(104a) Engineering Interleukin-2 For The Inhibition Of Regulatory T Cells

CD4⁺ CD25⁺ regulatory T cells suppress
the immune system and help to maintain self tolerance and prevent autoimmune
disease in healthy patients.  However, their suppressive activity also has
undesirable consequences during cancer.  In many cancer patients, there exist
effector T cells that recognize tumor antigens, but their ability to attack and
eradicate the cancer is hindered by regulatory T cells in the body.  Therefore,
if the suppressive function of regulatory T cells can be inhibited, this could
give rise to a more potent anti-tumor immune response, which could have
significant benefits in cancer immunotherapy.

Regulatory T cells require IL-2 for their expansion,
maintenance and suppressive abilities.  Here, we propose the use of IL-2
antagonists as a novel approach to inhibiting regulatory T cells.  Using
recently published crystal structures, we identified candidate mutations to
disrupt binding to the β or γ subunits of the IL-2 receptor. 
Inserting these mutations on an IL-2 variant with high affinity binding to CD25
(equivalent to IL-2Rα, the α subunit of the IL-2 receptor) would
create a signaling deficient IL-2 analogue that sequesters IL-2Rα from
binding wild type IL-2, thus antagonizing the IL-2 receptor. We have expressed
and purified two variants with residue substitutions that disrupt the β
and γ subunit binding interfaces and characterized them in a
non-regulatory T cell line that expresses the IL-2 receptor.  These mutants
retain their high affinity binding to IL-2Rα, and do not agonize the IL-2
receptor.  The two mutants also antagonize the IL-2 receptor with equal
efficacy.  We believe that these mutants and this general approach of
engineering IL-2 antagonists show promise for the inhibition of regulatory T
cells for cancer immunotherapy.