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

In Commemoration of Dr. Farrokh Modabber: An Iranian Pioneer of Cellular Immunology, and Leishmaniases Vaccine Research in Iran and the World

Born in 1940 in Rasht, Iran, Dr. Farrokh Modabber earned his B.A. in Bacteriology and Ph.D. in Microbiology from University of California, Los Angeles (UCLA). He joined the Harvard Medical School as a fellow before transitioning to a faculty role at Harvard School of Public Health (HSPH) and played a pivotal role in advancing Cellular Immunology. In the early 1970s, he returned to Iran as an Associate Professor at Pahlavi University in Shiraz. Subsequently, he rejoined HSPH before embarking on a tenure at Tehran University. As the head of the Pathobiology Department at Tehran University School of Public Health, he initiated the Tehran/Harvard joint M.Sc. program in Immunology, which played a crucial role in shaping the careers of numerous Iranian immunologists over the following decades. Dr. Modabber went on to hold esteemed positions such as Director General of the Pasteur Institute of Iran, visiting immunology lecturer at various universities, Coordinator of Research Capability Strengthening of WHO's Special Program for Research and Training in Tropical Diseases (TDR), Director of the Infectious Disease Research Institute (IDRI), and Senior Advisor of Drugs for Neglected Diseases initiative (DNDi), to name a few. This article highlights Dr. Modabber's impactful career, focusing on his efforts to combat global leishmaniasis.

From infection to vaccination: reviewing the global burden, history of vaccine development, and recurring challenges in global leishmaniasis protection

INTRODUCTION

Leishmaniasis is a major public health problem and the second most lethal parasitic disease in the world due to the lack of effective treatments and vaccines. Even when not lethal, leishmaniasis significantly affects individuals and communities through life-long disabilities, psycho-sociological trauma, poverty, and gender disparity in treatment.

AREAS COVERED

This review discusses the most relevant and recent research available on Pubmed and GoogleScholar highlighting leishmaniasis' global impact, pathogenesis, treatment options, and lack of effective control strategies. An effective vaccine is necessary to prevent morbidity and mortality, lower health care costs, and reduce the economic burden of leishmaniasis for endemic low- and middle-income countries. Since there are several forms of leishmaniasis, a pan-Leishmania vaccine without geographical restrictions is needed. This review also focuses on recent advances and common challenges in developing prophylactic strategies against leishmaniasis.

EXPERT OPINION

Despite advances in pre-clinical vaccine research, approval of a human leishmaniasis vaccine still faces major challenges - including manufacturing of candidate vaccines under Good Manufacturing Practices, developing well-designed clinical trials suitable in endemic countries, and defined correlates of protection. In addition, there is a need to explore Challenge Human Infection Model to avoid large trials because of fluctuating incidence and prevalence of leishmanasis.

Non-specific effects of BCG in protozoal infections: tegumentary leishmaniasis and malaria

BACKGROUND

Leishmaniasis and malaria are major causes of illness in the poorest countries. In the absence of efficient strategies to prevent infections and to control the transmission of the parasites by insect vectors, treatment relies on drug therapy. Vaccine development continues on several fronts; however none of the candidates developed has so far been shown to provide long-lasting protection at a population level. Because the bacillus Calmette-Guérin (BCG) vaccine can induce heterologous protective effects, we hypothesize that BCG has beneficial effects in the control of tegumentary leishmaniasis (TL) and malaria.

AIMS

In this review we describe evidence for the protective efficacy of BCG against tegumentary leishmaniasis and malaria in humans.

SOURCES

Relevant data from peer-reviewed scientific literature published on Pubmed up to January 2019 were examined.

CONTENT

From experimental animal and various human studies with BCG and one recent randomized malaria trial there is evidence that BCG has beneficial effects in Leishmania spp. and Plasmodium falciparum infections. Although the precise mechanisms remain unknown, BCG can activate innate immune responses, and an increasing body of evidence demonstrates that the induction of trained innate immunity could explain its non-specific protective effects.

