Alloreactivity of infused CTLs. Before infusing the donor CTLs, we characterized their cytotoxicity against phytohemagglutinin blasts obtained from the transplantation recipient in a standard chromium release assay.¹¹  The release criterion was that cytotoxicity should be less than 10%. (A) Mean cytotoxicity was 2.07% for EBV CTLs, 2.24% for trivirus CTLs, and 3.07% for bivirus CTLs. Each symbol represents a cell line infused into a single subject. (B) The response of CD8⁺ T cells in CTL line C3183, to the panel of T-APCs. Only cells producing both IL-2/IFN-γ and TNF-α were scored positive, and the responses are ranked according to their frequency. CD8⁺ T cells responding to APCs that expressed an HLA class I allele shared with the recipient of this cell line are indicated as blue bars. Because allo-HLA reactive CD8⁺ T cells can recognize HLA class II-presented antigens, we have displayed their reactivities with T-APCs expressing a recipient-matching HLA class II mismatch as gray bars. One T-APC expressed both an HLA class I and II mismatch shared with the recipient of C3183; the response to this APC is represented as a blue bar with bold striped gray border. (C) The response of CTL line C2910 to autologous EBV-lymphoblastoid cell line (LCL) and 3 representative T-APCs, plus the negative control: CTL line without APCs.