Mechanisms of rejection during OKT3 therapy: propagation and characterization of CD3 resistant allospecific cytotoxic T cells from a rejecting liver allograft

Cytokine profiles in early rejection following OKT3 treatment in liver transplant patients

OKT3 , a murine monoclonal antibody specific to the human CD3 complex, induces immunosuppression by depletion of T cells. Administration of OKT3 results in significant release of proinflammatory cytokines, such as TNFalpha and IL1beta. Liver recipients who experience rejection within 3 weeks after transplantation with OKT3 prophylaxis recover their T cells by postoperative day 10 despite complete initial clearance. We sought to analyze the role of proinflammatory and Th-1 cytokines in T cell recovery and rejection after liver transplantation with OKT3 prophylaxis. In plasma samples from 32 patients, we measured TNFalpha, IL1beta and IL6 (before transplant and on postoperative days 1, 2 and 3) and IL2, IFNgamma, sIL2R and slCAM (postoperative days 5, 7 and 10) and examined possible correlations with T-cell recovery and occurrence of rejection within 3 weeks. TNFalpha, IL1beta, and IL6 did not correlate with T-cell recovery. In patients who rejected, IL2 and IFNgamma on postoperative days 5 and 7 correlated with degree of T-cell recovery by day 10; a significant rise in sIL2R over time also correlated with T-cell recovery in this group. Our results emphasize the role of Th-1 cytokines in rejection following OKT3 induction and suggest that markers of T cell activation may predict risk.

Specific CD3ε Association of a Phosphodiesterase 4B Isoform Determines Its Selective Tyrosine Phosphorylation After CD3 Ligation

cAMP-specific phosphodiesterases (PDE) comprise an extensive family of enzymes that control intracellular levels of cAMP and thus regulate T cell responses. It is not known how the function of these enzymes is altered by TCR engagement. We have examined this issue by studying one of the PDE isozymes (PDE4B). PDE4B RNA and protein were detected in resting PBLs, and the levels of PDE4B protein increased with cell cycling. In peripheral blood T cells, two previously reported PDE4B isoforms could be detected: one was 75–80 kDa (PDE4B1) and the other was 65–67 kDa (PDE4B2). These two isoforms differed in their N-terminal sequence, with the presence of four potential myristylation sites in the PDE4B2 that are absent in PDE4B1. Consequently, only PDE4B2 was found in association with the CD3ε chain of the TCR. In addition, although both isoforms were phosphorylated in tyrosines in pervanadate-stimulated T cells, only the TCR-associated PDE4B2 was tyrosine-phosphorylated following CD3 ligation. The kinetics of phosphorylation of TCR-associated PDE4B2 correlated with changes in cAMP levels, suggesting that tyrosine phosphorylation of the TCR-associated PDE4B isoform upon engagement of this receptor may be an important regulatory step in PDE4B function. Our results reveal that selectivity of PDE4B activation can be achieved by differential receptor association and phosphorylation of the alternatively spliced forms of this PDE.

Use of OKT3 monoclonal antibody as induction therapy for control of rejection in liver transplantation

This report details a single center's experience with OKT3 induction immunosuppression for liver transplantation. One hundred ninety-nine consecutive, unselected adult liver recipients received OKT3 therapy for 9-10 days combined with low-dose steroids and azathioprine. Cyclosporine was begun to overlap with the last few days of OKT3 therapy. The average dose of OKT3 was 45 mg. Fifty-two patients (26.1%) experienced 57 episodes of acute rejection. The median time of onset of rejection was 18 days after grafting. Seventy-eight percent of the rejection episodes were steroid-sensitive. Recurrent rejection was uncommon and the need for OKT3 retreatment was infrequent. One year actuarial graft and patient survival was 79.7% and 82.3% respectively. Based on this evidence, it appears that OKT3 prophylaxis provides good control of acute rejection with a very low incidence of recurrent rejection.

Soluble MHC class I antigens (sHLA) and anti-HLA antibodies in heart and kidney allograft recipients

Soluble HLA (sHLA) antigens were measured in a panel of 50 renal and 50 cardiac graft recipients by a quantitative ELISA over periods ranging between 2 months and 3 years. 72% of the renal patients and 68% of the cardiac graft patients experienced episodes of acute rejection during the observation period. sHLA were elevated to over 2-5 times the normal levels up to 10 days before histological evidence of rejection. This duration was for each individual patient very variable. Cytomegalovirus (CMV) infections did not appear to elevate sHLA levels. Donor-specific HLA-A2 was measured in only 1 cardiac recipient. 15% of the sera obtained from cardiac patients had cytotoxic anti-HLA antibodies, when tested against a panel of 50 test cells. After thermal inactivation at 56 degrees C, 42.5% of the sera became positive against at least 10% of the test cells. This finding suggests thermal dissociation of immune complexed anti-HLA antibodies. sHLA measurement and careful monitoring of serum for the presence of cytotoxic anti-HLA antibodies in graft patients are useful techniques which could help predict the long-term fate of an allograft.