Whole tumor antigen vaccines

Abstract

Although cancer vaccines with defined antigens are commonly used, the use of whole tumor cell preparations in tumor immunotherapy is a very promising approach and can obviate some important limitations in vaccine development. Whole tumor cells are a good source of TAAs and can induce simultaneous CTLs and CD4(+) T helper cell activation. We review current approaches to prepare whole tumor cell vaccines, including traditional methods of freeze-thaw lysates, tumor cells treated with ultraviolet irradiation, and RNA electroporation, along with more recent methods to increase tumor cell immunogenicity with HOCl oxidation or infection with replication-incompetent herpes simplex virus.

Figure 1

Comparison of immunogenicity of human DCs pulsed with different lysate preparations of SKOV3 ovarian cancer cells. Autologous DC from HLA-A2+ donor, derived from elutriated peripheral blood monocytes treated with GM-CSF and IL-4 for 48 hours, were pulsed with lysates of SKOV3 cells, which express Her2, for 4 hours and matured overnight with LPS and IFN-γ. DCs were then used to prime naive, autologous lymphocytes for 10 days. Output T cells were incubated overnight with T2 cells pulsed with HLA-A2 restricted Her2 peptide or unpulsed T2 cells. The relative presence of functional Her-2 reactive lymphocytes was measured by IFN-γ ELISA. DCs were pulsed with freeze-thaw lysates of HOCl-treated whole tumor cells (HOCl); supernatants [HOCl (S)] or pellets [HOCl (P)] of freeze-thaw lysate of HOCl-treated tumor cells; freeze-thaw lysates of H₂O₂-treated whole tumor cells (H2O2); supernatants of freeze-thaw lysate of UVB-irradiated tumor cells (UV); and supernatants [F/T (S)] or whole freeze-thaw tumor cell lysate [F/T (L)]. Unpulsed DCs (No ag) were also matured with LPS and IFN-γ. Error bars represent data from duplicate co-culture wells. T cell priming against Her2 was highest in T cells incubated with DCs pulsed with HOCl-oxidized whole tumor cells.

Figure 2

Activation of mouse DCs by tumor cells killed with oncolytic replication-restricted HSV. (A) Tumor-infiltrating CD8+ T cells isolated from ID8 tumors were incubated with bone marrow derived DCs that were pulsed with ID8 ovarian tumor cells killed by HSV-1716 (clear) or DCs pulsed with UV-irradiated ID8 cells (gray). DCs pulsed with viral oncolysate induce more pronounced proliferation of CD8+ T cells, as assessed by CMTMR dilution. (B) Flow cytometry analysis of NKG2D ligand (NKG2DL) expression in (left) unpulsed immature DCs (gray) or unpulsed DCs matured with LPS (clear), and (right) control unpulsed DCs (gray) and DCs pulsed with ID8 cells killed by HSV-1716 (clear). NKG2DL was detected through NKG2D/FC chimera (R&D). (C) Percent of CD25+ activated NK cells as determined by flow cytometry analysis 48 hours after incubation with immature DCs or DCs pulsed with apoptotic cells killed with HSV-1716 (1716-APO), in the presence or absence of soluble NKG2D (5 g/ml).

Figure 3

Upregulation of stress response protein GRP94 in TC-1 cells 24 hours after infection with HSVd106 (1 MOI), TC-1 cells irradiated with UV-B and control TC-1 cells (CTRL). Magnification 200×.

Figure 4

Antitumoral effect of DCs electroporated with whole tumor RNA in the C56BL/6 mouse. (A) Kaplan-Meier curves depict tumor-free percentages in mice vaccinated prophylactically with DCs electroporated with total RNA extracted from TC-1 cells (50 μg of TC-1 RNA/10₆ DCs in 200 μL at 300 mV and capacitance of 150 μF) with or without CpG (5″ TCCATGACGTTCCTGATGCT-3″). CpG was added at 0.1 or 1 μg/ml to the RNA mixture immediately before DC electroporation. CpG enhanced DC efficacy in a dose-dependent manner, reducing significantly tumor incidence. (B) Growth of flank TC-1 tumors in the above animals.