Immune response in healthy volunteers vaccinated with killed leishmanial promastigotes plus BCG. I: Skin-test reactivity, T-cell proliferation and interferon-gamma production

The role of IL-32 in Bacillus Calmette-Guérin (BCG)-induced trained immunity in infections caused by different Leishmania spp

BACKGROUND

Cells of the innate immune system undergo long-term functional reprogramming in response to Bacillus Calmette-Guérin (BCG) exposure via a process called trained immunity, conferring nonspecific protection to unrelated infections. Here, we investigate whether BCG-induced trained immunity is able to protect against infections caused by different Leishmania spp., protozoa that cause cutaneous and mucosal or visceral lesions.

METHODS

We used training models of human monocytes with BCG and subsequent infection by L. braziliensis, L. amazonensis and L. infantum, and the vaccination of wild-type and transgenic mice for IL-32γ before in vivo challenge with parasites.

RESULTS

We demonstrated that monocytes trained with BCG presented enhanced ability to kill L. braziliensis, L. amazonensis and L. infantum through increased production of reactive oxygen species. Interleukin (IL)-32 appears to play an essential role in the development of trained immunity. Indeed, BCG exposure induced IL-32 production in human primary monocytes, both mRNA and protein. We have used a human IL-32γ transgenic mouse model (IL-32γTg) to study the effect of BCG vaccination in different Leishmania infection models. BCG vaccination decreased lesion size and parasite load in infections caused by L. braziliensis and reduced the spread of L. amazonensis to other organs in both infected wild-type (WT) and IL-32γTg mice. In addition, BCG reduced the parasite load in the spleen, liver and bone marrow of both WT and IL-32γTg mice infected with L. infantum. BCG vaccination increased inflammatory infiltrate in infected tissues caused by different Leishmania spp. In all infections, the presence of IL-32γ was not mandatory, but it increased the protective and inflammatory effects of BCG-induced training.

CONCLUSIONS

BCG's ability to train innate immune cells, providing protection against leishmaniasis, as well as the participation of IL-32γ in this process, pave the way for new treatment strategies for this neglected infectious disease.

Human cellular and humoral immune responses to Phlebotomus papatasi salivary gland antigens in endemic areas differing in prevalence of Leishmania major infection

Background

Sand fly saliva compounds are able to elicit specific immune responses that have a significant role in Leishmania parasite establishment and disease outcome. Characterizing anti-saliva immune responses in individuals living in well defined leishmaniasis endemic areas would provide valuable insights regarding their effect on parasite transmission and establishment in humans.

Methodology/Principal findings

We explored the cellular and humoral immune responses to Phlebotomus (P.) papatasi salivary gland extracts (SGE) in individuals living in cutaneous leishmaniasis (CL) old or emerging foci (OF, EF). OF was characterized by a higher infection prevalence as assessed by higher proportions of leishmanin skin test (LST) positive individuals compared to EF. Subjects were further subdivided into healed, asymptomatic or naïve groups. We showed anti-SGE proliferation in less than 30% of the individuals, regardless of the immune status, in both foci. IFN-γ production was higher in OF and only observed in immune individuals from OF and naïve subjects from EF. Although IL-10 was not detected, addition of anti-human IL-10 antibodies revealed an increase in proliferation and IFN-γ production only in individuals from OF. The percentage of seropositive individuals was similar in immune and naïves groups but was significantly higher in OF. No correlation was observed between anti-saliva immune responses and LST response. High anti-SGE-IgG responses were associated with an increased risk of developing ZCL. No differences were observed for anti-SGE humoral or cellular responses among naïve individuals who converted or not their LST response or developed or not ZCL after the transmission season.

Conclusions/Significance

These data suggest that individuals living in an old focus characterized by a frequent exposure to sand fly bites and a high prevalence of infection, develop higher anti-saliva IgG responses and IFN-γ levels and a skew towards a Th2-type cellular response, probably in favor of parasite establishment, compared to those living in an emerging focus.

During murine experimental leishmaniasis sand fly saliva components modulate the host immune response and facilitate infection while pre-exposition to uninfected sand fly bites is associated with a protective cellular response against subsequent infection. Human anti-saliva immune responses are not well defined in leishmaniasis endemic areas. Here, we report an analysis of anti P. papatasi saliva cellular and humoral responses in individuals residing in endemic foci showing different prevalence rates of L. major infection. Individuals were further subdivided based on LST response and presence of typical CL scars. We showed higher anti-saliva cellular and humoral responses and a skew towards a Th2 response in the old focus characterized by the highest prevalence of infection. No correlation was observed between LST and anti-saliva cellular or humoral response. We showed that high anti-saliva IgG responses constituted a risk factor for the development of CL. Our findings suggest that the anti-P. papatasi saliva cellular and humoral response profiles vary with the level of sand fly exposure and the prevalence of infection in CL endemic areas. Such studies in humans from highly endemic areas could contribute to a better understanding of the immune response to sand fly saliva and its role in leishmaniasis outcome.

Prevalence of Cutaneous Leishmaniasis in Districts of High and Low Endemicity in Mali

Historically the western sahelian dry regions of Mali are known to be highly endemic for cutaneous leishmaniasis (CL) caused by Leishmania major, while cases are rarely reported from the Southern savanna forest of the country. Here, we report baseline prevalence of CL infection in 3 ecologically distinct districts of Mali (dry sahelian, north savanna and southern savanna forest areas). We screened 195 to 250 subjects from 50 to 60 randomly selected households in each of the 6 villages (four from the western sahelian district of Diema in Kayes region, one from the central district of Kolokani and one from the southern savanna district of Kolodieba, region of Sikasso). The screening consisted of: 1] A Leishmanin Skin Test (LST) for detection of exposure to Leishmania parasites; 2] clinical examination of suspected lesions, followed by validation with PCR and 3] finger prick blood sample to determine antibody levels to sand fly saliva. LST positivity was higher in the western district of Diema (49.9%) than in Kolokani (24.9%) and was much lower in Kolondieba (2.6%). LST positivity increased with age rising from 13.8% to 88% in Diema for age groups 2-5 years and 41-65 years, respectively. All eight PCR-confirmed L. major CL cases were diagnosed in subjects below 18 years of age and all were residents of the district of Diema. Exposure to sand fly bites, measured by anti-saliva antibody titers, was comparable in individuals living in all three districts. However, antibody titers were significantly higher in LST positive individuals (P<0.0001). In conclusion, CL transmission remains active in the western region of Mali where lesions were mainly prevalent among children under 18 years old. LST positivity correlated to higher levels of antibodies to sand fly salivary proteins, suggesting their potential as a risk marker for CL acquisition in Mali.

