Abstract
Background:
While CD19-targeted chimeric antigen receptor (CAR) based T cell therapy has shown promise in the treatment of chronic lymphocytic leukemia (CLL), overall efficacy is limited due to impaired T-cell fitness. We have previously shown that dual inhibition of PI3Kδ and PI3Kγ enhanced mitochondrial mass and ex vivo expansion of central and stem cell memory T cells from CLL patients(Funk, 2019,Journal for Immunotherapy of Cancer). In this study, we hypothesized that pharmacological inhibition of these pathways during ex vivo culture would increase the expansion and in vivo anti-tumor cytotoxicity.
Methods: Peripheral blood mononuclear cells (PBMCs) were isolated from the blood of CLL patients by ficol hypaque centrifugation. T cells were negatively selected using MACS beads and transduced with CD19 CAR lentivirus (encoding CD28 or 41BB co-stimulatory domains) and stimulated with anti-CD3/CD28 beads in media containing 30 U/mL interleukin-2 with or without the PI3Kδ/γ inhibitor duvelisib (Duv) for 15 days. NOG mice were engrafted with the OSU-CLL cell line for 14 to 18 days with tumor burden measured by flow cytometry of blood samples from the mice, comprising a mean 0.15% of peripheral nucleated cell content. Control-CART or Duv-CART were injected by tail vein injection. Frequencies of CART, OSU-CLL cells and immune checkpoint molecule expression of CART or T cells in blood were measured by serial flow cytometry. Kaplan-Meier survival plots were represented as recipient survival on the indicated days
Results: Treatment with either CD28 or 4-1BB Duv-CART cells led to significantly prolonged survival relative to control-CART (Figure 1, P<0.05). Recipients of Duv-CART cleared circulating OSU-CLL faster than control CART (Figure 2. P<0.05 at day26 for CD28 CART) and exhibited greater peak expansion and persistence of total CART and CD8+ CART. Recipients of Duv-CART cells had significantly greater in vivo persistence and expansion of total CART and CD8+ CART (Figure 3, P<0.001, day14 after CART were infused). Consistent with improved survival, both CD28 Duv-CART and 4-BB Duv-CART show reduced expression of LAG3, TIM3 and PD1 in the CD4 (Figure 4) and CD8+ subsets at earlier time point in vivo. (* p<0.05, **p≤0.01, ***p≤0.001, ****p≤0.0001).
Conclusions: Inhibition of PI3Kd/g during CART cell culture decreased the expression of immune checkpoint molecules and enhanced in vivo expansion leading to greater efficacy in eliminating CLL.
Waller: Verastem Oncology: Consultancy, Research Funding; Cambium Oncology: Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company.
