Julien Flament1,2, Claire-Maëlle Fovet1,3, Lev Stimmer1,3, Philippe Hantraye1,2,4, and Ché Serguera1,2
1CEA/DSV/I2BM/MIRCen, Fontenay-aux-Roses, France, 2INSERM UMS 27, Fontenay-aux-Roses, France, 3INSERM UMR 1169, Fontenay-aux-Roses, France, 4CNRS Université Paris-Saclay UMR 9199, Fontenay-aux-Roses, France
Synopsis
Acquired demyelinating diseases are a major cause of
neurological disabilities. If Experimental Autoimmune Encephalomyelitis (EAE)
model has been widely used in rodents, it does not recapitulate disease
variability observed in humans. We propose for the first time a primate model
of EAE without immunomodulatory treatment in Macaca fascicularis which exhibited a more developed immune system
than rodents. All monkeys developed MRI visible lesions that were significantly correlated to clinical signs onset. Our longitudinal follow up allows a precise
monitoring of lesions and may offer the opportunity to better understand
biological and physiological processes underlying the pathology of
demyelinating diseases. Target audience
This work should
be of interest to all persons using animal models to study Multiple Sclerosis and Acquired Demyelinating Diseases.
Purpose
Acquired
demyelinating diseases are a major cause of neurological disabilities with an
incidence of about 7/100 000
1 in western Europe. Demyelinating diseases are mainly monophasic
with one attack and no relapse, such as acute demyelinating encephalomyelitis (ADEM), but 30% evolve in multiphasic pathologies such as multiple sclerosis (MS). Experimental Autoimmune
Encephalomyelitis (EAE) model has been widely used as a generic model of MS, especially in rodents
2. In contrast to the human immune
system, laboratory germ-free or gnotobiotic mice exhibit an immature and naive immune system.
Consequently, the relevance of this simplistic EAE rodent model has been often
criticized. Here, we propose a new Non-Human Primate (NHP) model of EAE in
Macaca fascicularis3 which
exhibite a more developed immune system and are biologically close to the
human.
Material and Methods
Animal model: 8 adult monkeys were induced with recombinant human myelin
oligodendrocyte glycoprotein (rhMOG) formulated in incomplete Freund’s adjuvant
(IFA)4. Immunogen was injected intradermally into the dorsal skin in
6 spots of 100μl each. Immunizations were repeated every 28 days until clinical
signs.
Clinical score: Monkeys were observed every day and clinical signs were scored using a
semi-quantitative scale from 0 to 5 (with respect to signs severity)5.
Endpoints based on maximum cumulative discomfort have been defined as the end
of the experimentation.
MRI: Images were acquired
on a 7T Agilent magnet. Turbo-Spin-Echo sequence was used to acquire T2-weighted
images (resolution=450μm2, 1.5mm thickness). FLAIR images were
acquired with an inversion time of 1450ms. A rapid T1-weighted
Gradient-Echo sequence was used to acquire images pre and post-gadolinium (Gd)
contrast agent intraveinous injection (0.1 mmolL/kg). T2 maps were obtained using
Multi-Echos-Multi-Slices sequence (10 echo times, TE1 = 15 ms and
echo-spacing of 15 ms).
Results
All monkeys immunized with rhMOG/IFA developed
EAE with clinical signs and brain lesions within 60 days post-immunization (dpi). We observed 70% of fulminent forms and 30% of relapsing-remitting forms. An example of clinical score time-course
is shown (Fig.1a). MRI sessions and corresponding image were represented by
colored arrows (Fig.1b). Clinical signs onset at 67 dpi was correlated with lesion onset (red arrow). Animal
was sacrificed at 290 dpi due to high clinical signs (grade 5) and ex-vivo MRI revealed a massive demyelinated and edematous lesion
through the brain (Fig.1b, orange image). Two other examples of white matter lesions
are shown (Fig.2). Lesion follow-up was performed using T
2-mapping
(Fig.3). T
2 maps were acquired before immunization (t
0),
and at 21 (t
1), 32 (t
2), 36 (t
3) and 42 (t
4)
dpi. If lesion was visible on T
2-weighted images (Fig.3, top panel, white
box), it was enhanced on T
2 maps (Fig.3, middle panel). Differences
between T
2 map at time ti and baseline T
2 map were also performed for each time point. A zoom in the lesion region is shown (Fig.3,
bottom panel, white box). Lesion detection was eased on difference images,
especially at t
3 and t
4. Difference maps revealed
heterogeneity with distinguishable core and rim in the lesion with various T
2
values.
Discussion and
Conclusion
This study proposes for the first time a monkey EAE
model of demyelinating diseases without immunomodulatory treatment
6. Our MRI protocol helps in discriminating nature of the lesion as on FLAIR sequence, only the central
part of the lesion remained hyperintense indicating a demyelination, whereas
the border was probably due to edema. Post Gd-injection images showed recently
active lesions, where the blood-brain barrier (BBB) was disrupted. Our approach
of longitudinal follow up of lesion based on a quantitative parameter (T
2
value) associated with an individual realignment of each T
2 map of
each animal should allow an automated detection of lesion load without
subjective bias due to misinterpretation of T
2 weighted images. The
development of a NHP model of EAE is a valuable tool for basic and clinical
research. It offers the opportunity to better understand biological and
physiological processes underlying the pathology of demyelinating diseases.
Moreover, this model could constitute an appropriate tool for preclinical
evaluation of new therapeutic strategies with disease follow-up using MRI.
Acknowledgements
No acknowledgement found.References
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