Chairman

Dr. Patrick J. Brennan
(1986- Member 1983-1986)
Professor
College of Veterinary Medicine and Biomedical Sciences
Department of Microbiology
Colorado State University
Fort Collins, Colorado 80523

Chairman

Dr. Hajime Saito
(1992-   , Member 1988-1992)
Director General
National Institute for Leprosy Research
4-2-1 Aoba-cho, Higashimurayama
Tokyo 189, Japan

Dr. Gilla Kaplan (1988-   )
Laboratory of Cellular Physiology and Immunology
Rockefeller University
1230 York Avenue
New York, New York 10021

Dr. Robert L. Modlin (1990-   )
University of California at Los Angeles
Department of Medicine
Division of Dermatology
52-121 CHS
10833 Le Conte Avenue
Los Angeles, California 90024-1750

Dr. Shinzo Izumi (1985-   )
Director
Department of Bioregulation
National Institute for Leprosy Research
4-2-1 Aoba-cho, Higashimurayama
Tokyo 189, Japan

Dr. Eiichi Matsuo (1994-   )
Professor
Faculty of Medicine
Kyorin University
6-20-2 Shinkawa, Mitaka
Tokyo 181, Japan

Dr. Takeshi Yamada (1991-   )
Professor
Faculty of Dentistry
Nagasaki University
1-7-1 Sakamoto-cho
Nagasaki 852, Japan

Leprosy Panels USJCMSP

All areas of leprosy research are relevant, but the following are of special interest and importance from the present-day perspective:

1. Further definition of the immunogens of the leprosy bacillus; development of recombinant DNA vectors for the production of defined antigens; development of procedures for the purification of recombinant antigens and for the synthesis of their antigenic domains
2. Identification of individual T- and B-cell epitopes on M. leprae antigens, study of the issue of their genetic restriction, and exploration of the question of segregation of epitopes toward T-cell subsets on defined antigens
3. Characterization of the cell wall components of M. leprae with a view to isolation and differentiation of suppression-inducing and helper/protection epitopes
4. Further exploration of the genome and metabolism of M. leprae with a view to mapping genes of interest, isolating genes that control synthesis of complex cell wall glycoconjugates, and allowing transfer of genes in order to construct, ultimately, through gene manipulation, whole cell or subunit vaccines. By a greater understanding of the metabolism of M. leprae, it may be possible to devise an appropriate culture medium and return again to the long-time goal of the growth of M. leprae.
5. Development of assays, based on antibody or antigen detection or recognition of nucleic acid fragments, suitable for the diagnosis of paucibacillary leprosy
6. Continuing expansion of the variety and supplies of monoclonal antibodies, recombinant DNA vectors, T-cell clones, and natural antigens for the fostering of cooperative research
7. Continuation of animal model and human studies on the modulation of host response to innovative chemotherapy, natural recombinant antigens, adjuvants, and lymphokines
8. Continuation of efforts using animal models to explore the efficacy of pure antigens/epitopes in conferring protective immunity.

Five-Year Summary

Broad Goals

At the end of the 1980's, the Leprosy Panels defined several goals.

1. Definition of the immunogenic proteins of the leprosy bacillus and development of recombinant DNA vectors for the production of defined antigens
2. Identification of individual T- and B-cell epitopes of M. leprae antigens
3. Characterization of the cell wall components of M. leprae with a view to isolating and identifying the suppression-inducing and the helper/ protection inducing epitopes
4. Exploration of the genome of M. leprae with a view to mapping genes of interest
5. Development of assays, based on antibody or antigen detection or the recognition of nucleic acid fragments, that would be suitable for the early diagnosis of leprosy
6. Supply of materials for cooperative research
7. Development of animal models and human studies on the modulation of host response to innovative chemotherapy, natural and recombinant antigens, adjuvants, and lymphokines.

Developments toward achieving these goals at the immunological and molecular level have been remarkable. However, the dramatic decrease in the incidence of leprosy over the past 5 years and the shifting of researchers to the more pressing problem of tuberculosis have necessitated a contraction and re-focusing of effort on

• The development of tests for early diagnosis and the epidemiological monitoring of disease
• Fundamental immunological understanding of the basis of neuropathy, reactions, and disabilities, and development of new interventions
• Sequencing of the M. leprae genome as the means of defining antigens, effectors of pathogenesis, and the basis of the obligate intracellular nature of M. leprae
• Study of the T-cells and cytokine response in leprosy lesions as a model of immune regulation in the epidermis of humans.