A sand fly salivary protein vaccine shows efficacy against vector-transmitted cutaneous leishmaniasis in nonhuman primates

Currently, there are no commercially available human vaccines against leishmaniasis. In rodents, cellular immunity to salivary proteins of sand fly vectors is associated to protection against leishmaniasis, making them worthy targets for further exploration as vaccines. We demonstrate that nonhuman primates (NHP) exposed to Phlebotomus duboscqi uninfected sand fly bites or immunized with salivary protein PdSP15 are protected against cutaneous leishmaniasis initiated by infected bites. Uninfected sand fly-exposed and 7 of 10 PdSP15-immunized rhesus macaques displayed a significant reduction in disease and parasite burden compared to controls. Protection correlated to the early appearance of Leishmania-specific CD4(+)IFN-γ(+) lymphocytes, suggesting that immunity to saliva or PdSP15 augments the host immune response to the parasites while maintaining minimal pathology. Notably, the 30% unprotected PdSP15-immunized NHP developed neither immunity to PdSP15 nor an accelerated Leishmania-specific immunity. Sera and peripheral blood mononuclear cells from individuals naturally exposed to P. duboscqi bites recognized PdSP15, demonstrating its immunogenicity in humans. PdSP15 sequence and structure show no homology to mammalian proteins, further demonstrating its potential as a component of a vaccine for human leishmaniasis.

Safety and immunogenicity of a defined vaccine for the prevention of cutaneous leishmaniasis

Healthy Colombian adult volunteers with no history of leishmaniasis were evaluated for evidence of previous subclinical infection with Leishmania based on the Montenegro skin test (MST). Twelve MST-positive subjects were enrolled in an open-label, uncontrolled clinical trial (the "MST-positive trial") and received three injections of the LEISH-F1+MPL-SE vaccine (consisting of 10 microg recombinant Leishmania polyprotein LEISH-F1 antigen [TSA+LmSTI1+LeIF]+25 microg MPL-SE adjuvant). Sixty-eight MST-negative subjects were enrolled in a randomized, double-blind, controlled trial (the "MST-negative trial") and were randomly assigned to receive three injections of either the vaccine (n=34), 10 microg LEISH-F1 protein alone (n=17), or saline placebo (n=17). In both trials, the study injections were given subcutaneously on Days 0, 28, and 56, and subjects were followed for safety and immunological endpoints. The LEISH-F1+MPL-SE vaccine was safe and well tolerated in MST-positive and MST-negative subjects. In both trials, an IFN-gamma response to the LEISH-F1 antigen at Day 84 was observed in more than half of the vaccine recipients. In the MST-negative trial, the IFN-gamma response was significantly more frequent and of greater magnitude in vaccine recipients than in protein-alone or placebo recipients. An IgG antibody response to LEISH-F1 was observed in all vaccine recipients. In both trials, delayed-type hypersensitivity (DTH) to LEISH-F1 was observed in most of the vaccine recipients. In the MST-negative trial, DTH was significantly higher in vaccine than placebo recipients. These clinical trials of the first defined vaccine for leishmaniasis show that the LEISH-F1+MPL-SE vaccine is safe and immunogenic in healthy subjects with and without evidence of previous subclinical infection with Leishmania.

Vector transmission of leishmania abrogates vaccine-induced protective immunity

Numerous experimental vaccines have been developed to protect against the cutaneous and visceral forms of leishmaniasis caused by infection with the obligate intracellular protozoan Leishmania, but a human vaccine still does not exist. Remarkably, the efficacy of anti-Leishmania vaccines has never been fully evaluated under experimental conditions following natural vector transmission by infected sand fly bite. The only immunization strategy known to protect humans against natural exposure is “leishmanization,” in which viable L. major parasites are intentionally inoculated into a selected site in the skin. We employed mice with healed L. major infections to mimic leishmanization, and found tissue-seeking, cytokine-producing CD4+ T cells specific for Leishmania at the site of challenge by infected sand fly bite within 24 hours, and these mice were highly resistant to sand fly transmitted infection. In contrast, mice vaccinated with a killed vaccine comprised of autoclaved L. major antigen (ALM)+CpG oligodeoxynucleotides that protected against needle inoculation of parasites, showed delayed expression of protective immunity and failed to protect against infected sand fly challenge. Two-photon intra-vital microscopy and flow cytometric analysis revealed that sand fly, but not needle challenge, resulted in the maintenance of a localized neutrophilic response at the inoculation site, and removal of neutrophils following vector transmission led to increased parasite-specific immune responses and promoted the efficacy of the killed vaccine. These observations identify the critical immunological factors influencing vaccine efficacy following natural transmission of Leishmania.

The generation of vaccines that protect against intracellular pathogens such as malaria, human immunodeficiency virus and leishmaniasis have met with limited success. A perplexing aspect of this failure as it relates to leishmaniasis is the knowledge that individuals typically get the disease only once, and that individuals who are experimentally infected with cultured parasites are protected against sand fly transmitted infection, thereby providing a “gold standard” for vaccine design. Many engineered, non-living vaccines have been developed to mimic the immune response observed in protected individuals and some of these have been shown to provide excellent protection against needle inoculation of Leishmania parasites in mice. However, very similar vaccine formulations adapted for use in people have failed to protect against natural exposure to infected sand fly bites. In the present study, we attempt to reconcile these long-standing differences, and to provide the critical correlates of immunity that will predict vaccination success against natural exposure.

Vaccines for leishmaniasis in the fore coming 25 years

Human vaccination against leishmaniasis using live Leishmania was used in Middle East and Russia (1941-1980). First-generation vaccines, composed by killed parasites induce low efficacies (54%) and were tested in humans and dogs Phase III trials in Asia and South America since 1940. Second-generation vaccines using live genetically modified parasites, or bacteria or viruses containing Leishmania genes, recombinant or native fractions are known since the 1990s. Due to the loss of PAMPs, the use of adjuvants increased vaccine efficacies of the purified antigens to 82%, in Phase III dog trials. Recombinant second-generation vaccines and third-generation DNA vaccines showed average values of parasite load reduction of 68% and 59% in laboratory animal models, respectively, but their success in field trials had not yet been reported. This review is focused on vaccine candidates that show any efficacy against leishmaniasis and that are already in different phase trials. A lot of interest though was generated in recent years, by the studies going on in experimental models. The promising candidates may find a place in the forth coming years. Among them most probably are the multiple-gene DNA vaccines that are stable and do not require cold-chain transportation. In the mean time, second-generation vaccines with native antigens and effective adjuvants are likely to be licensed and used in Public Health control programs in the fore coming 25 years. To date, only three vaccines have been licensed for use: one live vaccine for humans in Uzbekistan, one killed vaccine for human immunotherapy in Brazil and a second-generation vaccine for dog prophylaxis in Brazil.

Genes at human chromosome 5q31.1 regulate delayed-type hypersensitivity responses associated with Leishmania chagasi infection

Visceral leishmaniasis (VL) caused by Leishmania chagasi is endemic to northeast Brazil. A positive delayed-type hypersensitivity skin test response (DTH+) is a marker for acquired resistance to disease, clusters in families and may be genetically controlled. Twenty-three single nucleotide polymorphisms (SNPs) were genotyped in the cytokine 5q23.3-q31.1 region IRF1-IL5-IL13-IL4-IL9-LECT2-TGFBI in 102 families (323 DTH+; 190 DTH-; 123 VL individuals) from a VL endemic region in northeast Brazil. Data from 20 SNPs were analyzed for association with DTH+/- status and VL using family-based, stepwise conditional logistic regression analysis. Independent associations were observed between the DTH+ phenotype and markers in separate linkage disequilibrium blocks in LECT2 (OR 2.25; P=0.005; 95% CI=1.28-3.97) and TGFBI (OR 1.94; P=0.003; 95% CI=1.24-3.03). VL child/parent trios gave no evidence of association, but the DTH- phenotype was associated with SNP rs2070874 at IL4 (OR 3.14; P=0.006; 95% CI=1.38-7.14), and SNP rs30740 between LECT2 and TGFBI (OR 3.00; P=0.042; 95% CI=1.04-8.65). These results indicate several genes in the immune response gene cluster at 5q23.3-q31.1 influence outcomes of L. chagasi infection in this region of Brazil.

