Most Do, but Some Do Not: CD4(+)CD25(−) T Cells, but Not CD4(+)CD25(+) Treg Cells, Are Cytolytic When Redirected by a Chimeric Antigen Receptor (CAR)

Evidences are accumulating that CD4(+) T cells can physiologically mediate antigen specific target cell lysis. By circumventing major histocompatibility complex (MHC)-restrictions through an engineered chimeric antigen receptor (CAR), CD4(+) T cells lyse defined target cells as efficiently as do CD8(+) T cells. However, the cytolytic capacity of redirected CD4(+)CD25(−) T cells, in comparison with CD4(+)CD25(+) regulatory T (Treg) cells was so far not thoroughly defined. Treg cells require a strong CD28 signal together with CD3ζ for activation. We consequently used a CAR with combined CD28­CD3ζ signalling for redirecting CD4(+)CD25(−) T cells and CD4(+)CD25(+) Treg cells from the same donor. CAR redirected activation of these T cell subsets and induced a distinct cytokine pattern with high IL-10 and a lack of IL-2 release by Treg cells. Despite strong antigen-specific activation, CAR Treg cells produced only weak target cell lysis, whereas CD4(+)CD25(−) CAR T cells were potent killers. Cytolysis did not correlate with the target cell sensitivity to Fas/FasL mediated killing; CD4(+)CD25(−) T cells upregulated perforin and granzyme B upon CAR activation, whereas Treg cells did less. The different cytolytic capacities of CAR redirected conventional CD4(+) cells and Treg cells imply their use for different purposes in cell therapy.