HIV vaccines induce CD8+ T cells with low antigen receptor sensitivity

Current HIV vaccines designed to stimulate CD8+ T cells have failed to induce immunologic control upon infection. The functions of vaccine-induced HIV-specific CD8+ T cells were investigated here in detail. Cytotoxic capacity was significantly lower than in HIV controllers and was not a consequence of low frequency or unaccumulated functional cytotoxic proteins. Low cytotoxic capacity was attributable to impaired degranulation in response to the low antigen levels present on HIV-infected targets. The vaccine-induced T cell receptor (TCR) repertoire was polyclonal and transduction of these TCRs conferred the same reduced functions. These results define a mechanism accounting for poor antiviral activity induced by these vaccines and suggest that an effective CD8+ T cell response may require a vaccination strategy that drives further TCR clonal selection.

Abstract 3193: Development and functional characterization of NC762, a novel therapeutic antibody targeting B7-H4, for the treatment of malignancies

Human B7 homolog 4 (B7-H4) is a transmembrane protein in the B7 family of molecules that is expressed on tumor cells in the tumor microenvironment (TME). High protein expression on tumors and low expression on healthy tissue makes B7-H4 an attractive molecule for direct targeting with low off-target toxicity. NC762 is a humanized immunoglobulin gamma 1, kappa (IgG1κ) monoclonal antibody specific for human B7-H4 that is being developed for the treatment of cancer and demonstrates an excellent safety profile in IND-enabling studies. The IgG1κ region of NC762 contains three-point mutations (S239D/A330L/I332E a.k.a. DLE) which enhances binding to CD16a (FcγRIIIa) in order to increase antibody-dependent cellular cytotoxicity (ADCC) activity. NC762 binds to human B7-H4 on SKBR3 cells, a breast cancer cell line that endogenously expresses B7-H4 and induces in vitro ADCC activity. Despite the high homology, NC762 does not cross-react with rodent B7-H4, therefore, in vivo testing was performed in a humanized xenograft murine model in NSG mice, where NC762 restricted tumor growth in a dose-dependent manner. Depleting human natural killer (NK) cells prior to tumor inoculation reduced anti-B7-H4 parent antibody activity, supporting a role for NK-cell mediated ADCC in tumor growth retardation. However, in the absence of human PBMCs, NC762 also achieved significant anti-tumor activity. Furthermore, a mutant of NC762 with a low FcγR binding IgG1 domain showed similar activity as the DLE IgG1, demonstrating an ADCC-independent mechanism of tumor growth restriction mediated by B7-H4 mAb treatment. Together, these results indicate that even with the ADCC-enhanced IgG1κ region, NC762 is able to mediate ADCC-independent anti-tumor activity for the eradication of B7-H4 expressing tumors; and is expected to provide benefit in multiple oncology indications.

Citation Format: Kristina Archer, Justine Ceradoy, Tiffany Coupet, Jason Bosiacki, Chang Song, Ido Weiss, Sue Niu, Tete Obot, Jinglin Xu, Tom O'Neill, Alison Ferrell, Hasan Abukharma, Zac Cusumano, Dallas Flies, Sol Langermann, Linda N. Liu. Development and functional characterization of NC762, a novel therapeutic antibody targeting B7-H4, for the treatment of malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3193.

Abstract 1542: Bispecific T cell engager-induced toxicity in an immunocompetent solid tumor model

Chimeric antigen receptor (CAR) T cells and bispecific T cell engagers have demonstrated clinical efficacy, however are often accompanied by severe toxicity including cytokine release syndrome (CRS), neurotoxicity or macrophage activation syndrome (MAS). Mechanistic understanding of the development of these toxicities and testing of therapeutic interventions is limited by a lack of suitable immunocompetent pre-clinical models. We have developed both human and murine versions of a bispecific molecule with specific activity against target expressing tumor cells in vitro and in vivo. These bispecific proteins are constructed from the extracellular portion of either mouse or human NKG2D receptor and target cells expressing the cognate ligands by redirecting T cells through their CD3 binding arm. Using the murine bispecific protein, mNKG2DxCD3, we have developed an immunocompetent mouse tumor model which exhibits treatment induced toxicity and recapitulates key features similar to those observed in human CRS. Toxicity was observed between the 2nd and 4th bispecific protein injections but was not observed following subsequent injections. Monitoring of toxicity kinetics showed transient symptoms peaking 3-4 hours following bispecific protein injection with complete resolution after 8 hours. Weight loss and elevated plasma cytokines including IFNγ, IL6, TNFα, IL2 and IL10 were also associated with toxicity. Pathology analysis showed a reduction in white pulp in the mouse spleens, however, other organs evaluated (brain, kidney, lung and heart) were normal. Using mouse genetic knockout models, we were able to show that T cells, IFNγ and Perforin were required for development of this toxicity. Additionally, In vivo depletion of either CD4+ or CD8+ T cells was sufficient to prevent the onset of toxicity. These findings highlight the importance of T cell activation and function and shed light on the mechanistic underpinnings of bispecific T cell engager protein induced toxicity.

Citation Format: Claire Godbersen-Palmer, Tiffany Coupet, Zakaria Grada, Charles Sentman. Bispecific T cell engager-induced toxicity in an immunocompetent solid tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1542.