Introduction & Objectives
Adoptive T cell therapy (ATT) has shown efficacy in the treatment of hematologic neoplasms leading to its approval for acute lymphoblastic leukemia and diffuse large B cell lymphoma. However, major hurdles for successful immunotherapy of solid tumors are the prevention of T cell exhaustion and stromal inhibition of T cells. We aimed to overcome these using engineered T cells expressing chimeric costimulatory switch proteins (CSPs), which were tested in an orthotopic renal cell carcinoma (RCC) mouse model.
Materials & Methods
Two CSPs were used combining the extracellular domain of PD-1 with either the intracellular domains of CD28 or 4-1BB, thereby turning a coinhibitory into a costimulatory signal. RCC antigen-reactive TCR53-T-cells without CSP (NGFR) served as control. First, tumor formation within 1 week after orthotopic RCC53 injection was tested (n=3). For ATT, 28 mice bearing RCC53 tumors were divided into 4 groups: receiving no T cells, injection of tumor-reactive TCR53-T-cells without CSP (NGFR) or TCR53 engineered with either PD-1:BB or PD-1:28 CSP. T cells were injected 7 and 11 days after RCC53 implantation and animals were followed for 2 weeks. Tumor growth was analyzed by high resolution ultrasonography. Blood was collected 3, 7 and 10 days after T cell injection, tumors and organs were retrieved at day 14 after ATT and analyzed for the presence and phenotype of T cells by flow cytometry.
Results
The first experiment showed solid, vascularized tumors 1 week after RCC53 implantation in all mice. The ATT experiment demonstrated a significant reduction in tumor volume 2 weeks after the start of T cell therapy in the NGFR group compared to the no T cells group, which was further decreased in both CSP groups (p<0.01 for all comparisons; Fig. 1). Number and phenotype of T cells in blood, tumors and other organs are being analyzed and results will be available until EAU 2024.
Conclusions
We observed significant tumor control using RCC-specific T cells and complete tumor rejection when these were engineered with PD-1 based CSPs in an orthotopic RCC xenograft model. This is the first study of its kind applying a T cell/cancer cell system with a not affinity-enhanced T cell receptor isolated from a human tumor-infiltrating T cell and endogenous PD-L1 expression in cancer cells, which will pave the way for further testing of ATT in clinical trials for RCC.
