What is the Immune System?
The immune system is made up of a number of organs and tissues that work to defend the body against pathogens such as viruses and bacteria. It has the important role of being able to recognise, attack and eliminate the foreign molecules and cells without attacking the body’s own cells. The immune system is divided into two parts: the innate immune system and the adaptive immune system. The innate immune system is comprised of all the physical barriers such as skin and mucus membranes, as well as cells within the body that attack foreign cells non-specifically. The adaptive immune system is comprised of a specific type of white blood cells called lymphocytes. This system is able to specifically recognise foreign molecules, called antigens, which go on to induce an immune response. There are two main types of lymphocytes: B and T cells. In response to an antigen, B cells become production houses for antibodies which can specifically attach to the foreign cell or pathogen. This allows other cells of the immune system to tag into the fight and assist in the removal process. T cells can also directly kill cells infected with pathogens, as well as helping B cells to perform their role. Some of the B and T cells turn into memory cells after the pathogen has been eliminated and will recognise the same pathogen instantly if it invades the body in the future, allowing for a much quicker response.
Rejection of a Transplanted Organ
When an organ such as the pancreas or kidney is failing and is not able to function adequately, a possible treatment is transplantation, whereby another organ is taken from a human donor and transplanted into the patient. However, the immune system will recognise the new organ as foreign and attack to ‘reject’ it unless the immune response is reduced. The immune response can be modulated to some extent by matching the donor and recipient cell types, but almost always specific immunosuppressive drugs are needed to prevent the rejection of the transplanted organ.
Rejection of Regenerative Cellular Therapies
Regenerative cellular therapy refers to the transplantation of cells in order to treat a disease or condition. It is theoretically possible to use cellular therapies that are derived from a patient to treat the same patient. These cellular therapies are less likely to be recognised as foreign and rejected by the immune system of the patient. However, this approach has significant logistical, practical and financial challenges for the foreseeable future. It is therefore likely that most cellular therapies for the foreseeable future will be derived from donors, meaning that they will be recognised as foreign by the immune system of the patient. They will therefore be rejected by the immune system in a similar manner to transplanted whole organs unless the immune response is modulated.