470 Targeting Pan-Tumor Associated Antigen B7H3 via Combination of Tri-specific Killer Engager and Off-the-shelf NK Cell Therapy Enhances Specificity and Function Against a Broad Range of Solid Tumors

BackgroundB7H3 is a tumor associated antigen (TAA), found on numerous malignancies including prostate, lung, and breast cancers. High levels of B7H3 expression are correlated with late stage disease and poor prognosis. Furthermore, B7H3 is minimally expressed on normal tissue, making it an ideal TAA for broad cancer treatment strategy. We developed a tri-specific killer engager (TriKETM) consisting of a nanobody anti-CD16, IL-15, and nanobody anti-B7H3 joined by flexible linkers (camB7H3 TriKE) (figure 1A). The combination of B7H3 TriKE with an off-the-shelf NK cell therapy presents an appealing therapeutic strategy for the treatment of solid tumors with decreased risk of toxicity in allogeneic settings compared to T-cell derived products.MethodsAn anti-B7H3 nanobody was developed via biopanning and cloned into a TriKE vector. TriKE was produced in Expi293 cells and affinity purified using poly-His tag. NK cells were co-incubated with cell lines exhibiting a range of B7H3 expression and with 3nM of camelid B7H3 TriKE or control. We have previously derived NK cells expressing high affinity non-cleavable hnCD16, CD38 KO, and IL-15/IL-15R fusion from clonal master engineered iPSC lines. Engineered iNK cells were tested in conjunction with the TriKE. A repeated measures ANOVA was used for statistical comparisons as noted in figure legendsResultsEngineered iNK cells co-incubated with camB7H3 TriKE and C4-2 prostate cells significantly increased degranulation (CD107a) and cytokine production (IFN-gamma) compared to controls (figure 1B/C, P