Lymphocyte counts in the peripheral immune system and tumor are correlated with positive clinical outcomes in PD-(L)1 immunotherapy. Interleukin7 (IL7) is an immune homeostasis cytokine for T cells.
Treatment with recombinant human IL7 preferentially expands recent thymic emigrants, naïve and central memory T cells, but spares regulatory T cells. Here we constructed a series of immunocytokine L1I7 comprised of a PDL1 blocking mAb fused with an IL7 molecule with varying degrees of attenuated potency. The aim of the study was to identify the right molecule that achieves enhanced biodistribution at the tumor site and an optimal balance between synergistic anti-tumor activity and an acceptable safety profile.
PDL1 binding affinity and antagonist function of L1I7 were evaluated by BiaCore and PD1/PDL1 cell-based functional assay, respectively. IL7 receptor (IL7R) binding and internalization were evaluated in human primary CD4+ T cells by flow cytometry (FACS). IL7 potency was evaluated by p-STAT5 signaling assay and human CD4+ T cell proliferation assay. The in vitro synergistic effect of L1I7 was evaluated in the human mixed lymphocyte reaction (MLR) assay. The in vivo tracking assay was conducted by injecting fluorescence-labeled L1I7 into HCC827-transplanted CD34+ hematopoietic stem cells humanized mice. The in vivo efficacy of L1I7 was investigated in B16F10 melanoma syngeneic mice model with surrogate L1I7. Absolute numbers of tumor-infiltrating CD4+ T and CD8+ T cells were analyzed by FACS.
L1I7 series of immunocytokine maintained PDL1 binding and antagonist function when compared with PDL1 mAb. As compared with wildtype L1I7, L1I7 variants showed attenuated IL7 activity as evidenced by reduced IL7R binding/internalization, p-STAT5 activation and CD4+ T cell proliferation. Both wildtype and the attenuated variants were more effective in promoting CD4 T cell activation than anti-PDL1 or IL7 monotreatment in MLR. Similar with PDL1 mAb, L1I7 was enriched in the tumor site whereas IL7 was widely distributed in in vivo tracking experiment. In an anti-PDL1-resistant B16F10 tumor model, L1I7 showed superior efficacy as compared with either anti-PDL1, IL7 alone or in combination, which was correlated with an increased number of tumor-infiltrating CD4+ T and CD8+ T cells.
The novel immunocytokine L1I7 is designed to target poor and non-responders to PD-(L)1 treatment and even PD-(L)1 treatment relapsed patients. L1I7 represents potentially a best-in-class molecule with enhanced local immunostimulation achieved by concurrent PD-(L)1 blockade and IL7 stimulation. L1I7 is undergoing preclinical development with an aim to enter clinical studies in 2021.