The breakdown of the body's ability to fight infection because of a lack of T-cells results in a disease called Severe Combined Immunodeficiency (SCID).

Here's a breakdown:

* T-cells are a type of white blood cell crucial for the adaptive immune system. They recognize and attack specific pathogens (like bacteria, viruses, and fungi).

* SCID is a group of rare, life-threatening disorders characterized by a severe deficiency in T-cell function. This means the body is unable to mount an effective immune response against infections.

* Symptoms of SCID can vary depending on the specific type, but often include:

* Frequent and severe infections

* Failure to thrive

* Chronic diarrhea

* Persistent skin rashes

* Pneumocystis pneumonia

* Without treatment, SCID can be fatal.

SCID can be caused by various genetic mutations affecting T-cell development and function. It's often diagnosed in infancy, and treatment typically involves bone marrow transplantation or gene therapy.