Project Summary
Chimeric antigen receptor (CAR) T cell therapies are transforming clinical care of hematological malignancies;
however, they have shown limited clinical success in treating solid tumors. Numerous efforts are underway to
expand the use of CAR T cells for different cancer types, but their effectiveness in treating solid tumors have
been limited by the fact that solid tumors are heterogenous; targeting a single antigen using CAR T cells typically
results in tumor antigen escape, leading to relapse of the disease. Although systemic delivery of
immunomodulators can potentiate anti-tumor responses, it can also lead to debilitating adverse events from on-
target, off-tumor toxicity, cytokine release syndrome, and in some cases, life-threatening autoimmunity. By
contrast, intratumoral administration of immunomodulators has been shown to reduce systemic exposure while
improving efficacy of systemic therapies. Immunity against tumor antigens, resultant of epitope spreading after
tumor cell killing, leads to a diversification of epitope specificity from the initial epitope – priming the endogenous
immune system against larger pool of targets. This proposal seeks to use thermal sensitive CAR T cells, which
traffic and infiltrate deep within tumors, to intratumorally produce bispecific T cell engagers (BTEs) and induce
epitope spread by DC priming of endogenous anti-tumor T cells to develop robust immunity. Focused ultrasound
(FUS) will be used to spatially deposit heat within heterogenous tumors and activate CAR T cells engineered
with a thermal gene switch (TS) which allows for heat-triggered control of transgene expression in murine T cells.
TS constructs are transcriptionally silent at body temperature (37°C) but after exposure to a short duration of
heat (10 min. at 40–42°C), express transgenes to levels greater than 200-fold above basal levels. These studies
will focus on BTEs targeting natural killer group 2, member D ligands (NKG2DL), which are stress-induced
antigens highly expressed on tumor cells as well as on immunosuppressive cells. Preclinical evaluation will be
performed in murine models of breast cancer in fully immunocompetent mice. This approach is expected to
significantly enhance local CAR T cell activity against heterogenous tumors, while potentiating endogenous
antitumor immunity. To assess this, epitope spread by DC mediated priming of the endogenous T cells will be
investigated. Successful completion of the aims of this study is expected to elucidate mechanisms by which local
BTE secretion by CAR T cells can prime endogenous T cell immunity.