149P - HLA/SIRPa bispecifics-A novel multitarget therapeutic strategy to induce potent anti-tumor immune responses

Background

To develop novel anti-cancer therapeutics, we have used a reverse rational approach and searched for human HLA class I molecules known to induce autoimmunity as a surrogate marker for potential anti-cancer activity. HLA-B57 is one example of an HLA class I molecule described to target LILRB receptors in these studies. Here we demonstrate the proof of concept of a bispecific optimised HLA-Fc fusion conjugated to a SIRPa protein which shows potent in vitro anti-tumor efficacy through its multimodal binding of LILRB1, LILRB2 and CD47 receptors. This novel modality of HLA/SIRPa Bispecifics has the unique characteristic of targeting myeloid cells and the ability to be directed to tumor sites by targeting the CD47 on cancer cells.

Methods

Rational guided protein engineering and transient protein production in CHO was conducted. Affinity determination was measured by SPR/BLI. Binding to cells expressing the receptors was assessed by flow cytometry. Potency was measured using CD47/SIRPa reporter cell lines. Evaluation of in vitro safety was performed by binding assessment to red blood cells and hemagglutination induction. In vitro efficacy studies were performed for macrophage phagocytosis and NK cell cytotoxicity against cancer cells. Ex-vivo efficacy is currently being assessed using primary NSCLC tumor biopsies and measuring tumor cell killing and activation of immune cell markers.

Results

HLA/SIRPa Bispecifics were expressed as IgG4 Fc-fusion proteins in a 2+2 format. Affinity to LILRB1/LILRB2 and CD47 receptors are in low nM range. By optimization of the affinity of the c-terminal SIRPa we can show an enhanced safety profile compared to competitor CD47 targeting molecules through reduced binding to red blood cells and reduced hemagglutination. Reporter cells demonstrate that bispecifics effectively inhibit the interaction of CD47 with SIRPa. In vitro efficacy data shows that macrophage phagocytosis was enhanced by optimizing specific properties of the SIRPa arm.

Conclusions

HLA/SIRPa bispecifics are novel multi-functional agents that potentiate anti-tumor immunity through the interaction of multiple immune checkpoint receptors on one side and may function to engage macrophages towards cancer cells on the other side.

Legal entity responsible for the study

ImmunOs Therapeutics AG.

Funding

ImmunOs Therapeutics AG.

Disclosure

A. Rafiei: Non-Financial Interests, Personal, Full or part-time Employment: ImmunOs Therapeutics AG. O. Marroquin Belaunzaran: Financial Interests, Personal, Officer: ImmunOs Therapeutics AG. All other authors have declared no conflicts of interest.