Cynomolgus monkeys (Macaca fascicularis) in preclinical immune function safety testing: development of a delayed-type hypersensitivity procedure.

A delayed-type hypersensitivity (DTH) test commonly used for humans was adapted for use with cynomolgus monkeys (Macaca fascicularis). Pilot experiments showed naive animals had poor response rates and inconsistent reactivity to the antigens. In an exploratory phase, it was determined that monkeys could be experimentally sensitized by immunization with commercially available antigens. Animals were then sensitized with various concentrations of diphtheria and tetanus toxoids, Candida, and Trichophyton in the dose-response phase. Antigens were injected intradermally (i.d.) 3 times over a 7-day period and monkeys were tested 14 days after the last injection. Responses were measured 24, 48, and 72 h post-challenge, with skin biopsies taken from two animals per group at the 24 h interval. Optimal concentrations were 1.2 Lf diphtheria, 6 Lf tetanus, 1000 PNU Candida, and 1000 PNU Trichophyton. These concentrations produced the best balance between DTH responses, homogeneity of dermal mononuclear cell infiltrate and lowest frequency of undesirable skin reactions. Positive responses were seen at 24 and 48 h post-challenge and were waning by 72 h. DTH responses were inhibited by topical corticosteroids. The final phase of these studies assessed whether sensitization of naive animals could be achieved using subcutaneous (s.c.) administration of the optimal antigen concentrations. Comparable responses to i.d. sensitization were obtained and skin sores did not develop at injection sites. These studies show that the DTH test adapted to monkeys was reproducible, minimally invasive, did not require sacrifice of the test animal, allowed repeated measurements and paralleled the reactions observed in humans.