Progress/Accomplishments

Developments Vis-A-Vis the Decline of Leprosy

The dominant development in leprosy during the past 5 years is the dramatic decline in worldwide prevalence from a figure of 5.5 million cases in 1991 to 2.3 million in 1994. The initial dramatic drop was attributed to the medical redefinition of leprosy and to eliminating those socio-economical factors that contributed to the development of leprosy in Europe in the 1800's. It is now clear, however, that the aggressive use of multidrug therapy and the more efficient detection of active cases, combined with improved socioeconomical conditions in endemic areas, are major factors in the continued decline of leprosy. As yet no predisposing relationships between HIV infection and leprosy have been observed, and relapse/drug resistance (with a cumulative failure/relapse rate of less than 1 percent over a 9-year follow-up period) is not a problem. Members of the Leprosy Panels have contributed to these successful developments as epidemiologists, the design of the early drug combinations, initial testing of the mouse footpad/challenge assay and its wide-spread use, and the design of several successful alternative drug regimens. Effective sub-unit leprosy vaccines also were identified by means of the mouse footpad/challenge assay. However, small-scale initials human trial with heat-killed M. leprae proved to be disappointing, and the results of more extensive clinical trials with heterologous strains of Mycobacterium are contemplated.

In the absence of effective tests for early/sub-clinical leprosy, there is little information on the incidence of total disease, although we know that the number of new cases continues to rise at the rate of about 650,000 per year. The development of tests for the early diagnosis of leprosy and for charting its epidemiology are now the greatest needs. Intensive efforts over the past 5 years to develop serological tests, based on the specific phenolic glycolipid and other carbohydrate and protein antigens, reveal that such tests are insensitive and too difficult to apply for epidemiological purposes. However, they may have clinical uses. Protocols based on gene amplification in biopsy specimens and nasal swabs likewise did not have the requisite sensitivity. Current research efforts are focused on the development of skin test antigens (a "leprosy PPD"). Phase I trials are pending. Currently, there are about 3 million individuals suffering from various forms of neurological reactions and nerve damage (neuropathy). One important observation is that leprosy patients undergoing type 2 reactions generate antibodies that are selective for epitopes of the M. leprae LSR antigen (a 15 kDa protein), and that this test is prognostic for various neuropathies. Important developments have been made in studying the effects of thalidomide in alleviating erythema nodosum leprosum (ENL). Thalidomide therapy reduces not only serum TNF-alpha levels, but also the dermal infiltration of polymorphonuclear leukocyte T cells and TNF-alpha+ cells. This clearly demonstrates that the alleviation of clinical symptoms of ENL by thalidomide is linked to a reduction in TNF-alpha levels.

Thus, the Joint U.S.-Japan Leprosy Program, through its Panel members, participants, collaborations, and leadership, has been in the forefront of highly successful global efforts to reduce the prevalence of symptomatic leprosy, to develop epidemiological and diagnostic tools to measure incidence of asymptomatic disease, and to alleviate nerve damage often associated with such disease.

Basic Developments in the Molecular Biology and Immunology of Leprosy

The Leprosy Panels have always excelled in fostering the development of fundamental concepts of molecular biology with respect to M. leprae as an intracellular parasitism and the exceptional immunological and pathological characteristics of leprosy. Foremost among these developments over the past 5 years is the M. leprae genome project. The relatively small 2.8- megabase genome is now represented in 140 clones in four contigs. About 60 percent of those clones have been sequenced. The most surprising outcome is that there are very few genes in the M. leprae chromosome (less than 40 percent of the coding capacity). Thus, it is very likely that the proteins encoded by these are key "virulent factors" and are responsible for the tropism of M. leprae for Schwann cells, its obligate intracellularism, and its failure to grow in axenic culture. The majority of these gene products already have been identified. The theme emerging from this molecular approach is the existence of unique, perhaps deficient, pathways for handling "stress" (oxygen deficiency and heat), Fe and other metals, transport systems, and metabolic control. The dominant proteins of M. leprae are few and have been identified as the 10.8 kDa and 65 kDa small and large stress proteins, the 28 kDa superoxide dismutase, the 22 kDa bacterioferritin responsible for the secretion of thousands of atoms of Fe, and a 35 kDa protein with similarities to some sporulation proteins. Thus, it is felt that this molecular approach, rather than continuing to force axenic growth, will provide the answers as to why M. leprae is an obligate parasite. Moreover, the full definition of the major antigens of M. leprae has been achieved (a goal considered unrealistic a few years ago), paving the way for new diagnostics (e.g., specific skin test antigens and vaccines, if ever required).

