Immunomodulatory Effects of Combination of Pooled Human Gammaglobulin and Rapamycin on Cell Proliferation and Apoptosis in the Mixed Lymphocyte Reaction

Background. Multidrug immunosuppressive regimens benefit transplant recipients, reducing side effects and creating synergy between medications with different mechanisms of action. We have shown that pooled human gammaglobulin (intravenous immunoglobulin [ IVIG] ) inhibits the mixed lymphocyte reaction (MLR) and induces apoptosis primarily in B cells. Rapamycin (RAPA), a potent macrolide immunosuppressant, inhibits B- and T-cell proliferation through G 1 cell-cycle blockade and purportedly induces apoptosis. Here we examined the possible synergistic effects of IVIG and RAPA on cell proliferation and apoptosis induction in the MLR. Methods. MLR was performed with IVIG (0.2-5 mg/mL), RAPA (0.02-40 ng/mL), alone or in combination. Cell proliferation was detected by 3 H-thymidine incorporation, and apoptosis by Annexin V and terminal deoxynucleotide transferase-mediated dUTP nick-end labeling flow cytometry. Results. IVIG or RAPA inhibited cell proliferation in a dose-dependent manner. RAPA (0.02-40 ng/mL) in combination with IVIG (5 mg/mL) significantly augmented the inhibition compared with RAPA alone (70% vs. 34% at 0.2 ng/mL; 90% vs. 76% at 2 ng/mL). Apoptosis was significantly higher in IVIG-treated (5 mg/mL) CD19+ cells and less so in CD3+ cells. However, RAPA (0.2-40 ng/mL) neither induced apoptosis nor altered apoptosis induced by IVIG. Conclusions. Combined RAPA and IVIG at subtherapeutic concentrations inhibits cell proliferation in the MLR. RAPA neither induces apoptosis nor augments apoptosis induced by IVIG in the MLR. Lower-concentration RAPA (0.2-2 ng/mL) in combination with IVIG (5 mg/mL) versus therapeutic levels (2-50 ng/mL and 10-40 mg/mL, respectively) could represent an effective immunomodulatory drug combination.