1093 Development of TITAN: a new CD8-guided T cell engager platform for hematological and solid tumor applications

Background

Bispecific T cell engagers (TCEs) have shown promising rates of ORRs and CRs in the clinic, especially in the context of hematological malignancies, which led to several FDA approvals for the treatment of R/R DLBCL and FL, and more recently for the treatment of SCLC. However, these treatments are still associated with significant toxicities, including CRS and ICANS, limiting their therapeutic window and potential for clinical combinations.

Methods

Our goal was to develop a novel TCE format with the potential for an improved therapeutic index. To do so, we engineered a first-in-class CD8-guided TCE. CD8 guiding leverages the anti-tumor activity of CD8 cells and biases away from CD4 T cells which significantly reduces CD4 T cell-associated cytokine release. Our novel TCE format, TITAN (Target Induced T cell Activating Nanobodies), is an asymmetric, trispecific monoclonal IgG1 molecule which harbors two Fab binding domains to a TAA of interest, one VHH binding domain to TCR, one VHH binding domain to CD8 co-receptor. TITAN binding properties and mechanism of action were extensively interrogated, in vitro and in vivo. Control TITAN molecules with abrogated binding domains were generated to evaluate the relative contribution of each antibody component. In addition, biological activity was compared to conventional CD3xTAA TCEs.

Results

The VHH domains of TITAN allow preferential engagement of CD8+ T cells through CD8/TCR binding, leading to the formation of an artificial immunological synapse with TAA+ target cells, triggering T-cell activation and resulting in TAA+ target cell killing. Compared to conventional TAAxCD3 TCE, which equally engages and activates CD4+ and CD8+ T cells, TITAN drives potent TAA+-tumor cell killing through preferential engagement of CD8+ T cells, with reduced CD4+ T cell activation and associated cytokine production. Potent cytolytic activity of TITANs directed against heme or solid tumor TAAs was confirmed across a large array of target positive cell lines. Importantly, cytolytic activity was consistently associated with significantly lower cytokine release profiles compared to conventional bivalent TAAxCD3 TCEs. In subcutaneous and disseminated xenograft tumor models in NSG humanized mice, TITANs conferred potent and dose-dependent anti-tumor efficacy which, consistent with the in vitro data, was associated with significantly less systemic cytokine production.

Conclusions

TITAN platform represents a first-in-class T cell engager for cancer treatment and has the potential to significantly improve therapeutic index. AZD5492, a CD20-targeting TITAN is currently being developed for B-NHL and CLL indication.

Ethics Approval

The in vivo studies were conducted according to Institutional Animal Care and Use Committee approved protocols in the Laboratory Animal Resources facility at AstraZeneca, an Association for Animal Accreditation of Laboratory Animal Care and United States Department of Agriculture-licensed facility. Human PBMCs were used in accordance with Informed Consent Forms (ICF).