Features and protective efficacy of human mAbs targeting Mycobacterium tuberculosis arabinomannan
Yanyan Liu, Tingting Chen, Yongqi Zhu, Aisha Furey, Todd L. Lowary, John Chan, Stylianos Bournazos, Jeffrey V. Ravetch, Jacqueline M. Achkar
Yanyan Liu, Tingting Chen, Yongqi Zhu, Aisha Furey, Todd L. Lowary, John Chan, Stylianos Bournazos, Jeffrey V. Ravetch, Jacqueline M. Achkar
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Research Article Immunology Infectious disease

Features and protective efficacy of human mAbs targeting Mycobacterium tuberculosis arabinomannan

Abstract

A better understanding of the epitopes most relevant for antibody-mediated protection against tuberculosis (TB) remains a major knowledge gap. We have shown that human polyclonal IgG against the Mycobacterium tuberculosis (M. tuberculosis) surface glycan arabinomannan (AM) and related lipoarabinomannan (LAM) is protective against TB. To investigate the impact of AM epitope recognition and Fcγ receptor (FcγR) binding on antibody functions against M. tuberculosis, we isolated a high-affinity human monoclonal antibody (mAb; P1AM25) against AM and showed its binding to oligosaccharide (OS) motifs we previously found to be associated with in vitro functions of human polyclonal anti-AM IgG. Human IgG1 P1AM25, but not 2 other high-affinity human IgG1 anti-AM mAbs reactive with different AM OS motifs, enhanced M. tuberculosis phagocytosis by macrophages and reduced intracellular growth in an FcγR-dependent manner. P1AM25 in murine IgG2a, but neither murine IgG1 nor a non–FcγR-binding IgG, given intraperitoneally prior to and after aerosolized M. tuberculosis infection, was protective in C57BL/6 mice. Moreover, we demonstrated the protective efficacy of human IgG1 P1AM25 in passive transfer with M. tuberculosis–infected FcγR-humanized mice. These data enhance our knowledge of the important interplay between both antibody epitope specificity and Fc effector functions in the defense against M. tuberculosis and could inform development of vaccines against TB.

Authors

Yanyan Liu, Tingting Chen, Yongqi Zhu, Aisha Furey, Todd L. Lowary, John Chan, Stylianos Bournazos, Jeffrey V. Ravetch, Jacqueline M. Achkar

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Figure 4

M. tuberculosis intracellular growth is reduced in the presence of mAb P1AM25 but not T1AM09 or L1AM04 and is mediated by enhanced P-L fusion in human macrophages.

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M. tuberculosis intracellular growth is reduced in the presence of mAb ...
(A) M. tuberculosis (H37Rv; MOI 1) intracellular growth rates (CFU of [Day3 – Day1]/Day1) with anti-AM human IgG1 mAbs (5 μg/mL) in THP-1–differentiated human macrophages. An irrelevant human IgG1 mAb is included as an isotype control. Dots and error bars represent mean ± SD of sextuplicates. Data are representative of 2 independent experiments. Dashed line represents 1-way ANOVA. Solid line represents 2-tailed t test. (B) M. tuberculosis (H37Rv; MOI 1) intracellular growth rates in the presence of P1AM25 or control mAb (5 μg/mL) in blood MDMs from 7 different healthy donors. Dots are means of triplicate wells. Error bars represent mean ± SD of 7 donors. Individual colors shown for each donor with P1AM25 correspond to data for the same donor with isotype control mAb. Paired 2-tailed t test. (C) Confocal microscopy images of human MDMs from 2 healthy donors incubated with P1AM25 or an isotype-matched irrelevant IgG1 control mAb (5 μg/mL), followed by infection with Alexa Fluor 488–conjugated H37Rv and labeled with LysoTracker probes. Images show M. tuberculosis (green) localized within phagosomes, lysosomes (red), and colocalization of M. tuberculosis/phagosomes and lysosomes (yellow) indicating P-L fusion. (D) Degree of P-L fusion enhancement by P1AM25 compared with irrelevant isotype-matched control mAb (5 μg/mL). Circles and squares each represent mean P-L fusion data (from triplicate or duplicate wells) from the MDMs of the 2 healthy donors. T test. P-L, phagosome-lysosome.