Adoptive Cell Therapy for Lymphoma: Use of CpG-Loaded Tumor Cells to Generate Potent Anti-Tumor CD4 T Cell Immunity.

Recently, we have investigated adoptive cell therapy for treating lymphoma. The efficacy of this maneuver has been demonstrated by curing large established tumors. Specifically, we use active immunization to generate anti-tumor T cells in vivo and transfer these T cells into lymphodepleted recipient mice (Brody J, Goldstein MJ, Czerwinski DK, and Levy R; Blood, 2009). A major challenge in adoptive therapy is the method of generating anti-tumor T cells. Traditionally, tumor-specific T cells are expanded to large numbers ex vivo. Herein, we describe a new, whole-cell vaccine that is effective in inducing anti-tumor T cells in vivo. This vaccine combines tumor antigens with an immune stimulant: irradiated-tumor cells (a source of tumor antigens) are loaded with the TLR agonist CpG (an immune stimulant). Our vaccine approach has several potential advantages: (1) anti-tumor immunity generated by our CpG-loaded, whole-cell vaccine is poly-antigenic and thus, not limited by the expression of a single antigen target on tumor cells; (2) ex vivo expansion may generate large numbers of effector T cells that can induce tumor regression in the short-term, but have a limited ability to maintain a persistent anti-tumor response. Our model avoids ex vivo manipulation of anti-tumor T cells and thus, may preserve and enhance a memory T cell population that sustains the anti-tumor response.

We derived a new pre-B cell lymphoma cell line in the C57BL/6 background. Primary bone marrow cells were isolated from C57BL/6 donor mice and transfected with a recombinant retrovirus containing the Bcr-Abl oncogene. The emerging transformed cell line was designated H11. This cell line expressed the B lineage marker CD19 but was negative for MHC II and surface Ig. Irradiated H11 tumor cells were pre-loaded with CpG for 24 hours and administered to donor mice by daily, sub-cutaneous injections for five days. Donor splenocytes were harvested seven days following vaccination and adoptively transferred into lethally irradiated recipient mice that were subsequently challenged with a lethal dose of H11 tumor cells.

Vaccination with CpG-loaded H11 tumor cells (CpG-H11) generated anti-tumor T cells that are effective in adoptive cell therapy. 100% of mice receiving adoptive therapy with vaccine-induced T cells were protected from tumor challenge. In contrast, vaccination of donor mice with untreated H11 tumor was insufficient for generating anti-tumor T cells. Only 20% of mice treated with T cells from these donors were protected from tumor challenge. In spite of the H11 tumor being MHC Class II⁻, we observed that anti-tumor immunity generated by the CpG-H11 vaccine was CD4 T cell mediated. CD4 T cells were isolated from CpG-H11 vaccinated donors by flow cytometry. Fewer than 1.8×10⁶ CD4 T cells were sufficient to protect 80% of recipient mice from tumor challenge. In contrast, equivalent numbers of donor CD8 T cells provided no benefit. These results strongly suggest that the CpG-H11 vaccine induced cross-presentation of tumor antigens by antigen-presenting cells (APCs). We have demonstrated that CpG-loaded H11 tumor cells can leak CpG into the immediate environment activating nearby APCs. These APCs have greater phagocytic potential and express higher levels of co-stimulatory molecules such as CD40. Ongoing studies will determine whether APCs which encounter the CpG-H11 vaccine but not untreated H11 tumor cells, can stimulate proliferation of anti-tumor T cells.

Here we describe a novel, whole-cell vaccine approach that induces anti-tumor T cells for adoptive therapy to treat lymphoma. This vaccine is superior to vaccination with tumor cells alone. We are currently developing this therapy for evaluation in a clinical trial to treat mantle cell lymphoma.

No relevant conflicts of interest to declare.