Anti-PD-L1 antibody monotherapy shows limited efficacy in a significant proportion of the patients. A common explanation for the inefficacy is a lack of anti-tumor effector cells in the tumor microenvironment (TME). Recombinant human interleukin-15 (hIL15), a potent immune stimulant, has been investigated in clinical trial with encouraging results. However, hIL15 is constrained by the short half-life of hIL15 and a relatively unfavorable pharmacokinetics profile. We developed a recombinant fusion IL15 protein composed of human IL15 (hIL15) and albumin binding domain (hIL15-ABD) and explored the therapeutic efficacy and immune regulation of hIL-15, hIL15-ABD and/or combination with anti-PD-L1 on CT26 murine colon cancer (CC) and B16-F10 murine melanoma models. We demonstrated that hIL15-ABD has significant inhibitory effect on the CT26 and B16-F10 tumor growths as compared to hIL-15. hIL-15-ABD not only showed superior half-life and pharmacokinetics data than hIL-15, but also enhance anti-tumor efficacy of antibody against PD-L1 via suppressive effect on accumulation of Tregs and MDSCs and activation of NK and CD8+T cells. Immune suppressive factors including VEGF and IDO were also decreased by combination treatment. hIL15-ABD combined with anti-PD-L1 antibody increased the activity of anti-tumor effector cells involved in both innate and adaptive immunities, decreased the TME’s immunosuppressive cells, and showed greater anti-tumor effect than that of either monotherapy.

Nab-paclitaxel (Abraxane), which is a nanoparticle form of albumin-bound paclitaxel, is one of the standard chemotherapies for pancreatic ductal adenocarcinoma (PDAC).This study determined the effect of Abraxane in combination with a fusion protein, hIL15-ABD, on subcutaneous Panc02 and orthotopic KPC C57BL/6 murine PDAC models. Abraxane combined with hIL15-ABD best suppressed tumour growth and produced a 40%-60% reduction in the tumour size for Panc02 and KPC, compared to the vehicle group. In the combination group, the active form of interferonγ (IFNγ)-secreting CD8 + T cells and CD11b + CD86 + M1 macrophages in tumour infiltrating lymphocytes (TILs) were increased. In the tumour drainage lymph nodes (TDLNs) of the combination group, there was a 18% reduction in CD8 + IFNγ + T cells and a 0.47% reduction in CD4 + CD25 + FOXP3 + regulatory T cells, as opposed to 5.0% and 5.1% reductions, respectively, for the control group. Superior suppression of CD11b + GR-1 + myeloid-derived suppressor cells (MDSCs) and the induction of M1 macrophages in the spleen and bone marrow of mice were found in the combination group. Abraxane and hIL15-ABD effectively suppressed NF-κB-mediated immune suppressive