Evidence is accumulating that solid tumors contain a rare phenotypically distinct population of cells, termed cancer stem cells (CSC), which give rise to and maintain the bulk of the tumor. These CSC are thought to be resistant to current chemotherapeutic strategies due to their intrinsic stemlike properties and thus may provide the principal driving force behind recurrent tumor growth. Given the high frequency of recurrent metastasis associated with human ovarian cancer, we sought to determine whether primary human ovarian tumors contain populations of cells with enhanced tumor-initiating capacity, a characteristic of CSC. Using an in vivo serial transplantation model, we show that primary uncultured human ovarian tumors can be reliably propagated in NOD/SCID mice, generating heterogeneous tumors that maintain the histological integrity of the parental tumor. The observed frequency of tumor engraftment suggests only certain subpopulations of ovarian tumor cells have the capacity to recapitulate tumor growth. Further profiling of human ovarian tumors for expression of candidate CSC surface markers indicated consistent expression of CD133. To determine whether CD133 expression could define a tumor-initiating cell population in primary human ovarian tumors, fluorescence-activated cell sorting (FACS) methods were employed. Injection of sorted CD133 1 and CD133 2 cell populations into NOD/SCID mice established that tumor-derived CD133 1 cells have an increased tumorigenic capacity and are capable of recapitulating the original heterogeneous tumor. Our data indicate that CD133 expression defines a NOD/SCID tumor initiating subpopulation of cells in human ovarian cancer that may be an important target for new chemotherapeutic strategies aimed at eliminating ovarian cancer.

RT are former employees of Compass Therapeutics and are partners in the LLC. UE, SQH, and WG are now employees of Akrevia Therapeutics. CC is now an employee of CRISPR Therapeutics. SO is now an employee of Bluebird Bio. RT and JL are now employees of TCR2 Therapeutics. PB is now an employee of Sanofi. MO is now an employee of Bristol-Myers Squibb. WFC is now an employee of Astellas Pharmaceuticals. ACA is a member of the scientific advisory board for Tizona Therapeutics, Compass Therapeutics, and Zumutor Biologics and is a paid consultant for Aximmune. ACA, CL, and CW received research funding from Compass Therapeutics. PB, MS, JL, RT, CLL, and UE are inventors on the following issued U.S. patents held by applicant Compass Therapeutics: patent nos. 10,279,038B2; 10,279,039B2; and 10,279,040B1; these patents cover pharmaceutical compositions comprising CTX-471 and methods of using CTX-471 for treating cancer or inducing antitumor immune response in cancer patients.