Phenotypic Changes Associated with Acute Reductions In Leukemia Cell Counts In Patients with Chronic Lymphocytic Leukemia (CLL) Receiving Lenalidomide as Initial Therapy

Abstract 59

Immune therapy represents a promising treatment approach in CLL as demonstrated by long-term disease control in pts treated with allogeneic stem cell transplant as well as improved outcomes in pts treated with combination chemoimmunotherapy. Lenalidomide is an immunomodulatory agent with clinical efficacy in CLL. The precise mechanism of lenalidomide's clinical activity in CLL has not yet been defined. Previous reports have demonstrated upregulation of costimulatory molecules on leukemia cells following exposure to lenalidomide and improved capacity of CLL cells to form immune synapses with T cells. Lenalidomide treatment of CLL cells has been associated with an activation phenotype similar to that induced in CD154 gene therapy studies. The CLL Research Consortium is conducting a phase II study to evaluate the combination of lenalidomide and rituximab in treatment-naïve CLL pts who are in need of therapy. This previously untreated population provides a relatively uniform group in which to study the immunomodulatory effects of lenalidomide in CLL. Prior to the administration of rituximab, immunophenotyping was performed on peripheral blood mononuclear cells from pts before and after 21 days of single agent lenalidomide. Mean fluorescent intensity (MFI) was determined on CD19+ lymphocytes relative to isotype-control stained cells. Two-sided Student t-tests were used to assess statistical significance. All pts received lenalidomide 2.5 mg daily for the first 7 days. The dose was escalated to 5 mg on day 8 if they lacked toxicity. 53 pts have been enrolled on study and samples from 38 pts have been assessed for changes in the composition of blood lymphocytes and CLL-cell phenotype following 21 days of single-agent lenalidomide. The absolute numbers of CD19/CD5+ leukemia cells decreased in 35/38 pts (median 48%), whereas the relative percentages of CD4+ and CD8+ T cells increased after therapy. The absolute numbers of T cells increased in 11/38 pts. CLL-cell stained for CD40 had a median MFI of 22 before therapy and 31.1 after therapy (P ≤ 0.0001), increasing in 32/38 pts. Similarly, the median MFI of CLL cells labeled for CD80 or CD86 was respectively 0.7 or 1.8 prior to therapy and 0.9 (p ≤ 0,001) or 3 (P ≤0.02) on day 21. Consistently, the CLL expression of CD54 was increased in post-treatment samples relative to pretreatment CLL cells. The median MFI of CLL cells for CD54 was 54 prior to therapy and 107 on day 21 of therapy (P ≤ 0.00001). Similarly, the median MFI of CD95 (Fas) on CLL cells was 13.1 prior to and 22.5 on day 21 (P ≤ 0.0001). The median MFI of DR5 (CD262) on CLL cells prior to treatment was 10.4 and 15.2 (P ≤ 0.002) post. We observed heterogeneous changes in the expression of HLA-DR on CLL cells; the median MFI of CLL cells for HLA-DR was 189 prior to therapy and 236 (p=0.04) on day 21. We examined whether the relative changes in the CLL cell-surface phenotype were associated with the relative magnitude of the reductions observed in CLL-cell blood counts during the first 21 days of treatment for the first 21 pts studied. We found that leukemia cells from those pts who achieved a > 50% reduction in absolute leukemia cell counts during the first 3 weeks of therapy had significantly greater induction of CD95 (p = 0.01) and HLA-DR (p = 0.004). Similarly, the relative magnitude of increase in expression of CD95 or HLA-DR correlated with the relative reduction in leukemia counts when analyzed as a continuous variable. No significant relationship was observed between the change in CD40 expression and early response to lenalidomide. CD20 expression on CLL cells was not significantly changed from pretreatment levels. Relative increases in the percentage of NK cells observed in these pts may be related to lenalidomide priming of the immune system and contribute to sensitivity to rituximab. Accrual to this study is ongoing. At interim analysis the criteria for continuing accrual to a total of 40 pts in each stratum were met with at least 2 clinical complete responses in each arm. This study reveals a significant association between the relative induction of CD95 and HLA-DR on CLL cells and the relative magnitude of acute reductions observed in leukemia-cell blood counts during the first three weeks of treatment with single-agent lenalidomide. These data are consistent with a model that proposes the relative response to lenalidomide is associated with the relative extent of immune activation of CLL cells induced by lenalidomide in vivo.