WT male and female BALB/c mice were purchased from National Cancer Institute (NCI, Frederick, MD) and were allowed to habituate to the institutional animal facility for at least 1 week before experimental use (8–9 wks old). Breeding pairs for BALB/c CD154 KO mice were obtained from Dr. Abul Abbas at the University of California San Francisco and bred in the animal facility of University of New England (UNE). BALB/c CD4 KO mice were originally obtained from Dr. William T. Lee of the Wadsworth Center, New York State Department of Health and are currently maintained at the UNE animal facility by breeding homozygous KO mice. All mice were group-housed with food and water ad libitum and maintained on a 12-h light/dark cycle. Since no significant gender differences in all parameters measured were detected, both male and female mice (roughly 1:1 ratio) were used in all experiments. The Institutional Animal Care and Use Committee (IACUC) at UNE approved all experimental procedures. For the experiment conducted in the Dartmouth College (Figure 4A), The Institutional Animal Care and Use Committee (IACUC) at Dartmouth College approved the experimental procedures.