Strategies to boost anti-
tumor immunity are urgently needed to treat
therapy-resistant late-stage
cancers, including
colorectal cancers (
CRCs).
Cytokine stimulation and genetic modifications with
chimeric antigen receptors (CAR) represent promising strategies to more specifically redirect anti-
tumor activities of effector cells like natural killer (NK) and T cells. However, these approaches are critically dependent on
tumor-specific
antigens while circumventing the suppressive power of the solid tumor microenvironment and avoiding off-
tumor toxicities. Previously, we have shown that the stress-inducible
heat shock protein 70 (Hsp70) is frequently and specifically expressed on the cell surface of many different, highly aggressive
tumors but not normal tissues. We could take advantage of
tumors expressing Hsp70 on their membrane ('mHsp70') to attract and engage NK cells after in vitro stimulation with the 14-mer Hsp70
peptide TKDNNLLGRFELSG (TKD) plus low dose
interleukin (IL)-2. However, a potential limitation of activated primary NK cells after adoptive transfer is their comparably short life span. T cells are typically long-lived but do not recognize mHsp70 on
tumor cells, even after stimulation with TKD/IL-2. To combine the advantages of mHsp70-specificity with longevity, we constructed a CAR having specificity for mHsp70 and retrovirally transduced it into primary T cells. Co-culture of anti-Hsp70 CAR-transduced T cells with mHsp70-positive
tumor cells stimulates their functional responsiveness. Herein, we demonstrated that human
CRCs with a high mHsp70 expression similarly attract TKD/IL-2 stimulated NK cells and anti-Hsp70 CAR T cells, triggering the release of their lytic effector
protein granzyme B (GrB) and the pro-inflammatory
cytokine interferon (IFN)-γ, after 4 and 24 hours, respectively. In sum, stimulated NK cells and anti-Hsp70 CAR T cells demonstrated comparable anti-
tumor effects, albeit with somewhat differing kinetics. These findings, together with the fact that mHsp70 is expressed on a large variety of different
cancer entities, highlight the potential of TKD/IL-2 pre-stimulated NK, as well as anti-Hsp70 CAR T cells to provide a promising direction in the field of targeted, cell-based
immunotherapies which can address significant unmet clinical needs in a wide range of
cancer settings.