Use of Recombinant Virus Replicon Particles for Vaccination against Mycobacterium ulcerans Disease

Abstract

Buruli ulcer, caused by infection with Mycobacterium ulcerans, is a necrotizing disease of the skin and subcutaneous tissue, which is most prevalent in rural regions of West African countries. The majority of clinical presentations seen in patients are ulcers on limbs that can be treated by eight weeks of antibiotic therapy. Nevertheless, scarring and permanent disabilities occur frequently and Buruli ulcer still causes high morbidity. A vaccine against the disease is so far not available but would be of great benefit if used for prophylaxis as well as therapy. In the present study, vesicular stomatitis virus-based RNA replicon particles encoding the M. ulcerans proteins MUL2232 and MUL3720 were generated and the expression of the recombinant antigens characterized in vitro. Immunisation of mice with the recombinant replicon particles elicited antibodies that reacted with the endogenous antigens of M. ulcerans cells. A prime-boost immunization regimen with MUL2232-recombinant replicon particles and recombinant MUL2232 protein induced a strong immune response but only slightly reduced bacterial multiplication in a mouse model of M. ulcerans infection. We conclude that a monovalent vaccine based on the MUL2232 antigen will probably not sufficiently control M. ulcerans infection in humans.

FVB/N Mice Spontaneously Heal Ulcerative Lesions Induced by Mycobacterium ulcerans and Switch M. ulcerans into a Low Mycolactone Producer

“…Moreover, the healing tissue is not sterilized because the viable bacterial load is still high and stable, illustrating the absence of an efficient specific immune response against M. ulcerans. In this context, our results are not in favor of vaccine strategies targeting directly mycobacterial components, as already suggested (12,40,41). Surprisingly, histological approaches showed that the bacilli present in healed tissues are not surrounded by a granuloma-like structure, unlike in the context of latent tuberculosis (42,43).…”

“…Usually, all preclinical studies of M. ulcerans infection are performed in a mouse model, using either BALB/c or C57BL/6 mouse strains, and they study host colonization or evaluate efficacy of treatments or vaccines (7,(10)(11)(12)(13)(14). As a matter of fact, in both strains, s.c. inoculation with M. ulcerans invariably leads to ulceration after several weeks, with lesions evolving toward tissue necrosis and death of the animals.…”

Buruli Ulcer in Animals and Experimental Infection Models

“…As repeated passage by in vitro culture prompts some of the M. ulcerans strains to lose their virulence plasmid [47,48], some laboratories opted to passage their strains trough mouse foot pads in order to preserve their virulence [49][50][51]. Alternatively, low passage primary isolates have been used for productive infection of mice [52].…”

“…S1013 was originally isolated in 2010 from a swab taken from the undermined edges of the ulcerative lesion of a Cameroonian BU patient [57]. Its passage number has been kept to an absolute minimum in order to preserve its virulence for studies in the mouse footpad model and the pig model of BU [40,45,52,[58][59][60].…”

The Immunology of Buruli Ulcer

“…However, this study only evaluated protection for days, and thus it remains to be investigated whether protection is long-lasting. Moreover, it is unclear if protective immunogens could have been removed during the dewaxing process, in spite of a general lack of protection detected in immunization interventions employing surface proteins, such as the 18 kDa shsp and the 27 kDa laminar binding protein [32,160,161]. Still, these results add to others confirming the extreme hydrophobicity of the M. ulcerans cell wall, which cumulatively with mycolactone represents a virulence factor and aids in shielding the pathogen from immune surveillance mechanisms, consequently adding another layer of complexity to the development of preventive strategies [162].…”