Different forms of helper tolerance to carcinoembryonic antigen: ignorance and regulation.
OBJECTIVE
Understanding the mechanisms of immune tolerance to tumor-associated antigens (TAA) is an important step in the design of cancer immunotherapy. The aim was to determine how T helper (Th) cell tolerance is mediated for a prototypic TAA, carcinoembryonic antigen (CEA).


METHODS
Peripheral blood mononuclear cells from 50 healthy volunteers were stimulated with CEA, and the type and fine specificity of any Th cell responses were identified. The inhibitory effects of T regulatory (Tr) populations were determined by depleting "natural" CD25(+) Tr cells or neutralizing cytokine produced by the "induced" Tr form.


RESULTS
Proliferative Th cell responses were consistently induced by CEA in 22 of 50 individuals. Responding cells were drawn from the CD45RA(+) "naive" or quiescent population. Depleting the CD25(+) fraction did not enhance CEA responsiveness. However, CEA elicited secretion of the Tr cytokine interleukin-10 (IL-10) in 23 of 50 donors, including 20 of 22 where no proliferation was induced. Neutralizing IL-10 revealed previously unseen proliferation to CEA by CD45RO(+) "memory" Th cells. Epitope maps revealed differences in the fine specificities of Th cells capable of proliferating or secreting IL-10.


CONCLUSIONS
There are at least two major forms of CEA tolerance in different individuals. One is "ignorance," a failure of specific Th cells to respond to antigen presented in vivo. The other, seen when ignorance is lost, is mediated by IL-10-secreting Tr cells that recognize CEA. TAA tolerance, for example to colorectal carcinoma cells expressing CEA, may be overcome by peptide vaccines that exploit the differences in epitopes recognized by effector and Tr responses.
Department of Medicine and Therapeutics, Institute of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom. mmd508@abdn.ac.uk
Wendy J
WJ
Pickford
Angus J M
AJ
Watson
Robert N
RN
Barker
D000328:Adult; D000938:Antigen-Presenting Cells / Q000276:immunology*; D000951:Antigens, Neoplasm / Q000235:genetics / Q000276:immunology*; D001782:Blood Donors; D002272:Carcinoembryonic Antigen / Q000235:genetics / Q000276:immunology*; D049109:Cell Proliferation; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007108:Immune Tolerance; D016753:Interleukin-10 / Q000378:metabolism; D053645:Interleukin-2 Receptor alpha Subunit; D008297:Male; D008875:Middle Aged; D010446:Peptide Fragments / Q000235:genetics / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic; D050378:T-Lymphocytes, Regulatory / Q000276:immunology*; D018417:Th1 Cells / Q000276:immunology*
D000951:Antigens, Neoplasm; D002272:Carcinoembryonic Antigen; D053645:Interleukin-2 Receptor alpha Subunit; D010446:Peptide Fragments; D016753:Interleukin-10