Augmentation of antitumor immune responses after adoptive transfer of bone marrow derived from donors immunized with tumor lysate-pulsed dendritic cells.

We demonstrated previously that tumor lysate-pulsed dendritic cells (TP-DC) could mediate a specific and long-lasting antitumor immune response against a weakly immunogenic breast tumor during early lymphoid reconstitution. The purpose of this study was to examine the potential therapeutic efficacy of bone marrow transplants from TP-DC-vaccinated donors. In 2 aggressive metastatic models, bone marrow transplantation with donor bone marrow cells from TP-DC-immunized mice mediated a tumor-specific immune response in the recipient, and this caused regressions of preexisting tumor metastases. After vaccination with TP-DC, donors harbored increased numbers of both activated CD4+ and CD8+ T-cell populations in the bone marrow. Adoptive transfer of T cells purified from the bone marrow of TP-DC-vaccinated mice led to a reduction in preestablished lung metastases, whereas depletion of T cells from bone marrow abolished this effect. By using T cells derived from the bone marrow of TP-DC-vaccinated major histocompatibility complex class I and class II knockout mice, the effector cells required for the observed antitumor effect were determined to be major histocompatibility complex class I-restricted CD8+ T cells. Additionally, the tumor burden in TP-DC-immunized transplant recipients could be reduced further by repetitive TP-DC immunizations after bone marrow transplantation. Collectively, these results demonstrate an important therapeutic role of bone marrow from TP-DC-immunized donors and raise the potential for this approach in patients with advanced cancer.

Tumor lysate-pulsed dendritic cells can elicit an effective antitumor immune response during early lymphoid recovery.

Dendritic cells (DC) can serve to immunize the newborn immune system to foreign antigen. In a lymphopenic environment, naive T cells undergoing homeostasis-driven proliferation can acquire increased sensitivity to antigen stimulation. Here, we evaluated the capacity of DC to effectively prime the host immune system to elicit antitumor effects in the setting of early lymphoid reconstitution after bone marrow transplantation (BMT). Indeed, bone marrow-derived, cytokine-driven DC pulsed with whole tumor lysates (TP-DC) could, early on, prime a specific and long-lasting antitumor immune response, which mediated the rejection of a lethal challenge of a weakly immunogenic breast tumor. In the therapeutic setting, TP-DC could also inhibit the growth of preexisting breast tumor metastases by repetitive immunizations initiated early after BMT. Spleen T cells obtained from mice immunized with TP-DC early after BMT showed a substantial increase in tumor-specific IFN-gamma production. Our findings demonstrate that it is possible to promote effective antitumor immunity in a defined lymphopenic environment through DC-based immunization.