Monday, April 27, 1998
In an ideal world, the immune system would recognize cancerous
cells and eliminate them before tumor formation could take place. Unfortunately,
cancer cells appear to evade the immune system despite its best efforts, and
past approaches taken to stimulate the immune system to recognize and attack
cancer cells have not been successful. The issue for the numerous companies
pursuing this approach is thus why have past efforts failed, and what can be
done to increase their chances of success.
Cancer immunotherapies seek to use antigens present in or on
cancer cells to alert the immune system to mount a full-scale attack - like
vaccines used to prevent or treat infectious diseases. But despite the simple
idea behind such approaches, no cancer vaccine has yet been approved.
Cancer vaccines in development can be grouped into three major
classes. The first class is an older approach that involves immunization with
whole cells, either intact or as lysates. The two other classes attempt to incorporate
new technology to stimulate the immune response. One class focuses on generating
an antibody (humoral) response, while the other focuses on a cytotoxic T cell
Other approaches, such as nonspecific immunostimulation with
bacterial polysaccharides or patient-specific immunization with autologous cells,
do not fall neatly into these three classes (see chart for selected products
in development). In each case, however, tumor immunology presents an obstacle
to successful treatment.
"The major obstacle we've had in the past is that we haven't known the precise nature of what we need to target," said Steven Rosenberg, chief of surgery at the National Cancer Institute.