Randomized, double-blind, placebo-controlled study on the immunogenicity of the leishmanin skin test

A positive reaction to the leishmanin skin test (LST) indicates previous contact with Leishmania antigens and is a useful criterion for the diagnosis of cutaneous leishmaniasis. In leishmaniasis vaccine trials, selection of volunteers has always been based on skin testing. During 1999 we performed a randomized controlled study in order to evaluate the immunogenicity of the LST. Fifty-nine (29 male and 30 female) healthy volunteer undergraduate students from the Medical School of Volta Redonda, Rio de Janeiro State, Brazil, with no evidence of previous infection with Leishmania, were randomly assigned into 2 groups: 29 subjects received LST and 30 received a placebo (merthiolate-phosphate-buffered saline). All volunteers received LST 41 d after the first injection of LST or placebo. Blood samples were taken immediately before the applications of LST or placebo for the assessment of Leishmania antigen-induced proliferation and cytokine production in peripheral blood mononuclear cell cultures. A significant increase in proliferative responses to L. braziliensis (P < 0.005) and L. amazonensis (P = 0.01) antigens as well as in L. braziliensis antigen-induced interferon-gamma production (P < 0.01) followed the application of LST but not the administration of the placebo. A single LST application is therefore able to induce Leishmania-specific cell-mediated immune responses. This observation should be considered in human trials of candidate vaccines against leishmaniasis.

Alum-precipitated autoclaved Leishmania major plus bacille Calmette-Guérrin, a candidate vaccine for visceral leishmaniasis: safety, skin-delayed type hypersensitivity response and dose finding in healthy volunteers

In a previous efficacy study, autoclaved Leishmania major (ALM) + bacille Calmette-Guérrin (BCG) vaccine was shown to be safe, but not superior to BCG alone, in protecting against visceral leishmaniasis. From June 1999 to June 2000, we studied the safety and immunogenicity of different doses of alum-precipitated ALM + BCG vaccine mixture administered intradermally to evaluate whether the addition of alum improved the immunogenicity of ALM. Twenty-four healthy adult volunteers were recruited and sequentially allocated to receive either 10 microg, 100 microg, 200 microg, or 400 microg of leishmanial protein in the alum-precipitated ALM + BCG vaccine mixture. Side effects were minimal for all doses and confined to the site of injection. All volunteers in the 10 microg, 100 microg, and 400 microg groups had a leishmanin skin test (LST) reaction of > or = 5 mm by day 42 and this response was maintained when tested after 90 d. Only 1 volunteer out of 5 in the 200 microg group had a LST reaction of > or = 5 mm by day 42 and the reasons for the different LST responses in this group are unclear. This is the first time that an alum adjuvant with ALM has been in used in humans and the vaccine mixture was safe and induced a strong delayed type hypersensitivity (DTH) reaction in the study volunteers. On the basis of this study we suggest that 100 1 microg of leishmanial protein in the vaccine mixture is a suitable dose for future efficacy studies, as it induced the strongest DTH reaction following vaccination.

Gammadelta T cells in immunity induced by Mycobacterium bovis bacillus Calmette-Guérin vaccination

Mycobacterium bovis bacillus Calmette-Guérin (BCG) vaccination is efficacious for newborns or adults with no previous exposure to environmental mycobacteria. To determine the relative contribution and the nature of gammadelta T-cell receptor-positive T cells in newborns, compared to CD4(+) T cells, in immunity induced by M. bovis BCG vaccination, 4-week-old specific-pathogen-free pigs were vaccinated with M. bovis BCG and monitored by following the gammadelta T-cell immune responses. A flow cytometry-based proliferation assay and intracellular staining for gamma interferon (IFN-gamma) were used to examine gammadelta T-cell responses. Pigs were found to mount Th1-like responses to M. bovis BCG vaccination as determined by immunoproliferation and IFN-gamma production. The gammadelta T-cell lymphoproliferation and IFN-gamma production to stimulation with mycobacterial antigens were significantly enhanced by M. bovis BCG vaccination. The relative number of proliferating gammadelta T cells after stimulating peripheral blood mononuclear cells with Mycobacterium tuberculosis H37Rv culture filtrate protein was higher than that of CD4(+) T cells at an early time point after M. bovis BCG vaccination, but CD4(+) T cells were found to be more abundant at a later time point. Although the gammadelta T-cell responses were dependent on the presence of CD4(+) T cells for the cytokine interleukin-2, the enhanced gammadelta T cells were due to the intrinsic changes of gammadelta T cells caused by M. bovis BCG vaccination rather than being due solely to help from CD4(+) T cells. Our study shows that gammadelta T cells from pigs at early ages are functionally enhanced by M. bovis BCG vaccination and suggests an important role for this T-cell subset in acquired immunity conferred by M. bovis BCG vaccination.

Myd88-dependent in vivo maturation of splenic dendritic cells induced by Leishmania donovani and other Leishmania species

The usual agent of visceral leishmaniasis in the Old World is Leishmania donovani, which typically produces systemic diseases in humans and mice. L. donovani has developed efficient strategies to infect and persist in macrophages from spleen and liver. Dendritic cells (DC) are sentinels of the immune system. Following recognition of evolutionary conserved microbial products, DC undergo a maturation process and activate antigen-specific naïve T cells. In the present report we provide new insights into how DC detect Leishmania in vivo. We demonstrate that in both C57BL/6 and BALB/c mice, systemic injection of L. donovani induced the migration of splenic DC from marginal zones to T-cell areas. During migration, DC upregulated the expression of major histocompatibility complex II and costimulatory receptors (such as CD40, CD80, and CD86). Leishmania-induced maturation requires live parasites and is not restricted to L. donovani, as L. braziliensis, L. major, and L. mexicana induced a similar process. Using a green fluorescent protein-expressing parasite, we demonstrate that DC undergoing maturation in vivo display no parasite internalization. We also show that L. donovani-induced DC maturation was partially abolished in MyD88-deficient mice. Taken together, our data suggest that Leishmania-induced DC maturation results from direct recognition of Leishmania by DC, and not from DC infection, and that MyD88-dependent receptors are implicated in this process.

