Treatment of experimental disseminated Mycobacterium avium complex infection in mice with recombinant IL-2 and tumor necrosis factor

Mycobacterium avium complex (MAC) is the most common bloodstream pathogen isolated from patients with AIDS. We have previously shown that TNF alone or in combination with IL-2 can activate human and murine macrophages in vitro to kill MAC strains isolated from disseminated infections. To determine whether treatment with TNF and IL-2 could effect the course of disseminated MAC infections in a murine model of disseminated MAC infection, we infected C57BL mice with 3 x 10(8) bacteria i.v. and 1 wk later administered: 1) IL-2, 100 micrograms/kg; 2) TNF, 25 micrograms/kg; 3) IL-2, 50 micrograms/kg, and TNF, 12.5 micrograms/kg; and 4) saline. IL-2 was injected i.p. daily with TNF being administered in cycles of 3 out of 4 consecutive days. Fourteen days after starting therapy, blood was cultured and mice were sacrificed for quantitative cultures of liver and spleen homogenates. IL-2, TNF, and IL-2/TNF treated groups showed an 87 +/- 5%, 57 +/- 9%, 88 +/- 6% decrease in bacteremia (p = 0.05 for TNF-treated animals and less than 0.04 for the other two groups, compared with control). The combination IL-2/TNF was the only treatment that showed a trend toward an absolute decrease in the number of bacteria in the blood. Reduction in colony counts of liver and spleen were 77 +/- 4% and 87 +/- 6%, respectively, for treatment with IL-2, 58 +/- 7% and 87 +/- 5% for TNF, and 60 +/- 10% and 82 +/- 6% for IL-2/TNF, respectively. These results suggest that both cytokines may play a role in the control of Mycobacterium avium infection and that the combination of a half-dose of IL-2 and TNF, despite not showing any greater efficacy, can be less toxic than TNF or IL-2 alone and might be useful for the therapy of disseminated infection.