Sensitizing solid tumors to immunotherapy by bispecific nano conjugate

Introduction: Immunotherapy has revolutionized cancer treatment in the past decade. However, the response rates to immunotherapy in solid tumors are not as high as hematological malignancies. Part of the reasons of the disparity in response might be the unique immunological molecule expression patterns of different tumors. It is possible that the recognition of solid or hematological malignancies by the immune cells are mediated by different molecules. It is recently discovered that the signaling lymphocytic activation molecule family member 7 (SLAMF7) is the molecule that can stimulate the phagocytosis of cancer cells by macrophages, and it is expressed almost exclusively on hematological cancer cells but not on solid cancer cells. This unique molecule may stimulate strong responses in immune cells. We hypothesize that the decoration of SLAMF7 on solid cancer cells can resemble some characteristics of hematological cancers and enhance its visibility by the immune system, therefore eventually sensitize the tumor to immunotherapy. We try to accomplish this by conjugating nanoparticles with cancer-specific antibodies and SLAMF7 proteins to generate a bispecific nanoconjugate.



Materials and Methods: We conjugated anti-HER2 monoclonal antibody and recombinant SLAMF7 proteins to poly(ethylene glycol)-poly(D,L-lactic-co-glycolic acid) (PEG-PLGA) nanoparticles. The success of conjugation was verified by measurement of particle size and gel electrophoresis. The HER2-SLAMF7 bispecific nanoconjugate was used to treat various cancer cell lines and co-cultured with macrophages. Flow cytometry and immunofluorescent staining was used to examine the phagocytosis and antigen presentation as well as the activation of immune-stimulating pathways. Multiple animal models were used to test the anti-tumoral effect of the nanoconjugate. The tumor growth and survival were monitored after the treatment, and serum cytokines were examined by ELISA. Body weight and serum markers for liver and kidney functions were monitored to evaluate the toxicity of the treatment.



Results, Conclusions, and Discussions:


Results


The bispecific nanoconjugate bound to HER2-positive cancer cells and decorated the surface of target cell with SLAMF7. This decoration increased the phagocytosis of cancer cells by macrophages and enhanced the downstream antigen presentation and T-cell priming. The treatment of this nanoconjugate also activated the cyclic guanosine monophosphate–adenosine monophosphate synthase–stimulator of interferon genes (cGAS–STING) pathway in the antigen presentation cells resulting in secretion of immune-stimulation cytokines and activation of pro-inflammatory genes. Animal experiments showed that the HER2-SLAMF7 bispecific nanoconjugate treatment increased cytotoxic lymphocytes infiltration and activation, and stimulated interferon release in the tumor microenvironment without causing significant toxicity. The treatment effectively inhibited both primary and metastatic tumors growth and prolonged the overall survival of the mice. Greater treatment outcome was achieved when the nanoconjugate was combined with other immune checkpoint blockade therapies.




Conclusions


The HER2-SLAMF7 bispecific nanoconjugate can decorate the solid tumors and make them display characteristics like hematological malignancies. Such immunological conversion enhanced the recognition of cancer cells by the antigen presentation cells and sensitized the solid tumor to immunotherapy. The treatment also induced systemic immune response which can inhibit metastatic tumors. In summary, we developed a method to convert the immunological molecules’ expression patterns and sensitize the tumors to immunotherapy.




Discussions


Here we show that the nanoparticles conjugated with anti-HER2 antibody and recombinant SLAMF7 protein can bind to HER2 positive cancer cells and decorate the cell surface with SLAMF7 to significantly improve cancer cell phagocytosis by macrophages and immune activation. This proof-of-concept study highlights nanoconjugate as promising immunotherapy platforms. Our system is also highly versatile, allowing easily switching to different antibodies or recombinant proteins to target different cancers or engage various immune cells or molecules. Currently we are testing different forms of conjugates and their efficacy in additional cancer models.





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