Immunological and pathological evaluation of rhesus macaques infected with Leishmania major

Cutaneous leishmaniasis, a parasitic infection causing ulcerating skin lesions, is an important disease worldwide and urgently requires a vaccine. Animal models that closely mimic human disease are essential for designing preventive vaccines against Leishmania major. We have evaluated both biologic and immunologic parameters of cutaneous L. major infection in nonhuman primates. Naïve rhesus macaques or monkeys previously exposed to L. major were infected with varying doses of L. major metacyclic promastigotes, and lesion size was assessed over a 10-week period. Monkeys previously infected with L. major had much smaller lesions that resolved faster compared with those of naïve monkeys in response to the two higher doses of infection. Moreover, eight of nine naïve monkeys had parasites detected in their lesions during the course of the infection. In addition, the cellular infiltrate within the lesions was qualitatively and quantitatively different in naïve versus previously infected monkeys. Finally, an ELIspot assay determined that the magnitude and kinetics of responses differed between previously infected and naïve monkeys.

Vaccination against cutaneous leishmaniasis: current status

The different cutaneous leishmaniases are distinct in their etiology, epidemiology, transmission, and geographical distribution. In most instances cutaneous leishmaniasis is limited to one or a few skin ulcers that develop at the site where the parasites were deposited during the bite of the sandfly vector. Lesions typically heal spontaneously after several months but some lesions can be large and follow a chronic, more severe course. Protective immunity is usually acquired following cutaneous infection with Leishmania spp., so prevention of disease through prophylactic immunization appears to be feasible. Since vaccination with live, virulent parasites is associated with an unacceptable rate of adverse events, attention has turned to the use of killed or attenuated parasite vaccines and defined subunit vaccines. Whole parasite vaccines have the advantage of delivering multiple antigenic epitopes that may be necessary for initiation of a broad-based immune response. Persistent or repeated immune-stimulation by parasite antigens and/or sustained expression of interleukin-12 appear to be critical elements in the development of durable immunity. A number of purified or recombinant antigens, when co-administered with a vaccine adjuvant, appear promising as vaccine candidates against cutaneous leishmaniasis. The sustained expression of recombinant Leishmania antigens by vaccination with DNA is an attractive approach because it mimics the persistent antigenic stimulation of subclinical infection. Effective vaccine-induced immunity must generate an antigen-specific memory T cell population that, upon exposure to the infecting parasite, rapidly produces a type 1 effector T cell response that leads to interferon-gamma-mediated activation of infected macrophages to kill the intracellular parasites. This parasite-directed recall response must be prompt and of sufficient magnitude to overcome the subversive effect that the intracellular infection has on macrophage effector function. It is unlikely that vaccination against cutaneous leishmaniasis would induce sterile immunity, but a small number of parasites are likely to persist subclinically.

The role of BCG in human immune responses induced by multiple injections of autoclaved Leishmania major as a candidate vaccine against leishmaniasis

To determine if BCG was required in booster injections for autoclaved Leishmania major (ALM) vaccine, 75 volunteers with no response to leishmanin were injected double-blind and randomly with either ALM+BCG or BCG alone for the first injection and boosted either with ALM+BCG, ALM or BCG alone for the second and third. Addition of BCG to the boosters significantly increased the frequency and the magnitude of leishmanin skin tests (LSTs); however, there was no difference in proliferative and IFN-gamma responses (a month and a year later). Three injections of BCG produced no observable adverse reaction; hence BCG could be used in booster injections to increase the protective potential of this candidate vaccine.

Saponins, IL12 and BCG adjuvant in the FML-vaccine formulation against murine visceral leishmaniasis

The FML antigen of Leishmania donovani, in combination with either Riedel de Haën (R), QuilA, QS21 saponins, IL12 or BCG, was used in vaccination of an outbred murine model against visceral leishmaniasis (VL). Significant and specific increases in anti-FML IgG and IgM responses were detected for all adjuvants, and in anti-FML IgG1, IgG2a and IgG2b and delayed type of hypersensitivity to L. donovani lysate (DTH), only for all saponins and IL12. The QS21-FML and QuilA-FML groups achieved the highest IgG2a response. QuilA-FML developed the strongest DTH and QS21-FML animals showed the highest serum IFN-gamma concentrations. The reduction of parasitic load in the liver in response to each FML-vaccine formulation was: 52% (P<0.025) for BCG-FML, 73% (P<0.005) for R-FML, 93% (P<0.005) for QuilA-FML and 79.2% (P<0.025) for QS21-FML treated animals, respectively. Protection was specific for R-FML and QS21-FML while the QuilA saponin treatment itself induced 69% of LDU reduction. The FML-saponin vaccines promote significant, specific and strong protective effects against murine visceral leishmaniasis. BCG-FML induced minor and non-specific protection while IL12-FML, although enhancing the specific antibody and IDR response, failed to reduce the parasitic load of infected animals.

The effect of repeated leishmanin skin testing on the immune responses to Leishmania antigen in healthy volunteers

The leishmanin skin test (LST) is used in immunogenicity studies. The effect of multiple LSTs on immune responses was assessed. None of the volunteers converted to LST positive. IFN-gamma and IL-10 levels remained unchanged. Repetition of LST does not modulate the in vivo or in vitro immune responses to Leishmania antigen.

A randomized double-blind placebo-controlled trial to evaluate the immunogenicity of a candidate vaccine against American tegumentary leishmaniasis

This study was aimed at evaluating the immunogenicity of a vaccine composed of killed Leishmania amazonensis promastigotes using several different protocols in a randomized, double-blind and controlled trial design in order to select one of them for further efficacy trials. One hundred and fourteen leishmanin skin test (LST)-negative healthy volunteers were allocated into eight groups that received either two or three deep intramuscular injections of vaccine at doses of 180, 360 and 540 microg or similar injections of placebo. Cell-mediated immune responses were evaluated before and after vaccination by means of LST as well as proliferative responses and cytokine production in Leishmania antigen-stimulated peripheral blood mononuclear cell cultures. The majority of the subjects who actually received vaccine converted to positive LST (89.5%). On the other hand, none of the subjects who received placebo converted to positive LST. Proliferative responses and production of interferon-gamma and interleukin-2 were significantly higher after vaccination than before vaccination in all groups, including those that received placebo. The dose of 360 microg provided the highest LST conversion rate (100%), as well as the greatest increase in interferon-gamma and interleukin-2 production after vaccination.

[Evaluation of the sensitization power of Montenegro skin test]

The Montenegro skin test, used to diagnose cutaneous leishmaniasis, is now being considered to detect immunogenicity after vaccination. In this study, we evaluated the ability of this test to induce immune response and IFN-g production in subjects not previously exposed to Leishmania. The Montenegro skin test was performed using antigens of L. amazonensis produced by our laboratory (group I) or by FIOCRU-RJ (group II). At day 30, 33% of the subjects from group I and 42% from group II were positive, compared to 67% from group I and 50% from group II at day 90. IFN-y was detected in 56 % of subjects from group I and 17% from group II at day 30 (169+/-309 and 11+/-36pg/ml) and in 67% from group I and 58% from group II by day 360 (69+/-107 and 18+/-20pg/ml). These data demonstrate that the Montenegro skin test induces not only a delayed hypersensitivity reaction, but also IFN-y production.

