Molecular and cellular strategies to enhance efficacy of T cell-based cancer therapy

A combined approach of vaccination with β2-microglobulin (β2m)-deficient dendritic cells (DCs) and granulocyte-macrophage colony-stimulating factor (GM-CSF) as a potent adjuvant may link cellular and molecular strategies to further enhance anti-tumor T-cell responses. T lymphocytes can mediate a potent anti-tumor immune response. CD8+ T lymphocytes screen and recognize antigen in complex with a major histocompatibility complex (MHC) class I heavy chain (HQ and the β2m light chain. Metastatic cells commonly escape from "conventional" T lymphocyte-mediated recognition and elimination as a result of impaired cell surface expression of MHC class I antigen molecules. This impaired cell surface expression can be caused by loss or down-regulation of expression of different components of the MHC class I antigen processing machinery, such as MHC class I HCs, β2m, or the transporter associated with antigen processing (TAP). Such immune evasion poses a problem for autologous T cell-based cancer therapy.

In the first study we demonstrated protection against growth Of β2m-deficient tumor cells in syngeneic C57Bl/6 (B6) mice, following vaccination with β2m-deficient DCs. In vitro analysis of an effector cell population from vaccinated mice pointed to that CD3+ cells had been generated with the capability to induce apoptosis in syngeneic β2m-deficient tumor and nonmalignant cells. Further investigation of target cell recognition suggested that also tumor target cells lacking expression of classical MHC class I HCs and functional TAP were recognized by CD3+ effector cells from vaccinated mice. This study points to a new possible strategy to counteract the growth of metastatic cells.

The cytokine composition in the tumor microenvironment is a critical factor for an effective antitumor immune response. GM-CSF has been shown to be a very promising cytokine in anti-tumor immunomodulation. Continuously high concentrations of GM-CSF in the local tumor environment seem to be crucial to reach a therapeutic threshold. Such a favorable cytokine milieu can promote recruitment of DCs and augment DC activation with increased number of DCs expressing MHC and co-stimulatory molecules. GM-CSF can enhance tumor infiltration of T lymphocytes and their cross-priming. Furthermore, GM-CSF seems to trigger an increased and significantly more effective tumor lysis mediated by lymphocytes. GM-CSF has elicited anti-tumor immune responses in animal studies and clinical trials. However, the clinical efficacy has been limited, with local GM-CSF levels being therapeutically insufficient or systemic toxicity being a limiting factor.

In the second study, we developed and characterized a novel GM-CSF expression vector, pAD-HotAmp-GM-CSF, which can provide heat-inducible high-level expression of GM-CSF. In cytokine immunotherapy of cancer it is critical to deliver sufficiently high local cytokine concentrations in order to reach the therapeutic threshold needed for clinical efficacy. The novel vector, pAD-HotAmp-GM-CSF successfully integrates inducible and amplifying elements into a one-plasmid system. Moderate hyperthermia at 42°C for 30 min induced amplification of GM-CSF expression in pAD-HotAmp-GM-CSF that was over 2,8 fold higher than levels achieved with the prototypical human cytomegalovirus (CMV) promoter. Thus, the inducible amplifier vector, pAD-HotAmp-GM-CSF, represents a novel system for regulated and enhanced GM-CSF expression, which enables both greater efficacy and safety in cytokine immunotherapy of cancer.

List of scientific papers

I. Dammeyer P, Biberfeld P, Rethi B, Chiodi F, Wolpert EZ (2006). Enhanced protection against growth of an MHC I-deficient tumor after vaccination with beta2-microglobulin-deficient dendritic cells. [Manuscript]

II. Dammeyer P, Jaramillo MC, Pipes BL, Badowski MS, Tsang TC, Harris DT. (2006). Heat-inducible amplifier vector for high-level expression of granulocyte-macrophage colony-stimulating factor. Int J Hyperthermia. 22(5): 407-19.
https://pubmed.ncbi.nlm.nih.gov/16891243