Chronic lymphocytic leukemia (CLL) is an ideal disease for therapeutic vaccine strategies. While the leukemia cells are usually stealth-like, avoiding T cell recognition, they can be manipulated through ligation of CD40 on their surface to become very effective antigen presenting cells (APCs). Ligation of CD40 leads to expression of CD80, CD86 and upregulation of CD54. Other biochemical changes occur upon ligation of CD40, including upregulation of CD95, DR5, and expression of Bid, predisposing the leukemia cells to death-receptor-induced apoptosis. CLL cells can be made to express CD154 (CD40-ligand) using a replication-defective adenovirus. A phase I clinical trial with autologous CLL cells transduced to express murine CD154 previously demonstrated tolerability and clinical activity with this strategy (
Blood 96:2917, 2000
). More recently, a recombinant CD154 (ISF35) was produced, based on the human CD154 backbone, incorporating murine sequences needed for expression on CLL cells and with the proteinase cleavage site removed. We evaluated this new transgene in a phase I clinical trial, expecting to have similar tolerability to the murine CD154. Transduction of CLL cells results in expression of ISF35, ligation of CD40 on transduced and bystander cells, and the resultant downstream changes needed for antigen presentation and sensitivity to death receptor-induced apoptosis. We conducted a phase I study of a single infusion of autologous CLL cells transduced to express ISF35. Three dose levels were evaluated with 3 patients (pts) each: 1×108, 3×108, & 1×109 transduced cells. Infusions were well tolerated, no acute infusion-related toxicities were observed. ISF35-related toxicities consisted of grade 1–2 flu-like symptoms that occurred several hrs after the infusion and consisted of fever, arthralgia, myalgia, nausea, vomiting, and fatigue lasting 2–4 days and resolving in all cases. There were no dose-limiting toxicities at any dose level. Biologic responses were seen at all doses, there was no dose-response relationship. There were consistent decreases in absolute lymphocyte counts at all dose levels, indicating a therapeutic effect. This was not dose-related, and ALC returned to pre-treatment level after 1–2 months post-infusion. There was consistent induction of CD95 and DR5 expression on bystander cells in vivo by 3 days following infusion, which lasted 2–3 weeks. Furthermore, consistent induction of Bid expression in bystander cells was seen by wk 1, also lasting 2–3 wks. Finally, consistent increases in absolute T cell counts (both CD4+ & CD8+) were seen, peaking 1–4 wks post infusion. These results demonstrate that ISF34-transduced autologous leukemia cells can be given safely at up to 1×109 transduced cells, without dose-limiting toxicities, and resulting in phenotypic and biochemical changes in bystander leukemia cells in vivo that render the cells able to present antigen and priming them for death-receptor-induced apoptosis. Furthermore, clinical responses were seen with reduction in leukemia counts and increases in absolute T cell counts. We expect that multiple, sequential doses will be needed for maximal therapeutic effect with this strategy. Given these results, we have developed a phase II trial of repeated doses of autologous ISF35-transduced leukemia cells for patients with CLL.
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