Quality assessment of included studies.

“-”Articles did not report relevant information. “√-”Articles reported partial information.Criteria: (1) Peer reviewed publication. (2) Random allocation of treatment and control. (3) Animal species (inbred line, age-matched, MHC mismatch). (4) Sample size calculation (sample size of both control and experimental groups must be clarified). (5) Compliance with animal welfare regulation. (6) Statement of potential conflict of interest (source of funds must be clarified).