Immunization with A2 protein results in a mixed Th1/Th2 and a humoral response which protects mice against Leishmania donovani infections

The A2 genes of Leishmania donovani encode amastigote-specific A2 proteins, which are considered to be virulence factors required for the survival of this protozoan parasite in the mammalian host. The A2 genes are present within a multigene family and corresponding A2 proteins are composed predominantly of multiple copies of a 10 amino acid repeat sequences. A2-specific antibodies have been detected in the sera of patients suffering from visceral leishmaniasis (VL) and it has been shown that generation of A2 deficient L. donovani resulted in an avirulent phenotype. In this report, we show that immunization of mice with recombinant A2 protein conferred significant protection against challenge infection with L. donovani. The protection correlated with in vitro splenocyte proliferation, production of IFN-gamma in response to A2 protein and the presence of A2-specific antibodies in the sera of immunized mice. These data demonstrate that A2 represents a potential antigen for protection against infection with L. donovani and VL.

Leishmania (Leishmania) major-infected rhesus macaques (Macaca mulatta) develop varying levels of resistance against homologous re-infections

Seven rhesus macaques were infected intradermally with 10(7) promastigotes of Leishmania (Leishmania) major. All monkeys developed a localized, ulcerative, self-healing nodular skin lesion at the site of inoculation of the parasite. Non-specific chronic inflammation and/or tuberculoid-type granulomatous reaction were the main histopathological manifestations of the disease. Serum Leishmania-specific antibodies (IgG and IgG1) were detected by ELISA in all infected animals; immunoblot analyses indicated that numerous antigens were recognized. A very high degree of variability was observed in the parasite-specific cell-mediated immune responses [as detected by measuring delayed-type hypersensitivity (DTH) reaction, in vitro lymphocyte proliferation, and gamma interferon (IFN-gamma) production] for individuals over time post challenge. From all the recovered monkeys (which showed resolution of the lesions after 11 weeks of infection), 57.2% (4/7) and 28.6% (2/7) animals remained susceptible to secondary and tertiary infections, respectively, but the disease severity was altered (i.e. lesion size was smaller and healed faster than in the primary infection). The remaining monkeys exhibited complete resistance (i.e. no lesion) to each rechallenge. Despite the inability to consistently detect correlates of cell-mediated immunity to Leishmania or correlation between resistance to challenge and DTH, lymphocyte transformation or IFN-gamma production, partial or complete acquired resistance was conferred by experimental infection. This primate model should be useful for measuring vaccine effectiveness against the human disease.

Vaccination of Balb/c mice against experimental visceral leishmaniasis with the GP36 glycoprotein antigen of Leishmania donovani

Leishmania donovani GP36 glycoprotein is the main antigen of the FML Fucose Mannose Ligand (FML) complex specifically recognized by sera of kala-azar human patients. The GP36 was isolated by chemical elution + sonication and used for Balb/c mouse vaccination in combination with saponin, by the s.c. route, inducing a strong and specific protective effect against experimental visceral leishmaniasis shown by the increase of: specific IgG antibodies (82.6%), mainly IgG2a, the delayed type of hypersensitivity to promastigote lysate (37.8%, P < 0.001), the in vitro cellular proliferative response to GP36 of ganglia lymphocytes (53.5%, P < 0.005) and the decrease of liver parasite burden (68.1%, P < 0.025). Saponin treated controls reacted significantly differently from GP36 vaccinated animals at all the assayed variables (P < 0.05). GP36 induced significant protection against murine visceral leishmaniasis at concentrations commonly used for vaccination with recombinant antigens.

Leishmaniasis: current status of vaccine development

Leishmaniae are obligatory intracellular protozoa in mononuclear phagocytes. They cause a spectrum of diseases, ranging in severity from spontaneously healing skin lesions to fatal visceral disease. Worldwide, there are 2 million new cases each year and 1/10 of the world's population is at risk of infection. To date, there are no vaccines against leishmaniasis and control measures rely on chemotherapy to alleviate disease and on vector control to reduce transmission. However, a major vaccine development program aimed initially at cutaneous leishmaniasis is under way. Studies in animal models and humans are evaluating the potential of genetically modified live attenuated vaccines, as well as a variety of recombinant antigens or the DNA encoding them. The program also focuses on new adjuvants, including cytokines, and delivery systems to target the T helper type 1 immune responses required for the elimination of this intracellular organism. The availability, in the near future, of the DNA sequences of the human and Leishmania genomes will extend the vaccine program. New vaccine candidates such as parasite virulence factors will be identified. Host susceptibility genes will be mapped to allow the vaccine to be targeted to the population most in need of protection.

Immunogenicity and safety of autoclaved Leishmania major plus BCG vaccine in healthy Sudanese volunteers

In a longitudinal study in the epidemiology of Leishmania donovani infection in an endemic focus in eastern Sudan, we observed that previous exposure or infection with Leishmania major appeared to protect against visceral leishmaniasis caused by L. donovani. We therefore conducted a study to test the safety and immunogenicity of a vaccine consisting of autoclaved L. major (ALM) plus BCG in inducing protection in vaccinated individuals. Leishmanin-negative healthy Sudanese volunteers were enrolled in the study and were divided into three groups: group (A) received ALM+BCG, group (B) received BCG alone, and group (C) received the vaccine diluent. The subjects were examined for their clinical and immunological responses before intervention, following intervention and 6-8 weeks after vaccination. Vaccinated subjects (group A) developed localized reactions at the sites of vaccine inoculation that ulcerated and healed within 4-6 weeks; 61.6% of them converted to leishmanin reactive following vaccination. Only one subject in group (C) became leishmanin-positive. A total 76.9% of the vaccinated volunteers in group (A) produced significant levels of interferon-gamma in response to L. major antigen. The vaccine produced significant cellular immune responses that may protect against natural challenge. None of the groups had systemic reactions and all the reactions observed in the vaccinated group were comparable with the BCG-vaccinated group.

Autoclaved Leishmania major vaccine for prevention of visceral leishmaniasis: a randomised, double-blind, BCG-controlled trial in Sudan

BACKGROUND

Visceral leishmaniasis is a major cause of morbidity and mortality in the Sudan. Drug treatment is expensive, and drug resistance is becoming increasingly common. Safe, effective, and cheap vaccines are needed. We report the results of a vaccine trial against human visceral leishmaniasis.

METHODS

We undertook a double-blind randomised trial to test the safety and efficacy of an autoclaved Leishmania major (ALM) promastigote vaccine (1 mg per dose). Of 5093 volunteers screened, 2306 had negative leishmanin skin tests and reciprocal titres of less than 6400 in the direct agglutination test. They were randomly assigned two doses of ALM mixed with BCG or BCG alone. Volunteers were followed up for 2 years. The primary endpoint was clinical visceral leishmaniasis or post-kala-azar dermal leishmaniasis. Analyses were by intention to treat.

FINDINGS

Side-effects were confined to the injection site. The cumulative frequency of visceral leishmaniasis at 2 years did not differ significantly between the group assigned ALM plus BCG and that assigned BCG alone (133/1155 [11.5%] vs 141/1151 [12.3%], p=0.6). The vaccine efficacy was 6% (95% CI -18 to 25). The proportion of individuals showing leishmanin skin conversion was significantly higher in the ALM plus BCG group than in the BCG alone group throughout follow-up (303 [30%] vs 72 [7%] at 42 days). Individuals whose leishmanin test converted after vaccination (induration > or =5 mm) had a significantly lower frequency of visceral leishmaniasis than non-responders (27/375 [7.2%] vs 210/1660 [12.7%], p=0.003).