IMPLICATIONS

Despite many years of research to prevent and treat TL and malaria, these diseases remain a public health problem in tropical countries. Future studies are required to examine if BCG vaccination could be used as an effective treatment option.

Immunity Against Leishmania major Infection: Parasite-Specific Granzyme B Induction as a Correlate of Protection

Zoonotic cutaneous leishmaniasis (ZCL) caused by Leishmania (L.) major infection is characterized by different clinical presentations which depend in part on the host factors. In attempt to investigate the impact of the host's immune response in the outcome of the disease, we conducted a prospective study of 453 individuals living in endemic foci of L. major transmission in Central Tunisia. Several factors were assessed at the baseline including (i) the presence of typical scars of ZCL, (ii) in vivo hypersensitivity reaction to leishmanin, and (iii) the in vitro release of granzyme B (Grz B) by peripheral blood mononuclear cells (PBMC) in response to stimulation with live L. major promastigotes. After one season of parasite's transmission, repeated clinical examinations allowed us to diagnose the new emerging ZCL cases. Heterogeneity was observed in terms of number of lesions developed by each individual as well as their size and spontaneous outcome, which led us to establish the parameter “severity of the disease.” The efficacy of the presence of typical ZCL scar, the leishmanin skin test (LST) positive reactivity and the high levels of Grz B (≥2 ng/ml), in the protection against the development of ZCL were 29, 15, and 22%, respectively. However, these factors were more efficient against development of intermediate or severe forms of ZCL. Levels of Grz B >2 ng/ml showed the best efficacy of protection (equals to 72.8%) against development of these forms of ZCL. The association of such parameter with the positivity of the LST exhibited a better efficacy (equals to 83.6%). In conclusion, our results support the involvement of Leishmania-specific cytotoxic cellular immune response in host protection against Leishmania-infection. This factor could be of great interest in monitoring the success of vaccination against human leishmaniasis.

Leishmania vaccine development: exploiting the host-vector-parasite interface

Visceral leishmaniasis (VL) is a disease transmitted by phlebotomine sand flies, fatal if untreated, and with no available human vaccine. In rodents, cellular immunity to Leishmania parasite proteins as well as salivary proteins of the sand fly is associated with protection, making them worthy targets for further exploration as vaccines. This review discusses the notion that a combination vaccine including Leishmania and vector salivary antigens may improve vaccine efficacy by targeting the parasite at its most vulnerable stage just after transmission. Furthermore, we put forward the notion that better modeling of natural transmission is needed to test efficacy of vaccines. For example, the fact that individuals living in endemic areas are exposed to sand fly bites and will mount an immune response to salivary proteins should be considered in pre-clinical and clinical evaluation of leishmaniasis vaccines. Nevertheless, despite remaining obstacles there is good reason to be optimistic that safe and effective vaccines against leishmaniasis can be developed.

Trained immunity: consequences for the heterologous effects of BCG vaccination

A growing body of evidence from epidemiologic and immunologic studies have shown that in addition to target disease-specific effects, vaccines have heterologous effects towards unrelated pathogens. Like some other vaccines, bacille Calmette-Guerin (BCG) has shown in observational studies and randomized clinical trials to increase survival beyond the disease burden of the target disease. The immunologic substrate for these non-specific protective effects have been ascertained to heterologous T cell effects on the one hand, and to priming of innate immunity on the other hand. The term 'trained immunity' has been proposed to describe these potentiating effects of vaccines on innate immune responses. This process can explain the rapid effects of BCG vaccination and has been suggested to be mediated by epigenetic programming of monocytes or macrophages. This novel concept has important implications for the possible use of vaccines, for vaccination policy and even for the design of novel immunotherapeutic approaches.

