A fusion protein composed of a monoclonal antibody directed against the immunosuppressive ligand programmed cell death-1 ligand 1 (PD-L1; cluster of differentiation 274; CD274) fused to the immunostimulatory cytokine interleukin-15 (IL-15), with potential immunostimulatory and antineoplastic activities. Upon administration of the anti-PD-L1/IL-15 fusion protein KD033, the anti-PD-L1 antibody moiety specifically targets and binds to PD-L1 expressing cells in the tumor microenvironment (TME). In turn, IL-15 stimulates the proliferation of natural killer (NK) cells, cytotoxic T-lymphocytes (CTLs) and memory T-cells locally in the TME, which induces an anti-tumor immune response. This may increase tumor cell killing and decrease tumor cell proliferation. IL-15 regulates CD8+ T and NK cell development, activation and proliferation. PD-L1, a transmembrane protein, is expressed on the surface of antigen presenting cells (APCs) and on many cancer cell types. PD-L1 binding to PD-1, a negative regulator of the immune system on activated T-cells, limits the expansion and survival of CD8-positive T-cells, suppresses the immune system and results in immune evasion.