Download Aptamer-targeted inhibition of mTOR in T cells enhances antitumor

Aptamer-targeted inhibition of
mTOR in T cells enhances
antitumor immunity
Alexey Berezhnoy, Iris Castro, Agata Levay, Thomas R. Malek, and Eli
Gilboa
J Clin Invest. 2014;124(1):188–197
Background (siRNA)
• siRNA (small interfering RNA) - ability to inhibit
target genes
• Aptamer - oligonucleic acid molecules that bind
to a target molecule.
• Aptamer-siRNA conjugate - delivery vehicle
composed of a targeting part (aptamer) and a
therapeutic part (siRNA).
Background (T Cells)
• Memory T cells – T cells that have
encountered and responded to their
specific antigen.
• They can recognize invaders and at a 2nd
encounter can reproduce to mount a
faster and stronger immune
response than the 1st time.
Background
• Elevated levels of mTOR promote the accumulation of short-lived
effectors rather than memory cells.
• Pharmacological agents can have undesirable effects due to their
broad range
Aim of the study
Aptamer-targeted siRNA inhibition of mTOR in CD8+ T
cells enhances a vaccine-induced memory and an
antitumor immunity that is superior to pharmacological
treatment.
Methods
• siRNA specific to raptor (a component of mTORC1)
• Aptamer that binds to 4-1BB, a molecule that is expressed on CD8+ T
cells
Test if siRNA
inhibits mTORC1
activity.
Test if mTOR
inhibition causes
formation of
memory CD8+ T cell
Test if siRNA can
enhance vaccineinduced memory
responses
Methods
• Goal: 4-1BB-raptor is capable of inhibiting mTOR activity
• OT-I cells transferred into mice, and mice vaccinated with
OVA peptide and then treated with:
• rapamycin
• 4-1BB aptamer-GFP siRNA (4-1BB-GFP)
• 4-1BB aptamer-raptor siRNA (4-1BB-raptor)
• mTORC activity measured
Results
•
The 4-1BB-raptor conjugate
inhibited the activity of
mTORC1, but not mTORC2,
•
Rapamycin inhibited both
mTOR complexes.
•
The target specificity of
raptor siRNA inhibition is
shown
Methods
• Goal: mTOR inhibition leads to the generation of enhanced memory
CD8+ T cell responses
• OT-I cells transferred into mice, mice vaccinated with OVA peptide
and then treated with:
• rapamycin
• 4-1BB aptamer-GFP siRNA (4-1BB-GFP)
• 4-1BB aptamer-raptor siRNA (4-1BB-raptor)
• Cells were analyzed by flow cytometry.
• Cells treated with rapamycin
or 4-1BB-raptor have greater
CD62Lhi CD44hi or
CD62LhiCD127hi phenotype.
• Phenotypes show an
enhanced potential to
develop into memory cells.
Methods
• Goal: 4-1BB-raptor can enhance vaccine-induced memory responses
• Mice were vaccinated with B16 melanoma cells (GVAX) and then
treated with:
• Rapamycin
• 4-1BB aptamer-GFP siRNA conjugate (4-1BB-GFP)
• 4-1BB aptamer-raptor siRNA conjugate (4-1BB-raptor)
• Then, on day 50, the mice were challenged with parental B16 tumor
cells and survival was determined
Results
• Treatment with 4-1BB-raptor
enhanced GVAX-induced
antitumor immunity.
• Rapamycin is less effective at
promoting memory responses
and has less antitumor
immunity
Author’s Interpretation
• siRNA inhibition of mTORC1 enhances vaccine-induced immunity.
• Aptamer-targeted siRNA superior to rapamycin in terms of protective
antitumor immunity in mice.
• Rapamycin inhibits mTORC1 and mTORC2. Since mTORC2 is in cell
survival, and glucose homeostasis, inhibition could be harmful
• Cell targeting reduces dose of siRNA needed, reducing the risk of
nonspecific immune activation
Critique
• Side-effects of inhibition of mTOR on other cellular processes was not
examined
• Enhancement of memory T-cells not directly measured
• Mechanism of the immune response in the enhancement of
antitumor immunity still needs to be investigated
• 4-11B expression is upregulated on cells other than CD8+ so more
specific targeting receptors will improve the specificity
• Currently, only in mouse model, no human studies conducted so
therapeutic applications not completely confirmed
Questions?