Final answer:
The disease where B and T cells are not formed is Severe Combined Immunodeficiency (SCID), which severely impairs the immune response and leaves the individual vulnerable to infections, unable to effectively use vaccinations, and at a high risk of life-threatening diseases.
Step-by-step explanation:
The disease in which both B and T cells are not formed, leaving an individual unable to fight infections, is known as Severe Combined Immunodeficiency (SCID). SCID patients suffer from defects that impair antibody responses and cell-mediated immune responses. Additionally, this genetic disorder prevents the development of immunological memory, rendering vaccinations ineffective and potentially harmful if live attenuated vaccines are used, as they may cause the disease they're intended to prevent.
Without functioning T cells, a patient would lack several critical components of the adaptive immune response. B cells normally require 'help' from T cells to produce antibodies effectively in response to an infection. If there's a genetic disorder preventing the formation of functional T cells, the B cells won't receive the necessary signals to produce antibodies, leaving the individual susceptible to infections.
Immunodeficiency refers to a condition where the immune system's response is compromised. It can either be acquired during a person's lifetime or be caused by genetic disorders, with SCID being an example of the latter. Disorders like SCID demonstrate the critical roles that B and T cells play in defending the body against pathogens.