ICRC 'anti-leprosy vaccine'.

A vaccine containing ICRC bacilli, which are leprosy-derived cultivable mycobacteria, induces lepromin conversion in LL patients and lepromin-negative persons. 'Up-grading' of lesions and reversal reaction are observed in some vaccinated patients. The bacillus shows antigenic cross-reactivity with Mycobacterium leprae. These observations provided the basis for launching a large-scale field trial of the vaccine in India in February 1987. The objective of the two-arm trial is to assess efficacy of the ICRC vaccine against BCG, which forms the control arm, in lowering the incidence of leprosy in healthy household contacts of leprosy patients. Recently, a very high molecular weight fraction, named PP-I, has been isolated from the sonicate of ICRC bacilli. PP-I, which is a glycolipoprotein, is a strong T-cell immunogen and shows antigenic cross-reactivity with a similar fraction isolated from M. leprae. A 'subunit' vaccine containing the PP-I of ICRC bacilli is currently undergoing phase I and II clinical trials in India.