Preparation and evaluation of niosomes containing autoclaved Leishmania major: a preliminary study

In this study, different positively charged niosomal formulations containing sorbitan esters, cholesterol and cetyl trimethyl ammonium bromide were prepared by film hydration method for the entrapment of autoclaved Leishmania major (ALM). Size distribution pattern and stability of niosomes were investigated by laser light scattering method and ALM encapsulation per cent was measured by the bicinchoninic acid method. Finally, the selected formulation was used for the induction of the immune response against cutaneous leishmaniasis in BALB/c mice. Size distribution curves of all the formulations followed a log-normal pattern and the mean volume diameter was in the range 7.57-15.80 µm. The mean volume diameters were significantly increased by adding Tween to Span formulations (p < 0.05). The percentage of ALM entrapped in all formulations varied between 14.88% and 36.65%. In contrast to ALM, in vivo studies showed that the niosomes containing ALM have a moderate effect in the prevention of cutaneous leishmaniasis in BALB/c mice.

Alginate microspheres encapsulated with autoclaved Leishmania major (ALM) and CpG-ODN induced partial protection and enhanced immune response against murine model of leishmaniasis

A suitable adjuvant and delivery system are needed to enhance efficacy of vaccines against leishmaniasis. In this study, alginate microspheres as an antigen delivery system and CpG-ODN as an immunoadjuvant were used to enhance immune response and induce protection against an experimental autoclaved Leishmania major (ALM) vaccine. Alginate microspheres were prepared by an emulsification technique and the characteristics of the preparation such as size, encapsulation efficiency and release profile of encapsulates were studied. Mean diameter of microspheres was determined using SEM (Scanning Electron Microscopy) and particle size analyzer. The encapsulation efficiency was determined using Lowry protein assay method. The integrity of ALM antigens was assessed using SDS-PAGE. Mean diameter of microspheres was 1.8±1.0μm. BALB/c mice were immunized three times in 3-weeks intervals with ALM+CpG-ODN loaded microspheres [(ALM+CpG)(ALG)], ALM encapsulated alginate microspheres [(ALM)(ALG)], (ALM)(ALG)+CpG, ALM+CpG, ALM alone or PBS. The intensity of infection induced by L. major challenge was assessed by measuring size of footpad swelling. The strongest protection was observed in group of mice immunized with (ALM+CpG)(ALG). The groups of mice received (ALM+CpG)(ALG), (ALM)(ALG)+CpG, (ALM)(ALG) and ALM+CpG were also showed a significantly (P<0.05) smaller footpad swelling compared with the group that received either ALM alone or PBS. The mice immunized with (ALM+CpG)(ALG) or ALM+CpG showed the significantly (P<0.05) highest IgG2a/IgG1 ratio. The IFN-γ level was significantly (P<0.0001) highest in group of mice immunized with either (ALM)(ALG)+CpG or ALM+CpG. It is concluded that alginate microspheres and CpG-ODN adjuvant when are used simultaneously induced protection and enhanced immune response against ALM antigen.

Immunization against leishmaniasis by PLGA nanospheres encapsulated with autoclaved Leishmania major (ALM) and CpG-ODN