INTERPRETATION

We found no evidence that two doses of ALM plus BCG offered significant protective immunity against visceral leishmaniasis compared with BCG alone. Leishmanin skin conversion with an induration of 5 mm or more in either group was associated with protection from the disease.

Safety and immunogenicity of a killed Leishmania (L.) amazonensis vaccine against cutaneous leishmaniasis in Colombia: a randomized controlled trial

The safety and immunogenicity of an intramuscular (i.m.) and intradermal (ID) formulation of autoclaved Leishmania (Leishmania) amazonensis vaccine was evaluated in 296 volunteers in a randomized, placebo-controlled, double-blind trial in Colombia. There were 4 vaccination groups: i.m. vaccine, i.m. placebo, ID vaccine, and ID placebo. The ID formulations were mixed with BCG as adjuvant at the time of injection. For each group, 3 vaccinations were given with a 20-day interval between injections, and adverse events were monitored at 20 min, and at 2, 7 and 21 days after each injection. BCG-induced adverse reactions resulted in cancellation of the third vaccine administration in the ID groups. Antibody titres did not differ significantly between the groups. Montenegro skin-test conversion was achieved by 86.4% and 90% of the i.m. vaccine group and by 25% and 5% of the i.m. placebo group 80 days and 1 year after vaccination, respectively. A significant increase in mean Leishmania-antigen lymphocyte proliferation indexes was observed after i.m. vaccine immunization, but not after i.m. placebo immunization, 80 days and 1 year after vaccination. Significant levels of IFN gamma but not IL-10 were observed 1 year after vaccination in the i.m. vaccine group compared to the i.m. placebo group. The good safety profile and evidence of Th1 immune reactions due to i.m. vaccination in this phase-I/II study suggest that a population-based phase-III efficacy trial of the i.m. vaccine should be initiated.

IFN-gamma, IL-4, IL-10 and IL-12 gene expression in BCG-Leishmania vaccination of Trypanosoma cruzi-infected mice

We have previously shown that vaccination of BALB/c mice with a combination of BCG plus killed Leishmania promastigotes, applied by the i.p. route 10 and 3 days before Trypanosoma cruzi inoculation, prolonged their survival and decreased their parasitaemia. In the present study we show that the BCG-Leishmania vaccine induced higher levels of circulating IFN-gamma in acute and chronic infection of mice [on day 25 and 40 post-infection (p.i.) respectively], in comparison to unvaccinated animals (PBS-treated). Though the IFN-gamma mRNA content of spleen cells of vaccinated and infected mice (on day 25 p.i.) was similar to that of unvaccinated animals, the BCG-Leishmania vaccine enhanced significantly the production of IFN-gamma by spleen cells stimulated with T. cruzi antigens. This effect was observed to a lower extent in BCG- and Leishmania-treated mice. The BCG-Leishmania vaccine reduced the expression of the IL-10 mRNA of splenocytes as soon as day 12 p.i., before the peak parasitaemia. Such this effect was not observed in BCG- or Leishmania-treated animals. On day 25 p.i., the BCG plus Leishmania- or BCG-treatment of mice abolished the capacity of spleen cells to produce IL-10 in response to T. cruzi antigens. The levels of mIL-4 RNA and protein production were not modified in any group of mice. T. cruzi infection in BCG-Leishmania-vaccined mice stimulated an early and high production of IL-12 transcripts in spleen cells during the acute phase of the infection, that was prolonged during the chronic phase of infection. This effect was weaker or absent in BCG- and Leishmania-treated animals, respectively. These results indicate that the BCG-Leishmania vaccine stimulates the production of IL-12 and IFN-gamma, but inhibits that of IL-10 and is without effect on IL-4 when mice are infected with T. cruzi. This highlights the key role of endogenously produced IFN-gamma, IL-10 and IL-12 in the control of T. cruzi acute and chronic infection in mice and the favorable modulation of their balance by a vaccination combining BCG and Leishmania.

Subunit vaccination of mice against new world cutaneous leishmaniasis: comparison of three proteins expressed in amastigotes and six adjuvants

A mixture of well-defined recombinant antigens together with an adjuvant that preferentially stimulates specific gamma interferon (IFN-gamma)-secreting helper type 1 CD4(+) T cells (Th1 cells) presents a rational option for a vaccine against leishmaniasis. The potential of this approach was investigated in murine infections with Leishmania mexicana, which are characterized by the absence of a parasite-specific Th1 response and uncontrolled parasite proliferation. A mixture of three antigens (glycoprotein 63, cysteine proteinases, and a membrane-bound acid phosphatase), which are all expressed in amastigotes, the mammalian stage of the parasite, were used for the immunization of C57BL/6 mice in combination with six adjuvants (interleukin 12 [IL-12], Detox, 4'-monophosphoryl lipid A, QS-21, Mycobacterium bovis BCG, and Corynebacterium parvum). All six vaccine formulations containing the mixture of recombinant antigens were protective against challenge infections with promastigotes, the insect stage of the parasite, in that mice controlled and healed infections but developed transient and, in certain cases, accentuated disease. The most effective adjuvants were IL-12 followed by Detox. Further studies using these two adjuvants showed that a similar protective effect was observed with a mixture of the corresponding native proteins, and mice which had controlled the infection showed a preponderance of IFN-gamma-secreting CD4(+) T cells in the lymph nodes draining the lesion. Using the recombinant proteins individually, it is shown that the relatively abundant cysteine proteinases and glycoprotein 63, but not the acid phosphatase, are able to elicit a protective response. The results are discussed in comparison to previous studies with subunit vaccines and with respect to cell biological aspects of antigen presentation in Leishmania-infected macrophages.

Immunotherapy with live BCG plus heat killed Leishmania induces a T helper 1-like response in American cutaneous leishmaniasis patients

Previous work has shown that American cutaneous leishmaniasis (ACL) patients treated with viable BCG plus heat killed promastigotes of Leishmania amazonensis show the same rate of cure as patients receiving conventional chemotherapy. The treatment is safe and economical, but the immunological correlates of cure have not been examined. In the present study, T cell responses have been analysed in 43 ACL patients, including patient groups sampled before and after therapy, and in 10 endemic controls. Lymphocyte proliferation, interferon (IFN)-gamma and interleukin (IL)-5 responses to crude antigen (L. amazonensis, MEL; Mycobacterium tuberculosis PPD; M. bovis BCG) stimulation, and serum IL-5 levels, were analysed. In endemic volunteers, proliferative responses to BCG were high and IFN-gamma responses low. In contrast, localized cutaneous (LCL) and mucocutaneous (MCL) patients showed low proliferative and high IFN-gamma responses to BCG. Treatment enhanced the IFN-gamma response and further decreased the proliferative response to BCG, especially in MCL patients. LCL and MCL patients showed an increase in proliferative and IFN-gamma responses to MEL with treatment, but the response was not exaggerated in MCL patients, either before or after treatment, compared to LCL patients. IL-5 production was low in T cell assays, and > 62% of untreated patients had very low serum IL-5 levels. There were no significant changes in serum IL-5 with treatment. Overall results show enhanced antigen-specific IFN-gamma responses to the two components of the immunotherapy, live M. bovis BCG and heat killed L. amazonensis, which is consistent with a shift in balance of T cell response towards a T helper 1 response and clinical cure mediated by IFN-gamma.

