Adjunct antibody administration with standard treatment reduces relapse rates in a murine tuberculosis model of necrotic granulomas

<div><p>Matrix metalloproteinase (MMP)-9 is a zinc-dependent protease associated with early immune responses to <i>Mycobacterium tuberculosis</i> infection, macrophage recruitment and granuloma formation. We evaluated whether adjunctive inhibition of MMP-9 could improve the response to standard TB treatment in a mouse model that develops necrotic lesions. Six weeks after an aerosol infection with <i>M</i>. <i>tuberculosis</i>, C3HeB/FeJ mice received standard TB treatment (12 weeks) comprising rifampin, isoniazid and pyrazinamide alone or in combination with either anti-MMP-9 antibody, etanercept (positive control) or isotype antibody (negative control) for 6 weeks. Anti-MMP-9 and the isotype control had comparable high serum exposures and expected terminal half-life. The relapse rate in mice receiving standard TB treatment was 46.6%. Compared to the standard TB treatment, relapse rates in animals that received adjunctive treatments with anti-MMP-9 antibody or etanercept were significantly decreased to 25.9% (<i>P</i> = 0.006) and 29.8% (<i>P</i> = 0.019) respectively, but were not different from the arm that received the isotype control antibody (25.9%). Immunostaining demonstrated localization of MMP-9 primarily in macrophages in both murine and human lung tissues infected with <i>M</i>. <i>tuberculosis</i>, suggesting the importance of MMP-9 in TB pathogenesis. These data suggest that the relapse rates in <i>M</i>. <i>tuberculosis</i>-infected mice may be non-specifically improved by administration of antibodies in conjunction with standard TB treatments. Future studies are needed to evaluate the mechanism(s) leading to improved outcomes with adjunctive antibody treatments.</p></div

Relapse rates associated with each treatment arm.

<p>Additional cohorts of mice were held for 16 weeks after cessation of treatment to assess for stable, relapse free cure. Results are presented as proportion of mice with any viable bacteria in the lungs. RHZ = standard TB treatment comprising rifampin (R), isoniazid (H) and pyrazinamide (Z) administered by gavage.</p

MMP-9 expression in mouse and human <i>M</i>. <i>tuberculosis</i>-infected tissues.

<p>(A) MMP-9 immunohistochemistry in the lung tissue of a C3HeB/FeJ mouse, 10 weeks after <i>M</i>. <i>tuberculosis</i> aerosol infection. MMP-9 was visualized in macrophages (black solid arrows) and neutrophils (black dotted arrows). (B) Expression of MMP-9 in the human lung tissue with cavitary TB. MMP-9 was expressed in macrophages (black arrow) and multinucleated giant cells (red arrows).</p

Serum concentrations of anti-MMP-9 and isotype control antibodies in mice.

<p>Mean serum concentrations (± SD) from individual mice receiving standard TB treatment in combination with anti-MMP-9 (AB0046, red circle) or isotype control (AB5123, black circle) are depicted. Mice were sacrificed at week 2 (n = 13) and 6 (n = 13) during the dosing phase, and at week 8 (n = 13), 10 (n = 7), and 12 (n = 7) during the antibody elimination phase.</p