Targeting B7-H3 in ovarian cancer

ABSTRACT Remarkable clinical responses have been reported in B-cell malignancies by adoptive transfer of T cells redirected with a chimeric antigen receptor (CAR) specific for the CD19 antigen.

However, developing CAR-Ts for the treatment of solid tumors including ovarian cancer (OC) is challenging because: (1) OC-associated antigens that are targetable by CAR-Ts are limited, generally not exclusively expressed by OC, and act as passengers, not as drivers of tumorigenesis, allowing for antigenic drift; (2) OC tumor microenvironment (TME) is highly immunosuppressive.

In this proposal we aim at solving these critical issues. We have identified B7-H3 (CD276) as a suitable target for chimeric antigen receptor (CAR) T cells in OC.

B7-H3 is a tumor-promoting transmembrane protein aberrantly expressed in 60% to 93% of pancreatic cancer, melanoma, leukemia, breast, prostate and OC, while limited expression is seen on normal healthy tissues.

We have developed and tested B7-H3.CAR-Ts in xenogeneic and immunocompetent tumor models showing antitumor activity is several tumor models including OC and safety.

Thus in Aim 1 we propose to conduct a phase I clinical study in patients with OC to assess safety and antitumor activity of autologous B7-H3.CAR-Ts inoculated intraperitoneally.

An IND (IND19641) for this study has been obtained at University of North Carolina, and clinical grade reagents to manufacture B7-H3.CAR-Ts are in hands.

In Aim 2 we propose to conduct a comprehensive immunologic analysis of tumor biopsies and ascites collected from patients enrolled in the study before and after treatment to assess antigen loss and immunologic perturbation of the TME in OC.

In Aim 3, we propose to reprogram tumor-associated macrophages (TAMs) and myeloid derived suppressor cells (MDSC) of the OC TME to a non-immunosuppressive state by using potent and orally bioavailable TAM RTK small molecule inhibitors developed at University of North Carolina (IND128236).

We will thus perform preclinical studies to evaluate whether TAM RTK signaling inhibition in macrophages and MDSC would favor the antitumor activity of B7-H3.CAR-Ts in a syngeneic model of OC.

If successful, this strategy will be included into a second phase of the proposed Phase I clinical study with B7-H3.CAR-Ts.