Dichotomy of protective cellular immune responses to human visceral leishmaniasis.

Healing/protective responses in human visceral leishmaniasis (VL) are associated with stimulation/production of Th1 cytokines, such as interferon IFN-gamma, and conversion in the leishmanin skin test (LST). Such responses were studied for 90 days in 44 adult healthy volunteers from VL non-endemic areas, with no past history of VL/cutaneous leishmaniasis (CL) and LST non-reactivity following injection with one of four doses of Alum-precipitated autoclaved Leishmania major (Alum/ALM) +/- bacille Calmette-Guerin (BCG), a VL candidate vaccine. The vaccine was well tolerated with minimal localized side-effects and without an increase in antileishmanial antibodies or interleukin (IL)-5. Five volunteers (5/44; 11.4%) had significant IFN-gamma production by peripheral blood mononuclear cells (PBMCs) in response to Leishmania antigens in their prevaccination samples (P = 0.001) but were LST non-reactive. On day 45, more than half the volunteers (26/44; 59.0%) had significantly high LST indurations (mean 9.2 +/- 2.7 mm) and high IFN-gamma levels (mean 1008 +/- 395; median 1247 pg/ml). Five volunteers had significant L. donovani antigen-induced IFN-gamma production (mean 873 +/- 290; median 902; P = 0.001), but were non-reactive in LST. An additional five volunteers (5/44; 11.4%) had low IFN-gamma levels (mean 110 +/- 124 pg/ml; median 80) and were non-reactive in LST (induration = 00 mm). The remaining eight volunteers had low IFN-gamma levels, but significant LST induration (mean 10 +/- 2.9 mm; median 11). By day 90 the majority of volunteers (27/44; 61.4%) had significant LST induration (mean 10.8 +/- 9.9 mm; P < 0.001), but low levels of L. donovani antigen-induced IFN-gamma (mean 66.0 +/- 62 pg/ml; P > 0.05). Eleven volunteers (11/44; 25%) had significantly high levels of IFN-gamma and LST induration, while five volunteers had low levels of IFN-gamma (<100 pg/ml) and no LST reactivity (00 mm). One volunteer was lost to follow-up. In conclusion, it is hypothesized that cellular immune responses to human VL are dichotomatous, and that IFN-gamma production and the LST response are not in a causal relationship. Following vaccination and probably cure of VL infection, the IFN-gamma response declines with time while the LST response persists. LST is a simple test that can be used to assess candidate vaccine efficacy.

Immune response measured in human volunteers vaccinated with autoclaved Leishmania major vaccine mixed with low dose of BCG.

The immune responses induced against Leishmania antigens in volunteers who were vaccinated in a double-blind, randomized field efficacy trial of a preparation of autoclaved Leishmania major (ALM) mixed with a low dose of Bacille Calmette-Guerin vaccine (BCG) who developed either a cutaneous leishmaniasis (CL) lesion due to exposure to infected sandfly bite(s) or did not develop a lesion during the course of the trial were studied and compared with those of non-vaccinated controls. Blood samples were also assayed from different groups including volunteers with history of CL and volunteers with previous positive or negative leishmanin skin test (LST) without a history of CL. The vaccinated volunteers had received a single dose of either ALM mixed with a low dose of BCG or the same dose of BCG alone. The LST and in vitro proliferative response (stimulation index, SI), interferon gamma (IFN-gamma) production and, in a few cases, interleukin (IL)-4 production of peripheral blood mononuclear cells to soluble Leishmania antigens were measured. The results indicated that volunteers who developed CL in the vaccine arm showed a slightly higher SI than cases who received BCG alone. Volunteers with history of CL and volunteers with positive LST demonstrated the strongest proliferation indices and IFN-gamma production. The data suggest that a single dose of ALM + BCG induces a weak Th1 response in vaccinated volunteers that is far lower than that in volunteers with prior subclinical infection or volunteers with history of CL, who are presumed to be immune.

Treatment of cutaneous leishmaniasis with aminosidine (paromomycin) ointment: double-blind, randomized trial in the Islamic Republic of Iran.

