Safety and efficacy assessment of two new leprosy skin test antigens: randomized double blind clinical study.

BACKGROUND: New tools are required for the diagnosis of pre-symptomatic leprosy towards further reduction of disease burden and its associated reactions. To address this need, two new skin test antigens were developed to assess safety and efficacy in human trials. METHODS: A Phase I safety trial was first conducted in a non-endemic region for leprosy (U.S.A.). Healthy non-exposed subjects (n = 10) received three titrated doses (2.5 µg, 1.0 µg and 0.1 µg) of MLSA-LAM (n = 5) or MLCwA (n = 5) and control antigens [Rees MLSA (1.0 µg) and saline]. A randomized double blind Phase II safety and efficacy trial followed in an endemic region for leprosy (Nepal), but involved only the 1.0 µg (high dose) and 0.1 µg (low dose) of each antigen; Tuberculin PPD served as a control antigen. This Phase II safety and efficacy trial consisted of three Stages: Stage A and B studies were an expansion of Phase I involving 10 and 90 subjects respectively, and Stage C was then conducted in two parts (high dose and low dose), each enrolling 80 participants: 20 borderline lepromatous/lepromatous (BL/LL) leprosy patients, 20 borderline tuberculoid/tuberculoid (BT/TT) leprosy patients, 20 household contacts of leprosy patients (HC), and 20 tuberculosis (TB) patients. The primary outcome measure for the skin test was delayed type hypersensitivity induration. FINDINGS: In the small Phase I safety trial, reactions were primarily against the 2.5 µg dose of both antigens and Rees control antigen, which were then excluded from subsequent studies. In the Phase II, Stage A/B ramped-up safety study, 26% of subjects (13 of 50) showed induration against the high dose of each antigen, and 4% (2 of 50) reacted to the low dose of MLSA-LAM. Phase II, Stage C safety and initial efficacy trial showed that both antigens at the low dose exhibited low sensitivity at 20% and 25% in BT/TT leprosy patients, but high specificity at 100% and 95% compared to TB patients. The high dose of both antigens showed lower specificity (70% and 60%) and sensitivity (10% and 15%). BL/LL leprosy patients were anergic to the leprosy antigens. INTERPRETATION: MLSA-LAM and MLCwA at both high (1.0 µg) and low (0.1 µg) doses were found to be safe for use in humans without known exposure to leprosy and in target populations. At a sensitivity rate of 20-25% these antigens are not suitable as a skin test for the detection of the early stages of leprosy infection; however, the degree of specificity is impressive given the presence of cross-reactive antigens in these complex native M. leprae preparations. TRIAL REGISTRATION: ClinicalTrials.gov NCT01920750 (Phase I), NCT00128193 (Phase II).

Nerve damage following intraneural injection of Mycobacterium leprae into rabbits pre-sensitized to mycobacteria.

Nerve damage is a common feature of leprosy although the mechanism responsible for the damage is not clearly understood. In the tuberculoid end of the leprosy spectrum where both intraneural Mycobacterium leprae or their antigens and cell-mediated hypersensitivity to M. leprae co-exist, acute neuritis affecting major nerve trunks can occur during reversal reactions. These reactions are known to be associated with increased hypersensitivity to M. leprae antigens. The nerve involvement is therefore thought to be a direct consequence of the patient's hypersensitivity to M. leprae. So far the only indirect evidence based on in vitro studies have been produced to support such a contention. We sensitized rabbits with M. leprae and then injected M. leprae sonicate into the sciatic nerves at the peak of hypersensitivity. Seventy-two hours later, the nerves were dissected out and studied histologically. Our results show that cellular infiltration and axonal degeneration can occur as a direct consequence of hypersensitivity to intraneural M. leprae antigens. This study, therefore, offers direct evidence for the involvement of specific cell-mediated hypersensitivity to M. leprae antigens in the pathogenesis of major nerve trunk damage in the tuberculoid end of the leprosy spectrum especially during acute reversal reactions.