against Leishmania parasites, via their live, attenuated or killed forms, can be developed in dogs and humans. Moreover, genetically conserved antigens (in most of Leishmania species), and components of sand fly saliva confer potential immunogenic molecules for Leishmania vaccination. Vaccines successes in animal studies and some clinical trials clearly justify more researches and investments illuminating opportunities in suitable vaccine designation.

Live vaccination tactics: possible approaches for controlling visceral leishmaniasis

Vaccination with durable immunity is the main goal and fundamental to control leishmaniasis. To stimulate the immune response, small numbers of parasites are necessary to be presented in the mammalian host. Similar to natural course of infection, strategy using live vaccine is more attractive when compared to other approaches. Live vaccines present the whole spectrum of antigens to the host immune system in the absence of any adjuvant. Leishmanization was the first effort for live vaccination and currently used in a few countries against cutaneous leishmaniasis, in spite of their obstacle and safety. Then, live attenuated vaccines developed with similar promotion of creating long-term immunity in the host with lower side effect. Different examples of attenuated strains are generated through long-term in vitro culturing, culturing under drug pressure, temperature sensitivity, and chemical mutagenesis, but none is safe enough and their revision to virulent form is possible. Attenuation through genetic manipulation and disruption of virulence factors or essential enzymes for intracellular survival are among other approaches that are intensively under study. Other designs to develop live vaccines for visceral form of leishmaniasis are utilization of live avirulent microorganisms such as Lactococcus lactis, Salmonella enterica, and Leishmania tarentolae called as vectored vaccine. Apparently, these vaccines are intrinsically safer and can harbor the candidate antigens in their genome through different genetic manipulation and create more potential to control Leishmania parasite as an intracellular pathogen.

Mucosal targeting of therapeutic molecules using genetically modified lactic acid bacteria: an update

Lactic acid bacteria (LAB) represent a heterogeneous group of microorganisms naturally present in many foods and those have proved to be effective mucosal delivery vectors. Moreover, some specific strains of LAB exert beneficial properties (known as probiotic effect) on both human and animal health. Although probiotic effects are strain-specific traits, it is theoretically possible, using genetic engineering techniques, to design strains that can exert a variety of beneficial properties. During the two past decades, a large variety of therapeutic molecules has been successfully expressed in LAB, and although this field has been largely reviewed in recent years, approximately 20 new publications appear each year. Thus, the aim of this minireview is not to extensively assess the entire literature but to update progress made within the last 2 years regarding the use of the model LAB Lactococcus lactis and certain species of lactobacilli as live recombinant vectors for the development of new safe mucosal vaccines.

Oral immunization using live Lactococcus lactis co-expressing LACK and IL-12 protects BALB/c mice against Leishmania major infection

Leishmaniasis is a parasitic disease affecting over 12 million individuals worldwide. Current treatments are laborious, expensive, cause severe side effects, and emerging drug resistance has been reported. While vaccination is the most cost-effective means to control infectious diseases there is no human vaccine currently available against Leishmania infections. Lactococcus lactis is a non-pathogenic, non-colonizing Gram-positive lactic acid bacterium commonly used in the dairy industry. Recently, L. lactis was used for the expression and delivery of biologically active molecules, such as antigens and cytokines, in mice and humans. In this study, we report the generation of L. lactis(alr-) strains solely expressing the protective Leishmania antigen, LACK, in the cytoplasm, secreted or anchored to the bacterial cell wall or co-expressing mouse IL-12. We show that oral immunization using live L. lactis, secreting both LACK and IL-12 was the only regimen that partially protected BALB/c mice against subsequent Leishmania major challenge. This highlights the importance of temporal and physical proximity of the delivered antigen and adjuvant for optimal immune priming by oral immunization since co-administration of L. lactis strains independently expressing secLACK and secIL-12 did not induce protective immunity. Protected animals displayed a delay in footpad swelling, which correlated with a significant reduction of parasite burden. Immunization with the L. lactis strain secreting both LACK and IL-12 induced an antigen-specific mucosal immune response and a LACK-specific T(H)1 immune response in splenocytes and mesenteric lymph node cells. Further, protection in immunized animals correlated with a strong Leishmania-specific T(H)1 immune response post-challenge, detectable in splenocytes and lymph node cells draining the site of infection. This report demonstrates the use of L. lactis as an oral live vaccine against L. major infection in susceptible BALB/c mice. The vaccine strains generated in this study provide the basis for the development of an inexpensive and safe oral live vaccine against the human parasite Leishmania.