The Human Immune System Plays a Critical Role in Warding off Various Types of Human Cancer
THE HUMAN IMMUNE
SYSTEM PLAYS A
CRITICAL ROLE IN
WARDING OFF VARIOUS
TYPES OF HUMAN
• Human immune system plays an important role in defending against
• Past few decades, individuals with compromised immune systems
has extended life span
• For three reasons
• Organ Transplantation become common . Unwanted
reaction controlled by immunosuppressive drugs
• Almost 60 million people suffering from HIV virus
• For long-term survival, Both types are treated with
diverse range of antibiotics
• Thousands patients bearing transplanted organs --- developed solid
tumors & hematopoietic malignancies
• Small number of tumors -- derived from occasional metastatic
cancer cells that were hiding in the bodies of organ donors
• Tumors triggered by transplanted cells provides no insights about
whether tumors of endogenous origin arise with greater-than-
normal frequency in immunocompromised patients.
• Nonviral cancers occur with almost equal incidence among
immunocompetent and immunodeficient individuals
• Viral tumors occur at greatly increased incidence in
• Kaposi’s sarcoma (caused by human herpesvirus-8, HHV-8),
incidence rate is 3000 times higher in AIDS patients
Virus-induced cancers are normally controlled by the immune system
by two models
• (1) The immune system is normally responsible for protecting us
against all types of viral infections, independent of whether certain
viruses are bent on inducing cancer.
• (2) Alternatively, the normal immune system is responsible for
recognizing and eliminating virus-transformed cancer cells. In
immunocompromised individuals, however, such cells may be able
to survive indefinitely.
• Either or both mechanisms may explain the greatly increased rates
of virus-induced cancers in immunocompromised people.
• In AIDS patients, for example, high levels of circulating Epstein–Barr
virus are not commonly observed, while the levels of actively
proliferating EBV-infected lymphoid cells often increase
dramatically, yielding, in turn, virus-induced lymphomas.
• Whether a competent immune system also erects defenses against
the great majority of human tumors (~80%) that are of nonviral
• Two- to fourfold increased risk of melanoma has been found among
adult organ transplant recipients
• Non-Kaposi’s sarcomas were found at rates three times above
those of the general population.
how are nonviral tumors recognized and
• Authochthonous tumors of nonviral origin may not attract the
attentions of an immune system
• Some arms of the immune system can indeed recognize tumors
that have no associations with viral infections.
• Human tumors often have substantial numbers of lymphocytes that
have infiltrated into the tumor mass.
• These tumor-infiltrating lymphocytes (TILs) might represent yet
another type of stromal cell that has been recruited into the tumor
mass by neoplastic cells in order to support the expansion of the
tumor as a whole
• These TILs may have been dispatched by the immune system in
order to eliminate cancer cells.
In one group of patients, who had been treated initially by surgical
removal of the bulk of their tumors followed by chemotherapy, 74% were
alive five years later if their initial tumors carried large numbers of these
In contrast, among those patients whose ovarian tumors lacked
significant populations of TILs, only 12% were still alive
• Research reports have demonstrated the presence of anti-tumor
antibodies in the blood of patients suffering from various types of
• Presence of these antibodies clearly suggests some type of
• Remains unclear whether these antibodies actively contribute to
eliminating tumor cells from the body
• Antigens that are displayed by cancer cells and provoke immune
responses; their identities are often elusive.
• Even more complex are the identities of the immunocytes that are
responsible for responding to these antigenic signals.
• Multiple distinct types of leukocytes are recruited to tumors.
• Each type of leukocyte may be represented by multiple subtypes
that may play distinct, even conflicting roles in fostering or
suppressing tumor growth