Abstract 3749: Genetic blockade of the protein tyrosine phosphatase SHP1 augments CAR T cell activity against PDL1 expressing solid tumors
Authors: Moon Edmund , Kim Soyeon , Jean Naomi Saint , O'Brien Shaun , Maceyko Steven , Sun Jing , June Carl , Albelda Steven 
Published: July 2017

Background: Immunotherapy using chimeric antigen receptor (CAR) T cells has demonstrated profound, durable success in hematologic malignancies. Solid tumors present hurdles to the successful application of CAR T cells. One is the upregulation of inhibitory receptors (IRs), like PD1 and CTLA4, many of which rely on shared signaling molecules to shut off T cell activation. One such molecule is SHP1 (Src homology region 2 domain-containing phosphatase-1) which dephosphorylates key components of T cell receptor (TCR) signaling. We have engineered a unique dominant-negative SHP1 (dnSHP1) that is able to augment CAR T cell control of PDL1 positive solid tumors.

Materials and Methods: The human mesothelioma cell line, EMP, was transduced to express high levels of mesothelin and PDL1 (EMMESO-PDL1). Activated human T cells from healthy donors were lentivirally transduced to express a mesothelin-directed CAR (mesoCAR) with and without a dnSHP1. MesoCAR and mesoCAR/dnSHP1 T cells were cocultured with tumor cells x 18hrs and specific lysis was measured. These T cells were also restimulated with plate-bound anti-CD3 overnight and were subjected to intracellular flow cytometry staining (ICS) of cytokines. NSG mice were injected subcutaneously in the flanks with 5x106 EMMESO-PDL1 tumor cells. After tumors established and grew to ~150mm3, mice were randomly assigned to one of the following treatments: 1) non-transduced (NTD) T cells, 2) mesoCAR T cells, 3) mesoCAR T cells + sodium stibogluconate (SSG; a chemical inhibitor of SHP1), 4) mesoCAR/dnSHP1 T cells. T cells were injected IV once at a dose of 10x106 T cells/mouse. SSG was administered IM at 20mg/kg every 2 days. Tumors were measured serially. At the end, mice were sacrificed, tumors were harvested, digested, processed into single cell suspension, and subjected to flow cytometry analysis. The tumor infiltrating lymphocytes (TILs) were also isolated and tested for function ex-vivo.

Results/Conclusion: In vitro, mesoCAR T cells demonstrated suppressed lysis of EMMESO-PDL1 tumor cells compared to EMMESO cells. MesoCAR/dnSHP1 T cells were able to lyse EMMESO-PDL1 and EMMESO tumor cells with similar efficiency. Anti-CD3 restimulation of T cells revealed enhanced secretion of TNF-alpha and IL2 by mesoCAR/dnSHP1 vs. mesoCAR T cells as measured by ICS. In vivo, SSG injections had minimal impact on mesoCAR T cell control of tumors, whereas mesoCAR/dnSHP1 T cells demonstrated significantly enhanced control of EMMESO-PDL1 tumor growth compared to mesoCAR T cells (60% greater decrease in tumor volume compared to mesoCAR T cells). TIL infiltration was 3-fold higher in tumors harvested from mice that received mesoCAR/dnSHP1 T cells compared to other groups. Isolated mesoCAR/dnSHP1 TILs demonstrated the greatest ex-vivo lysis of fresh tumor cells. DnSHP1 engineering is a powerful and novel way of blocking the suppression of CAR T cells by PD1 and other similar IRs.

Citation Format: Edmund Moon, Soyeon Kim, Naomi Saint Jean, Shaun O'Brien, Steven Maceyko, Jing Sun, Carl June, Steven Albelda. Genetic blockade of the protein tyrosine phosphatase SHP1 augments CAR T cell activity against PDL1 expressing solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3749. doi:10.1158/1538-7445.AM2017-3749