JAK and mTOR inhibitors prevent cytokine release while retaining T cell bispecific antibody in vivo efficacy

BACKGROUND: T cell engaging therapies, like chimeric antigen receptor T cells and T cell bispecific antibodies (TCBs), efficiently redirect T cells towards tumor cells, facilitating the formation of a cytotoxic synapse and resulting in subsequent tumor cell killing, a process that is accompanied by the release of cytokines. Despite their promising efficacy in the clinic, treatment with TCBs is associated with a risk of cytokine release syndrome (CRS). The aim of this study was to identify small molecules able to mitigate cytokine release while retaining T cell-mediated tumor killing. METHODS: By screening a library of 52 Food and Drug Administration approved kinase inhibitors for their impact on T cell proliferation and cytokine release after CD3 stimulation, we identified mTOR, JAK and Src kinases inhibitors as potential candidates to modulate TCB-mediated cytokine release at pharmacologically active doses. Using an in vitro model of target cell killing by human peripheral blood mononuclear cells, we assessed the effects of mTOR, JAK and Src kinase inhibitors combined with 2+1 T cell bispecific antibodies (TCBs) including CEA-TCB and CD19-TCB on T cell activation, proliferation and target cell killing measured by flow cytometry and cytokine release measured by Luminex. The combination of mTOR, JAK and Src kinase inhibitors together with CD19-TCB was evaluated in vivo in non-tumor bearing stem cell humanized NSG mice in terms of B cell depletion and in a lymphoma patient-derived xenograft (PDX) model in humanized NSG mice in terms of antitumor efficacy. RESULTS: The effect of Src inhibitors differed from those of mTOR and JAK inhibitors with the suppression of CD19-TCB-induced tumor cell lysis in vitro, whereas mTOR and JAK inhibitors primarily affected TCB-mediated cytokine release. Importantly, we confirmed in vivo that Src, JAK and mTOR inhibitors strongly reduced CD19-TCB-induced cytokine release. In humanized NSG mice, continuous treatment with a Src inhibitor prevented CD19-TCB-mediated B cell depletion in contrast to mTOR and JAK inhibitors, which retained CD19-TCB efficacy. Ultimately, transient treatment with Src, mTOR and JAK inhibitors minimally interfered with antitumor efficacy in a lymphoma PDX model. CONCLUSIONS: Taken together, these data support further evaluation of the use of Src, JAK and mTOR inhibitors as prophylactic treatment to prevent occurrence of CRS.