Chimeric antigen receptor (CAR)
therapy has begun to demonstrate success as a novel treatment modality for
hematologic malignancies. The success observed thus far has been with T cells permanently engineered to express chimeric receptors. T cells engineered using
RNA electroporation represent an alternative with the potential for similar efficacy and greater safety when initially targeting novel
antigens.
Neuroblastoma is a common pediatric solid
tumor with the potential to be targeted using
immunotherapy. We performed xenograft studies in NSG mice in which we assessed the efficacy of both permanently modified and transiently modified CAR T cells directed against the
neuroblastoma antigen GD2 in both local and disseminated disease models. Disease response was monitored by
tumor volume measurement and histologic examination, as well as in vivo bioluminescence.
RNA-modified GD2 CAR T cells mediated rapid
tumor destruction when delivered locally. A single infusion of lentivirally modified GD2 CAR T cells resulted in long-term control of disseminated disease. Multiple infusions of
RNA GD2 CAR T cells slowed the progression of disseminated disease and improved survival, but did not result in long-term disease control. Histologic examination revealed that the transiently modified cells were unable to significantly penetrate the
tumor environment when delivered systemically, despite multiple infusions of CAR T cells. Thus, we demonstrate that
RNA-modified GD2 CAR T cells can mediate effective antitumor responses in vivo, and permanently modified cells are able to control disseminated
neuroblastoma in xenograft mice. Lack of long-term disease control by
RNA-engineered cells resulted from an inability to penetrate the tumor microenvironment.