IL-15, the homeostatic factor for NK cells is being clinically developed but it has little antitumor activity alone. We hypothesized that targeted delivery of IL-15 to NK cells along with ADCC would impart NK cells with specificity to tumor antigens. As proof of concept, a clinical trial of GTB-3550 (a CD33-targeted Tri-specific Killer Engager [TriKE] in AML) induced endogenous NK cell expansion and activation in refractory AML patients. Here we developed GTB-5550 (a B7H3 TriKE) as a novel dual camelid (cam) TriKE containing WT IL-15 and comprised of two cam engagers: targeting CD16 on NK cells and B7H3 on multiple solid tumors.
The IL-15 activity of the B7H3 TriKE was measured in proliferation assays. Tumors were incubated with NK cells with or without B7H3 TriKE. In some tumors, CRISPR was used to knockout B7H3 to serve as a specificity control as well as B7H3 negative hematologic tumors. NK cell function was measured by flow cytometry and in live tumor imaging assays.
B7H3 TriKE was titrated onto lymphocytes resulting in a dose-dependent proliferation of NK cells but not T cells. This was in marked contrast to rhIL-15, that stimulated both suggesting different biologic activity of IL-15 when delivered through the camCD16 engager. camB7H3 was broadly expressed on prostate, head and neck, ovarian and glioblastoma cancers as well as multiple myeloma. We observed a B7H3 TriKE dose–dependent increase in CD107a degranulation and inflammatory cytokines to all B7H3 positive targets that was highly specific, with no response seen with B7H3 negative hematologic targets and control lines created with a CRISPR KO of B7H3. Compared to rhIL-15, GTB-5550 given at molar equivalent dosing induced B7H3 killing in in a dose-dependent manner above that seen with rhIL-15 induced natural cytotoxicity. In vivo activity in xenogeneic models of human tumor is underway and already validating our in vitro studies.
B7H3 TriKE delivers an NK cell specific IL-15 signal to expand NK cells and is highly specific against a broad array of cancers. Clinical manufacturing is underway with an IND planned to open clinical trials in 2023 in a number of solid tumors and multiple myeloma.
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University of Minnesota.
J.S. Miller: Financial Interests, Personal and Institutional, Advisory Board, Consulting, research support, stock, royalties: GT Biopharma. G.I. Berk: Financial Interests, Personal, Full or part-time Employment, CMO: GT Biopharma. M. Felices: Financial Interests, Personal and Institutional, Advisory Board, Consulting, research support, stock, royalties: GT Biopharma. All other authors have declared no conflicts of interest.