OBJECTIVE: To compare the parasitological and clinical efficacy of four weeks versus two weeks of treatment with aminosidine (paromomycin) ointment in patients with cutaneous leishmaniasis caused by Leishmania major in the Islamic Republic of Iran. METHODS: Double-blind, randomized trial of four weeks of aminosidine ointment (n = 108) vs two weeks of aminosidine ointment and two weeks of placebo (n = 108). Patients were assessed on days 15, 29, 45, and 105 for clinical cures and clinical and parasitological cures. FINDINGS: Four weeks' treatment gave significantly better cure rates than two weeks' treatment: on day 29, there were 80/108 (74%) vs 64/108 (59%) clinical cures (P = 0.05) and 47 (44%) vs 26 (24%) clinical and parasitological cures (P = 0.005). By day 45, fewer patients who received four weeks' treatment had required rescue treatment with antimonials than those who received two weeks' treatment: 20 (19%) vs 36 (33%) (P = 0.02). On day 105, the results still favoured those who had been allocated four weeks of active treatment, but the differences were no longer as clearly significant. No side-effects were observed or reported. CONCLUSION: Approximately two-thirds of patients given ointment for four weeks were cured clinically. Although about half of those cured might have recovered spontaneously even without treatment, four weeks of aminosidine ointment could become the first-line treatment for uncomplicated cutaneous leishmaniasis due to L. major, with antimonials needed in only the one-third of patients not cured by the end of treatment with aminosidine. This would considerably reduce the costs and side-effects associated with antimonial drugs.

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.

Vervet monkeys vaccinated with killed Leishmania major parasites and interleukin-12 develop a type 1 immune response but are not protected against challenge infection.

Leishmania major is a protozoan parasite that causes chronic cutaneous lesions that often leave disfiguring scars. Infections in mice have demonstrated that leishmanial vaccines that include interleukin-12 (IL-12) as an adjuvant are able to induce protective immunity. In this study, we assessed the safety, immunopotency, and adjuvant potential of two doses of IL-12 when used with a killed L. major vaccine in vervet monkeys. The induction of cell-mediated immunity following vaccination was determined by measuring delayed-type hypersensitivity, in vitro lymphocyte proliferation, and gamma interferon (IFN-gamma) production. Protection was assessed by challenging the animals with L. major parasites and monitoring the course of infection. At low doses of IL-12 (10 microg), a small increase in the parameters of cell-mediated immunity was observed, relative to those in animals that received antigen without IL-12. However, none of these animals were protected against a challenge infection. At higher doses of IL-12 (30 microg), a substantial increase in Leishmania-specific immune responses was observed, and monkeys immunized with antigen and IL-12 exhibited an IFN-gamma response that was as great as that in animals that had resolved a primary infection and were immune. Nevertheless, despite the presence of correlates of protection, the disease course was only slightly altered, and protection was low compared to that in self-cured monkeys. These data suggest that protection against leishmaniasis may require more than the activation of Leishmania-specific IFN-gamma-producing T cells, which has important implications for designing a vaccine against leishmaniasis.

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.

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.

Randomised vaccine trial of single dose of killed Leishmania major plus BCG against anthroponotic cutaneous leishmaniasis in Bam, Iran.

