**4.2.2 Cell culture model**

Keratinocytes, dermal papilla cells, and melanocytes constitute the major cell types in the hair follicle. In CIA, massive apoptosis of keratinocytes occurs; thereby cultured keratinocytes are commonly used as a predictive model for chemotherapy-induced hair follicle damage. Primary and immortalized normal human keratinocytes (HaCaT) have been used to test the effects of chemotherapeutic agents and protectants (Matsumoto et al., 1995; Braun et al., 2006; Janssen et al., 2008). However, since different hair follicle cells interact and affect each other cell growth and cycling (Rogers and Hynd, 2001), the effects of chemotherapeutic agents on other cell types, e.g., dermal papilla cells and melanocytes, should also be evaluated, i.e., through the use of a co-culture system. Furthermore, current cell culture models lack biological measures of hair growth and cycling; however, they offer the advantages of gene manipulation, ease of use, high throughput, and low cost.
