379 Engineering of gamma/delta T cells derived from cord blood for chimeric antigen receptor-T cell therapies

BackgroundAdoptive cellular immunotherapy as a new paradigm to treat tumors is exemplified by the FDA approval of six different chimeric antigen receptor (CAR)-T cell therapies targeting hematological malignancies in recent years. Conventional alpha/beta (ab) T cells applied in these therapies have proven efficacy but with hitherto disappointing outcomes when applied to solid tumors, largely due to poor survival and reduced efficacy of CAR-T cells in the immunosuppressive solid tumor microenvironment (TME). Moreover, these therapies are confined exclusively to autologous use since, upon infusion, they elicit devastating graft-versus-host disease (GvHD) in human leukocyte antigen (HLA)-mismatched patients. One way to overcome these challenges is to use allogeneic immune cell types, in particular gamma/delta (gd) T cells, which occupy the interface between innate and adaptive immune cells and recognize a wide variety of ligands expressed on transformed cells. Importantly, specific gd T cell subsets such as Vd1 T cells, have a natural propensity to home to solid tissues.MethodsWe propose to harness these characteristics of gd T cells by generating CAR-T cells using cord blood (CB)- compared with peripheral blood (PB)-derived gd T cells. We expanded CB- and PB-gd T cells using a feeder cell-based protocol and transduced them with a HER2-targeting CAR bearing CD28 co-stimulatory endodomain and CD3z activation domain (4D5-28z CAR) via two-step retrovirus-based delivery. Both in vitro and in vivo cytotoxicity of 4D5-28z CB- and PB-gdT cells against selected solid tumor cell lines were assessed using bioluminescence-based methods.ResultsWe found that CB-gd cells were less amenable to CAR transduction, resulting in substantially lower frequencies of CAR-positive CB-gd T cells compared with PB-gd counterparts. Efforts are underway to optimize transduction to enhance CAR expression in CB-gd T cells. Despite fewer CAR-positive CB-gd T cells, we consistently observed that these cells exhibited increased in vitro cytotoxicity against SK-OV-3 ovarian tumor cells compared with non-CAR counterparts. However, our preliminary results demonstrated that both CAR- and non-CAR CB-gdT cells lacked persistence in vivo, alluding to the need for further genetic modifications of gd CAR-T cells to secrete cytokines which can help them overcome the immunosuppressive effects of TME and improve their in vivo functionality.ConclusionsTaken together, our findings highlight the potential of