IND-Enabling Studies of a Switchable Chimeric Antigen Receptor-T Cell (CLBR001+SWI019) to Support First in Human Clinical Study

Despite the tremendous clinical benefits, adverse events associated with CAR-T cell therapy remain a challenge. Most frequent adverse events are cytokine release and immune effector cell-associated neurotoxicity syndromes due to the inability to modulate the level of activity of current CAR-T cell products after administration to patients. Additional challenges include on target, off tumor toxicities and antigen loss mediated relapse of disease.

To address these challenges, we have developed a "switchable" CAR-T (sCAR-T) where the activity of the sCAR-T cells is controlled by an antibody-based switch. The switch targets the tumor antigen, and the sCAR recognizes a unique peptide engrafted on the switch. The switch creates a bridge between the sCAR-T cell and the tumor cell, activating the sCAR-T cells and inducing tumor cell killing. Combined, the switch and sCAR-T cells afford complete elimination of tumors in xenograft and syngeneic models, but individually, each is designed to be inactive. A short half-life of the switch allows for a rapid modulation of sCART-cell activity through the switch dosing. Moreover, by swapping different switches, sCAR-T cells can be modularly redirected against other tumor targets. Further, we have shown the cyclical on/off stimulation of the sCAR-T cells affords improved memory and persistence of the sCAR-T cells. Here, we report IND-enabling studies for an optimized CD19-targeted switch (SWI019) and sCAR-T cell (CLBR001) to support a first in human (FIH) clinical study of the combination.

The preclinical development of a platform which includes a sCAR-T cell that lacks any endogenous antigen target, in combination with an antibody-based switch molecule that lacks intrinsic activity in the absence of the sCAR-T cell, necessitated development of novel approaches. Fidelity of such a system is essential to control, thus, to confirm CLBR001 cells did not activate in the presence of normal tissues, in vitro activity studies were performed by co-culturing CLBR001 cells, in the presence or absence of SWI019, and a panel of 14 primary cells. This panel represented a survey of vital tissues throughout the body. CLBR001 did not demonstrate activity in any of the 14 cell types tested, supporting a high fidelity of CLBR001 recognition for SWI019.

Because SWI019 lacks activity in the absence of CLBR001 cells, traditional toxicology studies to identify the no adverse effect level (NOAEL) in support of the first in human starting dose were not applicable. In such cases, a minimal anticipated biological effect level (MABEL) is commonly used to support starting human dose based on the predicted Cmax; however, the femtomolar-level in vitro activity of SWI019 in combination with CLBR001 resulted in starting doses that were modeled to be far outside of the range of potential clinical activity. Therefore, an in vivo-based approach to determine MABEL was developed. CLBR001 cells were administered in NSG mice bearing CD19+ Nalm-6 cell tumors and a single dose titration of SWI019 was performed. Comparison of the SWI019 efficacious dose (ED ₅₀) values for anti-tumor activity, peripheral cytokines, and CLBR001 cells in peripheral blood demonstrated that reduction in Nalm-6 tumor burden was the most sensitive marker of activity. Extravasation of CLBR001 cells from peripheral blood and all three cytokines (IFN-γ, IL-2, and TNF-α) exhibited weaker ED ₅₀ values. Therefore, antitumor activity (Nalm-6 tumor burden reduction) was chosen as the parameter for which to determine in vivo MABEL. Allometric scaling, using mouse and NHP SWI019 PK data, was used to model a SWI019 recommended dose in humans corresponding to the ED ₂₀ of the in vivo MABEL study. Compared to the dose modelled using the in vitro MABEL approach, the in vivo MABEL approach afforded a first in human starting point which was ~13000-fold higher. We expect this approach provides an excellent starting point for the first in human study which balances safety and the potential for patient benefit.

In summary, the results presented in this abstract led to the initiation of clinical trial NCT04450069, the combination of CLBR001+SWI019 for the treatment of relapse/ refractory B cell malignancies.