Final answer:
The true statement about SCID is that T cells are not functional due to affected TCR recombination. SCID leads to a deficiency in the adaptive immune response, affecting both T cell and T-cell dependent B cell activities. Gene therapy offers new treatment possibilities for SCID.
Step-by-step explanation:
The direct answer to the question regarding SCID is B:
Severe Combined Immunodeficiency (SCID) is a genetic disorder that impairs the function of T cells and B cells, leading to an overall deficiency in the adaptive immune response. In SCID, the recombination of T-cell receptor (TCR) genes is hindered because of defects in the recombination activating genes (RAG), which play a crucial role in V(D)J recombination necessary for TCR and B-cell receptor (BCR) diversity.
Without functional TCRs, T cells cannot appropriately respond to pathogens, and T-cell dependent B cell antibody responses also fail. Therefore, SCID affects the adaptive immune system's ability to fight infections, with patients presenting severe, life-threatening, opportunistic infections. New gene therapy treatments for SCID show promise, inserting corrected genes into the patient's cells, potentially overcoming the limitations of traditional tissue-matched transplants.