Flow Cytometry Analysis of Peripheral Blood CD4+/CD25+/FOXP3+ T Regulator Cells from 11 Patients Treated with Ipilimumab Following Relapse of Malignancy after Allogeneic Hematopoietic Stem Cell Transplantation.

We conducted a multi-center dose-escalation trial to assess whether CTLA-4 blockade is safe and efficacious as immunotherapy in patients with relapse of malignancy following allogeneic hematopoietic stem cell transplantation (allo-HCT). We hypothesized that since CTLA-4 is a negative regulator of effector T-cell activation, inhibition of CTLA-4 ligation with a blocking human monoclonal antibody (ipilimumab) will augment graft-versus-malignancy. Here we report on the effects of a single dose of ipilimumab on in vivo T cell subsets from 11 patients treated at the highest dose level (3 mg/kg) and compare these findings with those in normal volunteer donor lymphocytes. We analyzed the expression of intracellular CTLA-4 and FOXP3 on CD4+/CD25+ Treg cells, intracellular cytokines and surface markers for T-cell activation on peripheral T cells from 11 patients and 9 normal donors. Peripheral blood mononuclear cells (PBMC) from patients before (day 0) and after the treatment at day 1, 3, 7, 14 and 30 were stained with a panel of antibodies and analyzed by flow cytometry. Lymphocytes from normal donors at time zero and 3 days after culture in IL-2 (200u/ml) were used as controls. The pre-treatment expression of intracellular CTLA-4 was significantly higher in CD4+ T cells from patients than normal controls and was increased further after antibody treatment from 7.1±3.8% at day 0 to 18.2±7.1% at day 30 (p=0.02). Although the expression of FOXP3 in CD4+/CD25+ T cells was higher in patients than in normal donors (6.3±4.8% compared with 2.0±1.6%, p=0.02), there was no significant change in the levels following ipilimumab infusion. The expression of CD4+/CD25high in the patients was 7.7±2.8%, higher than the normal donors (2.3±1.1%). However, 6/11 cases had increased expression while others had decrease or no change, overall there was no statistically significant change. CD4+/CD25low activated T cells were elevated in 10/11 patients before ipilimumab (42.1±8.5%). Their levels were not affected by CTLA-4 blockade. CD8+/CD69+ activated T-cells were significantly increased in 8/11 patients within the 30 days after ipilimumab treatment but typically returned to baseline values on longer follow-up. CD4+/CD69+ and CD4+/HLA-DR+ T-cells were unchanged following ipilimumab treatment. These data show that a single dose of ipilimumab enhances levels of some subsets of activated T cells without a significant effect on cells with a T-regulatory phenotype.