Protective Immunity Using Recombinant Human IL-12 and Alum as Adjuvants in a Primate Model of Cutaneous Leishmaniasis

Protection from cutaneous leishmaniasis, a chronic ulcerating skin lesion affecting millions, has been achieved historically using live virulent preparations of the parasite. Killed or recombinant Ags that could be safer as vaccines generally require an adjuvant for induction of a strong Th1 response in murine models. Murine rIL-12 as an adjuvant with soluble Leishmania Ag has been shown to protect susceptible mice. We used 48 rhesus macaques to assess the safety, immunogenicity, and efficacy of a vaccine combining heat-killed Leishmania amazonensis with human rIL-12 (rhIL-12) and alum (aluminum hydroxide gel) as adjuvants. The single s.c. vaccination was found to be safe and immunogenic, although a small transient s.c. nodule developed at the site. Groups receiving rhIL-12 had an augmented in vitro Ag-specific IFN-γ response after vaccination, as well as increased production of IgG. No increase in IL-4 or IL-10 was found in cell culture supernatants from either control or experimental groups. Delayed hypersensitivity reactions were not predictive of protection. Intradermal forehead challenge infection with 107 metacyclic L. amazonensis promastigotes at 4 wk demonstrated protective immunity in all 12 monkeys receiving 2 μg rhIL-12 with alum and Ag. Partial efficacy was seen with lower doses of rhIL-12 and in groups lacking either adjuvant. Thus, a single dose vaccine with killed Ag using rhIL-12 and alum as adjuvants was safe and fully effective in this primate model of cutaneous leishmaniasis. This study extends the murine data to primates, and provides a basis for further human trials.

Vaccination of Swiss Albino mice against experimental visceral leishmaniasis with the FML antigen of Leishmania donovani

The FML antigen of Leishmania donovani in combination with saponin, aluminum hydroxide (Al(OH)3) and Freund's incomplete adjuvant (FIA) was used in vaccines tested in an outbred murine model of visceral leishmaniasis, either through intraperitoneal or subcutaneous routes. The humoral response was significantly higher in the groups treated with FML + saponin or FML + Al(OH)3 than in controls, both before and after the infection. Animals immunized by the i.p. route developed higher antibody titres. A significant and specific reduction of parasitic load in relation to saline (85%, p < 0.01) and saponin (p < 0.025) controls, was seen in animals treated with FML + saponin by the i.p. Coincidentally with this reduction, an increase in antibodies of the IgG2a subtype was detected only in animals treated with FML + saponin i.p. A reduction of 88% in parasitic load was achieved by the combination of FML + Al(OH)3 (s.c.), but the Al(OH)3 treatment itself accounted for 68% of this protection. In our conditions, vaccination with FML + saponin i.p. was superior to other treatments and had no toxic effect due to saponin.

Vaccination of mice with a combination of BCG and killed Leishmania promastigotes reduces acute Trypanosoma cruzi infection by promoting an IFN-gamma response

The combination of BCG with killed Leishmania promastigotes, demonstrated to be efficient in the cure of patients suffering American cutaneous leishmaniasis and in the induction of a long-term immune response in healthy vaccinated volunteers, was tested in BALB/c mice infected with Trypanosoma cruzi, in comparison to BCG or Leishmania alone, and a vehicle (PBS) control. BCG-Leishmania vaccination, applied intra-peritoneally 10 and 3 days before T. cruzi trypomastigote inoculation, prolonged the survival, and reduced blood parasitaemia of infected animals. Proliferation studies indicated that splenocytes of mice vaccinated with BCG-Leishmania and harvested in the acute phase of T. cruzi infection displayed stimulation indices higher than cells from PBS-treated mice when stimulated with PHA mitogen, PPD, Leishmania or T. cruzi antigens. Injections of a monoclonal antibody able to neutralise IFN-gamma into BCG-Leishmania vaccinated mice increased parasitaemia to levels similar to those of control animals (treated with PBS) and reversed the beneficial effect of vaccination on the proliferative response to T. cruzi antigen. These results show that vaccination of mice with BCG plus killed Leishmania promastigotes delayed acute T. cruzi infection, stimulated a T-cell response to T. cruzi antigen and promoted IFN-gamma production.

A randomised, double-blind, controlled trial of a killed L. major vaccine plus BCG against zoonotic cutaneous leishmaniasis in Iran

Safety and efficacy of killed (autoclaved) L. major promastigotes, ALM, mixed with BCG against zoonotic cutaneous leishmaniasis was tested in healthy volunteers (n = 2453) in a randomized double blind trial vs. BCG as control. Side-effects were similar in both groups but tended to be slightly more frequent and prolonged in the ALM + BCG group. Leishmanin skin test conversion (induration > or =5 mm) was significantly greater in the ALM + BCG than in the BCG group (36.2% vs. 7.9% on day-80 and 33% vs. 19%, after 1 year, respectively). Cumulative incidence rates for 2 years, were similar in both groups (18.0% vs. 18.5%). However, LST responders on day 80 (> or =5 mm) had a significantly lower incidence (35%) of CL during the first year than non-responders. A single dose of ALM + BCG is not sufficiently immunogenic to provide a measurable response when compared to BCG alone. A single dose of this vaccine has been shown to be safe with no evidence of an exacerbating response following natural infection; hence, multiple doses or other adjuvants should be considered to increase its immunogenicity.

Phase 1 study of an inactivated vaccine against American tegumentary leishmaniasis in normal volunteers in Brazil

A Phase 1 double-blind placebo-controlled study was performed to evaluate a vaccine against American tegumentary leishmaniasis in 61 healthy male volunteers. Side effects and the immune response to the vaccine were evaluated, with 1- and 2- dose schemes, with intervals of 7 or 21 days, each dose containing 1440 mg of protein N antigen of a single strain of Leishmania amazonensis (PH8) diluted in merthiolated saline (1:10,000). Merthiolated saline and an inert substance were used as placebos. No significant clinical alterations were found following the respective injections in the vaccinated individuals as compared to the placebos, except for local pain, which was associated significantly with injection of the vaccine. The laboratory alterations we observed bore no association with the clinical findings and were unimportant. We observed no differences between the groups with regard to seroconversion of the Montenegro skin test. However, the group that received a single dose of the vaccine and the one that received two doses with a 21-day interval displayed cutaneous induration significantly larger than in the control group, with 100%, 100%, and 66% conversion in the skin test, respectively. We concluded that the vaccine does not present any major side effect that would contraindicate its use in healthy individuals.

