Cancer immunotherapy is an attractive and relatively newer method of treating cancer by enhancing the combat-readiness of the host immune system against cancer cells. It has succeeded with some refractory tumors.

Researchers in this field have mostly examined the role played by CD8+ cells, a type of T lymphocyte which recognizes and eliminates cells in the body on which cancer antigens are found. A cancer antigen is an abnormal protein formed from a mutated gene.

In this process, the contribution of CD4+ T cells to the fight against cancer antigens was overlooked, but these cells have gained new importance following the publication of a study in Cell, on September 20.

Major Histocompatibility Complex

The new study revolves around a bioinformatics-centered analysis of the Major Histocompatibility Complex (MHC), a molecular family found prominently on the surface of most of the cells in the body. There are two types of MHC molecules, namely, MHC-I and MHC-II.

These are concerned with presenting antigenic molecules from every type of antigen within the cell, whether belonging to the cell or not. Only then can these antigens be recognized by patrolling T cells.

If they are “self” antigens, the T cells do not react to them. However, if the antigens are “foreign,” either from viruses, bacteria or oncoproteins, instant T cell-mediated killing of the infected or tumorous cell occurs.

MHC-I molecules are found on all cell surfaces. MHC-II molecules are found only on the surface of immune cells, like macrophages. These molecules are both more complex and able to bind antigens of a greater variety than can MHC-I molecules.

The MHC-I and MHC-II molecules thus complement each other, making it less likely that a mutated cell will escape both systems. The more we know about the ability of a person's immune system to clear cancer cells before they take hold, and the more we can combine that with other information about their inherited risk factors or environmental exposures, the better we may get at predicting a person's cancer susceptibility."

Study leader and senior author Hannah Carter, Ph.D., assistant professor of medicine at UC San Diego School of Medicine. An older study by the same authors published in Cell had already revealed that a cancer antigen bound by an MHC-I molecule was unlikely to surface later in any tumor developed by that individual. This is because any antigen presented by the MHC-I system leads to the immediate elimination of that cell.