Promising Leprosy Vaccine Candidate

Photomicrograph of a skin tissue sample from a patient with leprosy reveals a cutaneous nerve invaded by numerous Mycobacterium leprae bacteria. Credit: Arthur E. Kaye, CDC

Characterized by the World Health Organization as a “neglected tropical disease,” leprosy (also known as Hansen’s disease) is caused by Mycobacterium leprae. Nearly a quarter of a million people are diagnosed with leprosy each year, with the infection progressing to cause disfiguration of the skin and mucous membranes as well as progressive and irreversible nerve damage.

While drug therapy exists for leprosy, it must be taken for many months, has many side effects and often is given too late to prevent the damage caused by the bacterial infection that leads to lifelong disability.

In a publication in Nature Partner Journals’ Vaccines, researchers show post-exposure prophylaxis with LepVax, a leprosy vaccine candidate from the Infectious Disease Research Institute, not only appears safe but also alleviates and delays the neurologic disruptions caused by Mycobacterium leprae infection in nine-banded armadillos.

This is an important finding because armadillos are the only other host of M. leprae that closely recapitulates many of the structural, physiological and functional aspects of leprosy observed in humans, including progressive and irreversible nerve damage.

“This report demonstrates the selection and advancement of the first defined subunit vaccine – LepVax — developed specifically for leprosy,” said Malcolm Duthie, PhD, a senior scientist at IDRI.

IDRI and The National Hansen’s Disease Laboratories (NHDP), under a research agreement with the National Institute of Allergy and Infectious Diseases (NIAID), conducted mouse experiments to demonstrate that the vaccine is immunogenic and can interrupt M. leprae infection. They also developed cutting edge neurological methods in nine-banded armadillos that were used to evaluate the effect of LepVax on nerve injury as an innovative advance to the field.

“Our results indicate that post-exposure immunization in nine-banded armadillos was not only safe but limited and delayed nerve damage,” Duthie added.

In stark contrast to BCG (a tuberculosis vaccine that provides some protection against leprosy), which precipitated rapid and severe motor nerve conduction abnormalities in previously infected armadillos, motor nerve injury was appreciably delayed in armadillos treated three times at monthly intervals with LepVax.

The data supported a successful Investigational New Drug (IND) application with the U.S. Food & Drug Administration, allowing advancement of LepVax into a Phase 1 clinical trial in humans in the U.S.

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