Vaccination with a Leishmania infantum HSP70-II null mutant confers long-term protective immunity against Leishmania major infection in two mice models

Abstract

BackgroundThe immunization with genetically attenuated Leishmania cell lines has been associated to the induction of memory and effector T cell responses against Leishmania able to control subsequent challenges. A Leishmania infantum null mutant for the HSP70-II genes has been described, possessing a non-virulent phenotype.Methodology/Principal findingsThe L. infantum attenuated parasites (LiΔHSP70-II) were inoculated in BALB/c (intravenously and subcutaneously) and C57BL/6 (subcutaneously) mice. An asymptomatic infection was generated and parasites diminished progressively to become undetectable in most of the analyzed organs. However, inoculation resulted in the long-term induction of parasite specific IFN-γ responses able to control the disease caused by a challenge of L. major infective promastigotes. BALB/c susceptible mice showed very low lesion development and a drastic decrease in parasite burdens in the lymph nodes draining the site of infection and internal organs. C57BL/6 mice did not show clinical manifestation of disease, correlated to the rapid migration of Leishmania specific IFN-γ producing T cells to the site of infection.Conclusion/SignificanceInoculation of the LiΔHSP70-II attenuated line activates mammalian immune system for inducing moderate pro-inflammatory responses. These responses are able to confer long-term protection in mice against the infection of L. major virulent parasites.

Subcutaneous Immunization of Leishmania HSP70-II Null Mutant Line Reduces the Severity of the Experimental Visceral Leishmaniasis in BALB/c Mice

“…Protection was observed in a resistant model that mimics human CL, namely C57BL/6 mice challenged in the ear dermis with a low dose of metacyclic promastigotes [33]. The Li∆HSP70-II-based vaccine also induced protection in the progressive form of leishmaniasis developed in the susceptible BALB/c mice strain when infected with the L. major model [18,20], a model that may reflect in part some aspects of the human VL disease [34]. It is clear that the experimental challenge of mice with viscerotropic species does not fully reproduce the peculiarities of human VL patients because of the different organ-dependent evolution of the disease [35].…”

“…For vaccination, the attenuated Li∆HSP70-IIline L. infantum MCAN/ES/96/BCN150 [∆hsp70-II::NEO/ ∆hsp70-II::HYG] was employed [16,18]. Mice were subcutaneously (s.c.) vaccinated with 10 7 Li∆HSP70-II stationary promastigotes (suspended in 30 µL of phosphate saline buffer (PBS)) into the right footpad.…”

“…Serum was obtained from blood samples taken at week 1 (silent phase), week 5 (initial phase), and week 11 (late phase) after the infective challenge. The reactivity against SLA was determined by ELISA as described in [18]. Serum samples were serially diluted two-fold starting with from 1/50.…”

“…In its absence, parasites are able to infect, but they have a limited capacity to replicate inside the parasitophorous vacuoles of phagocytic mononuclear cells [17]. More recently, we reported that inoculation of Li∆HSP70-II promastigotes caused a local persistent infection that induces short-term and long-term heterologous protection against CL development due to an L. major infective challenge in BALB/c and C57BL/6 mice [18][19][20]. This protection correlates with rapid migration of effector T cells producing IFN-γ to the site of the intradermal experimental infection [18].…”

Suicidal Leishmania

“…Such a deliberately weakened parasite could be used to vaccinate the host, as its viability is regulated by the toxin stabilization, causing a profoundly reduced pathogenesis.Pathogens 2020, 9, 79 2 of 12 trials based on killed or heat-inactivated parasites, recombinant proteins, and DNA vaccines have shown limitations in murine models and field studies [11]. Another promising experimental approach to this problem is a usage of the genetically modified Leishmania lines as attenuated vaccines [12][13][14][15][16]. There are two aspects that make generation of a successful vaccine particularly challenging.…”