Various adjuvants and delivery systems have been evaluated for increasing the protective immune responses against leishmaniasis and mostly have been shown not to be effective enough. In this study, poly(D,L-lactide-co-glycolide) (PLGA) nanospheres as an antigen delivery system and CpG-ODN as an immunoadjuvant have been used for the first time to enhance the immune response against autoclaved Leishmania major (ALM). PLGA nanospheres were prepared by a double-emulsion (W/O/W) technique. Particulate characteristics were studied by scanning electron microscopy and particle size analysis. Mean diameter of ALM + CpG-ODN-loaded nanospheres was 300 ± 128 nm. BALB/c mice were immunized three times in 3-week intervals using ALM plus CpG-ODN-loaded nanospheres [(ALM + CpG-ODN)(PLGA)], ALM encapsulated PLGA nanospheres [(ALM)(PLGA)], (ALM)(PLGA) + CpG, ALM + CpG, ALM alone, or phosphate buffer solution (PBS). The intensity of infection induced by L. major challenge was assessed by measuring size of footpad swelling. The strongest protection, showed by significantly (P<0.05) smaller footpad, was observed in mice immunized with (ALM + CpG-ODN)(PLGA). The (ALM)(PLGA), (ALM)(PLGA) + CpG, and ALM + CpG were also showed a significantly (P<0.05) smaller footpad swelling compared to the groups received either PBS or ALM alone. The mice immunized with (ALM + CpG-ODN)(PLGA), (ALM)(PLGA) + CpG, and ALM + CpG showed the highest IgG2a/IgG1 ratio, interferon-γ production, and lowest interleukin-4 production compared to the other groups. It is concluded that when both PLGA nanospheres and CpG-ODN adjuvants were used simultaneously, it induce stronger immune response and enhance protection rate against Leishmania infection.

Exposure to Leishmania major modulates the proportion of CD4+ T cells without affecting cellular immune responses

The immune responses of individuals exposed to Leishmania major were evaluated and compared with those of non-exposed volunteers. Forty-one patients with active lesion(s), 43 healed individuals, 15 vaccinees 1 month or 1 year post vaccination, and 15 non-exposed volunteers were studied. Leishmanin skin test (LST) response, proliferative response of lymphocyte (PRL) to L. major antigen, IFN-gamma and IL-4 production, and percentage of L. major-specific CD4+, CD8+ and CD16+/CD56+ cells in peripheral blood mononuclear cells were assessed. Data showed positive LST (>5 mm) in 92% of patients, 98% of healed, and 80% or 43% of vaccinees 1 month and 1 year post vaccination, respectively. Positive PRL (SI>2.5) was displayed in 90%, 84%, 46% and 7% of patients, healed, vaccinated (post 1 year) and non-exposed donors, respectively. The mean +/-S.E. of IFN-gamma was 924 +/- 149, 1,278 +/- 185, 470 +/- 282 or 258 +/- 82 pg/ml in patients, healed cases and vaccinees after 1 month or 1 year, respectively. Positive IFN-gamma responders (>300 pg/ml) were shown in 72% of patients, 81% of healed cases, 31% or 39% of vaccinees and 0% of non-exposed donors. A reduced percentage of CD4+ T-cells and an increased percentage of NK cells were found in exposed individuals compared to non-exposed donors. The data indicated that exposure to L. major modulates the proportion of CD4+ T cells and increases NK cells percentage. However, the cellular immune responses including induction of LST, and IFN-gamma production are increased in exposed individuals.

Surrogate markers of immunity to Leishmania major in leishmanin skin test negative individuals from an endemic area re-visited

BACKGROUND

In the screening of vaccine candidates it is important to select candidates that evoke immune responses associated with protection. Valid surrogate markers against human leishmaniasis are still lacking.

METHODS

A controlled injection of live Leishmania known as leishmanization, (LZ), was used to evaluate vaccine (alum-precipitated autoclaved Leishmania major with BCG) efficacy and more accurately define surrogate markers of immunity to leishmaniasis in humans. Cellular immune responses to this artificial infection were monitored in the volunteers prior to and 9 months post infection. Comparisons were made between those who developed a lesion after infection and those who did not.

RESULTS

In the volunteers monitored there was no significant difference in LST, IFNgamma production, or source of IFNgamma between those who developed a lesion and those who did not after LZ, with the exception that ulcer development was associated with an enhanced number of IFNgamma secreting CD4(+) CD45RA(-) (memory) T cells.

DISCUSSION

Ulcer development following LZ was lower than anticipated by a pilot study (47% versus 78%) using the same stabilate several years earlier. While this may be an effect of low viability/virulence of the LZ inocula, alternative explanations are also possible. The IFNgamma responses in the study subjects were significantly lower compared to volunteers with previous history of cutaneous leishmaniasis. The findings raise the possibility that the selection of LST-negative volunteers in an endemic area may bias the study towards potentially non/low L. major-reactive volunteers.

