Human Orthogonal IL-2/IL-2Rβ As a Tunable Approach to Enhance CD19-Speific CAR-T Cell Antitumor Activity

Immunotherapy using T cells engineered with a chimeric antigen receptors (CAR) can produce deep and durable control of B-cell malignancies that is associated with the engraftment and persistence of the CAR T cells following adoptive transfer. Interleukin-2 (IL-2) is a central T cell cytokine that promotes T cell proliferation and effector function with a potential to enhance CAR T cell immunotherapy; however, the use of recombinant IL-2 to support T cell immunotherapy is limited by the significant toxicity associated with IL-2 infusion. Previous work has demonstrated the feasibility of engineering murine IL-2 and it's receptor to create an orthogonal (ortho) cytokine-receptor pair capable of delivering IL-2's signal without the associated toxicity (Sockolosky JT et al. Science 2018). In order to translate this novel approach to humans, we engineered a human orthogonal IL-2 (ortho-hIL-2) and human orthogonal IL-2Rβ (ortho-hIL-2Rβ) pair based upon similar mutations to those required in the murine system. We show that hoIL-2 induces JAK-STAT signaling and supports proliferation of the IL-2 dependent cutaneous T-cell lymphoma (CTCL) line, SeAx, and primary human CD8+ primary T cells when hoIL-2Rb is expressed in these cells. HoIL-2 at concentrations 1000-fold higher than wild-type IL-2 failed to induce signaling in the absence of the orthogonal receptor illustrating the high selectivity of ortho-hIL-2 for the ortho-hIL-2Rβ. Using a CD19-specific, 4-1BB-costimulated CAR T cell (CART19), we show that ortho-hIL-2 induced a dose-dependent increase in ortho-hIL-2Rβ CAR-T cell expansion and serum cytokines in vivo by as much as 1000-fold at 2 weeks following adoptive transfer into NSG mice bearing CD19+ Nalm6 leukemia xenografts and daily ortho-hIL-2 treatment. We further demonstrate that hoIL-2 can rescue the anti-leukemic effect of an otherwise suboptimal CAR T cell dose. In addition to augmenting initial CAR T cell engraftment and efficacy, we also show that ortho-hIL-2 administration initiated at the time of leukemic relapse following CAR T cell therapy can rescue an otherwise failed anti-leukemic response. In aggregate, these data demonstrate the ability of the human orthogonal IL-2 cytokine-receptor system to support T cell expansion in vivo and the potential of combining this approach with CAR T cell immunotherapy to augment the anti-tumor efficacy of engineered T cells.