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IL-2 analogues: novel agents circumventing the expansion of T regulatory cells while promoting NK cell activation during IL-2 therapy
© Sim et al; licensee BioMed Central Ltd. 2013
Published: 7 November 2013
High dose (HD) IL-2 treatment is a potent form of immunotherapy that can induce durable complete responses in a fraction of metastatic melanoma patients. Its initial purpose was to activate the expansion and anti-tumor responses of NK cells. However, the efficacy of HD IL-2 in achieving this has been relatively limited due to two main reasons. First, IL-2 preferentially expands CD4+CD25+Foxp3+ T-regulatory cells (Tregs) constitutively expressing the high affinity IL-2R consisting of CD25 together with the IL-2Rβ and the common gamma chain rather than NK cells and effector T cells that are mostly CD25-negative and express mostly the IL-2Rβγ lower affinity receptor. In particular, we found that a highly suppressive CD25hi Treg subset expressing ICOS expands the most in response to IL-2. Second, HD IL-2 can be highly toxic by causing vascular leak syndrome due to a surge in pro-inflammatory cytokines and by its indirect activation of CD25 expressing endothelial cells facilitating NO release. Here, we characterized whether a mutant form of IL-2 (F42K) that preferentially binds to the lower affinity IL-2Rβγ complex can be an alternative to wild-type (WT) IL-2 therapy. We first tested the effects of equivalent concentrations of WT IL-2 on PBMC from healthy donors and melanoma patients for 6 or 14 days in vitro. F42K-treated PBMC produced much lower pro-inflammatory cytokines such as IL-6, IL-1α and IFN-γ, and VEGF than WT IL-2. Importantly, F42K selectively expanded NK cells with a decreased expansion of ICOS+ Tregs. In comparison to treatment with WT IL-2, F42K also induced increased NK cell activation by up-regulating the NK activation markers NKp30, NKp44 and TIM-3, but not NKG2D, CD226 and inhibitory KIR molecules such as CD158a and CD158b. F42K also enhanced survival of these highly activated NK cells and prevented apoptosis by inducing a higher expression of Bcl2 than WT IL-2. Furthermore, F42K increased NK cell cytotoxicity against breast cancer and melanoma cells than WT IL-2 associated with TRAIL and granulysin up-regulation in both CD56hi and cytotoxic CD16+CD56+ NK cell subsets. Using a hydrodynamic gene therapy (HGT) approach, C57BL/6 mice treated with plasmids encoding F42K had an earlier, more robust and persistent NK cell expansion in vivo with a dramatic reduction in the expansion of CD4+CD25+Foxp3+Tregs than WT IL-2 plasmid therapy. Lastly, we found that F42K was equally able to expand TILs from melanoma patients as WT IL-2. Our results suggest that F42K has great potential as a non-toxic substitute for WT IL-2 as a cytokine therapy for cancer by potently activating NK cells without Treg expansion either as a monotherapy or in combination with other therapies such as adoptive cell therapy.
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.