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Enhancing the antitumor functions of invariant natural killer T cells using a soluble CD1d-CD19 fusion protein

Rupali Das, Peng Guan, Susan J. Wiener, Nishant P. Patel, Trevor G. Gohl, Elizabeth Evans, Maurice Zauderer and Kim E. Nichols

Key Points

  • The CD1d-CD19 fusion binds to CD19+ targets and, once loaded with αGC, promotes iNKT cell activation.

  • The αGC-loaded CD1d-CD19 fusion induces robust iNKT cell lysis of CD19+ tumor cells in vitro and controls their growth in vivo.

Abstract

Invariant natural killer T (iNKT) cells comprise a unique lineage of CD1d-restricted lipid-reactive T lymphocytes that potently kill tumor cells and exhibit robust immunostimulatory functions. Optimal tumor-directed iNKT cell responses often require expression of the antigen-presenting molecule CD1d on tumors; however, many tumor cells downregulate CD1d and thus evade iNKT cell recognition. We generated a soluble bispecific fusion protein designed to direct iNKT cells to the site of B-cell cancers in a tumor antigen-specific but CD1d-independent manner. This fusion protein is composed of a human CD1d molecule joined to a single chain antibody FV fragment specific for CD19, an antigen widely expressed on B-cell cancers. The CD1d-CD19 fusion protein binds specifically to CD19-expressing, but not CD19-negative cells. Once loaded with the iNKT cell lipid agonist α-galactosyl ceramide (αGC), the CD1d-CD19 fusion induces robust in vitro activation of and cytokine production by human iNKT cells. iNKT cells stimulated by the αGC-loaded CD1d-CD19 fusion also strongly transactivate T-, B-, and NK-cell responses and promote dendritic cell maturation. Importantly, the αGC-loaded fusion induces robust lysis of CD19+CD1d Epstein-Barr virus immortalized human B-lymphoblastoid cell lines that are otherwise resistant to iNKT cell killing. Consistent with these findings; administration of the αGC-loaded fusion protein controlled the growth of CD19+CD1d tumors in vivo, suggesting that it can “link” iNKT cells and CD19+CD1d targets in a therapeutically beneficial manner. Taken together, these preclinical studies demonstrate that this B cell–directed fusion protein can be used to effectively induce iNKT cell antitumor responses in vitro and in vivo.

  • Submitted November 19, 2018.
  • Accepted January 17, 2019.
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