Abstract 5743: Reprogramming myeloid cells by JAK inhibition to enhance checkpoint blockade immunotherapy
Authors: Zak Jaroslav , Pratumchai Isaraphorn , Marro Brett S. , Marquardt Kristi L. , Oldstone Michael B. , Varner Judith A. , Bachanova Veronika , Teijaro John R. 
Published: April 2023

Background: Checkpoint inhibitors have achieved a wide adoption for treatment of advanced cancer, but the majority of patients fail to respond. Among the underlying causes are redundant mechanisms driving cytotoxic lymphocyte dysfunction. Motivated by the discovery of JAK inhibitors as hit compounds in a screen for the reversal of T cell exhaustion, this study investigates the hypothesis that JAK inhibition could enhance the efficacy of checkpoint inhibitors.

Methods: Murine immunocompetent models of cancer were utilized (A20, EL4, LLC1, MC38). The combination therapy of systemic treatment with the JAK inhibitor ruxolitinib with anti-PD1 + anti-CTLA4 was evaluated for efficacy and biomarkers compared to checkpoint inhibitors (ICI) alone. Tumor-infiltrating, blood and lymphoid organ immune cells were phenotyped using single-cell transcriptomics, functional assays and flow cytometry. The combination therapy was clinically tested in an investigator-initiated Phase I/II clinical trial of ruxolitinib with nivolumab in relapsed or refractory Hodgkin lymphoma (NCT03681561). Patients who previously failed to respond to ICI received ruxolitinib for 1 week then nivolumab every 4 weeks concurrent with ruxolitinib twice daily. Peripheral blood was collected at baseline, 1 week after ruxolitinib and 4 weeks after 1st nivolumab dose. Hematologic and transcriptomic analyses were performed on peripheral blood samples.

Results: The ruxolitinib + ICI combination was superior to ICI in 3/4 of the tumor models examined in controlling tumor growth. Tumor sizes were reduced by &gt;50% in the MC38 (mean volume 123.1 vs 283.2 mm3, ICI + rux vs ICI, respectively, n=9 per group, ANOVA p=0.0094), LLC1 and A20 models (survival hazard ratio 0.24, ICI + rux vs ICI, n=8 per group, p=0.048). Remarkably, we observed a broad shift of tumor monocytes and granulocytes from a suppressive into an immunostimulatory state characterized by the expression of MHC molecules and the ability to stimulate T cell proliferation. Hodgkin lymphoma patients in the ruxolitinib with nivolumab trial exhibited an interim disease control rate of 76% (13/17). Ruxolitinib treatment in these patients did not impair T cell cytokine production but significantly reduced the neutrophil-to-lymphocyte ratio (NLR, mean difference -0.82, n=14, p=0.0023) and the expression of myeloid derived suppressor cell markers in monocytes (normalized enrichment score -1.74, n=14, q&lt;0.001) compared to pre-treatment. The reduction in NLR was significantly greater in complete responders than in progressive disease patients (mean -2.6 vs -0.58, respectively, p=0.023).

Conclusions: The combination of ruxolitinib with ICI was effective in preclinical models of cancer and in a Phase I/II Hodgkin lymphoma clinical trial. Unexpectedly, JAK inhibitor-mediated reprogramming of myeloid cells and the associated enhanced T cell activity may be important for the observed efficacy.

Citation Format: Jaroslav Zak, Isaraphorn Pratumchai, Brett S. Marro, Kristi L. Marquardt, Michael B. Oldstone, Judith A. Varner, Veronika Bachanova, John R. Teijaro. Reprogramming myeloid cells by JAK inhibition to enhance checkpoint blockade immunotherapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5743.