Response to heterologous leishmanins in cutaneous leishmaniasis in Nigeria--discovery of a new focus

A pilot study was undertaken to preliminary illustrate the leishmanin skin test (LST) positivity to distinct antigen preparations (derived from promastigote of either Leishmania major or L. amazonensis, or pooled L. mexicana, L. amazonensis and L. guyanensis) in cutaneous leishmaniasis (CL) patients and healthy subjects living in two endemic foci in Nigeria. The study was designed to provide insights into whether cross-species leishmanin, such as that prepared from New World Leishmania could be useful to detect cases of Old World leishmanial infection and to compare the results with LST using L. major-derived leishmanin. The overall LST positivity in individuals from Keana tested with the cross-species leishmanin was 28.7% (27/94), while the positivity rate in the subjects from Kanana tested with the same leishmanin was 54.5% (6/11). Lower positivity values were obtained when L. major (12.5%; 11/88) or L. amazonensis (15.8%; 9/57) was tested as antigen in grossly comparable populations. Moreover, the pooled leishmanin identified most of the subjects (13/14; 92.9%) with active or healed CL, and the maximum reaction sizes were found among positive subjects in this group. No healthy controls (10 total) showed specific DTH response. The LST was useful for assessing the prevalence of subclinical infection and for measuring CL transmission over time. We report for the first time the occurrence of CL in Kanana village of Langtang South local government area of Plateau State.

Leishmania Amastigote Target Antigens: The Challenge of a Stealthy Intracellular Parasite

The development of a defined molecular vaccine against leishmaniasis involves the determination of candidate molecules that elicit protection against infection. As the amastigote stage is the developmental form found in the infected mammalian host, molecules specific to or upregulated in this stage represent potential antigenic vaccine targets. Diane McMahon-Pratt, Peter Kima and Lynn Soong summarize experiments which indicate that immunization with molecules upregulated in the amastigote stage can provide effective protection against infection. In the immunized host, both CD4(+) and CD8(+) T cells appear to be crucial to protection. Studies of antigen presentation of Leishmania-infected macrophages indicate that the amastigote stage can sequester endogenous leishmanial antigen from the major histocompatability complex (MHC) class II presentation pathway. However, evidence indicates that MHC class I presentation may be sustained in the infected macrophage. The effect of these findings on the design of a leishmanial vaccine are considered.

Vaccines against leishmaniasis

Unlike some other parasites, Leishmania can be grown in cell-free media with ease. This simple cultivation and the use of killed parasites as skin-test antigens (leishmanin) for diagnosis in humans during the past several decades have prompted scientists to try using the killed parasites, with or without adjuvant, as vaccines or for immunotherapy. In addition, different recombinant molecules, either parasite fractions or genetically engineered organisms (i.e. Leishmania made avirulent by removing specific genes, or bacteria carrying and expressing leishmanial genes), are being investigated as potential future vaccines against leishmaniasis. The 'first-generation' vaccines, composed of killed parasites with or without adjuvant, have been derived using an empirical approach. The 'second-generation' vaccines have been genetically constructed, using a more rational approach. At present, the first-generation vaccines are at various stages of Phase I (safety), II (reactivity) or III (efficacy) trials in humans. Results are expected in 1-2 years. The second-generation vaccines are, however, only in a preclinical state and are not expected to reach clinical trials for at least 3 years. The Special Programme for Research and Training in Tropical Diseases (TDR) is actively involved in most clinical trials of the first-generation vaccines and supports many of the second-generation candidates. In the present article, the advantages and disadvantages of each approach to vaccine development are discussed and the progress being made is briefly reviewed.

Polymorphism in tumor necrosis factor genes associated with mucocutaneous leishmaniasis

Recent studies have shown that mucocutaneous leishmaniasis (MCL), a severe and debilitating form of American cutaneous leishmaniasis (ACL) caused by Leishmania braziliensis infection, is accompanied by high circulating levels of tumor necrosis factor (TNF)-alpha. Analysis of TNF polymorphisms in Venezuelan ACL patients and endemic unaffected controls demonstrates a high relative risk (RR) of 7.5 (P < 0.001) of MCL disease in homozygotes for allele 2 of a polymorphism in intron 2 of the TNF-beta gene, especially in females (RR = 9.5; P < 0.001) compared with males (RR = 4; P < 0.05). A significantly higher frequency (P < 0.05) of allele 2 at the -308-basepair TNF-alpha gene polymorphism was also observed in MCL patients (0.18) compared with endemic control subjects (0.069), again associated with a high relative risk of disease (RR = 3.5; P < 0.05) even in the heterozygous condition. Because both the TNF-alpha and TNF-beta polymorphisms have previously been linked with functional differences in TNF-alpha levels, these data suggest that susceptibility to the mucocutaneous form of disease may be directly associated with regulatory polymorphisms affecting TNF-alpha production.

Immune response in healthy volunteers vaccinated with BCG plus killed leishmanial promastigotes: antibody responses to mycobacterial and leishmanial antigens

Antibody (IgG) responses to mycobacterial (BCG; PPD; Mycobacterium leprae soluble antigen, MLSA) and leishmanial (Leishmania mexicana LV4) antigens were measured in 208 initially PPD and leishmanin skin-test negative volunteers divided into four vaccine groups as follows: 68 received BCG plus killed promastigotes (group A), 47 received BCG alone (group B), 47 received killed promastigotes alone (group C), and 46 formed the diluent control (placebo, group D). Three vaccine doses were administered at 8-12 week intervals. Vaccinees were bled immediately prior to each vaccination, and again at 3- and 12-month follow-up. Skin tests were performed prevaccination, and again at the 3- and 12-month follow-up. Anti-BCG, anti-PPD and anti-MLSA IgG levels increased significantly in groups A and B receiving BCG. The presence of leishmanial antigen (with BCG) in the inoculum suppressed the IgG response to Mycobacterium tuberculosis/Mycobacterium bovis-related (PPD and BCG), but not M. leprae-related (MLSA)-related, antigens. A small but significant increase (relative to prevaccination level) in response to MLSA, but not to BCG or PPD was observed in the non-BCG-vaccinated groups. The background level of response to mycobacterial and leishmanial antigens was higher in the Venezuelan vaccinees than in non-endemic (British) volunteers. Responses to leishmanial antigen were not enhanced in the two vaccine groups receiving killed promastigotes (with/without BCG) compared with the BCG alone and placebo groups. Instead, all vaccine groups showed a pattern of response consistent with either (i) a response to the skin-test antigen or, more likely, (ii) seasonal endemic exposure to leishmanial antigen. Interestingly, this endemic response to leishmanial antigen was enhanced in the vaccine groups receiving BCG, despite the fact that group B received no leishmanial antigen in the vaccine inoculum. When prevaccination IgG levels (mean + 3 standard deviations) were used to determine a negative cut-off, a low percentage (< 38%) of vaccinees converted to responder status for either anti-mycobacterial or anti-leishmanial responses, and those who did would be classified as 'low-responder' status compared with titres observed in severe forms of disease. Hence, although there was evidence for a background endemic response to both leishmanial and mycobacterial antigens, there was no evidence that vaccination per se led to a potentially disease exacerbatory level of TH2-associated antibody response especially with respect to the anti-leishmanial response.(ABSTRACT TRUNCATED AT 400 WORDS)