Predicting Clinical Response and Safety of JCAR017 in B-NHL Patients: Potential Importance of Tumor Microenvironment Biomarkers and CAR T-Cell Tumor Infiltration

Introduction:

JCAR017 is a CD19-directed 4-1BB CAR T-cell product administered in a defined composition at a precise dose of CD8 and CD4 CAR T cells. TRANSCEND NHL 001 is the first multicenter phase 1 trial of JCAR017 in R/R B-cell NHL (NCT02631044). Interim results (Abramson, 14-ICML 2017) demonstrated high complete response rates and low incidence of cytokine release syndrome (CRS) and neurotoxicity (NT). Tumor cell density, T cell density and detection of known immunosuppressive pathways were assessed retrospectively in tumor biopsies from TRANSCEND patients to examine relationships with clinical efficacy, CAR T PK, and safety endpoints.

Method:

Patients with R/R DLBCL or MCL were eligible. Patients received lymphodepletion followed by JCAR017 at one of two dose levels (DL1, 5 × 10⁷ cells; DL2, 1 × 10⁸ cells). Tumor biopsies were collected prior to treatment and 7 to 20 days after JCAR017 administration. Pathology review of H&E staining confirmed tissue quality and identified tumor areas. In this July 7th, 2017 data cut, 43 biopsies (26 pretreatment; 17 post-treatment; 15 matched pairs) from 25 DLBCL and 3 MCL patients were examined. The best overall response (BOR), CRS and NT rates of this cohort were 71% (20/28), 36% (10/28; grade 1, 2) and 18% (5/28; grade 2-4). CAR T cell infiltration was quantified using in situ hybridization (ISH) probes specific to JCAR017 CAR mRNA. CAR T cells, non-CAR T cells and B cells were enumerated using a 5-plex immunofluorescence (IF) assay (EGFR, CD4, CD8, CD19, CD20). Immunosuppressive pathways were assessed using a second 5-plex IF assay (CD73, FOXP3, CD163, IDO, PD-L1). Images were analyzed using HALO software. Univariate t-tests were used for statistical analysis, and all reported p-values are 2-sided without multiplicity adjustment.

Results:

Pretreatment tumors had varying cellular compositions: tumor cells (median: 77%; range 5 - 96%), CD4⁺ cells (0.90%; 0.02-15%), and CD8⁺ cells (1.5%; 0-23%). Preliminary data showed patients with a CR or PR at month 3 had a higher percentage of endogenous CD4⁺ cells in pretreatment tumors than those with a PD (CR, PR median: 7.9%; PD median: 0.38%; p < 0.0001). Percentages of CD8⁺ cells in pretreatment tumors did not differ between month 3 response groups (CR, PR median: 1.9%; PD median: 0.47%; p = 0.6496).

Following JCAR017 therapy, CAR T cells infiltrated the tumor and comprised up to 22% of cells. The level of tumor infiltration trended higher in patients achieving a CR (median: 3.9%) or PR (median: 1.1%) compared to those with a BOR of SD, PD (median: 0.51%). Although both CD4⁺ and CD8⁺ CAR T cells were able to infiltrate the tumor area, patients with a CR had a higher ratio of CAR T cells that were CD8⁺ (as compared to CD4⁺) than those with a BOR of SD or PD (CR median: 0.83; SD,PD median: 0.14; p = 0.0097).

Comparing matched pre- and post-treatment biopsies, patients achieving a BOR of CR or PR trended toward having a larger increase in CD8⁺ cells (CAR T and non-CAR T) in tumors as compared to patients achieving a BOR of SD or PD (CR, PR median change: +5.3%; SD, PD median change: +0.06%; p = 0.1225). Although expression of immunosuppressive factors varied widely among patients at pre-treatment (CD73 (median: 1.5%; range 0-42%), FOXP3 (0.10%; 0-1.5%), IDO (0.06%; 0-11%), CD163 (1.2%; 0-24%) and PD-L1 (0.16%; 0-56%)) and post-treatment (CD73 (1.6%; 0-53%), FOXP3 (0.09%; 0-4.3%), IDO (0.28%; 0-15%), CD163 (3.6%; 0-22%) and PD-L1 (3.3%; 0-65%)), increases in CD8⁺ cells in matched biopsies were associated with increases in IDO (R² = 0.64) and PD-L1 (R² = 0.61) expression.

Conclusions:

The state of the tumor microenvironment prior to treatment may impact the efficacy of CAR T cell therapy. This initial analysis suggests durable response at month 3 is associated with higher levels of CD4⁺ cells in pretreatment tumors. Following JCAR017 therapy, CAR T cells, both CD4⁺ and CD8⁺, infiltrated the tumor and adjacent tissue. BOR was associated with an increase in CAR T cells. Increasing levels of CD8⁺ cells in the tumor were associated with increases in IDO and PD-L1, suggesting that therapies targeting these pathways may enhance JCAR017 activity. Detailed analyses are ongoing to examine additional associations of tumor burden, T cell infiltration, and immunosuppressive factor expression with clinical efficacy, PK and safety, and will be presented.