Mycobacterium hsp65 DNA entrapped into TDM-loaded PLGA microspheres induces protection in mice against Leishmania (Leishmania) major infection

Heat shock proteins (HSPs) are highly conserved among different organisms. A mycobacterial HSP65 DNA vaccine was previously shown to have prophylactic and immunotherapeutic effects against Mycobacterium tuberculosis infection in mice. Here, BALB/c mice were immunized with mycobacterial DNA-hsp65 or with DNA-hsp65 and trehalose dymicolate (TDM), both carried by biodegradable microspheres (MHSP/TDM), and challenged with Leishmania (Leishmania) major. MHSP/TDM conferred protection against L. major infection, as indicated by a significant reduction of edema and parasite loads in infected tissues. Although high levels of interferon-gamma and low levels of interleukin (IL)-4 and IL-10 were detected in mice immunized with DNA-hsp65 or MHSP/TDM, only animals immunized with MHSP/TDM displayed a consistent Th1 immune response, i.e., significantly higher levels of anti-soluble Leishmania antigen (SLA) immunoglobulin G (IgG)2a and low anti-SLA IgG1 antibodies. These findings indicate that encapsulated MHSP/TDM is more immunogenic than naked hsp65 DNA, and has great potential to improve vaccine effectiveness against leishmaniasis and tuberculosis.

Failure of a killed Leishmania amazonensis vaccine against American cutaneous leishmaniasis in Colombia

We report the results of a double-blind, randomized, placebo-controlled clinical trial of a killed whole-cell Leishmania amazonensis candidate vaccine against American cutaneous leishmaniasis (CL) in Colombia. The trial subjects were 2597 healthy volunteers with negative leishmanin skin test (LST) selected from rural Colombian soldiers who were going to patrol endemic areas. They were randomized to receive either three doses of vaccine (n=1295) or placebo (n=1302) given at 20-day intervals. An active and passive case detection system was established to follow-up volunteers for 1 year after vaccination. Safety and efficacy of the vaccine were determined by comparing local and systemic adverse reactions after each dose and the incidence of parasitologically confirmed CL. In the vaccine and placebo groups 101 (7.7%) and 88 (6.8%) volunteers developed CL respectively. The vaccine was shown to be safe but offered no protection against CL caused by L. panamensis in the proposed vaccination schedule.

Mononuclear cells from patients recovered from cutaneous leishmaniasis respond to Leishmania major amastigote class I nuclease with a predominant Th1-like response

The Leishmania major amastigote class I nuclease (LmaCIN) is a developmentally regulated protein that is highly expressed in the amastigote stage of L. major. This protein is homologous to the P4 nuclease of L. pifanoi, which has been shown to induce protective immune response in a murine model. To evaluate LmaCIN as a potential human vaccine candidate, cellular immune responses to recombinant LmaCIN were examined in individuals recovered from Old World cutaneous leishmaniasis. Peripheral blood mononuclear cells (PBMC) from patients recovered from L. major infection were cultured either with recombinant LmaCIN or autoclaved L. major (ALM) as control. rLmaCIN induced significant proliferation of PBMC from 90% of recovered patients. Phenotypic analysis of proliferating cells showed that CD8(+) cells were the predominant cell type proliferating in response to rLmaC1N. Screening of culture supernatants for cytokines showed that rLmaCIN induced high levels of interferon (IFN)-gamma (mean +/- s.e.m.: 1398 +/- 179 pg/ml) associated with little interleukin (IL)-10 and little or no IL-5 production. These findings show that LmaCIN is immunogenic in humans during L. major infection and that it can elicit immunological responses relevant to immunoprophylaxis of leishmaniasis.