Considerable progress also was made in understanding the mechanism for regulating cell-mediated immunity throughout the disease process. Leprosy, especially within the dermal regions where the disease takes hold, provides a human paradigm for Th1-Th2 immune response. At one point in the disease process, patients with tuberculoid leprosy are able to restrict growth of the mycobacterium. Here, their skin lesions are characterized by the predominance of CD4+ T cells and type 1 cytokines, especially interleukin 2 and interferon-y. At the opposite extreme in the disease process, patients with lepromatous leprosy are unable to contain the infection. Here, their skin lesions are characterized by the predominance of CD8+ T cells and type 2 cytokines, including interleukins 4 and 10. A key factor in regulating the precise cytokine/cellular response elicited is interleukin 12, which causes the selective expansion of CD4+ T cells and increases T-cell interferon-( production. Another factor that may contribute to the immunological and molecular balance between Th1-Th2/ immunoprotection-immunopathogenesis is the dominance of "special" T cells bearing alphaß receptors but devoid of the accessory molecular CD4 and CD8 in the lepromatous lesions. It now appears that these cells selectively recognize "good" antigens, i.e., those that promote cell-mediated immunity. The search for counteracting "immunosuppressive" cells and antigens continues. In general, these results, combined with the success of thalidomide-like products in counteracting pathological reactions, make the likelihood of devising specific immunologic interventions for aspects of leprosy pathology a realistic possibility.

Future Goals

The reality that leprosy is a rapidly declining disease raises special challenges and goals within the leprosy research community and the U.S.-Japan Cooperative Medical Sciences Program. Research should evolve in a few directions to address the need for a test/tool to detect pre-clinical/single lesional leprosy; measure disease incidence; understand the basis of the immunopathogenesis of nerve damage/reactions; develop innovative therapeutics; address the immunology and molecular biology of M. leprae, notably sequencing of the genome and further defining the immune response; and maintain a research infrastructure in case the optimistic predictions on the continuing effectiveness of multiple drug therapy, the insignificance of relapse, and the lack of a relationship between HIV and leprosy all should prove faulty. In this respect, research should evolve in four highly focused directions. It should:

1. Continue development of new drug combinations
2. Continue research on new early diagnostic and epidemiological tools, particularly skin test antigens
3. Continue research toward a basic understanding of the factors that regulate T-cell and cytokine responses in leprosy, particularly the Th1/Th2 paradigm, with an emphasis on examining those factors that alleviate pathogenesis of leprosy
4. Continue efforts to define the M. leprae genome and phenotype, particularly the nature of expressed proteins that govern the intracellular fate of M. leprae and the ultimate progression of disease
5. Maintain a research and material infrastructure (including a source of bacillus, antigens, antibodies, genetic tools, special facilities, such as nude mice and armadillo colonies, and mouse footpad capabilities) in case the goal of "eliminating leprosy" is not realized.

It is believed that these future goals can best be accomplished by a continuing evolution of the ongoing interaction with the Tuberculosis Panels.

Selected References

1. Gelber RH, Mehra V, Bloom B, Murray LP, Siu P, Tsang M, Brennan PJ. Vaccination with pure Mycobacterium leprae proteins inhibits M. leprae multiplication in mouse footpads. Infect Immun 1994; 62:4250-5.
2. Honore N, Bergh S, Chanteau S, Doucet-Populaire F, Eiglmeier K, Garnier T, Georges C, Launois P, Limpaiboon T, Newton S, Niang K, del Portillo P, Ramesh GR, Reddi P, Ridel PR, Sittisombut N, Wu-Hunter S, Cole ST. Nucleotide sequence of the first cosmid from the Mycobacterium leprosy genome project: Structure and function of the Rif-Str regions. Mol Microbiol 1993; 7:207-14.
3. Mehra V, Bloom BR, Bajardi AC, Sieling PA, Grisso CL, Sieling PA, Alland D, Convit J, Fan X, Hunter SW, Rea TH, Brennan PJ, Modlin L. A major T cell antigen of Mycobacterium leprae is a 10-kD heat-shock cognate protein. J Exp Med 1992; 175:275-84.
4. Modlin RL. Th1-Th2 paradigm: Insights from leprosy. J Invest Dermatol 1994; 102:828-32.
5. Moreira AL, Sampaio EP, Zmuidzinas A, Frindt P, Smith KA, Kaplan G. Thalidomide exerts its inhibitory action on tumor necrosis factor" by enhancing mRNA degradation. J Exp Med 1993; 177:1675-80.

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