Poster Presentation 8th Australasian Vaccines & Immunotherapeutics Development Meeting 2020

Stem cell memory like CAR-T cells persist better in vivo and induce solid tumour complete regression in combination with anti-PD1. (#204)

Deborah Meyran 1 2 , Joe Zhu 1 2 , Jeanne Butler 1 , Sean macdonald 1 , Daniela tantalo 1 , Kevin Sek 1 , Paul Ekert 3 , Michael Kershaw 1 2 , Joseph A Trapani 1 2 , Phil K Darcy 1 2 , Paul J Neeson 1 2
  1. Research Division, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia
  2. Sir Peter MacCallum Dept of Oncology, University of Melbourne, Melbourne, Victoria, Australia
  3. Medical Oncology, Peter MacCallum Cancer Centre, Melbourne, Vic, Australia

CAR-T cells targeting solid cancers have had limited success, reasons for this include poor long-term persistence in vivo. To address this issue, we used naïve T cells to generate second-generation CAR-T cells recognizing the tumor antigen Lewis Y (LeY), termed ‘early’ CAR-T cells. To do this, purified naïve T cells were activated by CD3/CD28 soluble tetrameric antibody complex, retrovirally transduced (LeY scFv-CD3z-CD28 CAR) and  expanded in IL-7/IL-15. The early-CAR-T cells comprised stem cell memory-like (CD95+, CD62L+, CD45RA+) and central memory phenotype (CD95+, CD62L+, CD45RA-) T cells with increased expression of ICOS, Ki67, TCF1 and CD27. The early LeY CAR-T cell function was tested in vitro for cytotoxicity (Cr-release and degranulation), proliferation, and cytokine secretion by CBA, either de novo or following chronic stimulation for 1 month. The early-CAR-T cells showed potent antigen-specific cytotoxicity, and secreted significantly higher levels of cytokines (IFN-γ, TNF-α and IL-2) and increased proliferation compared to conventional CAR-T cells. Importantly, after long-term chronic stimulation, early-CAR-T cells had significantly higher proliferative capacity compared to conventional CAR-T cells, and CD4+ CAR-T cells were critical for effective early CD8+ CAR-T cell proliferation capacity in vitro. Early CAR-T cells had significantly better in vivo tumour control (NSG-OVCAR3) compared to conventional CAR-T cells, this was associated with increased persistence of circulating CAR-T cells. Finally, early LeY-CAR-T cells combined with anti-PD-1 therapy completely regressed OVCAR3 tumours in the NSG mice. This was associated with a significantly increased percentage of circulating stem-cell memory like CAR-T cells in vivo.

In conclusion, our early CAR-T cells have better in vitro function and potent anti-tumor efficacy in vivo. Importantly, early-LeY-CAR-T cells combined with anti-PD1-treatment completely cleared LeY+ solid tumors in vivo. Finally, our early CAR-T cell production protocol is directly translatable for improving CAR-T cell efficacy  in clinical trials for patients with solid tumours.