ANTI-CD2 MONOCLONAL ANTIBODY-INDUCED RECEPTOR CHANGES .2. INTERACTIONOF CD2 AND CD3

Anti-CD3 monoclonal antibodies (mAbs) and anti-CD2 mAbs each prolong a llograft survival and cause transient downmodulation of homologous rec eptor expression. Anti-CD2 mAbs also act synergistically with anti-CD3 mAbs to prolong allograft survival and induce tolerance. The effect o f combined anti-CD2 and anti-CD3 mAb treatment on receptor expression was further analyzed with an in vitro model. The anti-CD2 mAb 12-15 ca used CD2 expression on purified splenic T cells to decrease from 72.6% [mean channel fluorescence (MCF) 0.68] to 41.5% (0.45) total positive cells while CD3 expression remained unchanged 169.1% (3.47) to 76.4% (4.04)]. The anti-CD3 mAb 2C11 caused CD2 expression to increase from 72.6% (0.68) to 93.0% (1.74) while CD3 expression decreased from 69.1% (3.47) to 62.6% (2.15). The combination of anti-CD2 plus anti-CDS pre served CD2 expression (72.6 to 71.1%) while still decreasing CD3 expre ssion [69.1% (3.47) to 69.9% (2.37)]. Modulation of CD2 and CD3 expres sion was similar on mixed splenic T lymphocytes and isolated CD4 and C DS subsets, Modulation did not change with the addition of the cytokin es IL-1, IL-2, IL-4, IL-6, IL-10, TNF alpha, or TGF beta. Kinetic stud ies showed that modulation of CD2 was rapid, persistent, and of the sa me magnitude from Day 1 to Day 7 of culture while CD3 downmodulation w as transient. The results of transcriptional analysis and receptor dis tribution suggested that downmodulation was due to receptor internaliz ation while upmodulation was due to increased transcription. Analysis of expression of other adhesion molecules demonstrated that CD11a, CD1 8, CD44, CD45, CD48, CD54, and CD62L were significantly increased by e ither anti-CD2 or anti-CD3 mAbs while the combination was not synergis tic. However, anti-CD3 significantly decreased VLA-4 alpha (CD49d) exp ression and anti-CD2 enhanced this decrease. Conversely anti-CDS signi ficantly increased IL-2R (CD25) expression and anti-CD2 profoundly inh ibited the increase. These results show that anti-CD2 and anti-CDS mAb s significantly modulate CD2 and CD3 expression on T cells and modulat ion is accompanied by changes in the array of other T cell surface rec eptors. Changes in cell surface receptor display may provide an additi onal explanation for the synergistic effect of anti-CD2 plus anti-CD3 in prolonging allograft survival. (C) 1996 Academic Press, Inc.