It is also becoming increasingly accepted that the
mutational load within cancer cells created by the
intrinsic genetic instability of the disease, stochastically
enhances the chance of the expression of altered protein
components that can be seen as ‘neo-antigen’ by
the host immune system and, therefore, are not subject
to natural tolerance mechanisms. Vormehr et al. describe
the technical advances made to identify these
neo-antigen bringing personalized medicine–in the
form of neo-epitope vaccines or TCR-redirected T
cells — very close to the clinic. The observation that
CD4+ T cells also recognize neo-epitopes reignites the
study of their role in tumor control. Similarly, Verdegaal
argues that the success of adoptive cell therapy for
hematological malignancies and solid tumors is based
on CD4+ and CD8+ T cells and neo-epitope specificity.
In an overview of the scientific basis for cell therapy
ways to reduce side effects and immune suppressive
factors requiring attention for therapy improvement are
provided.
The legitimacy of this theory has to face, however, some
basic challenges. Recognition of tumor-specific antigens
requires their processing and presentation by major histocompatibility
molecules. However, as discussed by
Garrido et al. the expression and function of molecules
necessary for classical antigen processing and presenta-
tion are often reduced if not completely shutdown in
several tumors. Therefore, better interpretation of this
theory will be possible when both of these parameters
(mutational burden and antigen presenting capability by
cancer and immune cells) will be considered and analyzed
in the same specimens. It should be expected that tumors
should not display an immunogenic phenotype in the
context of major histocompatibility molecule loss in dependent
of mutational status.
Tagliamonte et al. extend this discussion to hepatocellular
carcinoma, a highly immune resistant tumor type, which
is caused by a strong intrinsic immune suppressive microenvironment.
Bronte and Munn discuss such immune
suppressive mechanisms in the tumor microenvironment
and how they affect immune responsiveness. A complex
topic indeed that covers the broad spectrum of stromal
myeloid and lymphoid cells limiting anti-cancer activity
by the host’s immune system emphasizing the inducible
and plastic nature of suppressive mechanisms and consequently
discussing potential strategies to interfere with
their deleterious effects. Another layer of immune control
and regulation in cancer potentially is caused by the
patient’s microbiota. Perez-Chanona and Trinchieri argue
that a major determinant of immune responsiveness
is the relationship between the intestinal bacteria and the
immune response in the host’s gut, secondarily affecting
the systemic immune status. The gut microbiota plays a
role in educating the host’s immune landscape and as
such will determine cancer responsiveness not only to
immunotherapy but also to standard therapies such as
chemotherapy.
The intricate relationship between immune factors and
chemotherapy responsiveness should not come as a surprise.
Although the cytotoxic effect of these drugs under-
lie the primary reason for their use, their multiple
secondary effects on the immune system are now recognized
as an important part of their long term effects. Cook
et al. review our current understanding of the immunological
changes associated with chemotherapy and how
chemotherapy can be put in use for other immunothera-
peutic approaches.