Combination of docetaxel and recombinant vaccine enhances T-cell responses and antitumor activity: effects of docetaxel on immune enhancement

Abstract

Purpose: Taxanes comprise some of the most widely used cancer chemotherapeutic agents. Members of this drug family, including docetaxel, are commonly used to treat breast, prostate, and lung cancers, among others. This study was designed to determine if this taxane has the ability to modulate components of the immune system independent of antitumor activity and to investigate the potential synergistic activities of the combination of docetaxel and vaccine therapy.

Experimental design: We examined the in vivo effects of docetaxel on immune-cell subsets and on the function of CD4+, CD8+, and regulatory T-cell (Treg) populations in response to antigen-specific vaccination. We also examined the antitumor effects of the combination of docetaxel and vaccine in a preclinical model in which docetaxel has no observable effect on tumor growth.

Results: These studies show for the first time that (a) docetaxel modulates CD4+, CD8+, CD19+, natural killer cell, and Treg populations in non-tumor-bearing mice; (b) unlike cyclophosphamide, docetaxel does not inhibit the function of Tregs; (c) docetaxel enhances CD8+ but not CD4+ response to CD3 cross-linking; (d) docetaxel given after vaccination provides optimal enhancement of immune response to recombinant viral vaccines; (e) docetaxel combined with recombinant viral vaccine is superior to either agent alone at reducing tumor burden; and (f) docetaxel plus vaccine increases antigen-specific T-cell responses to antigen in the vaccine, as well as to cascade antigens derived from the tumor.

Conclusions: These findings suggest potential clinical benefit for the combined use of docetaxel and recombinant cancer vaccines.

Fig. 1

Lack of effect of docetaxel on Treg function. C57BL/6 mice (n = 5/group) were given 0.5 mg docetaxel i.p. on days -4, -2, and 0. Control mice received PBS only. Mice were sacrificed 1 day post-treatment. CD8⁺ cells from control mice were incubated with APCs (irradiated splenocytes depleted of CD4⁺ cells) and soluble anti-CD3 in the presence (black bars) or absence (gray bars) of Tregs from either control mice or docetaxel-treated mice. Control wells containing Tregs, APCs, and anti-CD3 without CD8⁺ cells (white bars) were used to determine background levels of proliferation in culture.

Fig. 2

Effect of docetaxel on splenic CD4⁺ and CD8⁺ T-cell cytokine production. C57BL/6 mice (n = 5/group) were given 0.5 mg docetaxel i.p. on days -4, -2, and 0. Control mice received PBS only. Mice were sacrificed 1, 3, and 7 days post-treatment. A-E, splenocytes from untreated mice (open circles and open bars) or docetaxel-treated mice (closed squares and closed bars) were incubated on plates coated with dilutions of anti-CD3 antibody. A-C, supernatants were harvested after 48 h and analyzed for IFN-γ production. D, E, CD4⁺ and CD8⁺ T cells were purified and incubated on plates coated with 1 μg/mL of anti-CD3 antibody. Supernatants were harvested after 48 h and assayed for IFN-γ levels. Proliferation of CD4⁺ and CD8⁺ T cells was similar.

Fig. 3

Antigen-specific T-cell responses combining vaccination plus docetaxel. A, CD4⁺ T-cell responses to foreign antigen. C57BL/6 mice (n = 3/group) were primed on day 0 with rV-LacZ/TRICOM s.c. and boosted on day 14 with rF-LacZ/TRICOM s.c. Both vaccinations were given with rF-GM-CSF. Docetaxel (0.5 mg) was given i.p. 1 day before (D-1; days 9, 11, 13), 1 day after (D+1; days 15, 17, 19), 7 days after (D+7; days 21, 23, 25), or 28 days after (D+28; days 42, 44, 46) the boost. Three weeks post-docetaxel administration, purified CD4⁺ splenic T cells were tested for reactivity to β-gal protein (100 μg/mL) in an in vitro lymphoproliferation assay. B, CD4⁺ T-cell responses to a self-antigen. CEA-Tg mice (n = 3/group) were primed on day 0 with rV-CEA/TRICOM s.c. and boosted on day 14 with rF-CEA/TRICOM s.c. Both vaccinations were given with rF-GM-CSF. Docetaxel (0.5 mg) was given i.p. 1 day before (D-1; days 9, 11, 13), the day of (D-0; days 14, 16, 18), 4 days after (D+4; days 18, 20, 22), or 14 days after (D+14; days 28, 30, 32) the boost. Four weeks after the boost, purified CD4⁺ splenic T cells were tested for reactivity to CEA protein (50 μg/mL) in an in vitro lymphoproliferation assay. C, CD8⁺ T-cell responses to a self-antigen. CEA-Tg mice (n = 5/group) were primed with rV-CEA/TRICOM on day 0, followed by boosts with rF-CEA/TRICOM on days 7 and 19. rF-GM-CSF was given with each vaccination. Docetaxel (0.5 mg) was given i.p. on days 11, 13, and 15. Mice were sacrificed 3 weeks after the last vaccine (day 45) and splenocytes were bulk cultured for 6 days with CAP-M8 peptide. Lymphocytes were recovered and restimulated for 24 h with CEA CAP-M8 peptide or negative control HIV-gag peptide. Specific IFN-γ secretion (HIV peptide background subtracted) is depicted. **p<0.05 vs Vaccine.

Fig. 4

Docetaxel given prior to recombinant viral vaccine can inhibit infection or transgene expression of susceptible cells. A, Murine tumor cells (MC38-CEA⁺) were infected with rF-TRICOM (black bar). B, Cells were incubated with 1100 ng/mL (equivalent to clinical dose of 30 mg/M²) of docetaxel either 24 h before infection, concurrent with infection (0 h), or 1 or 5 h after infection (open squares). After 24 h, cells were analyzed for transgene expression (B7-1).

Fig. 5

Increased antitumor activity of vaccine plus docetaxel. A, CEA-Tg mice (n = 15/group) were implanted s.c. with MC38-CEA⁺ tumors on day 0. Mice were primed with rV-CEA/TRICOM on day 4 and boosted with rF-CEA/TRICOM on day 11 (open arrows). Both vaccinations were given with rF-GM-CSF. Indicated groups were given 0.5 mg of docetaxel i.p. on days 15, 17, 19, 21, and 23 (closed arrows). Tumor volume was monitored twice a week. B, tumor volumes at day 37. Bold numbers indicate statistical significance (P < 0.05).

Fig. 6

Antigen-specific responses and antigen cascade following vaccine plus docetaxel. CEA-Tg mice (n = 3/group) were implanted s.c. with MC38-CEA⁺ tumors on day 0. Mice were primed with rV-CEA/TRICOM on day 4 and boosted with rF-CEA/TRICOM on day 11. Both vaccinations were given with rF-GM-CSF. In the indicated groups, mice were given 0.5 mg of docetaxel i.p. on days 15, 17, 19, 21, and 23. A, CD4⁺ T-cell responses to CEA. One week after the last dose of docetaxel (day 30), purified CD4⁺ splenic T cells were tested for reactivity to CEA protein (50 μg/mL) in an in vitro lymphoproliferation assay. B, CD8⁺ T-cell responses to CEA. One week after the last dose of docetaxel (day 30), splenic T cells were stained for CEA-specific CD8⁺ cells. Specific tetramer binding (control HIV tetramer background subtracted) is depicted. C, CD8⁺ T-cell responses to gp70. One week after the last dose of docetaxel (day 30), splenic T cells were stained for gp70 tetramer⁺/CD8⁺ cells. Specific tetramer binding (control HIV tetramer background subtracted) is depicted.