Abstract 3749: Genetic blockade of the protein tyrosine phosphatase SHP1 augments CAR T cell activity against PDL1 expressing solid tumors

• Published in: Cancer research (Chicago, Ill.) Ill.), 2017-07, Vol.77 (13_Supplement), p.3749-3749
• Main Authors: Moon, Edmund, Kim, Soyeon, Jean, Naomi Saint, O'Brien, Shaun, Maceyko, Steven, Sun, Jing, June, Carl, Albelda, Steven
• Format: Article
• Language: English
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/1538-7445.AM2017-3749

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 tum