BACKGROUND: A vaccine consisting of a single dose of whole-cell autoclave-killed Leishmania major (ALM) mixed with BCG was assessed in comparison with BCG alone against anthroponotic (human to human transmission) cutaneous leishmaniasis in a randomised double-blind trial in Bam, Iran. METHODS: 3637 schoolchildren, aged 6-15 years, with no history of cutaneous leishmaniasis and no response to a leishmanin skin test, were randomly assigned to receive 1 mg ALM mixed with BCG (n = 1839), or BCG alone (n = 1798). Safety of the vaccine and the incidence of confirmed cases of cutaneous leishmaniasis were followed up for 2 years. FINDINGS: Side-effects were those usually associated with BCG vaccination, but tended to persist longer in the ALM + BCG group. After exclusion of four cases occurring within 80 days of vaccination (one in the ALM + BCG group and three in the BCG group), the 2-year incidence of cutaneous leishmaniasis did not differ significantly between vaccine and BCG groups: 2.8% vs 3.3%, respectively (total cases 112). A sex-stratified analysis showed that in boys the vaccine conferred a protective efficacy of 18% and 78% for the first and second years, respectively--a crude 2-year overall protection of 55% (95% CI 19-75%, p < 0.01). In the first 9 months after vaccination, there was a non-significant excess of cases in the ALM + BCG group (25 vs 16), whereas the incidence of cutaneous leishmaniasis thereafter was significantly reduced in the ALM + BCG group (27 vs 44, p < 0.05). INTERPRETATION: A single dose of ALM + BCG was safe and more immunogenic than BCG alone, as measured by leishmanin skin test. The exact reason for the apparent protective effect of the vaccine in boys is unknown, and may be a chance finding. However, since boys are more exposed to the infection, which is indicated by higher disease prevalence in boys in this study population, the preferential protective effect in boys may have resulted from a greater booster effect produced by repeated exposure to infected sandflies. Booster injections or alternative adjuvants should be tried to improve the potential efficacy of this vaccine.

Efficacy of sodium stibogluconate alone and in combination with allopurinol for treatment of mucocutaneous leishmaniasis.

A randomized, open, controlled clinical trial was designed to evaluate the efficacy, tolerance, and safety of sodium stibogluconate plus allopurinol and sodium stibogluconate alone as treatment of patients with mucocutaneous leishmaniasis. In phase 1 of the study, all 22 patients with severe disease had improvement of their lesions, but only two had clinical cure (both of these patients received sodium stibogluconate alone). In phase 2, which included 59 patients with moderate disease, the cure rate among sodium stibogluconate recipients was 75% (21 of 28) compared with 63.6% (14 of 22) among the sodium stibogluconate plus allopurinol recipients. The rates of clinical adverse events were similar among both groups. Thrombocytopenia was more frequent in the sodium stibogluconate plus allopurinol recipients, but the difference was not statistically significant. Eight patients (two sodium stibogluconate recipients and six sodium stibogluconate plus allopurinol recipients) withdrew from the study because of severe thrombocytopenia. In this study, the addition of allopurinol to sodium stibogluconate provided no clinical benefit as treatment of mucocutaneous leishmaniasis.

Non-ulcerative cutaneous leishmaniasis in Honduras fails to respond to topical paromomycin.

A double-'blind', placebo-controlled trial of topical therapy with 15% paromomycin (aminosidine) and 10% urea in white paraffin was carried out on 53 patients with non-ulcerating cutaneous leishmaniasis in Honduras. Although the treatment was not effective, several unexpected findings emerged from the trial. Leishmania mexicana was found to be the cause of many of the skin lesions in one of the 2 study sites. These lesions were clinically indistinguishable from those caused by L. chagasi, the aetiologic agent previously found for this form of leishmaniasis. This is the first documented report of L. mexicana in Honduras.

Inefficacy of allopurinol as monotherapy for Colombian cutaneous leishmaniasis. A randomized, controlled trial.

BACKGROUND: Hundreds of thousands of cases of cutaneous leishmaniasis occur each year worldwide. Available therapies are parenteral, moderately toxic, and costly. OBJECTIVE: To determine the efficacy of and tolerance for oral allopurinol as monotherapy for cutaneous leishmaniasis. DESIGN: Randomized, controlled trial. SETTING: Outpatient clinics in 11 regions of Colombia in which cutaneous leishmaniasis is endemic. PATIENTS: 187 otherwise healthy adults with cutaneous leishmaniasis. Eighty-four percent of patients were infected with or were from regions with Leishmania panamensis; 16% were infected or were from regions with L. braziliensis. INTERVENTION: Patients were randomly assigned to one of three treatment groups. The first group received allopurinol, three 100-mg tablets four times daily (20 mg/kg of body weight per day) for 28 days. The second group received three placebo tablets four times daily for 28 days. The third group received Glucantime, 20 mg of intramuscular antimony/kg per day for 20 days. MEASUREMENT: Complete cure was defined as complete clinical reepithelialization of all lesions at 3 months and no relapse during 12 months of follow-up. RESULTS: Of 182 patients whose data could be analyzed, 157 (86%) were evaluated. In the allopurinol group, 18 of 55 (33% [95% CI, 21% to 47%]) patients were cured; in the placebo group, 17 of 46 patients (37% [CI, 23% to 52%]) were cured (difference, 4% [CI, -14% to 22%]; P = 0.68); and in the Glucantime group, 52 of 56 patients (93% [CI, 83% to 98%]) were cured (P < 0.001 compared with the allopurinol and placebo groups combined). In most cases, therapy was considered to have failed because the lesion did not reepithelialize by 1.5 months after the end of therapy. Three cases of relapse (two in the allopurinol group and one in the placebo group) at the nasal mucosa (mucosal leishmaniasis) had occurred by the end of 12 months of follow-up. CONCLUSIONS: Allopurinol monotherapy has no effect on Colombian cutaneous disease primarily caused by L. panamensis and therefore is unlikely to be effective against cutaneous leishmaniasis in other endemic regions.

