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

Becky L Rivoire, Nathan A Groathouse, Stephen TerLouw, Kapil Dev Neupane, Chaman Ranjit, Bishwa Raj Sapkota, Saraswoti Khadge, Chhatra B Kunwar, Murdo Macdonald, Rachel Hawksworth, Min B Thapa, Deanna A Hagge, Melinda Tibbals, Carol Smith, Tina Dube, Dewei She, Mark Wolff, Eric Zhou, Mamodikoe Makhene, Robin Mason, Christine Sizemore, Patrick J Brennan, Becky L Rivoire, Nathan A Groathouse, Stephen TerLouw, Kapil Dev Neupane, Chaman Ranjit, Bishwa Raj Sapkota, Saraswoti Khadge, Chhatra B Kunwar, Murdo Macdonald, Rachel Hawksworth, Min B Thapa, Deanna A Hagge, Melinda Tibbals, Carol Smith, Tina Dube, Dewei She, Mark Wolff, Eric Zhou, Mamodikoe Makhene, Robin Mason, Christine Sizemore, Patrick J Brennan

Abstract

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).

Conflict of interest statement

I have read the journal's policy and have the following conflict: The EMMES Corporation served as the Data Coordinating Center for these studies. This does not alter our adherence to all PLOS NTDs policies on sharing data and materials.

Figures

Figure 1. CONSORT flow diagram, Phase II,…
Figure 1. CONSORT flow diagram, Phase II, Stage C-1 Trial.
Figure 2. Phase II, Stage A/B –…
Figure 2. Phase II, Stage A/B – DTH induration by subject.
Phase II, Stage A/B graph depicting DTH indurations elicited by leprosy skin test antigens at the high dose (1.0 µg) and low dose (0.1 µg), and PPD at 5 TU: A) MLCwA, and B) MLSA-LAM. The first five subjects on both graphs represent subjects from Stage A, and the remaining 45 subjects on both graphs represent subjects from Stage B.
Figure 3. Dot plot of induration measurements.
Figure 3. Dot plot of induration measurements.
Induration results are provided across five subject groups, including BL/LL leprosy patients (n = 19 in low and n = 20 in high dose group), BT/TT leprosy patients (n = 20), HC (n = 20), TB (n = 20), and ECs (n = 50). Low and high dose groups were combined to show PPD responses: BL/LL leprosy patients (n = 39) and all other groups (n = 40). Mean and standard deviation are shown.
Figure 4. Distribution frequency of induration.
Figure 4. Distribution frequency of induration.
Frequency distribution graphs were used to establish cut off points for each skin test antigen at each dosage tested: A) MLSA-LAM low dose, B) MLCwA low dose, C) MLSA-LAM high dose, D) MLCwA high dose. Frequency of induration reaction (mm) of EC and TB groups were graphed against BT/TT and BL/LL leprosy groups. The anti-mode between the control and leprosy patient group represents the cut off for each antigen and antigen dose.

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