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T cells from patients successfully treated with OKT3 do not react with the T-cell receptor antibody
H M Gebel1, L K Lebeck, S C Jensik
1Department of Immunology, Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612.
Abstract:
The mechanism of OKT3 therapy is complex and may include depletion of circulating CD3 cells, modulation of the CD3 molecule, and/or functional inactivation of T cells. Although the absolute number of circulating CD3 cells in OKT3-treated patients is used to monitor therapy, many laboratories assign CD3 numbers based on reactivity with OKT3. These CD3 numbers could be artificially low since the epitope recognized by OKT3 may already be occupied. Using a monoclonal antibody against a different CD3 epitope, we detected CD3 expression on T lymphocytes from 18/18 OKT3-treated patients. Nonetheless, OKT3 therapy in these patients was clinically successful, suggesting that monitoring patients solely for CD3 is uninformative. Since CD3 is associated with the T-cell receptor (TcR), we also evaluated alpha-TcR-1, a monoclonal antibody which detects a conformational determinant of the CD3/TcR alpha/beta complex, and found that less than 1% of the CD3 cells from OKT3-treated patients reacted. Furthermore, these cells were unresponsive to allogeneic stimulation. However, when patient cells were cultured overnight in the absence of OKT3, both alpha-TcR 1 binding and responsiveness to allogeneic stimulation became detectable. Thus, the monitoring of patients treated with OKT3 can be more informative if lymphocytes are tested for reactivity with alpha-TcR-1 and an alpha-CD3 antibody other than OKT3.
Insights
Monitoring OKT3 therapy requires more than just CD3 cell counts. Using alternative antibodies like alpha-TcR-1 reveals T-cell receptor function, offering a clearer picture of treatment effectiveness in patients.
Area of Science:
- Immunology
- Transplantation Immunology
- Cellular Therapy
Background:
- OKT3 (muromonab-CD3) is an immunosuppressive monoclonal antibody used in transplantation.
- Its mechanism involves T-cell modulation, but monitoring its efficacy via CD3 cell counts can be misleading.
- Standard CD3 counts may be artificially low due to OKT3 binding to the CD3 epitope.
Purpose of the Study:
- To investigate reliable methods for monitoring OKT3 therapy effectiveness.
- To evaluate T-cell receptor (TcR) complex status in OKT3-treated patients.
- To determine if alternative antibody markers can provide more informative monitoring.
Main Methods:
- Analysis of CD3 expression on T lymphocytes using OKT3 and an alternative anti-CD3 antibody.
- Evaluation of alpha-TcR-1 binding to detect the CD3/TcR alpha/beta complex.
- Assessment of T-cell responsiveness to allogeneic stimulation in vitro.
- Comparison of results before and after overnight culture without OKT3.
Main Results:
- All OKT3-treated patients showed CD3 expression when using a non-OKT3 antibody.
- Less than 1% of CD3 cells from these patients reacted with alpha-TcR-1 and were unresponsive to stimulation.
- Post-culture, alpha-TcR-1 binding and responsiveness were restored, indicating functional T-cell recovery.
- Clinical success of OKT3 therapy was observed despite low CD3 counts.
Conclusions:
- Monitoring CD3 cell numbers alone is insufficient for assessing OKT3 therapy.
- The CD3/TcR alpha/beta complex detected by alpha-TcR-1 is functionally impaired during OKT3 treatment.
- Testing lymphocyte reactivity with alpha-TcR-1 and a non-OKT3 anti-CD3 antibody offers more informative monitoring of OKT3 therapy.