Responses to human CD40 ligand/human interleukin-2 autologous cell vaccine in patients with B-cell chronic lymphocytic leukemia

Purpose: Human CD40 ligand activates the malignant B-cell chronic lymphocytic leukemia cells and enhances their capacity to present tumor antigens. Human interteukin-2 further potentiates the immunogenicity of human CD40 ligand in preclinical marine models. Experimental Design: We prepared autologous B-cell chronic lymphocytic leukemia cells that expressed both human CD40 ligand (>90% positive) and human interleukin-2 (median secretion, 1,822 pg/mL/10⁶ cells; range, 174-3,604 pg). Nine patients were enrolled in a phase I trial, receiving three to eight s.c. vaccinations. Results: Vaccinations were administered without evidence of significant local or systemic toxicity. A B-cell chronic lymphocytic leukemia-specific T-cell response was detected in seven patients. The mean frequencies of IFN-γ, granzyme-B, and IL-5 spot-forming cells were 1/1,230, 1/1,450, and 1/4,500, respectively, representing a 43- to 164-fold increase over the frequency before vaccine administration. Three patients produced leukemia-specific immunoglobulins. Three patients had >50% reduction in the size of affected lymph nodes. Nonetheless, the antitumor immune responses were observed only transiently once immunization ceased. High levels of circulating CD4⁺/CD25 ⁺/LAG-3⁺/FoxP-3⁺ immunoregulatory T cells were present before, during and after treatment and in vitro removal of these cells increased the antileukemic T-cell reactivity. Conclusions: These results suggest that immune responses to B-cell chronic lymphocytic leukemia can be obtained with human CD40 ligand/human interleukin-2- expressing s.c. vaccines but that these responses are transient. High levels of circulating regulatory T cells are present, and it will be of interest to see if their removal in vivo augments and prolongs the antitumor immune response.