Efficacy of cytokine gene transfection may differ for autologous and allogeneic tumour cell vaccines

Abstract

Whole tumour cells are a logical basis for generating immunity against the cancers they comprise or represent. A number of human trials have been initiated using cytokine-transfected whole tumour cells of autologous (patient-derived) or allogeneic [major histocompatibility complex (MHC)-disparate] origin as vaccines. Although precedent exists for the efficacy of autologous-transfected cell vaccines in animal models, little preclinical evidence confirms that these findings will extrapolate to allogeneic-transfected cell vaccines. In order to address this issue a murine melanoma cell line (K1735) was transfected to secrete interleukin (IL)-2, IL-4, IL-7 or granulocyte-macrophage colony-stimulating factor (GM-CSF); cytokines currently in use in trials. The efficacy of these cells as irradiated vaccines was tested head-to-head in syngeneic (C3H) mice and in MHC-disparate (C57BL/6) mice, the former being subsequently challenged with K1735 cells and the latter with naturally cross-reactive B16-F10 melanoma cells. Whilst the GM-CSF-secreting vaccine was the most effective at generating protection in C3H mice, little enhancement in protection above the wild-type vaccine was seen with any of the transfections for the allogeneic vaccines, even though the wild-type vaccine was more effective than the autologous B16-F10 vaccine. Anti-tumour cytotoxic T-lymphocyte (CTL) activity was detected in both models but did not correlate well with protection, whilst in vitro anti-tumour interferon-gamma (IFN-gamma) secretion tended to be higher following the GM-CSF-secreting vaccine. Cytokine transfection of vaccines generally increased anti-tumour CTL activity and IFN-gamma secretion (T helper type 1 response). Further studies in other model systems are required to confirm this apparent lack of benefit of cytokine transduction over wild-type allogeneic vaccines, and to determine which in vitro assays will correlate best with protection in vivo.

Figure 1

Protection from tumour-challenge following vaccination. Groups of C3H mice (a, n = 9) or C57BL/6 (b, n = 6; c, n = 7) mice were given 5 × 10⁶ vaccine cells (irradiated 100 Gy) subcutaneously. Twelve days later mice were challenged with 5 × 10⁵ K1735wt (a), or 2 × 10⁴ B16-F10 (b,c) syngeneic tumour cells. Tumour development was monitored. Whilst K1735-GM-CSF elicited clearest protection in C3H mice, none of the transfectants elicited sustained protection over K1735-wt in C57BL/6 mice.

Figure 2

CTL activity following vaccination. Following vaccination of mice, as in Figure 1, spleens were taken on day 11 following vaccination and examined for in vitro CTL activity against autologous tumour cells (a, K1735wt; b, B16-F10) in a standard ⁵¹Cr assay. The mean percentage specific lysis from three separate mice is shown. (SD, not shown to maintain figure clarity, was typically < 15%). E : T, effector to target ratio.

Figure 3

Secretion of IFN-γ by splenocytes from vaccinated mice. Splenocytes were taken from mice (vaccinated as in Figure 1) on day 11 after vaccination and cultured at 10⁶/ml for 5 days with irradiated autologous tumour cells (a, K1735wt; b, B16-F10) at 5 × 10⁴/ml. IFN-γ production was measured by ELISA and expressed as the mean (+ SD) for three separate mice.

Figure 4

Proliferation of splenocytes from vaccinated mice. Splenocytes were taken from mice (vaccinated as in Figure 1) on day 11 after vaccination and cultured at 10⁵/well of a 96-well plate for 3 days, the last 6 hr of which was with [³H]thymidine. Cells were harvested and β-emmission was counte; c.p.m., counts per minute.

Figure 5

Growth of transfected tumour cells in vivo. Groups of C3H (a, n = 8) or nude (b, n = 4) mice were inoculated subcutaneously with 5 × 10⁵ unirradiated tumour cells and tumour development was monitored. K1375-wt and K1735-GM-CSF grew into progressing tumours in both (a) and (b). K1735-IL-2, IL-4 and IL-7 all grew in nude mice but failed to grow in the majority of C3H mice.