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 LT{beta}R (TNFSFR3). HVEM functions as a costimulatory molecule, whereas LT{beta}R 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 active Ig.Foldon-mLIGHT protein able to bind and engage HVEM and LT{beta}R in a reporter cell-based 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 cell infiltration. 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.