NEW VISTAS IN CANCER TREATMENT
Modern vaccines specifically designed to treat cancer have been in
development for well over a decade. Most of the early experimental
procedures were conducted on very small numbers of patients, with doctors
learning their craft one patient at a time. Another factor that prolonged
the development of cancer vaccines was the inherently long nature of
proving a successful outcome: when does it become significant that a
patient is still alive? But by the mid-nineties the long labors of many
dedicated researchers had begun to bear fruit, and viable product
candidates moved into larger clinical trials.
Cancer vaccines can be divided into two general classes. Some use cells
or material from cells that have been removed from a patient, modified to
be much more immunogenic, and then injected along with an adjuvant. These
are typically referred to as ?autologous cell? vaccines. Other cancer
vaccines contain immunogens that are antigens (derived from either
chemical synthesis or recombinant DNA engineering) known to be present on
whatever tumor type is being treated.
Both of these approaches have their proponents. Fans of ?synthetic?
vaccines point to the advantage of not requiring a patient to undergo
surgery or biopsy to obtain vaccine material. Theoretically they could be
used at the first hint of disease (or even before that). Synthetic
vaccines can be standardized and manufactured in large amounts and at
lower cost rather than be manufactured individually on site for each
patient. Backers of the autologous cell vaccines point out that each
patient?s tumor presents its own unique set of antigens, so their method
guarantees that the patients will receive a vaccine presenting all the
antigens that characterize their own genetically distinct tumors.
We think the clinical results so far have demonstrated the value of both
methods, and that each will find a role as immunotherapy emerges as part
of the new oncology paradigm.
There are currently over a dozen cancer vaccine product candidates in
advanced development. Melacine, from Corixa Corp. (CRXA, $30), is a
standardized mixture of lysed melanoma cell lines combined with an
immunogenic adjuvant. Melacine recently obtained regulatory approval in
Canada, and results from two Phase III trials against malignant melanoma
are due very soon. An autologous cell malignant melanoma treatment from
AVAX Technologies (AVXT, $9), known as MVAX, is now being commercialized
in Australia and two European countries and is just beginning a pivotal
trial in the United States. Other cancer vaccines under development
include inactivated and genetically modified cancer cells (from Cell
Genesys (CEGE, $16)); antibodies designed to mimic cancer antigens and
elicit an anticancer antibody response (from Titan Pharmaceuticals (TTP,
$18)); large immunogenic molecules carrying high concentrations of
specific cancer associated antigens (from Progenics (PGNX, $62) and
Biomira(BIOM, $8)); and DNA vaccines injected directly into tumors (from
Vical (VICL, $37)). Several of these products are in late stage trials and
could be available to US oncologists within a two to four year period.
Given the lack of toxicity and minimal side effects seen with many of
these vaccines so far, we think it likely that doctors will incorporate
these products and the new hope they bring to cancer sufferers into their
practices relatively quickly.
Next week we will begin a more detailed discussion of these and other
companies and their efforts to develop therapeutic cancer vaccines. |
