CD28 co‐stimulation via tumour‐specific chimaeric receptors induces an incomplete activation response in Epstein–Barr virus‐specific effector memory T cells

Summary Expression of tumour antigen‐specific chimaeric receptors in T lymphocytes can redirect their effector functions towards tumour cells. Integration of the signalling domains of the co‐stimulatory molecule CD28 into chRec enhances antigen‐specific proliferation of polyclonal human T cell populations. While CD28 plays an essential role in the priming of naive CD4 + T cells, its contribution to effector memory T cell responses is controversial. We compared the function of the chRec with and without the CD28 co‐stimulatory domain, expressing it in peripheral blood T cells or Epstein–Barr virus (EBV)‐specific T cell lines. The chimaeric T cell receptors contain an extracellular single‐chain antibody domain, to give specificity against the tumour ganglioside antigen G D2 . The transduced cytotoxic T lymphocytes (CTL) maintained their specificity for autologous EBV targets and their capacity to proliferate after stimulation with EBV‐infected B cells. Intracellular cytokine staining demonstrated efficient and comparable antigen‐specific interferon (IFN)‐γ secretion by CTL following engagement of both the native and the chimaeric receptor, independent of chimaeric CD28 signalling. Furthermore, tumour targets were lysed in an antigen‐specific manner by both chRec. However, while antigen engagement by CD28ζ chRec efficiently induced expansion of polyclonal peripheral blood lymphocytes in an antigen‐dependent manner, CD28 signalling did not induce proliferation of EBV–CTL in response to antigen‐expressing tumour cells. Thus, the co‐stimulatory requirement for the efficient activation response of antigen‐specific memory cells cannot be mimicked simply by combining CD28 and ζ signalling. The full potential of this highly cytolytic T cell population for adoptive immunotherapy of cancer requires further exploration of their co‐stimulatory requirements.