Some people with cancer respond favorably to
cancer immunotherapy, while others experience little or no benefit.
Fighting off cancer requires the concerted efforts of immune
molecules throughout the body, rather than just in the tumor itself, suggested a new study of laboratory mice by researchers at the
Stanford University School of Medicine.
‘Fighting off cancer requires the concerted efforts of immune molecules throughout the body, rather than just in the tumor itself.’
The finding helps settle an ongoing dispute among clinicians as to
whether systemic, or whole-body responses, are as important as a robust
response by immune cells in the tumor itself. The study also suggests ways that the effectiveness of ongoing therapies could be
quickly and easily monitored.
"Immunotherapy can be remarkably effective against cancer, but we
don't know why some patients respond and some don't," said Edgar
Engleman, professor of pathology and of medicine. "We don't
understand the parameters that determine efficacy. In this study, we
analyzed millions of living cells simultaneously for 40 parameters from
multiple tissues throughout the body to show that you need a systemwide
immune response to effectively attack and eradicate a tumor."
Engleman is the senior author of the study, which will be published
online in Cell
. The lead authors are Matthew Spitzer, a
former Stanford graduate student who is now a postdoctoral scholar at
the University of California-San Francisco; former Stanford postdoctoral
scholar Yaron Carmi, who is now an assistant professor at Tel Aviv
University; and Stanford postdoctoral scholar Nathan Reticker-Flynn.
The researchers compared the immune responses of a special group of
laboratory mice engineered to spontaneously develop triple-negative
breast cancers. These cancers are resistant to a type of immunotherapy
known as checkpoint blockade. Recently, however, Engleman and his
colleagues showed that they could stimulate a successful immune response
and eradicate tumors in the animals with a two-pronged approach that
incorporated both a tumor-binding antibody and molecules that activated a
type of immune cell called a dendritic cell.
"This finding allowed us to directly compare the responses to two
immunotherapies," said Engleman. "What's going on in an effective
response that's not happening in the ineffective response? What we found
was quite revealing and gratifying."
Spitzer, Carmi and their colleagues collaborated with co-author
Garry Nolan, a professor of microbiology and immunology at Stanford
who has developed a way to use a technique known as mass cytometry to
monitor the physical attributes of individual cells in samples of
millions or billions. This allows researchers to piece together a
dynamic picture of how multiple cell populations respond in real time to
changing conditions like disease or drug therapies.
Spitzer and his colleagues used the technology to monitor the rise
and fall of various populations of immune cells within the tumor as well
as in other tissues - including the lymph nodes, spleen, bone marrow
and peripheral blood - throughout the body immediately after
immunotherapy and throughout tumor rejection.
The researchers found that in animals treated with the effective,
two-pronged approach, the prevalence of immune cells - including
macrophages, dendritic cells and T cells - in the tumor itself
increased dramatically within three days of treatment, during a period
known as "priming." These cells also divided more rapidly. In contrast,
the tumors of the animals receiving the ineffective therapy, checkpoint
blockade, displayed no such increase in prevalence or proliferation.
Increase in regulatory T cells
Importantly, the researchers also observed an increase in a class of
T cells called regulatory T cells in the effectively treated animals
during priming. The presence of these cells during tumor rejection was
surprising because they have in the past been correlated with a negative
prognosis for many tumors.
"Our observation of an increase in the prevalence of these cells in
successfully treated tumors runs counter to conventional wisdom and
points out the complex nature of immune responses that lead to
successful immunotherapy," said Engleman.
Tumor rejection in the effectively treated animals began by day
eight. However, in contrast to the priming phase, the researchers
observed no differences in the rate of immune cell proliferation in
tumors between the two groups of animals during this time. In fact,
immune cell proliferation in the tumor ceased altogether by the
rejection phase. This finding suggests that, although the initial immune
response occurred primarily in the tumor, immune responses in other
parts of the body are likely responsible for sustaining the immune
Spitzer and his colleagues observed increases in the number and
activity of immune cells in lymph nodes near the tumor during both the
priming and rejection phases in the effectively treated animals.
Surprisingly, the same types of immune cell increases were seen during
the priming and rejection phases in the spleen as well as in lymph nodes
that were located a great distance from the tumor. Moreover, the
researchers were able to document similar stage-specific changes in the
activity and prevalence of immune cells in the peripheral blood.
In particular, a marked increase in a type of memory CD4 T cell was
seen in the blood, as well as in peripheral lymphoid organs, during the
rejection phase in mice that received effective therapy. This finding is
important because the rise in these CD4 T cells may prove useful as an
indicator of treatment efficacy in cancer patients who receive different
forms of immunotherapy, thus allowing researchers and clinicians to
develop a way to accurately monitor the effectiveness of ongoing
immunotherapies with a simple, noninvasive blood test. This possibility
was supported when the researchers analyzed immune cells in the blood of
patients with melanoma who had received immunotherapy. The results
showed that a similar subset of CD4 T cells was associated with a
"The idea would be to use the rise of these CD4 T cells as a
biomarker to tailor treatment to each individual," said Engleman.
"Physicians could learn quickly whether a therapy is working, or if it
should be abandoned in favor of a new approach."
Beyond identifying a potential biomarker of effective therapy, the
researchers showed that when the CD4 T cells in successfully treated
mice were injected into the tumors of untreated animals, the cells
stopped the tumors from growing.
Validating importance of systemic response
The importance of the systemic immune response was validated when
the researchers gave the mice a compound that inhibited the ability of
immune cells to migrate from secondary lymphoid organs, such as the
lymph nodes and spleen, to the tumor site. This intervention allowed
sustained tumor growth even in the face of a previously effective
"In the past, researchers focused on understanding in very minute
detail what is happening at the molecular level in immune cells inside
the tumor," said Engleman. "But we took an approach that allowed us to
zoom out and look at the immune system as a whole. This enabled us to
unveil how immune cells work together throughout the body to reject a
tumor, and the approach promises to be widely useful in many clinical
In addition to guiding cancer therapy, the researchers also believe
the technique could be useful in tracking the changes that occur during
an autoimmune disease flare, or to learn more about how the body
marshals its forces to fight off an infection.
The work is an example of Stanford Medicine's focus on precision
health, the goal of which is to anticipate and prevent disease in the
healthy and precisely diagnose and treat disease in the ill.