Cells at Work! S01E09 - Thymocyte

In the middle of a drill, Killer T Cell tosses a subordinate right into Helper T Cell's office. The two polar opposites start arguing. According to Dendritic Cell, although they play very different roles today, they were actually classmates at Thymus School. Not only that, but they were totally different back then. What was it that developed between these two during their days of enduring hellish training sessions at Thymus School where only two to three percent of cells manage to survive?