A prostate cancer vaccine comprising whole cells secreting IL-7, effective against subcutaneous challenge, requires local GM-CSF for intra-prostatic efficacy

Abstract

A panel of cytokine-secreting RM-9 prostate cancer cells were tested as whole cell vaccines to determine their capacity to evoke an anti-prostate cancer immune response. In our model, vaccines secreting mGM-CSF or mIL-7 resulted in the highest increase in circulating T lymphocytes after vaccination, prolonged survival and, in a proportion of animals, tumor-free survival. Anti-tumor effects were more evident after a subcutaneous RM-9 challenge than after an intraprostatic challenge. However, when the RM-9/mGM-CSF cell line was used as intraprostatic tumor challenge, protection after RM-9/mIL-7 vaccination was restored.

Fig. 1

Survival of vaccinated mice after subcutaneous challenge with RM-9 cells. Mice were vaccinated with 1 × 10⁶ γ-irradiated cells or PBS. Vaccines were administered once a week for three consecutive weeks, followed by a challenge of RM-9 cells in the fourth week. Tumor size was measured in time and survival determined (* P < 0.05 compared to the RM-9 vaccinated group)

Fig. 2

The systemic response of CD3⁺/CD4⁺ (a) and CD3⁺/CD8⁺ (b) lymphocytes at T = 0 (before vaccination) and T = 1 (after vaccination, before challenge administration). Blood was taken via retro-orbital puncture, stained for CD3⁺/CD4⁺ or CD3⁺/CD8⁺ lymphocytes and were quantified by FACS analysis. The mean cell count per 10,000 cells ± SEM is depicted (* P < 0.05 compared to the RM-9 vaccinated group)

Fig. 3

Immune histochemistry of endpoint tumors (tumor ≥ 1,500 mg) of the different vaccination groups. Frozen sections were stained with HE or for CD4⁺, CD8⁺, CD11b⁺ or CD19⁺ cell markers and scored three times on three different days

Fig. 4

Survival of vaccinated C57bl/6 mice after intraprostatic challenge. a C57bl/6 mice were subcutaneously vaccinated once a week for three consecutive weeks, followed by an intraprostatic RM-9 challenge in the fourth week and monitored for tumor development via transrectal ultrasonography (* P < 0.05 compared to the RM-9 vaccinated mice). b C57bl/6 mice were s.c. vaccinated with PBS or RM-9/mIL-7 once a week for three consecutive weeks, followed with an intraprostatic challenge with RM-9 or RM-9/mGM-CSF in the fourth week and was monitored for tumor development via transrectal ultrasonography and survival was determined (* P < 0.05 compared to RM-9/mIL-7 vaccinated mice challenged with an RM-9 challenge). c Immune histochemistry of endpoint tumors (tumor ≥ 1,000 mg) of mice challenged intraprostatically with either RM-9 or RM-9/mGM-CSF after vaccination with PBS or RM-9/mIL-7. Frozen sections were stained for HE or for CD4⁺, CD8⁺, CD11b⁺ or CD19⁺ cell markers and scored three times on three different days