A bioactive soluble recombinant mouse LIGHT promotes effective tumor immune cell infiltration delaying tumor growth.

The TNF family member LIGHT (TNFSF14) binds to two receptors, HVEM (TNFSFR14) and LTβR (TNFSFR3). HVEM functions as a costimulatory molecule, whereas LTβR is involved in the development of lymph nodes and ectopic tertiary lymphoid structures at chronic inflammation sites. The classical approach of fusing soluble recombinant proteins to the Fc fragment of IgG resulted in a functionally inactive Ig.mouse (m) LIGHT protein. However, in line with the fact that TNF family members cluster receptors as trimers, addition of a small homotrimeric domain (foldon) N-terminal of mLIGHT produced an Ig.Foldon-mLIGHT protein able to bind and engage HVEM and LTβR in a cell-based reporter bioassay. In the tumor model of B16.F10 melanoma cells implanted into syngeneic recipients, cells transduced with membrane-bound mLIGHT grew as aggressively as mock-transduced cells, but growth of tumors of B16.F10 cells expressing Ig.Foldon-mLIGHT was delayed and characterized by significant immune infiltration of dendritic cells and cytotoxic cells. This work unveils the potential of active soluble LIGHT, as a single agent, to recruit cytotoxic cells and dendritic cells at the tumor site to inhibit tumor growth. This effect may be further enhanced with immune checkpoint blockade therapies. KEY MESSAGES: The classical approach of fusing soluble recombinant proteins to the Fc fragment of IgG resulted in a functionally inactive Ig.mouse (m) LIGHT (TNFSF14) protein. The addition of a small homotrimeric domain (foldon) N-terminal of mouse LIGHT produces a proper folded bioactive mouse LIGHT recombinant protein. Constitutive intratumor expression of secreted Ig-Foldon-LIGHT, but not membrane LIGHT, delays tumor growth. Tumors secreting LIGHT, as a single agent, promote beneficial anti-tumor responses through the recruitment and infiltration of cytotoxic cells and dendritic cells.