A nonhuman primate scrub typhus model: protective immune responses induced by pKarp47 DNA vaccination in cynomolgus macaques.

We developed an intradermal (ID) challenge cynomolgus macaque (Macaca fascicularis) model of scrub typhus, the leading cause of treatable undifferentiated febrile illness in tropical Asia, caused by the obligate intracellular bacterium, Orientia tsutsugamushi. A well-characterized animal model is required for the development of clinically relevant diagnostic assays and evaluation of therapeutic agents and candidate vaccines. We investigated scrub typhus disease pathophysiology and evaluated two O. tsutsugamushi 47-kDa, Ag-based candidate vaccines, a DNA plasmid vaccine (pKarp47), and a virus-vectored vaccine (Kp47/47-Venezuelan equine encephalitis virus replicon particle) for safety, immunogenicity, and efficacy against homologous ID challenge with O. tsutsugamushi Karp. Control cynomolgus macaques developed fever, classic eschars, lymphadenopathy, bacteremia, altered liver function, increased WBC counts, pathogen-specific Ab (IgM and IgG), and cell-mediated immune responses. Vaccinated macaques receiving the DNA plasmid pKarp47 vaccine had significantly increased O. tsutsugamushi-specific, IFN-γ-producing PBMCs (p = 0.04), reduced eschar frequency and bacteremia duration (p ≤ 0.01), delayed bacteremia onset (p < 0.05), reduced circulating bacterial biomass (p = 0.01), and greater reduction of liver transaminase levels (p < 0.03) than controls. This study demonstrates a vaccine-induced immune response capable of conferring sterile immunity against high-dose homologous ID challenge of O. tsutsugamushi in a nonhuman primate model, and it provides insight into cell-mediated immune control of O. tsutsugamushi and dissemination dynamics, highlights the importance of bacteremia indices for evaluation of both natural and vaccine-induced immune responses, and importantly, to our knowledge, has determined the first phenotypic correlates of immune protection in scrub typhus. We conclude that this model is suitable for detailed investigations into vaccine-induced immune responses and correlates of immunity for scrub typhus.

Defined tuberculosis vaccine, Mtb72F/AS02A, evidence of protection in cynomolgus monkeys.

The development of a vaccine for tuberculosis requires a combination of antigens and adjuvants capable of inducing appropriate and long-lasting T cell immunity. We evaluated Mtb72F formulated in AS02A in the cynomolgus monkey model. The vaccine was immunogenic and caused no adverse reactions. When monkeys were immunized with bacillus Calmette-Guérin (BCG) and then boosted with Mtb72F in AS02A, protection superior to that afforded by using BCG alone was achieved, as measured by clinical parameters, pathology, and survival. We observed long-term survival and evidence of reversal of disease progression in monkeys immunized with the prime-boost regimen. Antigen-specific responses from protected monkeys receiving BCG and Mtb72F/AS02A had a distinctive cytokine profile characterized by an increased ratio between 3 Th1 cytokines, IFN-gamma, TNF, and IL-2 and an innate cytokine, IL-6. To our knowledge, this is an initial report of a vaccine capable of inducing long-term protection against tuberculosis in a nonhuman primate model, as determined by protection against severe disease and death, and by other clinical and histopathological parameters.

Powerful bactericidal activity of moxifloxacin in human leprosy.

In a clinical trial of moxifloxacin in eight multibacillary leprosy patients, moxifloxacin proved highly effective. In all trial patients, a single 400-mg dose of moxifloxacin resulted in significant killing (P

Clinical and histologic features of skin lesions in a cynomolgus monkey experimentally infected with mycobacterium ulcerans (Buruli ulcer) by intradermal inoculation.

Buruli ulcer, caused by Mycobacterium ulcerans, is a destructive infection that most commonly affects the skin. Animal models for Buruli ulcer include guinea pigs, rats, mice, and armadillos, but each is limited in replicating the spectrum of human disease. Here, a cynomolgus monkey was infected with two concentrations of M. ulcerans (1.0 and 2.2 x 10(8)) by intradermal inoculation, 3 months apart. All injection sites developed papules that progressed to ulcers with undermined borders within 2-4 weeks. The rate of progression and size of the ulcers were proportional to the numbers of organisms inoculated. Biopsies from ulcer edges showed ulceration, robust inflammatory cell infiltrates, granulomatous-like responses, mild edema, and extracellular acid-fast bacilli. The ulcers healed spontaneously between Weeks 8 and 12, with no signs of systemic infection. This report, the first to describe a non-human primate experimentally infected with M. ulcerans, suggests that cynomolgus monkeys are modestly susceptible and develop some of the clinical and histologic features of Buruli ulcer.

A clinical trial of ethionamide and prothionamide for treatment of lepromatous leprosy.

In 1982-1984 we conducted a six-month clinical trial in 50 previously untreated lepromatous leprosy patients randomly assigned to directly observed monotherapy with one of two thioamides, ethionamide or prothionamide, each given six times a week at doses of either 250 mg or 500 mg. The findings of this study have only recently been analyzed, and the potential for the use of these thioamides in leprosy patients placed in perspective. However, because of the small number of patients included in this study, the results must be interpreted with some caution. Clinical improvement was noted in 74% of the patients treated with ethionamide and in 83% of those treated with prothionamide. Therapy was well tolerated and drug-related hepatotoxicity did not require discontinuation of therapy. The 500-mg dose of both ethionamide and prothionamide resulted in loss in Mycobacterium leprae viability more rapidly than did the 250-mg dose, and prothionamide at both dose levels was superior to the equivalent dose of ethionamide. Overall killing of M. leprae in this study was found to be similar to that obtained previously with dapsone and clofazimine, but less than was obtained with rifampin, minocycline, clarithromycin, pefloxacin, and ofloxacin.

