Vaccination with a recombinant Saccharomyces cerevisiae expressing a tumor antigen breaks immune tolerance and elicits therapeutic antitumor responses.
OBJECTIVE
Saccharomyces cerevisiae, a nonpathogenic yeast, has been used previously as a vehicle to elicit immune responses to foreign antigens, and tumor-associated antigens, and has been shown to reduce tumor burden in mice. Studies were designed to determine if vaccination of human carcinoembryonic antigen (CEA)-transgenic (CEA-Tg) mice (where CEA is a self-antigen) with a recombinant S. cerevisiae construct expressing human CEA (yeast-CEA) elicits CEA-specific T-cell responses and antitumor activity.


METHODS
CEA-Tg mice were vaccinated with yeast-CEA, and CD4(+) and CD8(+) T-cell responses were assessed after one and multiple administrations or vaccinations at multiple sites per administration. Antitumor activity was determined by tumor growth and overall survival in both pulmonary metastasis and s.c. pancreatic tumor models.


RESULTS
These studies demonstrate that recombinant yeast can break tolerance and that (a) yeast-CEA constructs elicit both CEA-specific CD4(+) and CD8(+) T-cell responses; (b) repeated yeast-CEA administration causes increased antigen-specific T-cell responses after each vaccination; (c) vaccination with yeast-CEA at multiple sites induces a greater T-cell response than the same dose given at a single site; and (d) tumor-bearing mice vaccinated with yeast-CEA show a reduction in tumor burden and increased overall survival compared to mock-treated or control yeast-vaccinated mice in both pulmonary metastasis and s.c. pancreatic tumor models.


CONCLUSIONS
Vaccination with a heat-killed recombinant yeast expressing the tumor-associated antigen CEA induces CEA-specific immune responses, reduces tumor burden, and extends overall survival in CEA-Tg mice. These studies thus form the rationale for the incorporation of recombinant yeast-CEA and other recombinant yeast constructs in cancer immunotherapy protocols.
Wansley
Elizabeth K
EK
Laboratory of Tumor Immunology and Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland 20892, USA.
Chakraborty
Mala
M
Hance
Kenneth W
KW
Bernstein
Michael B
MB
Boehm
Amanda L
AL
Guo
Zhimin
Z
Quick
Deborah
D
Franzusoff
Alex
A
Greiner
John W
JW
Schlom
Jeffrey
J
Hodge
James W
JW
D000818:Animals; D000951:Antigens, Neoplasm / Q000737:chemistry* / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D018414:CD8-Positive T-Lymphocytes / Q000378:metabolism; D019496:Cancer Vaccines; D002272:Carcinoembryonic Antigen / Q000737:chemistry* / Q000378:metabolism; D049109:Cell Proliferation; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D007167:Immunotherapy / Q000379:methods*; D008214:Lymphocytes / Q000166:cytology; D051379:Mice; D008810:Mice, Inbred C57BL; D011994:Recombinant Proteins / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D019444:Vaccines, DNA / Q000737:chemistry* / Q000378:metabolism
D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D019496:Cancer Vaccines; D002272:Carcinoembryonic Antigen; D011994:Recombinant Proteins; D019444:Vaccines, DNA; C588090:yeast-CEA vaccine