R. Khanna et al., EBV PEPTIDE EPITOPE SENSITIZATION RESTORES HUMAN CYTOTOXIC T-CELL RECOGNITION OF BURKITTS-LYMPHOMA CELLS - EVIDENCE FOR A CRITICAL ROLE FORICAM-2, The Journal of immunology, 150(11), 1993, pp. 5154-5162
The pathogenesis of EBV+ Burkitt's lymphoma (BL) suggests evasion of t
he CTL response against EBV Two important features of this tumor have
been previously suggested to explain this immune evasion, (a) absence/
low expression of cellular adhesion molecules and (b) restricted expre
ssion of EBV latent Ag. To determine the relative importance of these
features in relation to evasion of EBV-specific CTL, a group of BL cel
l lines with variable expression of the aforementioned phenotypic char
acteristics were assayed for specific CTL lysis after exogenous additi
on of EBV peptide epitopes. In spite of down-regulated expression of t
he adhesion molecules LFA-1, LFA-3, and/or ICAM-1, peptide-sensitized
BL cells were recognized and lysed by EBV-specific CTL. Moreover, ther
e was no significant difference between the CTL lysis of the BL cells
and that of adhesion molecule-positive control cells over a wide range
of peptide epitope concentrations. Blocking experiments with mAb to i
ndividual adhesion molecules suggested that virus-specific CTL recogni
tion of lymphoblastoid cell lines was dependent on an intact LFA-3/CD2
pathway. In contrast, the CTL recognition of peptide-sensitized BL ce
lls was critically dependent on the LFA-1/ICAM pathway, with an insign
ificant contribution by CD2/LFA-3. The consistently high expression of
ICAM-2 on all BL cell lines suggests that the accessory function in C
TL recognition of these cells is mediated by the LFA-1/ICAM-2 pathway.
Thus, down-regulation of LFA-1, LFA-3, and/or ICAM-1 expression on BL
cells does not provide an absolute barrier to tumor cell recognition
by virus-specific CTL. The ability of virus-specific CTL to recognize
peptide epitope-sensitized BL cells as efficiently as normal cells has
demonstrated the importance of latent Ag expression in the CTL contro
l of EBV+ tumors.