Parallel assessment of 24 monthly doses of rifampin, ofloxacin, and minocycline versus two years of World Health Organization multi-drug therapy for multi-bacillary leprosy.

Monthly doses of rifampin, ofloxacin, and minocycline (ROM) are expected to be effective treatment for multi-bacillary leprosy. Patients with MB leprosy received ROM (n = 10) or World Health Organization multi-drug therapy (MDT) (n = 11). Treatment with ROM was given as 24 consecutive monthly observed doses of rifampin (600 mg), ofloxacin (400 mg), and minocycline (100 mg). Treatment with MDT was given as 24 consecutive monthly observed doses of rifampin (600 mg) and clofazimine (300 mg), and unobserved daily dapsone (100 mg) and clofazimine (50 mg). Twenty patients completed the 24-month regimens with > 99% compliance. Treatments with ROM and MDT were safe, tolerable, and caused similar improvements in lesions, bacterial indices, and histology. All MDT recipients developed clofazimine-induced pigmentation. Six ROM and nine MDT recipients assessed at five or more years after completion of treatment had no evidence of relapse. Twenty-four months of treatment with ROM is a safe, well-tolerated, and convenient regimen that may provide an alternate therapy to MDT for MB leprosy. Larger trials with sufficient follow-up would better define the role of ROM.

Limited susceptibility of cynomolgus monkeys (Macaca fascicularis) to leprosy after experimental administration of Mycobacterium leprae.

Cynomolgus monkeys are a useful model for human tuberculosis, but susceptibility to M. leprae is unknown. A cynomolgus model of leprosy could increase understanding of pathogenesis-importantly, neuritis and nerve-damaging reactions. We administered viable Mycobacterium leprae to 24 cynomolgus monkeys by three routes, with a median follow-up period of 6 years (range = 1-19 years) involving biopsies, nasal smears, antiphenolic glycolipid-1 (PGL-1) antibody serology, and lepromin skin testing. Most developed evanescent papules at intradermal M. leprae inoculation sites that, on biopsy, showed a robust cellular immune response akin to a lepromin skin test reaction; many produced PGL-1 antibodies. At necropsy, four monkeys, without cutaneous or gross neurological signs of leprosy but with elevated PGL-1 antibodies, including three with nasal smears (+) for acid fast bacilli (AFB), showed histological features, including AFB, suggestive of leprosy at several sites. Overall, however, cynomolgus monkeys seem minimally susceptible to leprosy after experimental M. leprae administration.

A comparative clinical trial in multibacillary leprosy with long-term relapse rates of four different multidrug regimens.

As a participant in a multicenter trial, we evaluated the relapse rate in 189 multibacillary (MB) leprosy patients treated with four different regimens and followed-up for as many as 12 years after the initiation of treatment. Treatment regimens included 1 year of WHO MDT (a regimen including dapsone, clofazimine, and rifampin), 2 years of WHO MDT, 1 month of daily rifampin and daily ofloxacin, and 1 year of WHO MDT plus an initial 1 month of daily rifampin and daily ofloxacin. Relapse rates after 9 and 12 years from the initiation of therapy in the three regimens that included WHO MDT were 0-3%, whereas relapses occurred in those treated with the 1-month regimen alone at a significantly greater rate (P < 0.05): 11% at 9 years and 25% at 12 years. Relapses occurred late, beginning at 5 years after the initiation of therapy, and were confined to those patients histopathologically borderline lepromatous and polar lepromatous having a high bacterial burden. Prospects for an alternative effective short-course therapy of leprosy are presented.

Long-term efficacy of 2 year WHO multiple drug therapy (MDT) in multibacillary (MB) leprosy patients.

Relapse rate estimates after 2 year WHO multiple drug therapy (MDT) in multi-bacillary (MB) leprosy vary. Between 1987 and 1994, 500 MB leprosy patients completing 2 year MDT were enrolled in a prospective relapse study. The majority of patients (N = 316) were treated and followed at the physician-staffed Cebu Skin Clinic (CSC), whereas others (N = 184) received therapy from government clinics and were followed by CSC technicians in the field. Relapse definition was an increased bacteriologic index (BI) and new skin lesions, supplemented with mouse footpad inoculations. Through 2002, follow-up was 5368 person-years, with a mean of 10.8 years per patient. The absolute relapse rate was 3% (15/498; 0.28/100 person-years), with a cumulative risk estimate of 3.9% at 15 yrs. For a subset of 217 patients followed for >or=12 yrs or until relapse, relapses occurred in 9% (13/142) attending the CSC, versus 3% (2/75) assessed in the field (p = 0.09). The rate for patients followed at CSC for >or=12 yrs and a pre-treatment BI >or=2.7+ was 13% (13/98). All relapses were BL or LL, with pre-treatment BI's of >or=2.7+. Relapses occurred long after completion of therapy, between 3 and 11 yrs from the midpoint of the examination without relapse to detection, or between 6 to 13 yrs to the actual year of detection, 7 occurring at >or=10 yrs. Lesion material from all relapses contained M. leprae that was rifampin and clofazimine sensitive, whereas 3 showed partial or full dapsone resistance. [Follow-up rigor and time], medical expertise, and pre-treatment bacterial load influence relapse rates after 2 yr MDT.