Progress on vaccines against parasites.

There has been significant progress in attempts to develop effective vaccines against parasitic diseases, including malaria, leishmaniasis and schistosomiasis. In malaria, in addition to field trials with SPf66, the Colombian malaria vaccine, several Plasmodium falciparum candidate vaccines are under Phase I testing, including NYVAC-7, a multi-antigen, attenuated recombinant vaccinia virus. Additional candidate antigens are at an advanced stage of pre-clinical development. In leishmaniasis, Phase III clinical trials on first generation vaccines (killed Leishmania, with or without BCG) are proceeding in several countries. Use of IL-12 as an adjuvant for use with killed Leishmania vaccine is being studied in non-human primates. A genetically constructed (gene knock-out) live avirulent Leishmania is being developed in preclinical studies as a potential live vaccine. Research is also underway to evaluate several recombinant proteins. The genes coding for such leading candidate antigens are also being incorporated into various live vectors to yield recombinant organisms with vaccination potential. In schistosomiasis, a strategy for the development of a vaccine against Schistosoma mansoni has been established, focussing on six priority recombinant antigens. An Asian S. japonicum vaccine development network has also been established, initially to develop a vaccine to block transmission in cattle and oxen, important reservoirs of the disease in Asia, and ultimately a human vaccine. As all of the above-mentioned vaccines will be used in the field in disease-endemic tropical countries, optimal stability will be of paramount importance.

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.

Development of vaccines against leishmaniasis.

A vaccine against leishmaniasis is the only practical means to control this disease in many epidemiological situations. Two approaches have been adopted: pragmatic and systematic. The pragmatic approach involves trial of crude leishmanial components in animals and then in humans if they meet safety requirements. The systematic approach requires identification of the protective immunogen(s), appropriate carrier and adjuvant, and determination of the immune responses and modes of presentation of the immunogens to achieve the desired effect. Progress have been made with both approaches. Killed Leishmania promastigotes have been used in Brazil for high risk individuals with encouraging results. Impressive results have also been observed with killed Leishmania plus BCG for immunotherapy of cutaneous leishmaniasis in Venezuela. With the systematic approach, recent research has identified some protective immunogens, cloned protective murine T-cells, developed primate models resembling the human disease, cloned and expressed genes of some potential immunogens, identified some features of the protective immune response, determined modes of presentation of immunogen to produce a protective response, and been able to protect mice (even/Balb/c) against L. major infection. The difficult part that remains is the implementation of a vaccine or any control measure in the poor communities where they are needed and where the lack of required infrastructure does not allow adequate coverage.

Experiences with vaccines against cutaneous leishmaniasis: of men and mice.

The need for a vaccine(s) against cutaneous leishmaniasis and the populations at risk for whom such vaccines should be developed are briefly discussed. The current human vaccine studies are reviewed, as are some experimental mouse studies with emphasis on Leishmania major infection relevant to vaccine development. Based on the information available from the mouse model and those data which are being sought in human studies, the benign nature of the cutaneous disease, the ease with which L. major can be manipulated to yield the required material, and the ongoing practice of leishmanization which allows rapid evaluation of candidate vaccine(s), it is suggested that a vaccine, at least against L. major, is imminent in the not too distant future.